I have a 10,000 BTU Ventless Natural Gas Heater in my small greenhouse. I do insure adequate ventilation by supplying an intake for air and an outlet. The type is the blue flame not the type with the element in front. I am going to change it to a 15 or 20 BTU type. Mine is Pro Comm similar to the one shown. They are banned in Canada for no good reason if installed with a vent. I would like your experience.