Condensate drain system general rules

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Rules for the condensate drain trap and field drain line.

Check in this order

1. Use the drain trap supplied with the furnace.
2. Prime the drain trap before the first start. Both sides of the trap must be primed.
3. Route the drain line to meet local and national codes.
4. Slope the drain line 1/4 in per foot downward toward the drain.
5. Do not trap the drain line anywhere except at the furnace drain trap.
6. Protect the drain line from freezing where it runs through cold areas.
7. With an AC coil on a common drain, install an open tee near the coil to relieve positive pressure.
8. Vent a common drain with an open tee no higher than the bottom of the collector box.
9. Vertical installs AC coil condensate may drain into the furnace trap only if a trap sits between the coil and furnace trap and the drain does not end below the furnace trap water level.

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)