Blocked Supply Ducts?

My brother from out of state called with a supply problem and wanted my input. NG forced air furnace supplies little, if any, heated air to all rooms within the house. Fan sounds (to him) like it’s working fine, burners firing, and return air appears to be functioning (e.g., he put an 8.5x11 sheet of paper against them and it sucked up to the cover). Furnace is in the garage. Filter is new (he replaced it today and saw no improvement). He’s lived in the house for years so he knows the furnace definitely works, but is now renting it and the renters brought this to his attention.

Sounds, to me, like a blocked supply in the main trunk, but I’d love your opinion. Thanks very much in advance!

Try the cheep shots first, are there any shutoff valves in side the ducts?

This is a thermostat controlled damper, I see the manual ones far more often, and in odd places. Make sure they are open.

Is this HVAC unit on one zone?

Sounds like the supply duct is either disconnected or blocked. Either way, the air coming out somewhere.

It would be best to have the furnace TESP (static pressure) tested and that pressure referenced against the manufacturers blower chart for the selected motor speed.

It may be that the furnace blower, secondary heat exchanger (if 90 percent efficiency furnace) and evaporator coil needs to be cleaned.

If the furnace is in the garage, where is the supply for the combustion air?

Have the unit serviced by a qualified HVAC Contractor.

Geez, Brian you always take the easy way out. :slight_smile:

Look for a detached or torn supply duct.

If the entire supply is blocked so the fan can’t blow, it won’t draw well either. From your description, his system seems to be moving air, just not where it’s supposed to. Dirty evaporator coil would impede airflow too.