Finish basement code questions for ventilation, return air, and combustion air...

[dominogold]

I'm planning on finishing the basement myself and want to make sure it is up to code according to the 2003 Michigan Residential Code. I'm just in the budgeting stages and planning at this point, and hope to start framing in a few weeks. The area I need the most help on is the code requirements for ventilation, ductwork/return air, and combustion air. I can handle the electrical/framing/plumbing as I'm pretty familiar with those codes, but really don't know much about HVAC.

There are a few areas I have questions and need clarification on.

1. In section 303.1 the code states that 4% of the floor area for each room much be openable to the outdoors, via windows or provide mechanical ventilation. How do I calculate this and provide this? What exactly is "mechanical ventilation"? I'm finishing an 1100 sq ft section and only have one egress window.

2. What exactly do I need to do to make sure my return air for the basement complies with section M1602 in the code?

3. Combustion air must meet chapter 17 (M1702.1) codes from inside the building. Specifically I have questions about installing two openings and the requirement for each opening to have a free area equal to a minimum of 1 square inch per 1000 BTU of the input of all the appliances installed within the space. How do I install and calculate this?

Thanks

[vern p]

Which Detroit suburb are you in?
Not enough info here to properly address all your questions.
Example: When was the home originally built?
If after 1978, IT is considered to be unusually tight construction, if energy upgrades such as glass block windows installed in the basement if built before 1978, that also could warrant the tight construction considerations.
A lot depends on the layout of the finished area. Naturally the bathroom will need exhaust to the exterior, 50 cfm's per toilet, and you have to replace that air.
The Mi. code requires .35 air changes per hour. The code gives 2 ways of figuring this and you have to take the whole home into consideration here. Generally you can accomplish this with a make up air kit installed into the return duct if one isn't already installed. If a 4" MUA is presently there you will need to increase it to at least 6", (Total cubic feet of air, lenght X width X height per floor in the home X .35 divided by 60 gives you the cfm requirement for the mechanical ventilation) average static at .1 and a 4" MUA will give you approx. 45 cfms where a 6" will get you approx. 100 cfms.
Supply air and return air are required in all habitable spaces period, and since your finishing it, the rooms other than baths and halls become habitable.
As far as combustion air, if your enclosing the furnace room you have 3 methods you can use. The easiest way is the 1 opening method, which is 1 sq. inch per 3000 btu's of the total of the gas appliances in the room located within 12" of the ceiling. The 2 opening method gets too complex depending on vertical or horizontal ducting. Some inspectors will allow you to use a toe kick register without a damper on the furnace supply plenum if the MUA is large enough to provide excess air over and above the ventilation air requirement.
The best thing would be to check with the mechanical inspector of your jurisdiction or post the city/town and I can give you his/her phone number.
Hope this helps,
Vern, City of Walled Lake Mechanical Inspector

[johnl45]

Do you really plan on pulling a permit for this job?

[dominogold]

Thanks for the reply Vern, I'll PM you separately for the personal info.

The home is just 1 year old as we had a C of O issued last December.

What is confusing to me is I have the requirements from the city for finishing a basement, and it says right on it that combustion air must meet the requirements of chapter 17 of the MRC. Then it says, in bold, "M1702.1: All combustion air from inside of building" and goes on to say that two openings shall be installed one at the top and one at the bottom, etc.

I do have a make up air return installed and it's at least 6" (looks bigger than that even), but there is no combustion air return. I thought it was code to require combustion air also, but why wouldn't my 1 year old home already have it and why does their handout say from inside of building only? Makes a person confused for sure.

I will be installing heat runs and cold air returns in all habitable rooms.

I'm still a little confused on this other line item on the list that says according to code 4% of the floor area for each room must be openable to the outdoors via windows or mechanical ventilation (section 303.1). I have about a 1000 sq foot area I'm finishing with only 1 egress window, and 1 glass block vented window. Does my existing MUA line already meet this requirement?

[Christheheatingdude]

If it is that recent of a home, do you have a 90+ furnace? Is it piped to the exterior with two pvc pipes? If so, you do not need combustion air for that. Water heater will require combustion air though.

I work in northern michigan, and regardles of if the basement is finished or not we are required to have combustion air to appliances.

Might help if we knew what you have for equipment, to properly size the combustion air.

[dominogold]

Bryant 80% builder model furnance 107,000 or 132,000 BTUs (says both on the tag?)

Water heater is a 50 gallon 40,000 BTU

There is only one line going to the furnance which is for the make up air that ties into the cold air return.


I don't see anything going to the water heater but it may go staight up through the walls to the roof where I can't see it.

Come to think of it there is a vent coming out of my roof that is pretty thick. Could that be it? I guess I was looking for a line coming in from the side of the house (which I only have one of those for the make up air).

[Edited by dominogold on 12-29-2005 at 09:53 PM]

[Christheheatingdude]

Are there supply registers in the basement, or one near the equipment? How large is the makeup air 6" or more? Inspectors here used to allow using makeup air as a source of combustion air. So that could be how it passed inspection.

[dominogold]

To johnl45: "Do you really plan on pulling a permit for this job?"

I guess I'm curious why you are asking. Are you implying maybe it doesn't matter?

The thought has crossed my mind just how necessary a lot of this really is. I do know dozens of people that did their own basement and just enclosed their furnance/water heater in a small room with a big hole in the wall for combustion air, and their houses didn't explode or anything.

[dominogold]

Yes, I have 4 supply registers in the floor joists in the basement. The makeup air looks like a 6"... says Hart and Cooley Flexible Air duct and has 6" on it with an R-6.

