the warning that come with UTH's say to ventilate to prevent fire hazards, but that is when they are un-regulated by a thermostat or dimmer or rheostat. when the heat source is controlled there is no need for ventilation because your thermostat or other device should prevent ur heat source from getting so hot it will be a fire hazard. i have my stuff taped down in the back of a rack with foil tape and the tubs sit right on it. there is very little air flow getting to the heat source and i have not had any issues. also, if u dont have ur tubs sitting right on the heat source then u have to turn up ur thermostat so that the air between the tub and heat source gets hot enough and gets ur tubs to the appropriate temps.