Temporary heating during building construction

What is going on

I see it all the time, a builder wants the new furnace running while drywall dust is still flying. The manufacturer allows it only if every listed condition is met. Drywall dust, sanding dust and cold return air are what kill a heat exchanger and a blower in a few weeks, so the conditions are not optional. If you cannot meet them all, do not use the furnace as a construction heater.

Likely causes

• Venting not finished or not installed per the instructions
• Field jumpers on the thermostat or controls
• Return duct incomplete or unsealed, pulling in dust and cold air
• Combustion air coming from inside a dusty building
• Return air temperature below 55 or above 80 degrees F

Check in this order

1. Make sure the venting system is complete and installed per the instructions.
2. Control the furnace only with a room thermostat, with no field jumpers.
3. Make sure the return air duct is complete, sealed to the furnace, and clean filters are installed.
4. Verify input rate and temperature rise are within the nameplate values.
5. Make sure 100% of combustion air comes from outside the structure.
6. Keep return air temperature between 55 and 80 degrees F.
7. After construction, clean the furnace, ducts and components and verify ignition, input, temperature rise and venting per the manufacturer's instructions.
8. Replace filters before the homeowner takes over.

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)