Duct connection and return air

What is going on

Duct layout and return air requirements for the furnace.

Check in this order

1. Size ducts per ACCA Manual D and install them per NFPA 90.
2. If a cooling coil is used, install the furnace upstream of the coil or in parallel with it. Parallel dampers must stop chilled air entering the furnace.
3. Use flexible connectors on supply and return to reduce vibration.
4. Route returns away from the living area where possible to cut noise.
5. If supply ducts carry air outside the furnace room, seal the return to the furnace and terminate it outside that space.
6. Make sure the return duct includes provision for return air filters.
7. On side return upflow installs, remove the insulation around the opening in the blower compartment.
8. Cut the return opening using the locating notches on the side panels and the outline drawing dimensions.
9. If a 3/4 in flange is needed, extend the cut as shown, cut corners diagonally and bend outward.
10. If no flange is needed and a filter frame is used, cut along the knockout guidelines.
11. Connect supply and return ducts to the furnace using the outline drawing sizes and locations.
12. When replacing a furnace, clean out old ductwork, cover registers with thin cloths and run the fan for 10 minutes. Remove the cloths before starting the furnace.

More furnace guides

• Abnormal conditions and protection
• Adjust gas valve manifold pressure
• Air for combustion and ventilation in non-direct vent installs
• Airflow adjustment check
• Airflow and temperature rise check
• Bottom return filter rack installation (upflow)