[rsmith46]

Your really not going to save a lot by doing the ductwork yourself. You need to do a load calculation for the basement and design the ducting accordingly. If you cut supply runs into the trunk line in the wrong places you'll screw up the airflow needed to your rooms upstairs and end up with an uncomfortable house.
The combustion air is the easy part but the most important as far as safety is concerned.
You can probably pay an HVA/C company to consult you on how to do it if you want to do it yourself. Try the Co. that installed the system.

[vern p]

Dom, you could make an arguement that when the home was built the basement was unfinished or wide open. Is the basement stairway wide open to the upstairs also and going to remain that way? If so I'd say they gave you credit for the MUA excess air in lieu of the combustion air requirement, just a guess but probably how it happened and as an unfinished basement not considered a habitable space. As far as M1702.1 is concerned that is IF you are using all air from inside. The chapter goes on to give you 3 methods for using outside combustion air, and since your enclosing the furnace room your much better off using the 1 opening method of 3000 BTU's per sq. inch for that room (172M divided by 3000= 57,1/3 sq. inches or approx an 8" run. Now some are going to tell you thats wrong but its what the Code states in black and white using this method.
You may get by with a 6" outside run and cut transfer grills high and low (14 X 6) using a combination method which is also allowed.
This work your planning REQUIRES permitting and inspection per the MRC,2003. Don't give your insurance company any reason NOT to pay off in case of an EVENT in your home. For the people that tell you different pay no attention. Its for your own saftey and investment protection to do so.
Your MUA should be sufficient if you put the outside combustion air in.
You can call your mechanical inspector and verify this info for your purposes since he will have the final word at some point.

[dominogold]

Thanks for the reply.

So amoung the 3 methods, how do I determine which method I use?

I'd like to finish it without having to bring in combustion air from outside if possible. I just had an HVAC tech on another board tell me I don't need it from outside because 174,000 BTU devided by 1,000 = 174 Free square inches. One standard residential return air grille with 1/2" spacing listed size of 20X14 gives you 180 free square inches so just installing two grills one 12" from the top and one 12" from the bottom should be sufficient.

I just read over M1701 also, and I guess I'm wondering how do you determine if you should use M1701.1 or M1701.3, which requires to get the air from outside.

Also how do you determine if the house is "tight construction" or not. This house is only 1 year old with R-13 walls and R-38 attic insulation.

What about the 4% mechanical ventilation (or openable to via windows) requirement? How can I tell if I have met that requirement with a 6" make up air and egress window? The area I am finishing is about 1000 square feet.

Basically as long as I provide ventilation am I going to have a problem with this if I don't bring in outside combustion air?

Is there a way to post pictures on this chat board? I have a rough sketch.

[vern p]

Dom, in Michigan each and every home built since 1978 is considered to be tight construction period, no ifs, ands or buts, yours is TIGHT being built last year.
4% is not an issue since you don't have 4% operable opening windows in each area. Mind you this is the operable opening portion not the entire window so to even use this as an option can't be considered.
Combustion air methods are your choice which to use. Choose the easiest/cheapest method you like.
Its up to you or your designer to come up with code compliant methods on all aspects. I can't design it or give you the step by step methods but I can tell you what the code book states is compliant.
Once again, call your inspector when you decide your approach and run it by him/her PRIOR to starting something you may have to change later.

[dominogold]

Got it, I'll draw the plans up so that they pull the air from the inside with one opening 12" from bottom and one 12" from top, then give the inspector a call to confirm.

Thanks for all your help I have enjoyed learning about this.

[propmanage]

This site has good stuff

[johnl45]

Originally posted by vern p
Dom, in Michigan each and every home built since 1978 is considered to be tight construction period, no ifs, ands or buts, yours is TIGHT being built last year.
Where does it state in the code every house built since 1998 is of tight construction?

[vern p]

John, its 1978 not 1998. That is the year the Michigan Energy Code went into effect. Thats where we get it from. If you think thats bad, wait till the new energy code goes into effect.

[johnl45]

Originally posted by vern p
John, its 1978 not 1998. That is the year the Michigan Energy Code went into effect. Thats where we get it from. If you think thats bad, wait till the new energy code goes into effect. ON FEBRUARY 24, 2005, THE INGHAM COUNTY CIRCUIT COURT ISSUED AN INJUNCTION ON THE IMPLEMENTATION DATE OF THE REVISED MICHIGAN UNIFORM ENERGY CODE. AS A RESULT OF THE JUDGE’S ORDER, THE CODE DID NOT GO INTO EFFECT ON FEBRUARY 28, 2005 AND IS NOT BEING ENFORCED.

[Xavier]

dominogold

Happy New Year, I will not comment on Combustion and Make-up Air, as most posters know my position on the current codes affect on ROI, Energy Cost and Radon. (Vern got a note on Radon from a homeowner who installed “XXX”, last year rather then the new codes or a sub-slab system. The Radon level went from 5.1 to 0.1, on this year’s long-term test!)

However, I do have some recommendations for the basement. No Plastic anywhere (Baggy Affect), No Insulation on the walls (No ROI)! My best suggestion is when you build the walls; build them on the floor and use "Duplex Nails" to nail the sill plate to the wall studs. This will allow any water leaks to flow under the sill and also allows air to flow behind the wall and avoid the "Baggy Affect--Mold & Musty etc!

[dominogold]

Happy new year to you as well.

I'm not familiar with your combustion and makeup air viewpoint, so I'd be interested in hearing that.

So are you telling me there is no point to insulate and install a vapor barrier?

