From: On Demand

The gas-fired TK-3 Pro is designed to withstand space-heating and domestic recirculation systems in residential applications. It starts heating water at flow rates as low as 0.5 gallons per minute, but it can generate an unlimited supply of hot water at a maximum flow rate of 7 gallons per minute. The unit measures 13.8 inches wide and weighs 40 pounds. It can be installed inside or outside and can be direct-vented. Energy factor: Natural gas: 0.827; LP: 0.833. 888.882.5244.