United States Stove Company Outdoor Warm Air Furnace - 180,000 BTU, 1800 CFM, Model# 1600EF Works with existing furnaces and HVAC duct work to heat up to 3000 square feet Easy connection to existing duct work Secondary heat exchanger with firebrick baffle for extra long life Manual damper system allows fine tuning for maximum efficiency Firebrick-lined firebox boosts efficiency and heating capacity