A schoolmate and close neighbor live in a home that requires a/c for it to be comfortable, however this means that she has to have the AC and furnace running when it is summer time and winter, respectively; She depends on the Heating, Ventilation and A/C system honestly to survive.
This one time, she felt some unusual plastic aroma from her furnace, but it had been a long time before it was used since my buddy and I had just come from a long summer time season.
It is possible for one to feel the burning aroma after a while of furnace disuse. Typically, this results from accumulated dust and dirt, which must burn first before the furnace can heat up. It should take a few minutes before the burning aroma dissipates! However, when the scent tends towards plastic, then you have to be cautious. This could mean many things, with the first being that some plastic material may have been accidentally left inside the furnace and is now burning when you light it. It is also possible that wires could be burning or worn out and in need of repairs. The latter case is the most proper occurrence, components that need to be upgraded in this case include capacitors that are often plastic coated and will aroma burnt plastic when they malfunction. Others that could lead to this aroma also have the fan belt and plastic-coated wires, when these components wear out, they are easily affected by heat and, as a result, will burn. In her case, the pieces were worn out and needed urgent upgradement. However, constantly call an Heating, Ventilation and A/C professional to assess the disfigurement and advise otherwise. If the aroma intensifies with time despite switching off the furnace, you need to contact the fire repair to be on standby just in case something serious happens.