Furnace exhaust pipe size. The PVC pipes are used for air intake exhaust gas and to remove the corrosive condensation resulting from the combustion process. I have an oil boiler which does take a 6 inch flue pipe but i have not seen a newer aka last 10 or 15 years gas installation which Uses anything any where near that size even it is an atmospheric vented furnace or boiler. Do propane heaters give off moisture. But wait you just contradicted yourself when you told me what size screens will fit. The pipe you purchase should match the inside diameter of the hole. There will be a point where these factors counter-balance the momentum of the flue-gases. Measure the vertical distance from the upper side of the ceiling to the underside of the roof sheathing and add 36 inches for clearance above the roof.
Methane produces 2 cubic feet of water vapor for every cubic foot of gas burned while propane produces 4 cubic feet of vapor for every cubic foot. It can be larger but must never be smaller or leaks will result. PVC intake and exhaust vent pipes must be supported all the way from the furnace to the discharge points outside. If the BTU is 80K or above it is preferred to have 3 inch vent pipes but HVAC person said BTU size normally doesnt change or change just a bit unless I add a new living space area to a house that will require more capacity of furnace and will need 3 inch vents. Make the pipe too long. Now that you have safely sealed the air leaks around the furnace exhaust you can work on insulating your attic space.
The greater the BTUH input of the furnace the greater is the amount. In contrast modern high-efficiency condensing furnaces exhaust much cooler gasses and need only plastic pipe materialssuch as PVC CPVC or ABSfor their exhaust vents. I did my research and found out that BTU size of the furnace drives the flu pipe size. This is what will make up your flue pipe.
Teah a single exhaust pipe is safe to the occupants but it makes the furnace use pre heated air for combustion wasting energy. This is what will make up your flue pipe. Traditional gas-fired forced-air furnaces produce hot combustion exhaust gasses and therefore need metal vent pipes or chimneys. Heres a quick table that shows how many CFM each common pipe size will flow as well as the estimated max horsepower for each pipe size.