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Outside Cold Air Intake Into Cold Air Duct

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Old 12-17-2010, 12:13 PM   #1
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Outside Cold Air Intake Into Cold Air Duct

In my personal home I just moved into there is a outside air intake into the cold air duct work. Which is a cardboard tube 4" diameter and frosted up near the wall. Is this needed or a good idea? When it is -20C outside (gets down to -30C here at times) that's a long way to heat it up to plus 20C.

The house is a 988sf 1975 bungalow, full unfinished basement. The only cold air return in the house is right above the furnace in the hall. It also looks like there is a gap near the floor joists which would allow basement air into the cold air return.

The furnace was replace 2 years ago with an Olsen which is 93% efficient.

Should I plug off this outside cold air intake? There is another cold air intake for combustion air, a 2" abs pipe.

Thanks for any help.
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Old 12-17-2010, 06:48 PM   #2
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Re: Outside Cold Air Intake Into Cold Air Duct

I don't see any reason for a seperate cold air intake into the return. I certainly would not want it in my house. As long as there is a seperate pipe for the combustion air intake and exhaust i do not see why closing it up or putting a damper in it would be a issue.


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Old 12-17-2010, 07:59 PM   #3
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Re: Outside Cold Air Intake Into Cold Air Duct

My son's furnace is set up that way but it has an inline damper...guess it is more for summer use.
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Old 12-17-2010, 10:27 PM   #4
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Re: Outside Cold Air Intake Into Cold Air Duct

If you're saying that that 2" ABS is pulling makeup air from the outside, then that's where your furnace is getting air for combustion. That 4" tube was prolly for fresh air. And even if your waterheater wasn't powervented with its own intake, I'd think a house from 1975 was loose enough to allow plenty of makeup for any and all other combustion appliances, except maybe an open air fireplace and assuming the house hasn't been remodeled and wrapped tighter. Then again, I wouldn't dump that cold of air directly into the return because it could stress the heat exchanger by increasing the temp difference across it. Not that the heat exchanger would crack after only a few years, but that could shorten its life....

....Maybe damper it and see if you notice any changes.
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Old 12-17-2010, 11:08 PM   #5
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Re: Outside Cold Air Intake Into Cold Air Duct

There is no damper in the line, I will plug it and see what happens
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Old 12-19-2010, 07:15 PM   #6
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Re: Outside Cold Air Intake Into Cold Air Duct

The pipe you are refering to is a fresh air inlet for the house. It is code here and can have no damper in it. Other places you can have a damper. It should be insulated.
The thought is that houses are getting tighter and people are sealing them up better so the house needs air to breath. Fresh air is also needed to help with the bad air in the house from things like cleaning supplies and such.
I would make sure its insulated and not worry about it.
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Old 12-22-2010, 04:25 PM   #7
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Re: Outside Cold Air Intake Into Cold Air Duct

The national building code requires that houses are positively pressurized. This is the purpose of an outdoor intake. It is also to prevent sick building syndrome, toxins build up in the home over time from cleaning products and out gassing of building material and furniture. If you are concerned about heat loss invest in an erv.


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