Never idle a car inside a garage. Never use gas lanterns and heaters in a camper unless they are vented to the outside. Be sure the chimney is free of blockages, corrosion, and loose connections. Have a professional check all heating appliances for proper function. Service your individual appliances regularly.
Proper installation is critical to the safe operation of combustion appliances.
Carefully follow the manufacturer's instructions on installation. Follow all building codes as well. Correctly install all vented appliances based on the manufacturers' instructions. Follow operating instructions as recommended by the manufacturer. Your local utility company will normally check your home for sources of carbon monoxide for a nominal charge.