I have gas heat in my home. Sometimes it seems like there's cool air coming out of the vents through the duct work even though I am heating the house. Is this normal?

Thank you very much.

At times this would be normal, but those times would normally be limited to the beginning or end of a heating cycle. A unit that short-cycles can run excessively while producing this effect.

As would a unit that has a flame sensor failing intermittently.

Well, I really am an idiot.

The thermostat was set to "circulate" instead of just "heat".

So, my next question: I have it set to "circulate" for spring, summer, and fall, would you suggest I also leave it there for winter, or just leave it at "heat"?

Thanks so much,
Steve