Thursday, September 22, 2011

Cold air coming out of vents yet set temp reads 74?

my temp reads 74. my set temp is at 82. how can i get the vents to consistently blow out hot air. the heating guy came over. but everytime he comes, it blowing out hot air. the hot air doesnt last long. its like hot air for 30 min. cool air for about an hr, hot air- 30 min. and so forth. the heating guy changed the thermostat. right as we speak. its blowing out hot air. Cold air coming out of vents yet set temp reads 74?
The furnace may be too small for your house and/or your home insulation may be too weak if the room temperature reads 74 when you want 82.

Cold air coming out of vents yet set temp reads 74?
It sounds like you are tripping out on the high temp limit on the furnace.

Nothing wrong with the wall thermostat if the fan keeps blowing. Changing that was dumb. If the fan keeps going blowing cold it means the wall thermostat is still calling for heat. If it was the wall thermostat the unit would just shut off.

I have had customers shut off half the vents in the house thinking they will save heat and then call me to fix an overheating furnace.

Or they put filters in the return, in the furnace, and in each vent too and wonder why it is not acting right.

Plugged filters and a dirty blower wheel will do that as well. How long since the blower was cleaned? Ever? Could be a bad high temp limit switch too, or both if it takes an hour to reset.

First check I would do is measure the heat rise at the vent closest to the furnace while it is running %26quot;hot%26quot;. It should be about 30-60 degrees above room temps. Modern furnaces operate closer to the lower than the upper. The heat rise will be marked on the model number plate.

Some times people don't realize they have closed so many vents. They vacumn over them and close them by accident. They shut off a couple to put a couch over it. Then others so as not to blow on a plant or blow curtains around then shut off one unused room or so. Before they know it most of them are closed and the furnace overheats.

Go around and check each one to make sure it is open, don't assume.

Good LuckCold air coming out of vents yet set temp reads 74?

Just a thought but you might have an air leak from a damper or from the pipes somewhere . Take a smoke pencil and start checking around all the pipes in the crawl space or basement at the furnace , and anywhere else you can to find an air draw.

Good luck

Joe Woodall, Managing Partner

Georgia Adobe Rammed Earth And Renewable Energy

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