Sulfur smell from heated air

snowbrush

Every morning when our gas furnace starts up (off all night) the first hour of operation brings a mild smell of sulfur. After that the rest of the day the furnace operates without smell. I have checked the flame and it is always bright blue (not orange or yellow) and our C02 monitor shows no readings. What could be causing this odor only during startup after an overnight shutdown?

jogr

My biggest concern is that it could be some sort of gas leak since gas has a sulphur compound put in it to alert you to leaks. Other than that I can't think of a source for the sulphur smell.

A gas leak would be very serious so don't ignore it. Unless you're comfortable tracking down the source and fixing it you should call in a pro.