Install condensate trap and drain

What is going on

This covers setting up the condensate trap and drain line on the furnace. A high efficiency furnace makes condensate every cycle, and a trap or drain that is wrong will back up, leak onto the floor, or trip the pressure switch. Take your time to decide the routing before you glue anything. A trap that is not primed at startup can let flue gas escape through the drain, so do not skip that step.

Likely causes

• New installation or trap replacement
• Changing the drain side after relocating the furnace
• Cracked or leaking trap found during service
• Drain line without proper slope holding water back

Check in this order

1. Decide which side the condensate line exits, where the trap goes, and how much PVC is needed before cutting anything.
2. Remove the plug from the cold end header box and install a 1/2 in NPT male fitting. Use Teflon tape or pipe dope.
3. Install the trap cap over the clean-out opening at the base of the trap and secure it with a clamp.
4. Glue the PVC trap assembly and drain line. Keep the 1/4 in per ft downward slope to the drain.
5. Install the field-supplied vent on the trap assembly so it does not block service access.
6. Prime the trap before start-up so flue gas cannot pass through it.
7. After firing, watch the drain flow and check all joints for drips.

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