makeup air

[Cascadian]

The other thread on makeup air made me think.

We will soon be installing some new kitchen appliances, including a hood. We were planning on going with a 900 CFM hood -- we like to fry asian style with high heat, so we need higher than normal air flow.

In a house originally built in '67, do we have to worry about makeup air?

Walls are drywall, with R-21 fiberglass batts. Outside is plywood some places and OSB in others (it's been added on to over the years), with cedar siding. No membrane sealing it up. Windows are pretty well sealed though. All dual pane, mostly aluminum, a few new vinyl. When we redid the walls we used some Great Stuff foam insulation around the windows to make sure they weren't leaking around the frame.

Furnace is direct vent, water heater is direct vent. We have a gas fireplace insert that (I'm pretty sure) is not direct vent. The fireplace is in the same great room that the kitchen is in. (edit: I found the paperwork from the original owners, the fireplace insert is in fact direct vent. So all our gas appliances are direct vent.)

So, with such a structure, would makeup air likely be needed for a 900 CFM vent hood?

[surenuff]

I am sure you will. I need to crunch some numbers. You said direct vent appliances, but none of them are sealed combustion right?! In other words, they take their combustion air from the conditioned space right? How many sq. ft. is the house, and what is the average ceiling height? how many occupants? Did you mean full fireplace insert with doors and dampner?

[carmon]

fire place not gonna e happy...............

[Cascadian]

No, I meant they take their combustion air from outside. My new Coleman Echelon that was just installed definitely has intake and exhaust from/to outside. My gas water heater is also definitely using outside air. I just found the manual for my gas insert and the venting diagram shows two pipes, one for intake one for exhaust. So that sounds like it's taking air from outside as well.

The fireplace insert is a Quadra Fire Columbia Bay gas insert: http://www.quadrafire.com/Products/Columbia-Bay-Gas-Insert.aspx
It certainly seems fully sealed off from the living space.

The gas water heater and fireplace were installed in 2005.

The house is ~3000 sq ft. Downstairs the ceilings are vaulted, but are low slope... about 10 feet in the middle, 8 feet at the sides.

2 adults, 1 child, 1 70 pound dog.

[surenuff]

very funny about the 70 lb dog. while I am reading on this, just out of curiosity, who is installling this type of hood in your home?

[Cascadian]

The gas water heater is a State Select model PR650XODS.

[Cascadian]

We're not that close to installing yet so we haven't found someone yet.

Are you getting at you don't think the average kitchen remodeling guys would be able to properly install higher CFM hoods?

[surenuff]

It is late and I am tired. I have not looked at IMC, but did look at ASHRAE 62.2-03 which states that the upper threshold for depressurization with exhaust air for atmospherically vented appliances be no more than 15cfm per 100 sq. ft. With 3000 sq. ft, I am showing 3.33 cfm per sq. ft. Good question, I will look some more on this tomorrow. Goodnight.

[surenuff]

We're not that close to installing yet so we haven't found someone yet.

Are you getting at you don't think the average kitchen remodeling guys would be able to properly install higher CFM hoods?

Not at all. I will do some reading on this as well tomorrow. It is just that I used to work for a commercial kitchen service company that did range hoods and exhaust hoods. There was a lot of special requirements on the installation of those to pass code. Special welding requirements, clearance issues, and makeup air issues. Not to mention fire supression above certain cfm rates. etc... I will see what I can dig up. I love to have these types of questions I do not have to answer everyday. keeps my nose in the books and my mind working.

[Cascadian]

BTW the vent we're planning on using is this one:
http://www.anconahoods.com/ProductDetails.php?id=29

Actually we already bought the 36" version of that, but since then have decided to not redo all the cabinets and instead just replace appliances and countertops. There's only space for a 30" in the existing cabinetry, so we have to return this and get the 30" one.

[motoguy128]

If everything is direct vent, codes aside, do you want 900CFM of air being sucked in through all sorets of leaks and cracks in a uncontrolled, unfiltered manner? In the summer you could even cause condensation to form inside you walls as hot humid air is exposed to cool interior surfaces. You partially defeat the purpose of your vapor barrier when you make your house negative.

[surenuff]

If everything is direct vent, codes aside, do you want 900CFM of air being sucked in through all sorets of leaks and cracks in a uncontrolled, unfiltered manner? In the summer you could even cause condensation to form inside you walls as hot humid air is exposed to cool interior surfaces. You partially defeat the purpose of your vapor barrier when you make your house negative.

He said there was not vapor barrier in the first post.

Cascadian, I have just got in tonight. I will do some more digging. He is right about the fact that the infiltration air will be unfiltered. As far as "all of that moisture in the air", that depends on where your house is located, and just how cool you keep it in the house. IF I get some more reading done, I will post more.

[Cascadian]

I'm near Seattle, Washington. About 20 miles inland. No A/C in the summer (not hot or humid enough to need it). Just the gas furnace for heat late fall until around this time (just got our first bout of 70+ weather this week).

The exterior doesn't have any plastic Tyvek home wrap or similar, but it does have tar paper under the siding I believe. Nothing that is going to stop any air flow.

I understand the issue with the air infiltrating throughout all the walls. There is a window we can open easily off the side of the kitchen area if we need to crank the hood up full blast, but I want to be sure that if we forget some times it's not going to be disastrous. With all the appliances direct vent it shouldn't be too bad, right?

[surenuff]

I'm near Seattle, Washington. About 20 miles inland. No A/C in the summer (not hot or humid enough to need it). Just the gas furnace for heat late fall until around this time (just got our first bout of 70+ weather this week).

The exterior doesn't have any plastic Tyvek home wrap or similar, but it does have tar paper under the siding I believe. Nothing that is going to stop any air flow.

