Converting a furnace to propane from natural gas or vice versa is a straight forward simple process but great care has to be taken because of the possible danger if done wrong.
Converting natural gas to propane or propane to natural gas is the same processes. Which involves changing out the furnace orifices/jets and the gas valve spring. The only main difference is that propane gas usually has a regulator at the tank to regulate the gas pressure.
Many newer furnaces often have these parts to convert a furnace 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.
Propane burns hotter than natural gas so the orifices need to be smaller allowing out less gas.
A furnaces heat exchanger, which is where the flames burn, is rated up to a certain temperature. 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 kits on Amazon
Modine 53080 Gas to LP Conversion Kit for 100K BTU
Steps for Converting a Basic Furnace
1…Turn the gas off to the unit and turn the power off to the unit.
2…Take pictures and write down the wiring connections to the gas valve
3…Disconnect the gas valve
4…Locate the orifices/jets and with the correct size wrench remove them.
5…Install the new orifices.
6…Locate the spring in the gas valve
7…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.
Here is a video of the entire process being done.