Apologies if this was double-posted.

My furnace seems to be running way too often, upwards of 30 minutes
every 30 minutes. It doesn't seem to matter how cold it gets outside,
it's always the same.

One thing that bothers me is, with the system "professionally"
balanced, the temperature at the registers was in the low 70's using
an infrared thermometer. I've since closed off the vents to all
unoccupied/unused rooms in the house, and even with just the living
room and main hallway heated, the vent temperature is still only in
the upper 80's. My understanding is that it should be around 100
degrees.

I think all the heat is going up the chimney. The exhaust pipe on the
furnace is RIPPING hot, can't even put my hand near it. It's putting
out a clean blue flame. Changing the filter didn't help. Pros say the
furnace is in perfect working order.

The furnace itself is a 1999 Amana, but I can't tell which model
because the labels are all in French (I'm in upstate NY, not Quebec)
and apparently use technical terms that the online translators can't
deal with. It's either a 48,000 or 65,000 BTU unit, depending on which
part of the label you read.

Mostly, I'm sick of being cold and listening to the furnace fan howl
all the time. I've got plenty of insulation (R38 batts over R19 in the
ceiliing joists). Walls are R11 with an extra inch of styrofoam and
housewrap under the siding. Windows are all double-pane vinyl units.
It's a pretty tight house, as I can't feel any drafts or hear any
whistles in high winds.