HVACopediaGoodman · Furnace troubleshooting
Multiple direct vent furnaces at one termination
What is going on
Multiple direct vent Goodman furnaces on one roof or one side wall. Same clearances as a single unit, per pair. Keep terminals level.
Likely causes
- Adjacent terminations closer than the single-unit clearances
- Exhaust outlets at different elevations
- Air intakes at different elevations, so one furnace pulls in another's flue gas
Check in this order
- On a common roof, keep the same minimum clearances between exhaust and intake terminations of adjacent units as for a single unit.
- On a common side wall, follow the clearance figure in the manual.
- Terminate all exhaust outlets at the same elevation.
- Terminate all air intakes at the same elevation.
- Check the layout against the manual before drilling any holes.
Applies to: Multiple direct vent furnaces
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)
Take it to the job
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Source: Goodman GMVC96 service manual, p. 19. Written in our own words; check the manual for your exact model.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.