How to Install Air-Handling Units

Place the air handler in the desired position, which depends on the direction of the air flow -- upflow, downflow, horizontal right-hand or horizontal left-hand. Connect the ductwork accordingly.

Place a carpenter’s level on the unit to check if it’s level. Insert wood shim underneath the unit to level low spots. Position the unit to ensure access to the controls, filter rack and blower compartment.

Check the existing ductwork system or install new duct. Ensure the installation complies with "ACCA Manual D Duct Design for Residential Winter and Summer Air Conditioning and Equipment Selection." This is critical for assuring the honoring of the warranty by the product manufacturer.

Cut the opening for the return air supply in the bottom of the cabinet with aviation snips. Connect the return air ducts. Follow the manufacturer’s instructions for attaching the elbow required for connecting the return air drop.

Assemble the plenum, which consists of a sheet metal box that fits on the top of the unit. Attach the plenum to the flanges surrounding the blower opening and secure with sheet-metal screws. Cut a hole in the plenum and install starting collars. Connect the existing supply ducts or install new ducts. Wrap ducts in unconditioned spaces with insulation with a vapor barrier.

Turn off the electricity at the main electrical panel. Consult the wiring diagram in the installation manual, as well as local and national electrical codes, for proper wiring. This includes the installation of the correct number of circuit breakers, designated circuit breaker and a disconnect switch in close proximity to the air-handling unit. Install circuit protection and secure the ground wire to the cabinet in accordance with the manual. Wire the control with low-voltage conductor.

Refer to the installation manual to determine the correct tubing diameter. Keep the seals on the coils until ready for connection. Run the copper tubing for the unit refrigerant. Do not install in a manner that blocks the service access at the front of the unit. Follow the building codes for charging the unit. Most codes required a licensed professional to perform this aspect of the installation.

Install the drain line to the drain pan in a manner that allows at least 24 inches of clearance access to the front of the unit. Use copper tubing. Apply pipe wrap to the fittings at the drain pan. Pitch the line a minimum of 1/8 inch per linear foot toward the drain opening.

Consult the air-handling installation manual’s checklist for the start-up of the unit and adjustment of the control. Schedule an inspection with the local building-code inspector to have the unit approved.