View Full Version : Combustion Air Intake, Distance to Appliances
09-24-2005, 12:42 PM
I am a homeowner, not a technician - to clairify.
I was trying to determine if there is any negative effect to moving my combustion air intake hose. My gas fired furnace (Bryant 315 Evolution) 44/66k BTU, Gas fired water heater (40k BTU), gas dryer (15k BTU) are all in the same utility room of about 900 square feet (1/2 my basement, other 1/2 is sealed off from this area and finished). When my furnace was installed a combustion air intake was put in the room. It was draped down and placed in a 20 gallon bucket about 2 foot from the furnace and water heater. (See picture from day the furnace was being installed - pre wiring) The furnace and water heater just sit in the open in the room. I'd like to move the hose about 6 foot further away from the furnace/water heater but still in the open room.
Is there any disadvantage to moving a combustion air intake further away from the heat plant? I could not find anything in ASHARE documents that estabished a rule about this. Local building codes don't seem to dictate this - just that one must be present.
I appreciate any input.
[Edited by skidder on 09-24-2005 at 03:38 PM]
I would never do this but I must ask , Are you sure that is your combustion air intake?
you need two things here
1) the manufactures installation guide that came with the furnace
2) an experienced HVAC contractor to correct any other problems that you may have with that custom job there .
I dont think I would use the same guy that stuck that flex in the bucket either
I would say that that outside air in the bucket is probably way more efficant then having outside air pouring on the floor. It will lift the air out of the bucket when needed. Some may laugh at how it looks but as far as it working it works well and thats what counts.
09-24-2005, 02:23 PM
If thats your combustion air intake, then moving it a few feet won't hurt.
09-24-2005, 03:28 PM
The system was a residental retrofit performed by a licenced and experienced contractor that is among the best in the city. It is a full Evolution system and works great. That photo was taken while it was "in process" before electrial and certification/inspection. It all passed.
In retrospect the question seems rather silly given the concept - it's just negative pressure bringing in outside air thru the path of least resistance - not rocket science. However, I just wanted to make sure I wasn't doing something forbidden or something that requires a certain distance.
I just don't like the location of the hose as that is where I want to put a shelf for tools. (This is my workroom also)
That IS the combustion air intake. The hose routes up thru the floor joists and outside to an approved outside combustion air intake about 3 foot above ground. I specifically requested they do NOT route the combustion air intake into a return run as I've read that can cause cause issues I read about on this board.
I added the bucket at the installer's recommendation. (I also read about it here) It does exactly what is stated; prevents cold air from flooding in during the winter. (This is Minneapolis.) The bucket does nothing to stop the air inflow. I make sure the hose is at least 1 inch from the bottom of the bucket and not obstructed. It also did wonders in helping my wood burning fireplaces on both floors draft correctly. Before, I always had to open a window to get them to draft correctly, now the air comes the combustion air hose and works great.
I do have the installer's manual - I will look there also - thanks.
[Edited by skidder on 09-24-2005 at 03:41 PM]
oil lp man
09-24-2005, 04:26 PM
Looks ok to me. 900 sq. feet is pretty large area. But the fresh air will definitely help as the area isn't quite enough for all those appliances.
If you can, I wouldn't move that bucket and put a tool rack and stuff right in front of the furnace. Servicing equipment can be a real joy or a real PIA. The way it is now would be a joy. When I see a pile of stuff in front of the furnace, the cost just doubled in labor.
09-24-2005, 05:10 PM
haha - I know better than to cover up the equipment. I used to work on computer servers and mainframes. The labor goes up as the number of thigs I have to move gets moved at the the hourly rate...
I definately won't box the system in. I'm putting in a 12 inch deep steel shelving flat against the wall and keeping it at least 3 foot from the unit. I'd move it anyway if I had to have the unit serviced. As the installer put it "this installation was a dream - a huge open cleaned up room" ...I even scraped the floor tiles up (they were loose from leakage on the old central humidifier) before they came to put in the water heater and furnace - they were impresssed...
[Edited by skidder on 09-24-2005 at 05:12 PM]
09-24-2005, 05:22 PM
The bucket method is fine. Another alternative is to have the duct make a "U" turn so that the opening is facing upwards.
As stated, it should not really matter where in the room the make up air is located as long as it is still in the same room.
Personally, I like it where it is.
09-24-2005, 06:14 PM
I did the "U" on mine like Robteq suggested. It can be put anywhere in the room if you want.
Going to redo the floors in the room?
09-24-2005, 08:07 PM
Need to correct your terminology. Since that is Cat.1 furnace and water heater, the combustion air is actually just room air aspirated into the burners.
At 50 cu.ft/1K BTU input, you need 6050 and have 7200 if you have 8 ft ceilings. Therefore, this air intake is an adjunct and not required so it does not have to meet code requirements of 100 sq. in cross section min.;3" min one dimension; one high/ one low, each 12" from floor/ ceiling, and wherer you're pulling air from( outdoors vs. other parts of house.
The air hose should have a positive means of assuring it does not seal the opening against the bottom of the bucket.
