Average BTU Ratings. A typical furnace is rated at 100,000 or 80,000 BTU per hour, but furnaces might be as small as 40,000 or as large as more than 200,000 BTU. A 90 percent high-efficiency rated at 60,000 BTU will deliver about 54,000 BTUs per hour of heat energy to your home.Jun 19, 2017read more >>