Cold air return sending up cold air when furnace not running

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Old 12-28-12, 02:30 PM
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Cold air return sending up cold air when furnace not running

I just bought a cabin (30 years old) with a newer furnace (within 5 years), that runs good and heats place well. The issue is when it is not running the cold air from the basement where the furnace is, comes back up thru the cold-air return into the family room. What can be done to stop this? thanks
 
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Old 12-28-12, 03:22 PM
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With the furnace and ducts in the basement they are subject to natural pressures that force cold air into the lower portions of our homes and up through the house. It sounds like you could use some sealing on those ducts and perhaps some sealing around the house where it sirs on the foundation. Search sealing leaks on forced hot air ducts and you should find some guidance. If not let me know and I will dig one up.

The problem could also be at the supply duct end. If the supplies are getting cold, that air will sink back to the furnace, through the fan, and into the return ducts. Any supply ducts exposed to the cold need to be well insulated.

Bud
 
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Old 12-28-12, 04:57 PM
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Thanks Bud. So if my intake/supply air is 10-12 feet long, which is 2-3 pvc pipe, do I wrap that in insulation? Wouldn't cold air still come in the opening?
That makes sense on the foundation. I actually sit on a boulder with the foundation poured right to that, so I'll have to see how to seal that better.
thanks again!
 
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Old 12-28-12, 06:59 PM
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We need to get our terms straight. The pvc pipe sounds like combustion air for your furnace. The supply I'm talking about is the hot air supply to each room. Supply registers are hot and if they run through cold spaces they lose heat and the air can get cold when the system is not running.

Where your foundation sits on the rock is probably not leaking. Where your house sits on the foundation usually does.

If you have metal ducts, where they join together and the long seam that forms the round duct all leak under pressure. Where the plenum attaches to the furnace also leaks. Metal foil tape is easiest to work with. Some use duct mastic, but messy.

Am I understanding you correctly and vice versa?

Bud
 
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Old 12-28-12, 08:33 PM
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Hi Bud, there is just 1 cold-air return that is right above the furnance. This is where the cold air is coming back up. All of the registers that supply heat do not have a cold draft when the furnace is not running. It could be that when there is a fire in the fireplace it it pulling that air up the flue. Is there a way to add louvers to the cold-air return vent so that it will open and allow air to flow when the furnace is running and then block the cold air from coming up when not running?
 
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Old 12-29-12, 07:00 AM
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You added a fireplace, that complicates the issue. You started with cold air coming back up the return when the furnace was not running, but is it only happening when you use the fireplace as well?

Your fireplace will need a source of combustion air. Sealing off the return would be a patch and not a solution and not recommended. If you air seal as suggested before all ducts, then air from the basement (which is actually from the outside) will not be able to come up through the return.

If your problem is only occuring when the fp is being run, then you will need to address a source of combustion air. But there are other safety issues you need to be careful of, like CO.

Bud
 
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