Using Wood Furnace and Rinnai Gas Together

Tnelson7

We recently bought this house that has a Rinnai Natural gas unit and a wood burning furnace. The wood furnace is ducted throughout the house and apparently also has a warm vent through the gas heater. Should the gas heater be turned completely off when wood furnace is in use?

I am mainly wondering if it’s possible to leave the gas heater on as backup when fire in the furnace burns out or does the wood furnace need to be unplugged and completely cold to use the gas heater for safety?

GroundUp

Are you referring to a Rinnai direct vent wall heater? What do you mean it has a warm vent through the heater? Like there is a supply duct from that unit back into the ductwork?

Tnelson7

Yes a Rinnai direct vent wall heater. With the gas heater off, heat from the wood burning furnace blows through the vents of the gas wall heater.

bburd

You have a dangerous condition, and if things go badly you may have a problem collecting from your homeowner's insurance.

If the gas heater is on and its return air, which should be at room temperature, is hot from the wood furnace, the gas heater will not be able to transfer enough of the heat from the burning gas to the room to operate safely. If the high limit switch fails to trip this could start a fire.

The solution is to reroute that supply duct from the wood furnace away from the gas heater's return air inlet. 

Tnelson7

The gas heater is off and the wood furnace air is coming through the warm air outlet of the gas heater. I don’t know how it’s connected or if it has anything to do with the intake?

bburd

If you post some photos of the gas heater and surrounding area we can probably help you figure out what to do. Someone must've modified the return air inlet area of the gas heater and connected it to the furnace ductwork.