Intake piping for non-direct vent installations (air from indoors)

What is going on

On a non-direct vent install, the furnace takes its combustion air from the room, so the air intake pipe is really just a protected opening. Before relying on indoor air, think about what is in it. Dust, laundry chemicals, paint fumes or insulation fibres can damage components and foul the burners. The Combustion, Dilution and Ventilation Air guidelines apply here, and the room must meet them before the furnace is fired.

Likely causes

• Dirty or chemical-laden indoor air drawn into the burner
• Intake opening too close to the floor, a platform or a wall
• Loose insulation or debris clogging the intake screen
• Room too tight to supply enough combustion air

Check in this order

1. Check the room first against the Combustion, Dilution and Ventilation Air guidelines before routing any pipe.
2. Use field-supplied materials and the factory air intake screen to route the intake piping as shown in figure 26 or 27.
3. Keep at least 3 in. (76 mm) clear around the air intake opening.
4. In upflow, point the intake opening forward or to either side.
5. In horizontal, point the intake opening straight out (preferred) or down.
6. Keep the intake away from the floor or a platform so it is not obstructed.
7. Keep loose insulation or other debris away from the screen.
8. Use a sheet metal screw on the intake pipe connector if desired.

More furnace guides

• Annual planned service inspection
• Annual service checklist
• Blower access panel and carbon monoxide hazard
• Burner assembly cleaning
• Change blower speed tap
• Check temperature rise and adjust blower speed