Vent and inlet air connection and pipe support

What is going on

Pipe joints have to be fastened and sealed so combustion products stay out of the building. Think of it as two jobs. The inlet is a friction fit sealed so it can come apart for service. The vent pipe is connected to the vent collar the same way, with RTV, so you can separate it later. Keep both pipes supported along their whole length, and terminate them in the same pressure zone, otherwise the pressure switch will nuisance trip.

Likely causes

• Flue gas leaking at an unsealed or loose joint
• Pipes unsupported and sagging, stressing the joints
• Vent and inlet ending in different pressure zones
• Joints glued solid so the furnace cannot be serviced or moved

Check in this order

1. Make the combustion air inlet connection a friction fit. Seal the inlet joint with RTV so it can be separated for service.
2. Connect the vent pipe to the vent collar with RTV sealant so it can be separated later for service or clearance.
3. Support the inlet and vent pipes along their entire length.
4. Keep the vent and inlet in the same pressure zone so the vent lengths stay valid.
5. Terminating in different pressure zones can cause nuisance pressure switch trips. If zones differ, the inlet must be in the higher (more positive) zone.
6. Check for flue gas leaks after the first run.

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)