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drewhart 01-17-2011 09:00 PM

furnace blows cold air but burner is workin
i have an old bryant furnace. its real big but not a gravity furnace. the air it blows is cold, even from the vent coming out of the plenum. when you look inside the burner is burning good. it runs almost constantly and it only stays at 62 even though its set for 67. i live in cleveland, ohio. any ideas?

unicursalhex 01-18-2011 01:59 AM

Probably time for a new furnace... I bet the fan quit

beenthere 01-18-2011 04:51 AM

Probably needs a clean and tune. Orifice/orifices are probably dirty, and manifold pressure may be too low.

drewhart 01-18-2011 11:49 AM

the fan is blowing strong. what orifices do you think i should clean? the air comes out strong in the vents upstairs, its just cold.

drewhart 01-18-2011 08:20 PM

i just dont understand where all that heat could be going. there's a huge fire in there. maybe something in the plenum is clogged driving all the heat out of the flue?

kenmac 01-18-2011 08:47 PM

Is your duct work is in crawl space ?

1acman 01-18-2011 09:09 PM

Do you have outside air ducted into the return? What is the gas pressure in and out of manifold (gas valve)?

AllanJ 01-18-2011 10:06 PM

The heat exchanger could be caked with dust (where the room air passes through from the return duct to the supply duct) and/or carbon deposits (where the smoke from the fire passes through from the firebox to the chimney and also down where the flames are). The fire should be blue which gives maximum heat and minimum carbon deposits. If the fire is yellow (more carbon deposits) you need to adjust the air/gas mixture using flaps in the burner assembly.

drewhart 01-19-2011 08:20 AM

the ducts are in the basement. there isnt really a return duct. it just sucks air in from the basement. what is the best way to access the heat exchanger to clean it? and where is the spot where the smoke from the fire passes the fire box to the chimney? should i just brush and vacuum the area down by the burner?

drewhart 01-19-2011 08:22 AM

it just seems like if its still burning fine i dont need to buy a new furnace. maybe the mechanism that causes the fan to turn off is broke. so in between when the burner is on, its blowing cold air up.

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