My basement is pretty cold and I can't imagine that insulation wouldn't help.

What exactly is this "baggy affect" you describe?

So are you saying the walls just sit on top of nailheads rather than flat against the floor? Seems like it wouldn't be very structurally sound to me.

[old educator]

Dom
I have been following this post for the last few days with high interest. I hope the following will help!
First/ The Michigan codes are based off the ICC codes. Any home built either under the old CABO or the new IRC is a home built of Unusually Tight Construction. Makeup air for the combustion air of a gas or oil furnace or boiler is a necessity. Too many times, basements are finished off, furnace rooms are sealed off from porper combustion air and Carbon Monoxide poisoning is the end result.

Second/ If you are worried about energy conservation and the lack of combustion air, then a direct vent high efficiency system is the way to go. Don't take a chance on not having enough combustion air!! Too many deaths have resulted from this.

The Energy Code and Building Codes are a minimum standard!
Have a professional check out your particular situation, make the proper recommendations and do the work!

Good luck!!

[dominogold]

Thanks for the post.

I do have a "makeup air" line of 6" already installed. I just don't have a separate line freely flowing to the outside for separate combustion air.

According to what I'm reading, pulling from the outside is not required IF you can get it from the inside and certain interior requirements are met. My house was just built a year ago, and passed code, and they didn't put in an outside combustion air line so as long as I keep these rooms freely communicating with air according to code why would it be any different? The only difference is that I have walls now instead of concrete, right?

I'm reading an excellent book right now, "Build Like a Pro, Remodelling a Basement" by Roger German copyright 2004. He has a lot of good code citations in here.

One thing he says is that you can calculate the cubic feet needed for combustion air by taking your BTUs of your Furnance and Water Heater and dividing by 20.

So in my case, I have 172,000 BTU / 20 = 8600 cubic feet needed. The room I'm enclosing with the furnance / water heater has 1980 cubic feet. The adjacent rooms next to it has about 1000 square feet which is about 7500 cubic feet of air, adding these together puts me well over the requirement for combustion air 9480 cubic feet of air available. As long as I install two opengins, one 12" from top and one 12" from bottom with a free area equal to a minimum of 1 sq in per 1000 BTU, then I should be fine.

[johnl45]

Originally posted by dominogold
One thing he says is that you can calculate the cubic feet needed for combustion air by taking your BTUs of your Furnance and Water Heater and dividing by 20.

So in my case, I have 172,000 BTU / 20 = 8600 cubic feet needed. The room I'm enclosing with the furnance / water heater has 1980 cubic feet. The adjacent rooms next to it has about 1000 square feet which is about 7500 cubic feet of air, adding these together puts me well over the requirement for combustion air 9480 cubic feet of air available. As long as I install two opengins, one 12" from top and one 12" from bottom with a free area equal to a minimum of 1 sq in per 1000 BTU, then I should be fine.
This isn't good enough; according to Vern P you must obtain combustion air from the outdoors or a space communicating with the outdoors if your house was built after 1978.

[Christheheatingdude]

Originally posted by johnl45

Originally posted by dominogold
One thing he says is that you can calculate the cubic feet needed for combustion air by taking your BTUs of your Furnance and Water Heater and dividing by 20.

So in my case, I have 172,000 BTU / 20 = 8600 cubic feet needed. The room I'm enclosing with the furnance / water heater has 1980 cubic feet. The adjacent rooms next to it has about 1000 square feet which is about 7500 cubic feet of air, adding these together puts me well over the requirement for combustion air 9480 cubic feet of air available. As long as I install two opengins, one 12" from top and one 12" from bottom with a free area equal to a minimum of 1 sq in per 1000 BTU, then I should be fine.
This isn't good enough; according to Vern P you must obtain combustion air from the outdoors or a space communicating with the outdoors if your house was built after 1978.

Thats correct. Just because it passed its original inspection, when the basement was unfinished, does not mean it was right. Your home was built after 1978 and needs to have combustion air brought in from the outside. Best bet is to find a contractor to size and install it for you. It is not going to be terribly expensive. And will save you headaches down the road.

[Xavier]

I waited to reply to read if there were other posts, below are my answers to your questions.

I'm not familiar with your combustion and makeup air viewpoint, so I'd be interested in hearing that.

Do a search and take the time to read all my posts and web site. You will then understand my position on Make-Up, Ventilation and Combustion Air for homes. It will be evident that someone who did not major in physics, thermodynamics and common sense wrote the code requirements. To prove this, if one can do algebra and knowing the fact that if you heat air it EXPANDS for a given volume, then the combustion air intake can always be SMALLER then the exhaust/flue pipe to flow the same volume! For example using a 100,000 BTU Natural Draft furnace the combustion area would be (depending on how you read the codes), somewhere between 33 to 100 sq. in. However the area of the flue pipe is ONLY 27 sq. in.! Furthermore what is the area of the combustion air intake compared to the area of the exhaust on a sealed combustion furnace? Mine are the same diameter! When today’s codes are followed in new construction, the first thing a homeowner does when they move in, is to stuff a towel in the ducts! As a Licensed Michigan Instructor, I have raised this to Lansing years ago but nothing has been done to improve/correct the codes! Perhaps because of Lawyers!

So are you telling me there is no point to insulate and install a vapor barrier?

Yes, if are you putting something on the walls your insulation will be that substrate and the air space. Do a Heat loss study to calculate the ROI!

My basement is pretty cold and I can't imagine that insulation wouldn't help.

