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Old 12-08-2009, 11:27 PM   #1
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Combustion / Fresh Air Intake Safety


I did not get a inspection when i purchased my home and i won’t be making that mistake again. My latest concern is that my furnace is lacking a city inspection of when it was installed and a separate combustion air supply, which is what I was used to in my last home. All I have is a fresh air supply which is connected to the cold air return on my forced air furnace.

Furnace make Carrier Weathermaker 8000

Is/was this type of install allowed (Calgary, AB)? Am I safe from co?

One thing I noticed is that the air initially blowing through the system is very cold, especially when its -30c outside, like it is today.

See the attached sketchup drawing…

Thanks

Eric
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Old 12-08-2009, 11:36 PM   #2
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Combustion / Fresh Air Intake Safety


I'm in Edmonton and from my basement development experience this is what I've found:

If you have a mid-efficiency furnace with an open basement and nothing boxing in the furnace, you can use the room air as combustion air and do not require the additional combustion pot intake fresh air supply.

If you have a mid-efficiency furnace with a closed basement and an enclosed furnace room, you require the two fresh air intakes - one to the return air side of the ducts, and one to a combustion pot preferably mounted near the furnace - I believe a 6" fresh air combustion pot is good for 225000 BTU's by code here in Alberta.(don't forget to combine the furnace AND hot water tank in your calculation). You still have the option of using the rest of the basement as combustion air if you install grills a certain size and at a particular location on the furnace room wall or use a louvered door but I do not know the exact specifications for this.

If you have a high-efficiency furnace regardless if the furnace room is closed or not, you do not require the additional fresh air combustion pot as this type of furnace utilizes two PVC pipes - one for exhaust and one for fresh air, however, you will need to verify what combustion air requirements are necessary if you have a gas heated hot water tank.

In your case, your furnace room may be large enough to not require the additional fresh air supply but it would be VERY wise to have this verified because if you do not have a sufficient combustion air supply you are at an extremely high risk of carbon monoxide poisoning.

On a side note, all builders around here automatically drop a 6" fresh air intake to the floor on all mid-efficiency furnace installations regardless if the basement is finished or not. Sometimes they don't put it near the furnace either making basement development a challenge.


Last edited by n0c7; 12-08-2009 at 11:47 PM.
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Old 12-08-2009, 11:52 PM   #3
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Combustion / Fresh Air Intake Safety


For reference, this is what I'm referring to when I say combustion pot:



Please ignore the junk in the background, it's gone now.
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Old 12-08-2009, 11:55 PM   #4
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Combustion / Fresh Air Intake Safety


that fresh air you show is not for combustion it only pulls fresh air into your return air which is why youre getting such cold air on start up if it were me id remove it or seal it up
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Old 12-09-2009, 12:00 AM   #5
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Combustion / Fresh Air Intake Safety


Yeah, as i understood it, "non-pvc systems" require the combustion pot to stop people from permanently falling asleep. I did not realize there was a rooms size allowance. Ill get it inspected by a pro. Thanks for your help.
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Old 12-09-2009, 05:09 AM   #6
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Combustion / Fresh Air Intake Safety


You need 50 cubic foot of room volume per 1,000 BTUs of total appliance input. Meaning if your water heater is gas fired also. You must include that with your furnace input.

EG: 80,000 BTU furnace + 40,000 BTU water heater = 120,000 BTU / 1,000 = 120 X 50 = 6000 cubic foot of volume. If furnace is in a room with only 3,000 cubic foot of volume. You need combustion air intake.
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Old 12-09-2009, 08:00 AM   #7
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Combustion / Fresh Air Intake Safety


Been there is absolutly right. Here is a link explaining it.
http://www.comfort-calc.net/Combusti...lculation.html
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Old 12-09-2009, 09:18 AM   #8
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Combustion / Fresh Air Intake Safety


Eric,

Further to my previous reply, during my research I also stumbled upon motorized dampers to help keep that cold draft out. http://www.hoyme.com/ has designed them both for the return air side and the combustion pot supply.

Their an Alberta company as well.

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Old 12-09-2009, 09:22 AM   #9
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Combustion / Fresh Air Intake Safety


Quote:
Originally Posted by Eric J View Post
Yeah, as i understood it, "non-pvc systems" require the combustion pot to stop people from permanently falling asleep. I did not realize there was a rooms size allowance. Ill get it inspected by a pro. Thanks for your help.
Sounds good, I'm curious to know what they say, keep us posted!

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