High-efficiency furnaces use outside air for combustion, since its heat exchangers are well-sealed in the unit. The air intake plays a role in combustion. If obstructed or too small, the high-efficiency furnace becomes less so. Properly installing and maintaining the air intake, therefore, enables the furnace to operate with maximum energy efficiency
Every high-efficiency furnace has two ports for a hookup to thick-wall PVC piping. One slot serves the exhaust pipe, while another is for the air-intake pipe. The diameter of both pipes should be the same, per the manufactures specifications: typically, a diameter of four inches, although the diameter may vary.
The vent pipes should be pitched to the outside. This enables pipes to drain away from the furnace (if condensation forms inside the pipes). Also, pipes should be installed next to each other so they are properly pressurized. This avoids competing pressures within the heat exchanger and allows for more complete combustion.
Using screens on the air intake outlet prevents critters from entering the furnace's heat exchanger. An Small animals may get trapped in the heat exchange, killing them when the furnace kicks on. You can prevent this by installing a screen on the inside of the exterior pipe. A screen also should be placed on the exhaust pipe.
Supporting the Vent
Supporting the weight of the vent is critical. Depending on the length of the pipe, an air intake may weigh between 20 pounds and 50 pounds. Installing supporting vents to the ceiling every four feet keeps the pipe from shifting or getting disconnected.
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