Horizontal installation: suspension, leveling and drain

What is going on

Horizontal furnaces need proper support, a level end-to-end set-up with a slight forward tilt, and a trap drop for condensate. Crawl space units must be suspended from floor joists or set on a concrete pad.

Likely causes

• Furnace sagging or sloping backward, so condensate does not drain
• Drain trap too close to the furnace bottom

Check in this order

1. If suspending from rafters or joists, use 3/8 in. threaded rod and 2 x 2 x 1/8 in. angle iron as shown in the figure.
2. Crawl space suspend from the floor joist or support on a concrete pad. Never set it on the ground or let it sit in water.
3. Level the furnace from end to end with a slight forward tilt so the access doors sit about 1/2 to 3/4 in. lower than the back panel.
4. Mount the condensate trap to the side panel with at least 5 1/2 in. of clearance below the furnace.
5. Slope the drain line down from the trap to the drain point.
6. Protect the trap and drain line from freezing if they are exposed to near-freezing temperatures.

More furnace guides

• Airflow lower than demanded, furnace runs on low stage when high stage is expected
• Alternate combustion air opening (upflow or horizontal)
• Alternate vent/flue location (upflow or horizontal left)
• Annual inspection checklist
• Auxiliary limit control (location and purpose)
• Auxiliary limit switch open (blower compartment)