On Dec 2, 9:55*pm, mike wrote:
Has anybody mentioned the obvious: Check the filter???
Verify that the air volume and temperature outa the vents seems reasonable?

Nope, and you're right: I neglected to mention that we had recently
changed the filter, and when the furnace comes on, air is moving out
of all vents well. Temperature is acceptable - neither cool nor too
hot - when air is moving. It's just getting the frelling furnace to
fire up that's the issue.