We have an add-on wood burning stove on our gas furnace. We have our own supply of wood for the stove so the cost for us consists mainly of gas for the saw to cut up the wood. We live in southern mich so it make a considerable difference in our heating costs over running the gas furnace.
Tom works 3rd shift but if you want to talk to him about ours (which is an older one) let me know and I'll PM our number to you and the best time to reach him.
It cut our heat bill enough the gas company called and wanted to know why we weren't spending a fortune with them in the winter.
Ours is an older model than the ones now and not quite as efficient but we would get another one if this one goes bad.