You Bought a Natural Gas Water Heater, But Propane Is All You Have
It happens more often than you’d think. You move into a house with a natural gas line that never got connected, or you buy an RV with a propane-only setup. The water heater is brand new, and someone told you, just hook it up to propane, it’ll work fine.
That advice is dangerously incomplete. Running propane through a natural gas water heater without modifying it is a fire hazard and a carbon monoxide risk. This article walks you through exactly what has to change, what you can do yourself, and when it’s smarter to hire a professional or replace the unit outright.
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You’ll also see a product that can keep you from burning through propane once the conversion is done—but more on that in a moment.
If you plan to use propane as your primary fuel, you might want a way to cut consumption when shore power is available. The RVGUARD RV Water Heater Electric Conversion Kit (B0F6L76H42) lets you run your water heater on electricity, keeping the propane system intact for backup. It connects to Suburban, Atwood, American, and More-Flo water heaters, includes a stainless steel heating rod with adjustable thermostat (90°F to 150°F), and snaps together with color-coded wiring. No pro skills required. It’s not a replacement for the conversion itself, but it saves propane every time you plug into a 120V outlet.
The Short Answer: Yes, But It’s Not Just a Tank Swap
You can convert a natural gas water heater to propane. But you cannot just connect a propane tank and call it done. Propane burns at a higher temperature and a different air-to-fuel ratio than natural gas. If you leave the natural gas orifice in place, the flame will be too large and yellow, producing soot and carbon monoxide. The gas valve regulator also sees the wrong pressure, which can overfire the burner or cause flame rollout.
The core changes are: orifice size, gas valve pressure setting, and often the burner air shutter adjustment. Some water heaters also require a different pilot assembly or a conversion kit specific to the brand.
Most modern water heaters sold in the US are dual-fuel capable out of the box—they ship with one orifice installed but include the other in the packaging. Check the owner’s manual or look behind the access panel. If your water heater is older than 10 years, it’s probably not dual-fuel, and the gas valve itself may need replacement.
What Parts Actually Need to Change
Here’s what a proper conversion involves, component by component. Numbers vary by brand and BTU rating, but the pattern holds.
The Orifice(s)
Natural gas orifices are larger because natural gas has about half the energy density of propane. For a typical 40,000 BTU burner, a natural gas orifice might be 0.055 inches in diameter. Propane needs roughly 0.040 inches. That difference is tiny—less than 1/64 of an inch—but it determines flame height and completeness of combustion.
Most water heaters have one orifice for the main burner and a smaller one for the pilot. Both need swapping. Some manufacturers sell conversion kits with the exact orifices and a label to stick on the unit. Use those if available. Buying generic orifices from a hardware store works, but you’ll need a drill size chart and a steady hand to get the right opening.
The Gas Valve Regulator
Natural gas comes into a home at around 5 to 7 inches of water column (WC). Propane systems supply 11 to 14 inches WC. The water heater’s gas valve has a regulator that expects a specific inlet pressure. On some models it can be adjusted with a screw. On others it’s fixed and the entire gas valve must be replaced. This is the step most DIYers miss. Running 11 inches of propane pressure through a regulator set for 7 inches will push the burner harder than designed and shorten the heat exchanger life.
Air Shutter Adjustment
Propane requires more air per cubic foot of gas to burn cleanly. The burner tube usually has a sliding metal sleeve (the air shutter) that changes how much primary air mixes before the flame. Opening it slightly (often just a quarter turn) prevents yellow tipping and sooting. Mark the original position before moving it so you can go back if needed.
Gas Pressure: The Difference Nobody Talks About
I’ve seen people install a propane orifice, fire up the water heater, and wonder why the flame still looks wrong. The culprit is almost always pressure mismatch. Propane appliances are designed to see 11 inches WC at the inlet. If your water heater’s gas valve can’t handle that, you get incomplete combustion.
How do you check? Buy a $20 manometer (water column gauge) and measure the pressure at the gas valve test port with the burner running. You’re looking for the manufacturer’s specified manifold pressure, usually stamped on the gas valve or in the manual. For a converted unit, the typical propane manifold pressure is around 10 inches WC. If it’s off by more than 0.5 inches, adjust or replace the regulator.
Never guess at pressure. You can’t hear or see the difference between 10 and 12 inches WC, but your water heater will degrade 20% faster at the wrong pressure.
When It Makes More Sense to Buy a New Propane Water Heater
Conversion kits run $30 to $150 on average. Hiring a licensed plumber to do the job costs $200 to $400. A new propane water heater, installed, is $500 to $900. If your current water heater is over eight years old, the math leans toward replacement. You get a fresh tank, a factory-rated propane burner, and zero guesswork about gas valve compatibility.
