Slow house temperature rise-gas furnace

[rudyh]

Hi.  I have a problem with my downdraft Tempstar gas furnace.  The house temperature is very slow to increase (over 1/2 hour for a 2 degree increase).  The main burners cycle on/off because the over temp. t-stat on the front of the heat exchanger compartment opens/closes - it has been replaced.  This sounds like an inadequate volume of airflow. 

Could this be caused by leaks in the ducts?  Ideas on finding such leaks?  There is also cold air falling from the return air registers when the furnace is not running.

Any ideas would be appreciated.

Thank You

Rudy

[AccApp]

[user=11243]rudyh[/user] wrote:

1.  This sounds like an inadequate volume of airflow. 

2. Could this be caused by leaks in the ducts?  Ideas on finding such leaks? 

3. There is also cold air falling from the return air registers when the furnace is not running.

1. Ya hit the nail right on the head.

2. Probably not, even with leaky ducts the furnace will shove enough air through it to keep the high limit from tripping. To find any leaks is as simple as it might seem, inspect the ducts with as many senses as you have. Some are visual with flapping tape being an obvious tell-tale, some you must feel with the hairs on the back of your hand, others can be heard. Smell and taste, not so much but you get the idea. Irony, urgency and direction may come into play as well.

3. Heat rises, 'nuf said

Back to #1, look for a blocked filter, a loose or filthy blower wheel, a tight blower motor or an evap coil covered in schmutz. Making any suspicious noises? Can you get an amp draw on the motor? Tried switching the t-stat to "Fan On"? This will put the furnace into the high speed used for cooling. Most furnaces have at least a low speed used for heating and a high speed for cooling.