I have a Heil brand gas forced hot ait furnace. It comes on & heats
up, but doesn't blow hot air in the house. The blower comes on, but
usually doesn't blow very hot air.

I had a tech come out four times. He said it is heating up to the right
temp of 140 degrees. He replaced the fan control switch, and then the
electronic thermostac. It is still doing it. Now he says that we do
not have enough vents and wants to run another return.

The problem I have with that is the furnace is 10 years old and we
lived her 4 years. It was never a problem before. Until this winter
it would get very hot. I'd be swetting at 75 degrees. Now it feels
cold and damp at 75, if it even reaches that temp. I'll have it set
for 78 degrees and it will never show more than 69 or 70 at night.
During the day it gets warmer, but I think that's from the sun coming
in the windows.

Could sombody please share an opinion of what to do. It's going to
start getting colder at night here in New Jersey. Thanks.