Insufficient Furnace Heat

[frjeff]

1989 Excella 29:
I believe we have the original furnace in our unit.
Thermostat properly controls the unit; furnace fan comes on, furnace ignites (super hot exhaust from outside vents) and air is blowing from ducts.
However, the duct air is not hot; it is barely warm.
The exterior vent exhaust is too hot to hold hand there very long.

What might be be the problem? Seems like it should blow interior heat which is far warmer than we are getting.Gratitude for any ideas offered.

[GCinSC2]

Haven't looked at your setup but might be time to explore the connections from the furnace to the vents.

Example, mine has a fabric flex hose and I found a hole in the fabric. Maybe yours has split, torn, or something. And a cell phone can take a look and take a pic for you in many cases.

[BayouBiker]

Also could be excessively dirty and corroded heating tubes in the Furnace air handler. The heat transfer from the burner exhaust to the duct air sounds low.

[frjeff]

Originally Posted by GCinSC2

Haven't looked at your setup but might be time to explore the connections from the furnace to the vents.

Example, mine has a fabric flex hose and I found a hole in the fabric. Maybe yours has split, torn, or something. And a cell phone can take a look and take a pic for you in many cases.

Pulled off cabinet access panel and found the furnace metal front panel (which is actually one side of the “plenum” that allows access to the firebox, etc) was loose (one screw missing and other not tight). Thus, the furnace was blowing air which was entering the “plenum” from the AS interior (cold) mixed with a bit of heated air. Duct hoses all appear fine.

Tightened it down and BINGO, HOT air blowing through the ductwork.

Off to the hardware where I will buy some foam gasket material to make that panel even more air-tight.

My gratitude for a simple but perfect bit of advice!!

[BayouBiker]

Oh nice, I didn't think about how forced cold air might be bypassing the fire tubes. that would better explain both the cool vent air and the hot exhaust. Thanks for the feedback, and thanks to GC for heading you down the leaking air path!

[GCinSC2]

Fr. Jeff,

COOL, oops I mean HOT AIR! Glad a simple fix got things toasty again.

I have actually recorded the discharge air temp as a ref and posted it inside my furnace access door. IIRC it's 160 degrees F. Last outing it was only 100 but sounded "OK". I pulled burner, looked good, but a stink bug found a home and I thing maybe some Jr stinkys tried to find shelter behind the orifice restricting the gas flow. Removed carcasses from orifice and it's back to 160.

Glad you fixed it.

Gary

[88Limited]

Originally Posted by frjeff

Pulled off cabinet access panel and found the furnace metal front panel (which is actually one side of the “plenum” that allows access to the firebox, etc) was loose (one screw missing and other not tight). Thus, the furnace was blowing air which was entering the “plenum” from the AS interior (cold) mixed with a bit of heated air. Duct hoses all appear fine.

Tightened it down and BINGO, HOT air blowing through the ductwork.

Off to the hardware where I will buy some foam gasket material to make that panel even more air-tight.

My gratitude for a simple but perfect bit of advice!!

frjeff, Awesome that you found the problem. While you're working on the door take a good close look at the heat exchanger. Look for any cracks etc. If the heat exchanger is cracked it needs replacing as it's dumping carbon monoxide into your living space. Carbon monoxide will kill you in your sleep.
I'm an hvac tech by trade - have a 1988 Limited. The heat exchanger on mine is still in good condition and I'm dreading when it's time for a replacement as they don't make a direct fit one any more, I have three ports on the outside of my trailer. Everything now is two...