Proper ventilation is required to maintain proper operation of your greenhouse heater. The Therma Grow heaters require 2.5 CFM per 1000 Btu/h of air exchange (i.e., 120 requires 300 CFM and 220 requires 550 CFM). For easy installation and proper air exchange for uniform temperatures, you can get the Indoor Ventilation Kit for your Therma Grow heater. This ventilation/mounting kit comes with a hooded air inlet with a transition duct for proper air intake to the heater. As well as an exhaust fan to ensure enough air exchange within the greenhouse to prevent build up of emissions. Therma Grow heaters meet all OSHA emission requirements for greenhouses.