Reznor UDZ-45 Unit Heater, 45,000 BTU - Liquid PropaneFor air circulation, the Reznor UDZ uses an axial propellor fan. Model UDZ gas fired, separated combustion unit heaters are great for space heating applications. These models use outside air for combustion to prevent dirt, lint, dust, or other contaminants in the indoor atmosphere from being burned. Model UDZ is available in 14 sizes ranging from 30,000 to 400,000 BTUH gas input and are approved for installation in the United States and Canada by ETL.