I just bought my first home a few months ago in July. The home is 15 years old and sat for 6 months before I bought it. We have a Central Heat and Air unit that uses Natural Gas for the heat. The air conditioner works fine, but we have been smelling a burnt plastic smell when using the heat. Since the nights have been getting cooler, we have been running the heat at 66 to 68 degrees to stay warm at night. By running the heat at this temperature we haven't had any problems or burnt plastic smell. We have had some nights that have dipped down into the 20's, so we started running the heat at 70 degrees. We awoke that night to a terrible smell that smelled like burnt plastic. We thought that the house was on fire, but there was no smoke or signs of a fire anywhere. We put the thermostat back down to 68 degrees and the smell went away. What do I need to do?