Do I need a source of fresh air when using in an ice house?

This is an unvented gas-fired heater. The heater uses air (oxygen) from the area in which the heater is used. Adequate combustion and ventilation air must be provided. The Heat Hog does have a safety Oxygen Depletion Sensor (ODS) to keep you safe but you must follow the instructions as outlined in the Heat Hog owners’ manual.