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Cold Air Coming Out Of Heater Vents


I always have cold air blowing out of my floor registers from my oil heat furnace and it's not even turned on. I turned the heat on today and I get the warm air then followed by the cold. Any ideas? I had a plummer come to fix the same thing last year. Guess it didn't work.

Robin from Burlington, CT



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By Kathy (Guest Post) 10/22/2008 Flag

I get the same thing and I asked my neighbor who is a contractor. He said that when your furnace is running (that you can hear it) it is heating up the air that is within the furnace. The air blowing out of vent is that air, so when it starts to get cool it just means that that inside unit is cooling down and you just need to adjust something on the furnace that controls how long it runs after temperature achieved (that you set on thermostat) I am not sure what your valves, dials look like, but maybe you could google your furnace brand and find out, or check

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By Sandi/Poor But Proud 463 2,122 10/22/2008 Flag

You don't need a plumber. You need a hvac person...someone who specializes in Heating, Ventilation and Air Conditioning. I worked for energy weatherization here in Oregon, and most likely, you have a hole or break in the seam of one of your vents under the house or in the crawl space in the attic.
It's like having a leak in your plumbing, but instead of water coming out, cold air is coming in.
Another possibility, is that you have a coil or thermostat damaged or in need of replacement.
If you are elderly and low income, you can often contact your county services listing, and find someone who will check it for free, or at a low cost.
If you know someone who might do it like a relitive or someone in your neighborhood, church, or community center, you can find the leak and fix it. Good Luck!!

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By Mr phil (Guest Post) 10/22/2008 Flag

If your furnace is in the basement, is it wet or damp down there? It may just be moist air cooling down the warm air the furnace is pushing into the heat ducts. That may be cured by a de-humidifier.

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By Robin (Guest Post) 10/23/2008 Flag

Thank you all so very much. Everyday is a new problem with my house lately. lol.

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By BeanTownSteve (Guest Post) 10/23/2008 Flag

Kathy's on a good track, but first;
some systems allow you to have the fan on all the time, sometimes at a slower speed than when the furnace is actually heating. Check.
Then what Kathy said, there is a sensor that starts the fan when the heated air is "hot enough" and when the thermostat turns off the air still runs for a while because there's still heat in the system. When it gets cool enough, it should shut off stopping the fan. If it's broke...

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By Louise B. 6 2,509 10/23/2008 Flag

If air is blowing ALL the time, I think you must have the fan turned on. Many furnaces have a summer fan setting, which means that the fan is running all the time, circulating cooler air from the basement thoughout the house. This is dandy in the summer. I think you must have this turned on now. You shouldn't have to call a plumber to find that switch. If you don't have such a thing, you may need to get someone in to figure out why the fan runs constantly.

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By Trudi 1 04/14/2009 Flag

Help! I'm freezing and for the past 2-3 months, when I turn on my thermostat to turn the central air on (the original from 1984) it blows out nice warm air most of the time, but lately it has been blowing out cool air from the vents which makes me colder! My thermostat is in the attic. And there are vents in each room.

Sometimes, I turn the thermostat on & off or the one upstairs on & off and suddenly the warm air will start going through, but that doesn't always work. Who can I call to take a look at this and see what's going on. I can't tell and I also can't spend a fortune as I'm on disability.

I'm really cold right now because it's windy & cold in the attic, and when I turn the thermostat on, it's blowing cool air right now. But then I stop worrying when I turn it on and warm air comes through like it is supposed to. Help, please.

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11/30/2012 Flag

Same thing happened to our apartment. I thought for sure it was just the pilot light that was out but after a heating service in Concord CA came and looked at it it turned out to be something completely different. I know it's not how you want to spend your money but it is worth having heat within 45 minutes of getting it looked at by a professional.

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