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A direct-vent sealed-combustion fireplace takes its combustion air directly from outside through a dedicated air inlet and vents combustion products directly outside
A direct-vent sealed-combustion furnace has dedicated pipes for combustion air and exhaust
A portable CO monitor is used to test for ambient CO near a ventless combustion fireplace
A ventless gas fireplace has no chimney
Because flue temperatures are cool, intake and exhaust ducts on a Category 4 direct-vent sealed-combustion condensing furnace can be made of PVC
Direct vent appliance installed
For fireplaces that are not mechanically drafted or direct-vented to outdoors, total net rated exhaust flow of the two largest exhaust fans is .15 CFM per 100 sq. ft. of occupiable space when at full capacity
Furnaces, boilers, and water heaters located within the home’s pressure boundary are mechanically drafted or direct-vented
National Fuel Gas Code (NFPA 2012) identifies four categories for combustion furnaces and water heaters based on combustion type (sealed or unsealed) and vent pipe temperature
Naturally drafted heater installed. Requires combustion safety testing
Naturally drafted water heater installed. Requires combustion safety testing
Power vented water heater installed
The natural draft and induced draft furnace are both Category I appliances that receive combustion air from the combustion appliance zone
The raised hood at the base of the vent stack on this water heater shows that it is an atmospheric vented gas water heater