If the water heater is relatively new (under five years) or a high-end model you want to keep, conversion is practical. But know that once you convert, the original manufacturer warranty often voids unless you use their specific kit and have a pro install it.
There’s also the RVGUARD electric conversion kit mentioned earlier. For an RV or a cabin where you sometimes have grid power, that kit lets you avoid propane entirely during those periods. It won’t help if you’re off-grid full-time, but it’s a nice middle ground if you’re doing partial conversion work anyway.
| Option | Cost Range | Skill Required | Safety Risk | Best For |
|---|---|---|---|---|
| DIY with manufacturer kit | Low to moderate | Medium (basic tools, careful reading) | Medium (if pressure not checked) | Newish water heater, confident DIYer |
| DIY with generic parts | Low | High (need to match orifices, adjust pressure) | High (easy to get wrong) | Only if factory kit unavailable and you own a manometer |
| Hire a licensed plumber | Moderate to high | Low (you just pay) | Low | Old water heater you want to keep, or any gas work you’re uneasy about |
| Replace with propane model | High | Low (pro install recommended) | Low | Water heater over 8 years old, or zero tolerance for risk |
That table simplifies a few nuances, but it gives you the trade-offs at a glance. If I had a five-year-old Rheem and could get the factory conversion kit for $60, I’d do that and spend an hour on it. If it were a fifteen-year-old unit from a brand that stopped making parts, I’d buy new.
Frequently Asked Questions About Converting Natural Gas Water Heaters to Propane
Can I just swap the gas line and leave the water heater as-is?
No. The gas line connection itself is the same (1/2-inch NPT or flare fitting). But the appliance internals are tuned for a specific fuel. Propane flowing through a natural gas orifice will produce a large, sooty flame that deposits carbon on the heat exchanger and spills carbon monoxide. At best you waste fuel. At worst you fill the room with combustion byproducts.
How do I know if my water heater is convertible?
Look for a sticker or a tag near the gas valve that says something like Convertible for LP/Propane or lists conversion kit part numbers. Check the owner’s manual under the section Gas Type Conversion. If you see nothing, call the manufacturer’s tech support with the model number. Many brands, including Rheem, Bradford White, and AO Smith, make convertible models but don’t always label them conspicuously.
What happens if I use propane without changing the orifice?
The flame will be tall, yellow, and lazy. It will produce soot that clogs the burner ports and can fall onto the gas valve. Combustion efficiency drops, carbon monoxide levels rise, and the flue may not handle the extra heat. You’ll also likely hear a roaring sound instead of a steady blue flame. Do not operate it this way for more than a test second.
Does the RVGUARD electric conversion kit bypass the need to convert to propane?
Only if you never use propane. The RVGUARD kit adds an electric heating element to your water heater. When you have shore power, you run electric and burn zero propane. But if you need propane backup (for boondocking or a power outage), the original gas burner still needs to be set up for propane. So you still have to do the conversion described above. The kit saves propane when you’re plugged in; it doesn’t replace the conversion.
Do I need different venting for propane compared to natural gas?
Usually not. The same draft hood and flue pipe work for both fuels as long as the conversion is done correctly. However, propane produces slightly more water vapor in the exhaust, so if your vent has horizontal runs or is undersized, you might see more condensation. Code requires a minimum clearance of 6 inches from combustible materials for single-wall vent pipe regardless of fuel.
What to Do Next—Seven Actions You Can Take Right Now
- Find your water heater’s model number and check the manual for a conversion kit part number. If it exists, buy that kit—it includes the correct orifices and often a new regulator spring.
- Buy a digital manometer before lighting the burner. Measure the inlet pressure at the gas valve while running. Adjust the regulator if your gas line has one, or replace the gas valve if it’s not adjustable.
- When installing a new propane orifice, clean the threads with a wire brush and apply a tiny amount of pipe dope. Avoid Teflon tape on gas fittings—it can shred and clog the orifice.
- After conversion, test for carbon monoxide with a portable detector held near the flue outlet while the burner runs. Anything above 50 ppm (parts per million) means something’s off.
- If your water heater is over 8 years old, price a new propane unit before buying a conversion kit. The breakeven is often just two years of fuel savings.
- For RV or cabin use, consider the RVGUARD electric conversion kit as an add-on. It’ll cut your propane use dramatically whenever you have 120V power, and the adjustable thermostat lets you dial in the temperature without touching the gas side.
- If you’re not comfortable with gas line work or don’t own a manometer, hire a certified gas fitter. The $300 you spend is cheap insurance against a house fire or CO poisoning.
