"John Szydelko" wrote in message
At night we turn the furnace down to 55 and in the morning turn it
back up
to 70. Every morning there is a distinct odor when the furnace first
kicks
in. We've cleaned the burners to no avail. This doesn't happen when
just
the fan is turned on, only when the burners ignite.
Any ideas?

You have poop in your vents?