I too am in Detroit and have only paneling on the basement walls with ¾ in. air space. My home is 2500 sq ft. with 1000 sq ft in the basement that I use as my office/recreation room. I am heating my entire home with a sealed combustion 45,000 BTU Bryant. This supports my research/statements/recommendations!

What exactly is this "baggy affect" you describe?

Imagine putting a plastic bag around/over something. What is the IAQ? I have heard that Minnesota has a “CODE” not to use plastic on or below grade. I do recommend plastic under a cement slab. Can anyone from Minnesota confirm or explain

So are you saying the walls just sit on top of nailheads rather than flat against the floor? Seems like it wouldn't be very structurally sound to me.

The basement walls are NOT support walls! You can also anchor the sill to the floor if you prefer.

My best advice is to continue your research, review your plans with the city and get all necessary permits before you start.

Good Luck

P. S. You are using the three correct terms: Make-Up, Ventilation, & Combustion Air.
Per Code, Combustion Air “cannot” be connected to the return duct (AKA Dryer Vent)!

[Carnak]

Originally posted by Xavier
P. S. You are using the three correct terms: Make-Up, Ventilation, & Combustion Air.



Wow after three years I am rubbing off on you. You going to add a third port now?

[dominogold]

Now I'm back to being confused again.

1. Vern said you can "choose your method" to use to provide combustion air
2. The requirements I have from the city specifically say in bold "All combustion air from inside the building"

Regardless of this, I'm starting to agree with Xavier on this in that the code makes little sense. Right now I have an unfinished basement with about 1200 sq ft. There is no combustion air from the outside, and this house just passed code and they don't require it be put in for any of the homes in this sub. So if I finish 1000 sq ft of that 1200 sq ft area, as long as I have plenty of freely flowing air from the furnance room to the other room then why is bringing in air from the outside necessary? Because to me, it's the SAME space as it is right now, which just passed inspection within the last year. This makes little logical sense to me. Why wouldn't a louvered door or multiple wall openings do the trick?

Seems crazy to me. It's the same space.

[Xavier]

Originally posted by Carnak


[/B]

Wow after three years I am rubbing off on you. You going to add a third port now? [/B][/QUOTE]



Still do not understand how it works.

Must be all that "Positive Pressure" from the dryer vent without a flapper!

Perhaps Next Year?

[Carnak]

Originally posted by Xavier

Originally posted by Carnak




Wow after three years I am rubbing off on you. You going to add a third port now? [/B]



Still do not understand how it works.

Must be all that "Positive Pressure" from the dryer vent without a flapper!

Perhaps Next Year?

[/B][/QUOTE]

Actually you got three ports now, sounds like you upgraded to direct vent. At least something was learned :)

[vern p]

john your right about the NEW 2003 Energy Code being temporarily held up by a court injunction which was brought on by the NHBA. This does not negate the existing energy code that originally went into effect in 1978 and has been modified numerous times.

Dom take the plan to the building dept. and if they buy your thoughts go with it. Without seeing it we really can't comment in great detail. If it was in my jurisdiction your putting in outside combustion air by the book.

[dominogold]

Hi sorry I've been away for a while.

I've decided to just put in the combustion air line from the outside and be done with it. I've insulated the walls tightly and my furnace is loud so this way I can keep that room completely sealed off from the rest of the basement and it will be sealed and quiet from the rest of the basement.

I have two quick questions:

Is there any way to somehow filter the combustion line so that it's only open when the furnance is on so that it doesn't pump cold air into the basement 24/7?

Also how do I determine if I need a 4, 6, 8 or 10" pipe and where it needs to be located relative to the furnace, etc?

[vern p]

Domino, the easiest way is to add all the btu's of the appliances in the room and divide by 3000. This will give you your square inch requirement for the size. Now a suggestion, bring the pipe into the basement and run flex down to the floor, then form a trap in the bottom of the flex. Doing this the only time you will get air coming in is if you get to a negative condition in that room. This also assumes the opening is not on a prevailing wind wall. Yoy can't filter or damper that opening. It needs to be the free area of the calc. This is the one opening method that the code allows. The trap is just a suggestion and not a requirement. The exact wording, from memory here, is the opening commences within 12" of the ceiling.

[dominogold]

So it looks like I need an 8" pipe. Can't I run flex pipe all the way to the furnace area from the wall (like they did with makeup air)?

My furnace has two marks on it one says 107K BTU the other 132K BTU. Water Heater is 40K BTU.

I don't quite understand what you mean by a trap with flex pipe, do you have any pictures?

I am concerned about cold air blasting in because we are on a corner and get blasted with heavy winds without many windbreaks.

So I just leave this pipe dangling in front of the furnance? Does it have to be within a few feet of the furnance and does it matter in front or back etc?

Thanks again

[propmanage]

You need to pay some one to do this for you or you could find your self paying one way or another, some other time down the road.

[dominogold]

Ok, I'm getting some quotes but I have a hard time spending $300 just to drill a hole through the wall and run a flex insulated pipe 15 feet across a room. Seems awfully simple.

I just spoke with a HVAC guy who insists he's never put larger than a 6" pipe in and been fine.

[vern p]

Dom, it just needs to be in the room with the appliances. You use the higher btu ratings. Making a trap, look at your plumbing traps its the same thing. just a basic S with the top being 12" above the floor in that room will be fine. If your total calc is equal to 8" then 8" is required. 6" equals approx 28" may or may not be enough. Try to find a non prevailing wind wall.

[Xavier]

Dom not sure by your statements that you completely understand how your home works and the requirement for replacement outside air (Make-up, Ventilation and Combustion Air) to reenter your home.

