" used improper usenet message composition style
by unnecessarily full-quoting:

If your furnace really is undersized, then it should basically be
on all the time (and not be able to bring the house up to the
temperature you want). I doubt that's whats really happening,
because your system appears to be cycling.

That depends on how cold it is outside. The above problem would
only present itself when it's really cold outside.

The way the OP is describing the situation, it seems that the
contractors are telling him that the reason for his environmental
discomfort is because is furnace is undersized (which would be a
bull-**** reason for such a problem).

You will note that the OP is not posting this question in the middle of
winter - and he's not complaining that his home is generally colder than
he wants it to be.

it's hard to imagine what an undersized furnace looks like
for a 10 year-old house.

But here in NJ I've seen a trend to err on the other side now
with systems that are too small.

And would you expect comfort problems in November with an undersized
furnace?

Or in January?

We don't even know where this guy is, or that he has a nat-gas furnace.