something was over heated. After I searched and checked possible locations and items I still had no clue. The smell had gone gradually after a few hours. When I came back to indoor from cleaning of snow outside, I found the heating system was not normal from the display of heating controller. I checked and tested the heating system further. Finally I found the blower didn't work when the furnace' s flame was lighted up. For safety reason, I turned off the setting of heating from the controller. Now I can go to sleep without worrying about "over heated" , even though there is no heating tonight. Tomorrow I will have to find someone to check and repair it.