Click on the link below to read an article from the Minnesota Department of Energy from 1988, which will explain what Vern (Figure 5) is explaining (ignore the clouds as this is the only file I have!) Depending on the height of the short leg it will determine the flow of outside air entering the home.

If you run a duct from outside to the return air trunk line DO NOT insulate it as this can increase the risk of mold in the trunk line (Physics 101 "Dew Point")

Regarding the size of the Combustion duct, it can be smaller then the outgoing ducts (Physics 102 "Delta T"). Proof: the size of the two ducts on a sealed combustion furnace. Does the combustion duct equal 1 inch for each 3000 btu or is it bigger then the exhaust duct?

It is clear to me that who ever wrote the building codes must have failed all their science classes.

http://members.aol.com/equalizair/combust.pdf

Good Luck

P.S. perhaps someone else can explain a simple way (product)to coordinate when and how the combustion air duct should open!

[vern p]

X, first off a 2 pipe intake/exhaust system on a furnace doesn't equate into the inside combustion air requirements of the code. The mfg's have tested and have a listing for their products so lets not try to equate the mfg's sizing for these into this discussion.
2nd, in the one opening method, as I tried to explain, if we delve further into that section it states that the sq. inch calc can be NOT less than the SUM of the vent connectors combined. This assumes an 80% furnace and standard vented hot water heater. This quirk is not normally questioned unless somebody tries to bring in a lesser size combustion air duct to the space. This also assumes a less than adaquate size room to use indoor air.
As far as the damper on combustion air here is as simple an answer as you can get. ITS NOT ALLOWED unless the damper is interlocked to open prior to firing of any gas appliance in the space that your providing the combustion air to.

[dominogold]

Thanks for the posts, both of you.

Is there an online site where I can read chapter 17 of the code?

Also I get the S-Trap idea now. Basically you're using the natural heat of the room to "supress" the cold air if I'm getting that right by having the upward bend in the line. That way not much cold air comes out unless needed? Neat idea if I have that right. So if this is flexible tubing, does some kind of U shaped thing go inside the tubing to give it the bend? Sorry for the silly question but my HVAC guy normally just leaves it hanging there facing downward.

I've found a reputable HVAC guy to do the install but he swears he's never put in larger than a 6" pipe and doesn't see why this would be any different. My makeup air line is a 6" also, so wouldn't it be the same diameter/calculation as that was?

[vern p]

Dom I think your close to understanding this now. The trap is just that, to only allow air when needed. Since you do have a 6" MUA installed you can take a small credit for the excess air in that part of the system, therefor, the 6" combustion air duct should work out fine for your application.
Sorry, no codes online butttttttttttt, go to your local library and ask them to copy that chapter for you. We can't do it since there are copyright infringments we have to worry about but the library is your best bet unless you spend the money for the whole book.
Good luck.

[dominogold]

Thank you for the advice and I will look into this more.

[klyons20]

If you have that 6 in pipe comming in from the out side near the furnace then you are ok for combustion air.

If you are going to have a furnace room then install vent grills to basement side. One up and one down. This will give the furnace a second source of make up air.

It will also give you ventalation air to the basement.


As far as a return a 1" gap under the door will give return.

You have plent duct over you head to cut a return from the basement.

I use the air from under my kitchen door leading to the outside for ventalation and combustion air. Open windows can be used as ventilation. According to the code ventilaion is only required when the building is being occupied.

regards,
Kelvin Lyons

Vern I talked to mechanical people in lansing. She said it will be a couple of years before something goes down with the forbs act.

[Edited by klyons20 on 04-01-2006 at 09:48 PM]

[dominogold]

Thanks for the tip I'm going out and buying the material today (my HVAC guy works by the hour but I buy material).

I'm assuming I should get the 6" insulated flexible duct for this. Correct me if I'm wrong...

Thanks

[klyons20]

A 4 inch hole will do for the size your house.

regards,
kelvin

[vern p]

Kelvin please read the whole thread and you will see what i've been trying to convey to this H.O. so we don't confuse him any more than he already is. Nothing in the resi code regarding unoccupied not needing ventilation, and in comm'l you need to function the fan for so many mins per hr. in unoccupied times based on ASHRAE 90.1. Undercuts will only work if you meet the 100" minimum rule so a 3' wide door would need a 3" undercut so I don't think thats feasible.

Dom get the 6" as we discussed before and you will be done with it.

[dominogold]

Thanks for the followup, again...

One quick question.... since this furnance room is pretty big... 20'W x 14'L x 9'H... and I have a 6" Makeup Air already... don't those count for something in regards to combusion air so I might be able to get a smaller pipe with those two factors? Or just stay with the 6" and forget it?

Thanks

[vern p]

Dom, I believe your calculated area for combustion was 52" or there abouts. Using 6" (27") and the 2" excess from the make up air gets you very close but not quite there. Going to a 4" is just reduces it that much more. Use the 6" as we discussed and be sure.

[Xavier]

I will attempt to explain again the relationship between the size of the exhaust flue on a furnace and the size of the inlet. The exhaust flue of a furnace will be larger than the combustion inlet for two reasons. First, the exhaust temperature is higher than the inlet temperature as hot air has a larger volume than colder air. To explain this, we can examine what happens to a balloon when it is heated. If we blow up a balloon with 70º air, it has a certain volume and mass. If we now heat that balloon to 400 ºF the size of the volume of the balloon will increase but the mass will remain the same. Alternately, if we cool the balloon to 30ºF the volume of the balloon will DECREASE! However, in all three cases, the mass in the balloon is constant! Second, the furnace consumes fuel, which is also exhausted with the incoming air. This addition of gas increases the volume of what is being exhausted. So the air going up the chimney includes BOTH the air required for combustion (and dilution/draft) PLUS the volume of natural gas, propane, or oil.

