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!