Maybe someone can correct me, but these engines are at best, what, 30% efficient? More or less anyway. So 70% of the fuel you purchase ends up as heat instead of turning the drive wheels. At normal highway speeds you're consuming about 4 gallons per hour, so you have, in effect, a gasoline fire consuming about 2.8 gallons an hour, or about 320,000 BTUs.
The typical home furnace puts out about 100,000 BTUs.