I understand the issue with the air infiltrating throughout all the walls. There is a window we can open easily off the side of the kitchen area if we need to crank the hood up full blast, but I want to be sure that if we forget some times it's not going to be disastrous. With all the appliances direct vent it shouldn't be too bad, right?

you keep saying sirect vent, and I keep getting sidetracked with work stuff and have not looked up the equipment you have listed to see exactly what you have. The issue is spillage of your appliaces back into the structure, and infiltration issues if the house is depressurized. If your appliances are sealed combustion(combustion air comes directly ducted from outside the conditioned space) and is induced or power vented to the outdoors, then spilliage should not be an issue in my mind. Sorry it is taking me awhile to look this stuff up, I have just been busy. I am surprised no one else is jumping on this, there are alot of people out here who usually are faster than me.

[Cascadian]

So the issue is that not all direct vent is created equal?

In other words, it might be direct vent where all the combustion air comes from outside under ideal conditions, but if it's not completely sealed and there is huge negative pressure, then there is the possibility of having the gases come into the house?

Am I understanding you right?

What might I be able to look for in spec sheets / manuals to know what my appliances are? If it only says direct vent but not powered or sealed then it's probably a problem, yes?

[crymtide]

Ok, looked at your fire place. It does get it's combustion air from outside, and vents outside. If your water heater has both a sealed intake pipe and sealed vent pipe as well as a sealed combustion chamber; it would fall into the same class. As for exhaust hoods I've seen some real nightmares when these are installed by persons other than those who understand commercial hood installation. Make up air can be supplied by the hood as in this example:

http://www.captiveaire.com/CATALOGCONTENT/HOODS/ND2/index.ASP?catid=29

The makeup air is optional in the example and I would not purchase any hood before talking with a manufacturers commercial engineering dept. They can explain the parameters and requirements as well as make recomendations.

[Cascadian]

The water heater, from what I can tell, has a pipe-within-a-pipe design where the vent pipe is inside the intake pipe. Is that common?

edit: not sure if it matters, but it might since combustion air is one issue in people's minds, we were planning on using electric induction for cooking heat, not gas burners.

[second opinion]

The water heater, from what I can tell, has a pipe-within-a-pipe design where the vent pipe is inside the intake pipe. Is that common?

edit: not sure if it matters, but it might since combustion air is one issue in people's minds, we were planning on using electric induction for cooking heat, not gas burners.

Even using the electric to cook with you still need to provide 900 cfm of make up air to replace what is being removed by the exhaust. Infiltration air is calculated in providing combustion air but not makeup air for exhaust. install either a gravity duct system or mechanical to compensate for the exhaust air.

[Cascadian]

Yah, I wasn't saying it would create less of a need to replace the 900 cfm, but that there was no combustion going on in the living area.

[Cascadian]

To recap, it sounds like there's no danger of my gas appliances backdrafting but I should still get some makeup air somehow so I'm not pulling unfiltered air in through all my walls, and so that the high CFM hood has enough air to actually push the CFM it is rated for.

[second opinion]

To recap, it sounds like there's no danger of my gas appliances backdrafting but I should still get some makeup air somehow so I'm not pulling unfiltered air in through all my walls, and so that the high CFM hood has enough air to actually push the CFM it is rated for.

Even though you have category 4 appliances if put in a negative atmosphere there is still a high possibility that they will back draft.

[crymtide]

I agree with Second Opinion completely. Nature abhors a vacuum and if you apply one to your gas appliances you'll find out that they aren't really completely sealed. Like electricity and water air follows the path of least resistance.

[Cascadian]

Thanks for all the feedback. We'll be sure to have some makeup air added when we do the hood. Is it something your standard kitchen installer/remodeler will know nothing about? Generally just HVAC guys deal with it?

[crymtide]

Generally in my area HVAC guys know nothing about it and commercial kitchen types know about it usually

[surenuff]

International Mechanical Code Section 505.2 "make air required. Exhaust hood systems capable of exhausting more than 400 cfm shall be provided with makeup air at a rate approximately equal to the exhausted air rate. Such makeup air systems shall be equipped with some means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system".
In the commercial kitchen environment, we try to hit a level of makeup air that is within 10% of the exhaust cfm. If not, the building will most likely go negative in pressure. Each business is different from another with one building having large opening in the structure that stay open unless they have bad weather. In those cases it would not matter much.
If all of your appliances are class 4 and installed and sealed correctly, it is very unlikely in my opinion that they would ever spill. Especially on your gas furnaces which will be induced draft ensuring a steady supply of fresh combustion air from the outdoors and aiding in the venting of combustion products to the outdoors as well. If they were atmospheric vented(depening on the natural draft of the hotter flue gases to cause them to rise out of the vent pipes and draw in their combustion air in the process, then a negative pressure in the building would be very hazzardous.
As I stated earlier, ASHRAE requirements of no more exhaust cfm than 15 cfm per sq. ft. is depending on enough infiltration to adequately compensate for the exhausted air. But your heating and cooling load will be very much affected by the use of this hood even if it is perfectly balanced. After all you are taking out 900 cfm and introducing 900 cfm of unconditioned air. But I do understand that you only plan to use it a small percentage of the time.
I do not see any other special requirements of fire supression or the like on domestic range hoods regardless of the cfm. However, manufacturer's and local code requirements will dictate your clearance allowances, and may require special high temperature fire insulation.(i don't know) And I too can't figure out what HERS is doing in a domestic remodel of this nature. I hope this has helped. Whatever you do, go into this with your eyes wide open, and think about the effects of 900 cfm of exhaust and consider whether or not that much is really needed. A 400 cfm fan will move a whole lot of air.

[Cascadian]

No HERS here, I think you got the threads crossed. :)

[surenuff]

I did. Sorry!!