Since you already have the hole in the wall, why not duct it into the return? Install a damper about mid-way, then tie it in at least 10 ft. from the return plenum. This way it mixes with the stale in from the house so the delta T isn't so far off you crack your heat exchanger. However, even at standby, the ducts will allow the air pressure to equilibrate. If the incoming air is really cold, which you have in Minny, you really should consider a powered makeup air fan with heater. Check out http://www.sheltersupply.com which is right in town for you. They have a unit that can take a slave switch so the makeup air fan energizes when the largest exhaust fan in the house is on, such as the dryer or Suck-O-Matic over the kitchen stove; You can get this in a current sensing switch that fits over the romex to that appliance so installation is literally a snap.
Make sure those Fps are closed off when not in use. The upper one will act as a massive exhaust. Consider a top sealing damper, which is tighter than those crappy throat dampers. If you really want to go for the gusto, have a sweep blow out the damper and smoke shelf to Rumfordize the Fps for better performance. Check with Jack Pixley Sweeps.
09-24-2005, 08:44 PM
I prefer not having the make up air ducted into the return. By being passive, it does not pressurize the home.
09-24-2005, 09:42 PM
The 50 cu.ft/1k btu does not apply to tightly constructed buildings or in this case basements.
The newer rheem water heater is very sensitive to combustion air.(sealed combustion with air/fuel shut down in case of negative venting) Plus dryer removes 100 cfm when in operation. Plus homeowner states fire place burns much better.(flame not being snuffed out do to air issues)
I for one have never heard or read of the bucket thing but can comprehend the application.(this is why I love this site)
Our company installs 600 water heaters a year and since the introduction of sealed combustion technology we've had to re-think combustion air fromulas as laid out in the code books.
09-25-2005, 01:05 AM
Where do you get the 50cu.ft./1K BTU requirement does Not apply and what does a basement have to do with it?
Also, where do you get power vented water heater? The furnace and water heater in the photo from Skidder show B-vented equipment. You can clearly see the draft hood on the water heater.
There are all sorts of makeup air systems on the market now. The US Plusaire is a manifold that takes freshly heated air and tempers the cold incoming air before it hits the plenum.
RoBo, because of the inherent shortcomings with passive systems such as the hose in the bucket and combustion air kits, that's why I posted about the powered makeup air kit from Shelter Supply.
You don't want to pressurize the house--that could drive moisture into the walls. You want it at equilibium, if possible.
Yes, the Fps should burn better with the introduction of makeup air below the Neutral Pressure Plane.
09-25-2005, 01:58 AM
Who said anything azbout a power vent water heater? Tune in buddy.
09-25-2005, 02:19 AM
The design of all atmospheric type waterheaters has changed as of Jan 2004. The combustion chambers are designed to not let the burn spill out of the chamber. If there is a combustion air problem they are designed to shut down.
The rules for unusually tight construction are different and require fresh air from outdoors.
The home is obviously tight because the fireplace burns mush better since the addition of the combustion air duct.
09-25-2005, 08:21 AM
Attached is an article from the Minnesota Department of Energy that was written in the early 1980's (Reprinted in the 1990's) showing and explaining this "New Technology” It also addresses Fireplaces. Minnesota Department of Energy also has common sense articles on recessed lights, stack affect etc. wrintten in the 1980's that still apply.
For some of you posters please IGNORE the comments in “CLOUDS” and only read the article!
As Robin explained the concept works well and will not pressurize the home.
My comment is to raise the duct in the bucket or on the floor to at least “equal to the diameter” of the duct.
09-25-2005, 12:52 PM
For wood burning stoves I have had, I deliberately utilize an open window in my bedroom to provide make up air for the stove.
This way my bedroom stays nice and cool, the way I like it, while the heat from the stove is allowed to passively rise into the rest of the home.
This method only really works for multi-story homes with people who like cold bedrooms.
09-25-2005, 04:27 PM
Interesting article. Yes, the house is rather air tight. The windows are double and interlocking track in style. The doors are well weatherstripped.
I never really thought about how the fireplace should have a combustion air source right by it... I open the laundry chute door when I want to use the upstairs fireplace. Classy... The laundry chute comes in right by the furnace in the utility room into the upstairs main hallway - the house is a very open rambler in configuration. A guest once remarked "Why is all this cold air coming up the laundry chute?" I took them downstairs and showed them "the hose". They were amazed at how much air was coming in. Obviously a roaring fire thru a open masonary chimney diplaces a lot of air.
My hose isn't attached to the bucket and I see the point that the hose could shift or whatever. I live here alone, but if I had kids - I'd definately fix it. I'll deal with that when I move it - I may go the gooseneck route. Looks cleaner.
FWIW, the installer of the water heater made the same comments said here. He said the new Rheems like mine are pretty sensitive and he was glad to see the exhisting combustion air intake.
It would be one HELL of a huge combustion air hose if I was to make it as big as the chimney flue for the fireplace. I've never seen a home that had a combustion duct by the fireplace? I don't see myself doing that anytime soon. I'd like to have the downstairs fireplace converted to natural gas anyway...but I may sell in the spring all dreams and not much $$$! The fireplace is on the same flue. I do have them inspected/cleaned annually.
http://home.mn.rr.com/skidder/fireplaceplant.jpg <---upstairs fireplace.
http://home.mn.rr.com/skidder/LOWERSCREEN.jpg <---downstairs fireplace or http://home.mn.rr.com/skidder/LOWERTOSPAREBATH.jpg
Thanks for all the advice.
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