I’ve read nearly gas stove can be configured to burn either natural gas (NG) or liquid propane (LP) gas. Depending on the stove, it can take a few minor adjustments or, in some cases, some replacement parts or parts upgrade to convert between the two gas types. In some parts of the world, gas stoves burn butane!
I know my 1953 OKM is designed to handle either NG or LPG. Right now my stove is set for natural. Since I moved to a rural place with no natural gas infrastructure, I need to convert Lucy to burn propane gas.
Note: Modern gas stoves may come with a conversion “kit”. Vintage gas stoves do not.
There are a number of the steps, possible supplies, parts, etc. needed to perform a proper conversion. And there are but a few shops in the country that can execute the conversion and include necessary safety updates. I haven’t priced the service, but I will assume the expertise required is out of my price range. Add to that, the cost of shipping the stove to and back home.On my budget, I’ll have to learn to do the conversion myself. If I’m lucky I might find a local tech for advice or assistance, if needed.
There’s one video that I use as a gauge of how knowledgeable I’m becoming about portable propane tank issues and the hurdles set up by some extremely greedy gas suppliers who don’t want to bother with only supplying gas for a stove. When I reach the point where I can understand everything the guy in the video is saying, I’ll be ready. “Installing a Gas Range with Portable Propane Tanks, will it work?” https://www.youtube.com/watch?v=wF6yeaOw_Os
There are a few very important things to understand so the conversion goes as intended.
LP gas is more potent than natural gas. One cubic foot of natural gas generates about 1,000 BTUs (British Thermal Units) of heat. Propane generates about 2,500 BTUs per cubic foot! It also tends to be delivered to the stove burners at a higher pressure than NG (0.4 psi for LP vs 0.25 psi for NG). When converting a stove from NG to LP gas, the gas flow has to be throttled back to maintain the same BTUs the stove burners are designed to sustain. If I just piped LP into my NG-configured stove I could turn my stove into a modest flame thrower. Pass.
| psi | BTU per cubic ft | air/gas ratio | |
| Natural gas | 0.25 | 1000 | 90% / 10% |
| Liquid propane gas | 0.40 | 2500 | 96% / 4% |
If you are hardcore and want hardcore details about NG and LP pressure specs, try this: http://inspectapedia.com/plumbing/Gas_Pressures.php
The basic procedure for converting stoves from one gas to another (between NG and LP) is the same, in concept. The components in the stove that tightly control the amount of gas delivered into the stove’s plumbing are called valves. The tiny opening in a valve where the gas is emitted is called an orifice. Each orifice size in a stove has to match the gas type in accordance to the burner’s size. Relatively speaking, orifice sizes for LP are smaller than for NG. If a stove configured to burn NG is supplied with LP gas, you can turn your stove into a flame thrower because it’s getting too much fuel to burn. If a stove configured to burn LP gas is fed NG, there could be very weak to no flames.
Fortunately, my stove has adjustable orifices. The orifice caps are threaded. I can turn the caps to increase or decrease how much gas can pass through the orifice. If my stove had fixed orifices, I’d have to get a different set of orifice caps sized for the other gas.
Down to the nitty gritty
The heart of conversion for my stove is to adjust all the stove valve orifices and air shutters that cover the venturi mixing space (the little spaces where gas and air mix). Valve orifices are where the raw gas is expelled, aimed at the mixing space. Those orifices can be adjusted, throttled own in this case, to handle propane. From the valves, the gas flows into the mixing gas assembly mixing space. The air shutters (look like butterfly wings) can be manually adjusted to control the amount of air allowed into the space. The proper balance of combustible gas and air will create the optimal burn. Too much or too little of air or gas can cause serious problems (soot, excessive carbon monoxide, excessive heat, etc.)
Over time, I’ve learned to identify the various places in my OKM where I will need to adjust the gas flow and the air flow and what the flame should look like when the mix is correct. l
1. Cooktop burner adjustable Alltrol double valve orifices (4 x 2 = 8) (each double gas valve has one orifice for the main burner and another for the little simmer burner) photo Note: If my stove has fixed valves, I’d have to remove the NG orifice sized caps and install the LP ones. With adjustables, I just have to rotate the caps so the opening gets closer to the needle, while watching the flames. If I screw the caps all the way in and the flame is still too wild and woolly, I’ll have get a cap with an opening sized for propane gas.
2. Cooktop burner air shutters (8) (each valve inserts into its own air chamber with an air shutter). The orifice cap and the air shutter need to be adjusted in concert to produce the best flame profile.
3. Pilot burner valves (4) . My stove has four pilot valves attached directly to the manifold; one for the left side cooktop pilot burner, one for the right pilot burner, one for the oven and a final valve for the broiler.
4. The oven and broiler pilot burners also have orifices sized for the two different gases. Remember to change those when converting the gas plumbing.
5. Oven burner orifice and air shutter. Way in the back of the of and below the oven burner, I’ve seen the air shutter and the orifice cap behind it. I am not looking forward to trying the tweak that!
6. Broiler burner orifice and air shutter. Way in the back of the of and below the oven burner, is another air shutter/orifice cap set.
7. Robertshaw BJWAZ oven thermostat bypass. This valve(adjustor) is far easier to reach. The bypass flame is the minimum oven flame.
8. Add an NG/LP regulator for stove gas supply. Adding a stove regulator doesn’t hurt. The stove regulator is a very simple mechanism designed to prevent the gas type it’s set to from exceeding the prescribed pressure. However, most propane delivery systems are replete with regulators, because the difference between the tank pressure and the pressure prescribed per appliance is HUGE.
Propane pressure in most tanks should be between 100 and 200 psi to ensure that the liquid propane gas remains in a liquid state. Pressure at the gas stove for propane should be about 0.40 psi.
Consequently, there are several regulators required the step the pressure down. Having one more that’s dedicated to the stove is a nice addition, in case a regulator upstream fails.
9. Optional: Updated safety valve: The vintage safety valves were configured to only handle the main oven burner gas supply. Modern safety valves also allow the oven pilot burner gas supply to be routed through them. If I wanted to take advantage of that extra safety measure, I’d need to reroute the oven pilot gas line to and from the safety.
10. Carbon monoxide and raw combustible gas detectors. Carbon monoxide detectors are advisable in any instance where fuel (wood, gas or oil) is burned. A detector for raw propane is a smart addition. Propane gas is heavier than air. If it leaked out, anything at lower levels (babies on floors, pets, and basements might have to deal with the accumulation of propane.
Lots to do
Ok, so that seems like a lot to unpack, right? Depending on the number of cooktop, oven and broiler burners , there could be quite a number of things for me to do. I’ll take things in stages to make it all more manageable. I will be going through this process soon. Adventures ahead!
Inspectapedia
How to Convert a Heating Appliance from LP to Natural Gas
or from Natural Gas to Propane
Calibrating a Robertshaw BJ Thermostat
Here are a couple of decent youtube videos to you might be interested in. Good stuff.
Why? Once the conversion is done, you should test the oven temperature is spot on. If not, the thermostat might need to be recalibrated. Don’t forget to check the bypass response.
How to calibrate BJ thermostat tutorial DIY Windy City Restaurant Equipment Parts
American Range – Calibrating BJ Thermostat
