Development Services

Mechanical Details

The information below provides a checklist for the typical installation of a forced air unit in attic.
  • Obtain the furnace manufacturers installation instructions and install the forced air furnace to their specifications.
  • Establish the best location for installation of forced air unit and vent.
  • An attic in which a FAU is installed shall be accessible by an opening and passageway 30" x 30" in size. Attic access may be reduced to 22" x 30" provided the largest piece of equipment can be removed through the opening.
  • Install passageway platform minimum 24" inches width and maximum 20 feet in length to FAU.
  • Install working platform not less than 30" in depth and width in front of the entire firebox side of the FAU.
  • A permanent electric outlet and lighting fixture controlled by a switch located at the required passageway opening shall be provided at or near the furnace.
  • Install vent, roof flashing and vent cap. Double wall type vent requires minimum 1" clearance to combustible materials and requires a minimum 5' - 0" vent termination above the highest vent collar it serves.
  • A means shall be provided to disconnect the FAU from the power source for servicing the appliance. See manufacturers installation instructions for approved disconnect method.
  • An approved shut-off valve is required to be installed at the gas piping outlet, immediately ahead of the flex connector, and must be accessible.
The information below provides a checklist for a typical wall furnace installation. 
  • Obtain the furnace manufacturer’s installation instructions and install the furnace to their specifications.
  • Establish location of the wall furnace. Maintain six-inch minimum from the inside corner of rooms and 12" from the swing of doors and windows. Establish best location for installation of vent.
  • Cut out double top plate in a minimum four-inch nominal wall to a full 14 2".
  • Head out any ceiling joists that will be closer than one inch to the vent when installed.
  • Cut hole in roof sheathing to accommodate vent penetration.
  • Install furnace header plate in the stud bay. Secure with screws or nails.
  • Attach hold-down base plate to furnace header plate with sheet metal screws.
  • Install ABW gas vent in stud space that is free of obstructions. Snap vent into hold-down base plate. Snap sections of vent together. Maintain 12-foot minimum vent termination from bottom plate to top of vent.
  • Install listed ceiling plate spacer. The plate spacer is designed to center the furnace vent in the stud space and to allow heat to dissipate from stud space into the attic space above.
  • Install Attic shield. An attic shield is a sheet metal sleeve that shall extend around the gas vent from the top of the ceiling plate into the attic at least 12" below the roof sheathing.
  • Install roof flashing and storm collar.
  • Install vent cap.
  • Install gas line to stud space serving wall furnace.
  • Provide gas test. Install thermostat wire.