With regard to a duct to the return air trunk line, I do not recommend one insulate the duct to the return air in cold climates, as this can significantly increase the possibility for mold to form in the return air trunk line. Reason is, when the cold outside air meets the return air it can lower the temperature at the connection to the dew point. I have seen insulated one hose systems with the damper in conditioned space with rust and mold. If no damper is inline I have seen inside air flow OUT of the duct to the outside, both on the windy side and non-windy side of the home!

Next we could discuss in detail the affect on air circulation within a home by installing a 6-inch duct to the return air and a 6-inch bypass humidifier. However, this is another topic, but needless to say, I do not recommend either!

Vern to answer your questions, as we discussed last year I have been researching air requirements for a home since 1978. I installed my first “hole in the wall” in 1979 for combustion air requirements for the furnace and I installed my first “interlock” system for combustion air in 1981 using an old “Effical” flue damper in the rim joist. I think I understand the requirements for a hole in the wall!

In conclusion Dom, continue your research and select the right size “hole in the wall” for your home. Also Dom, there is a code requirement on the size of the openings in the screen which many inspectors do not know/enforce.

Good Luck.

[klyons20]

We are talking about ventilation and make up air. Not what comming out of vent.

regards,
Kelvin

[klyons20]

Vern, I dont have time to look it up .. Goto chapter that say ventilation (mechanical code 2003). Thats one of the first things you will learn is that ventilation is no required when there is not one in the building. I would not have said it if it was not true.

regards,
Kelvin

[dominogold]

So, just to summarize, here are the various answers I've been given by all of the experts here and other HVAC forums, and the 4 different HVAC installers I've talked to.

a) I don't need anything it because the furnance room is plenty big already, it will probably be fine without it and if not you can always add it later, also since the house is 1 year old without a combustion run and it passed inspection a year ago you don't need it

b) All you need to do is cut 2 14x6 openings in the wall that is shared with the finished portion of the basement, 12" from top and bottom

c) Bring in a 4" insulated flexible duct from the outside to 12" from the floor of the front of the furnance

d) Bring in a 6" insulated flexible duct from the outside to 12" from the floor of the front of the furnance

e) Bring in a 8" insulated flexible duct from the outside to 12" from the floor of the front of the furnance

f) Bring in a 4, 6, or 8" duct but don't use the insulated flexible tube

g) If communication ducts are horizontal (which I think they are) you need one 9" duct because that uses 2000 btu per sq inch. The 4000 btu per square inch is only for vertical openings.

h) According to code bring in two 6" round ducts

i) Use combined indoor and outdoor, with two 30 square inch openings and one 6" square round from the outside

j) Install a special type of device to manage combustion air

With all this confusion, I'm leaning towards option B again and just living with the furnance noise. That's what my city "finish basement requirements" say as well as what someone from the ICC said. How is it possible to get so many different answers on something that should be clearly defined.


[Edited by dominogold on 04-04-2006 at 10:53 AM]

[Xavier]

Dom, I am confused by the following statement:

a) I don't need anything it because the furnance room is plenty big already, it will probably be fine without it and if not you can always add it later, also since the house is 1 year old without a combustion run and it passed inspection a year ago you don't need it

Please answer this question: When your dryer is operating and if you go outside and place a large plastic bag over the vent it will blow up in seconds. Question: The air coming out of the dryer vent that filled the bag, WHERE DID THAT AIR COME FORM? (Clue NOT the dryer!).

As soon as you answer the question, someone will explain the different suggestions.

[lbjheat]

Dom you hit the nail on the head. Not all Codes are clearly defined. Talk to 3 inspectors and you'll probably get three different answers. Just because your home past inspection doesn't mean its 100% correct. You now have an opportunity to make it correct. The confusion lies in the definition of an unusually tight construction. If your home is not usually tight then combustion air can come from inside the structure. If your home is unusually tight combustion air should come from outside. Do you need to determine this? IMO the answer is don't worry about it and, assume it is unusually tight, err on the side of caution, and bring your combustionn air in from outside. That leaves you with only one option that meets the requirments of the code and that is option E(an 8 inch duct has a area of 3.1416X4X4=50.2 sq inches) that is pretty close to the 57inches needed. Chances are that the furnace, water heater, and dryer will not all be working at the same time much.

[paul42]

[i]Chances are that the furnace, water heater, and dryer will not all be working at the same time much. [/B]

Add the fireplace and the range hood to your list.

[dominogold]

Allow me to clarify a few things...

Xavier, hey it wasn't me that came up with this "I don't need anything it because the furnance room is plenty big already, it will probably be fine without it and if not you can always add it later, also since the house is 1 year old without a combustion run and it passed inspection a year ago you don't need it"...

...that is what most HVAC people I call tell me... they also say "basements have been finished for decades without combustion air lines, I'd wait and see if your furnance clips out first before cutting a big hole in the wall." That's 3 separate liscenced reputable HVAC people I've spoken with that said that or very similar.

lbjheat & paul42, the only gas appliances I have in the house are the furnance (basement), water heater (basement), fireplace (main floor with chimney), and dryer (2nd floor upstairs).

