Furnace will not get to tempurature. Goodman 80% eff.??model #

[climber]

3 year old furnace, up in the attic, 800 sq ft house with 9 ft ceilings. Has a 75,000 BTU furnace. Lowered the return air from the ceiling to the floor and added one on the other side of tha one. We increased the speed to high on the blower motor, but still the temp will not get above 60 degrees with the temp set at 72 degrees. AC works fine. Rehabed house, insulated just can't seem to get the heat to thermostat level.

[ACtechGUY]

A 75000 btu furnace will heat a 800 sq ft house very nicely almost too much heat really.

Do you by chance have a mercury bulb thermostat? Kinda sounds like the classic symptom of a incorrectly set heat anticipator in the themostat.

[RegUS_PatOff]

[user=25792]climber[/user] wrote:

... but still the temp will not get above 60 degrees with the temp set at 72 degrees. ...

What is the Vent output air temperature ?

Does the Furnace run "forever" or is it like [user=57399]ACtechGUY[/user] said, the Furnace shuts OFF before the Thermostat setting is reached ?

 

[climber]

it has a digitial

[climber]

and yes the furance runs forever this only really happens when its very cold. the temp at vents was 130 about a month ago at 30 to 40 degrees outside now windchill at -5 about 90 degrees

[Guest]

that's a good temp at vents whats it at with in 2 feet of the furnace? is buy chance a 2-stage? what type of gas? furnaces don't normaly heat better on high speed. watch operation closely make sure flame isn't going off and on.

[ACtechGUY]

Here is what I can tell you . A furnace that is working properly will rise the temperature from 35 to 65 degrees (temperature reading compared from return air to suply air outlet). The temp difference will be lower if you have the fan on a higher speed. If you do not have at least a 35 degree temp rise on medium speed, you may have a problem with the furnace. Make sure the flame stays lit and is not cutting in and out.

Inspect the return air ductwork and check that the blower doors are all on. If you are pulling in cold air from an attic space that will kill the leaving air temp.The house may never get to set point due to all the cold air being sucked in from undesired areas.

If you are getting the correct temp difference and you have no air leaks then maybe the heater is not large enough when you consider the level of insulation /air leaks in the home at 5 degree outside temp.

At my 40 yr old house I have a 75000btu heater on a 1500 sq ft home(4 ton condenser).Down here houses are built very loosly with much air leakage and so at 30 degrees outside my heater might run for about 20 minutes out of the hour.