The part(s) or condition(s) listed below for the symptom Furnace smells like gas are ordered from most likely to least likely to occur. Check or test each item, starting with the items at the top of the page.
If varnish or stain fumes are drawn into a furnace and burned it will produce a pungent odor. Unlike a gas leak that will smell like a skunk, this odor is more of a nuisance. Opening a window should help. After the room has had sufficent time to vent out the smell should dissipate.
The smell could be from the incoming gas line or from a gas valve leak. Please schedule a technician for repairs.
If the smell occurs only when the furnace is heating, one of the components suppling gas to the furnace may be leaking. In this case it is best to call a licensed technician to diagnose and repair the furnace.