Bio-King Model BK40 furnaces feature a variable heating capacity of up to 40,000 Btu, a large fuel hopper and heavy cast-iron doors and burn pot. The firebox and 20-tube heat-exchanger system have a combined heat-transfer area of over 35 square feet, maximizing efficiency and extracting as much heat as possible from your fuel. Bio-King furnaces comply with UL39 test standards. Contact: (715) 720-1794, sales@energyking.com or www.energyking.com.