HVACopediaTrane · Furnace troubleshooting
Twinning furnaces
What is going on
Twinned Trane furnaces share a duct system, so they have to be matched and see equal resistance. Before wiring anything, confirm both units are identical in configuration and size, and that the returns and ducts are balanced. Wire per the field wiring diagrams only.
Likely causes
- Furnaces of different configuration, capacity or airflow
- Unequal return pressure drops between the two furnaces
- Duct lengths and sizes not equivalent
Check in this order
- Confirm both furnaces have the same configuration, capacity and airflow.
- Use common returns with equal pressure drops, or ducts with equivalent lengths and sizes.
- Wire the furnaces per the field wiring diagrams for the hookup.
- Power down both units before working on the control wiring.
- After startup, compare temperature rise on each furnace.
Applies to: Twinned furnace installations
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Source: Trane installer's guide, p. 28. 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.