I have a hard time with all this code stuff. Why? Common sense. Common sense tells me that the house was built 1 year ago with an unfinished basement without a combustion air line, which was approved by the city. Further, the city's "finish basement requirements" worksheet suggests it's ok to get all air from the inside. Now that I'm finishing it, as long as I allow those rooms to breath how is that ANY different than what I currently have?




[Edited by dominogold on 04-05-2006 at 11:19 PM]

[Carnak]

Originally posted by Xavier
I will attempt to explain again the relationship between the size of the exhaust flue on a furnace and the size of the inlet. The exhaust flue of a furnace will be larger than the combustion inlet for two reasons. First, the exhaust temperature is higher than the inlet temperature as hot air has a larger volume than colder air. To explain this, we can examine what happens to a balloon when it is heated. If we blow up a balloon with 70º air, it has a certain volume and mass. If we now heat that balloon to 400 ºF the size of the volume of the balloon will increase but the mass will remain the same. Alternately, if we cool the balloon to 30ºF the volume of the balloon will DECREASE! However, in all three cases, the mass in the balloon is constant! Second, the furnace consumes fuel, which is also exhausted with the incoming air. This addition of gas increases the volume of what is being exhausted. So the air going up the chimney includes BOTH the air required for combustion (and dilution/draft) PLUS the volume of natural gas, propane, or oil.

With regard to a duct to the return air trunk line, I do not recommend one insulate the duct to the return air in cold climates, as this can significantly increase the possibility for mold to form in the return air trunk line. Reason is, when the cold outside air meets the return air it can lower the temperature at the connection to the dew point. I have seen insulated one hose systems with the damper in conditioned space with rust and mold. If no damper is inline I have seen inside air flow OUT of the duct to the outside, both on the windy side and non-windy side of the home!

Next we could discuss in detail the affect on air circulation within a home by installing a 6-inch duct to the return air and a 6-inch bypass humidifier. However, this is another topic, but needless to say, I do not recommend either!

Vern to answer your questions, as we discussed last year I have been researching air requirements for a home since 1978. I installed my first “hole in the wall” in 1979 for combustion air requirements for the furnace and I installed my first “interlock” system for combustion air in 1981 using an old “Effical” flue damper in the rim joist. I think I understand the requirements for a hole in the wall!

In conclusion Dom, continue your research and select the right size “hole in the wall” for your home. Also Dom, there is a code requirement on the size of the openings in the screen which many inspectors do not know/enforce.

Good Luck.




X, don't quit your day job.

Your product does not meet any code as far as combustion air goes and is an accident waiting to happen for people building tight homes in areas where there are no building inspectors to catch your POS in action.

So do not try to rationalize out why your product should work, especially with your reckoning on what size things should be.

Combustion first requires excess air and natural draft requires dilution air on top of that. So yes you mentioned dilution air but where the hell does it ultimately have to come from. How about outside of the house. I suggest you continue with your research of what happens in the combustion process and quit spreading the misinformation of your 'physics'.

[Edited by Carnak on 04-05-2006 at 11:47 PM]

[lbjheat]

Paul we are talking about the neeed for combustion air in a confined space. The range hood doesn't use air for combustion and would be covered under make up air which Dom has. The fireplace uses air for combustion but is most likely not in a confined space so it doesn't have to be counted. You only count the fuel burning appliances located in the confined space.
Dom I did't realize your dryer was upstairs. Should have figured it out though, most new homes today don't have them located in the basement. You now only have to provide enough fresh air for the water heater and furnace in the confined space area. If you are confident that your home is not a tight home then get the needed air from inside. If you aren't sure then get the air from outside. Its very simple. Tight construction or not tight. Reason you didn't need it before was that your basement is not considered a confined space when unfinished.

[Xavier]

Dom, please answer the questions on where the air leaving the home comes from?

As you can see in these posts there are a lot of opinions and little facts.

In particular if anyone will reread my post, I stated that the size of the exhaust flue is such that it has; combustion air, dilution air, draft air AND moles of the gas being burned. Remember the moles of gas DOES NOT come from the home! Therefore, the size of the duct for: combustion, dilution and draft air will never be bigger then the size of the exhaust duct because of the temperature difference! Physics and Chemistry 101!

Dom if you want to calculate the size of the combustion air for your home here is a formula that can assist you. The temperature is in Kelvin.

V1 = T1
V2 = T2

I recommend you have/add a “hole in the wall” The only question is what size and the best way.

Good Luck

[lbjheat]

What is V1=T2 and V2=T1? That is nothing. Did you mean Charles' Law?
Charles Law is stated V1xT2=V2xT1 where T is absolute temperature (rankine or kelvin)
Charles Law is not stated in the code.

[Carnak]

Originally posted by Xavier
Dom, please answer the questions on where the air leaving the home comes from?

As you can see in these posts there are a lot of opinions and little facts.

In particular if anyone will reread my post, I stated that the size of the exhaust flue is such that it has; combustion air, dilution air, draft air AND moles of the gas being burned. Remember the moles of gas DOES NOT come from the home! Therefore, the size of the duct for: combustion, dilution and draft air will never be bigger then the size of the exhaust duct because of the temperature difference! Physics and Chemistry 101!

Dom if you want to calculate the size of the combustion air for your home here is a formula that can assist you. The temperature is in Kelvin.

V1 = T1
V2 = T2

I recommend you have/add a “hole in the wall” The only question is what size and the best way.

Good Luck


What is draft air

[Xavier]

Here are the replies:

What is draft air? IT IS AN "AMERICAN" TERM!

