Why does it smell like burnt plastic when we turn our heat on?

Has there been anyone in the attic? I had a similar problem, I accidentally stepped on the thermostat wires causing a 'short' as the control transformer burnt I smelled it throughout the house. I turned it off and replaced the wire, didn't kill the transformer. It is possible to get a piece of plastic resting against the heating chambers, as it burns you'll smell it, replace the filters! I keep a pack of new filters on hand, the filter, if installed right, should catch any debris from going into the furnace.

If this is the first time this year then furnace's will burn all the dust and stuff that find their way to the fire. Something plastic could have fallen into the fire area of your furnace it should burn up. If you still smell it after 5 hours of the furnace burning or a couple days then you need to start looking into the furnace. If the smell goes away then the plastic is burnt up.

This suggests furnace wiring that may have been chewed by mice and is shorting out, or wiring that has contact with the heat exchanger.

refer to a HVAC certified tech.

The furnace is now at the upper limits of its useful life.

If it's not a part burning out, we had smoke one time also, and it turned out to be a piece of cardboard that had fallen from the packing of it or something like that. (even after it being 12 yrs. old) So, something could be in there. A fire could start.

Try this article , Good Luck! :)

http://www.ehow.com/info_7749907_burning-smells-fu...