Converting natural gas to propane or propane to natural gas is the same processes by installing new orifices.
It involves changing out the the correct sized furnace orifices/jets and the gas valve spring.
The same procedure is done to switch between gas types.
The main difference is that propane gas usually has a regulator at the tank to regulate the gas pressure.
Many newer furnaces often have the parts (orifice and spring) to convert a system in a small packet somewhere in the control box or with the instructions.
If you don’t have the parts a conversion kit will need to be ordered.
An experienced technician can solder or braze the tips of the orifices and then drill out the correct diameter needed but I don’t suggest this. It is difficult to get the correct diameter needed even for an experienced technician.
Buying the correct propane/natural gas conversion kit and following the instructions for your furnace is key.
If the temperature goes over the rating for the furnace the heat exchanger can become cracked and allow carbon monoxide and other toxic gasses to enter a home.
Example LP Gas Conversion Kit on Amazon
Modine 53080 Gas to LP Conversion Kit for 100K BTU
Steps for Converting a Furnace to Propane Natural Gas (Basic Over)
- Turn the gas and power off the unit.
- Take pictures and write down the wiring connections to the gas valve.
- Disconnect the gas valve.
- Locate the orifices/jets and with the correct size wrench remove them.
- Install the new orifices.
- Locate the spring in the gas valve.
- Remove and replace the gas valve spring with the replacement.
After these steps are done to the furnace it should have the pressure set correctly with a water column manometer.
Propane units runs around 9 to 11 inches and natural gas runs around 3 to 4 inches. Again this will depend on your furnace documentation.
Converting from natural gas to propane involves steps that may differ for manufactured to manufacture because of design differences of propane gas valves.
For example, converting from natural gas to propane gas will include changing the regulator pressure, installing smaller main burner orifices, and installing a new pilot orifice, this process may also include changing the ignition control module to 100% shut off module because propane gas is heavier than air.