What is V1=T2 and V2=T1? That is nothing. Did you mean Charles' Law?
IF I REMEMBER MY ALGEBRA, YOU CAN CROSS-MULTIPLY FRACTIONS. Did not know how to show fractions, but selected to show it this way to "HIGHLIGHT" the affect of temperature on volume!

Charles Law is stated V1xT2=V2xT1 where T is absolute temperature (rankine or kelvin)
SO THEY ARE THE SAME!!

Charles Law is not stated in the code.
THAT IS THE PROBLEM AND THE MISUNDERSTANDING WITH THE CODES AND ANYONE WHO DOES NOT UNDERSTAND CHARLES LAW!!

You are the first to restate the relationship between volume and temperature correctly. Perhaps you want to correct the building codes on this one to save homeowners money!

[propmanage]

You will need 30 cfm per minute per burner

[Carnak]

Originally posted by Xavier
Here are the replies:

What is draft air? IT IS AN "AMERICAN" TERM!

What is V1=T2 and V2=T1? That is nothing. Did you mean Charles' Law?
IF I REMEMBER MY ALGEBRA, YOU CAN CROSS-MULTIPLY FRACTIONS. Did not know how to show fractions, but selected to show it this way to "HIGHLIGHT" the affect of temperature on volume!

Charles Law is stated V1xT2=V2xT1 where T is absolute temperature (rankine or kelvin)
SO THEY ARE THE SAME!!

Charles Law is not stated in the code.
THAT IS THE PROBLEM AND THE MISUNDERSTANDING WITH THE CODES AND ANYONE WHO DOES NOT UNDERSTAND CHARLES LAW!!

You are the first to restate the relationship between volume and temperature correctly. Perhaps you want to correct the building codes on this one to save homeowners money!



I figured you dodged the draft , but what exactly is draft air?

[Carnak]

Xamedes, does draft air have anything to do with bouyancy?

[lbjheat]

Poor homeowner, he must be pulling his hair out. This issue is a dead horse and don't need to be beat anymore.

[Carnak]

I find the physics lessons of our degreed colleague quite enlightening.

[Xavier]

Dom, you have not answered the question on where the air that leaves a home comes from and how/where it reenters the home.

Here is a quote that may answer your questions:

"COMMON SENSE is the knack of seeing things as they are, and doing things as they ought to be done" Calvin Ellis Stowe

My recommendation for you home is: a two hose system 4 inches in diameter! Or open a window!

Good Luck

[Carnak]

Common sense suggests fire fighters and gardeners use hoses

[propmanage]

Read the code book again and again you will see what they want. oil reqires 30 cfm per min per 140,000 btu

[cem-bsee]

if HO has a death wish for him & his family should I chime in?

HO: protect your family: add a duct to bring in air from the outside to near the furnace & HWH & fireplace & any commercial sized cooking stove! do not skimp on size!

One can not with inspection provide quality or safety. They can just comment about that.

said air = makeup, combustion, for draft, ____ , maybe 2- 3 other terms.

fire requires: fuel in the form of gas, oxygen, an ignition source. [yes, even wood or coal must be heated enuf to have it off- gas for burning.]

BTW, I put a duct from attic to bsmt beside my furnace in 1957. = "new" home.

I have yet to see a house having a basement with the upper structure supported by something other than the bsmt exterior walls, mostly. Yes, most times support columns are necessary under the beams used -- however, one can use LARGE beams to span from exterior wall to ext wall --

if one has seen bulging bsmt walls, one might look as to why & learn how to insulate in "cold" areas. see BUILDINGSCIENCE.com; a book: From The Walls In.

likewise, one must insulate & apply vapor barriers differently for hot humid areas, hot dry areas, dry cold areas of the world.

[coolwhip]

Vern, that was very nice of you taking the time to explain this to DG. :)

[Carnak]

Pretty much nothing but cow patties posted since vern's useful comments, don't be mislead by mis-applied physics of some one who makes a product that does not comply with codes

[Xavier]

A person with “Common Sense” does not bloviate feeble attempts to make one larger then they are!


http://members.aol.com/equalizair/natas.pd

[Carnak]

the $3 hood passes more air than your baby. You keep trying to rationalize why your device will work even tho it does not pass enough air for a water heater even if you cut out the 'flapper'

[Edited by Carnak on 04-13-2006 at 08:15 PM]

[Xavier]

Carnak, keep posting your contumelious remarks as many of us read them before the comics each day!

P.S. My invention will work on all electric water heaters too!

[Carnak]

All it is good for is electric water heaters.

Works good in a hot humid environment too great for positive pressure ventilation in homes that do not burn fuel. If you could offer designer colours I could market them here as one size fits all.

For a small house you block off one port and hook a 4-inch 'hose'(LMAO) to the return duct. For a big house, hook up both ports and run two 'hoses' to the return duct.

The restrictive plastic grille would catch all the monster mosquitoes, the gnats may make it in so I would have to retrofit a filter downstream.

Great non-corrosive product for a salty, hot humid environment. Unfortunately a severley over priced plastic POS for a cold climate with fuel fired furnaces that does not comply with any building or fuel code. Could by a pair of hoods for 6 dollars and beat the hell out of any ROI you could come up with.

No such thing as bad publicity so keep posting Xamedes.

You must be retired now from your day job as you seem to post fanatically up until Christmas and then resurface at Easter. Either that or you are part lemming, or bear or perhaps groundhog.

[vern p]

Thanks CW & Carns, unfortunately sometimes people don't like the message or want to listen to the message, but at least we got the message across for whatever its worth. What they do with the info is another story. In this instance maybe DG will be fine for now, who knows what will happen down the road. My crystal ball isn't working very well anymore lol.