How to Convert a Propane Water Heater to Natural Gas

Check the rating plate before you buy any parts

The first step in any fuel project is finding out whether your water heater is allowed to burn natural gas. Look for the rating plate, which is a metal data sticker on the side of the tank or inside the front access panel on a tankless model. This label lists the serial number, model number, and the specific fuel the unit was built to use.

Read the line labeled "Equipped For" or "Fuel Type." If the label says "Propane Only" or "LP Only," stop right there. Most standard storage tank water heaters in the United States are built for a single fuel. Major tank manufacturers, including Rheem, A.O. Smith, and Bradford White, do not produce conversion kits for their standard storage models. They engineer the burners, valves, and combustion chambers for one gas type and certify them under that exact setup.

If you have a tankless water heater, your odds are better. Many modern tankless units use modular burner trays that can adapt to either fuel. Check your owner manual or look at the rating plate for a note on field conversions. If the plate lists an approved kit part number, you can proceed.

Here is a quick checklist to verify feasibility:

• Locate the rating plate on the outer jacket or behind the front cover.
• Look for the words "Natural Gas" or a note stating that conversion is permitted.
• Look up your model number in the manual to confirm an official kit exists.
• Check your local plumbing codes to verify if field conversions are legal.

If the rating plate forbids conversion, you cannot convert the heater. Installing unapproved parts voids your warranty, violates building codes, and creates severe safety hazards.

Understand why gas pressure and nozzle sizes differ

You might wonder why you cannot simply disconnect your propane line, hook up natural gas, and fire the burner. Propane and natural gas are both clean-burning heating fuels, but their physical behavior is drastically different.

Propane is a dense, high-energy fuel. One cubic foot of propane contains roughly 2,500 British Thermal Units (BTU) of heat energy. Natural gas contains only about 1,000 BTU per cubic foot. You need about two and a half times more natural gas by volume to produce the same heating power as propane.

Because propane is so energy-dense, it passes through an orifice, which is a tiny brass nozzle that sprays gas into the burner. On a propane water heater, this orifice has a tiny pinhole opening. Natural gas requires a much wider opening so enough fuel volume can reach the burner flame.

Fuel delivery pressure is also very different. Utility natural gas flows into your home at low pressure. The manifold pressure, which is the gas pressure delivered directly to the burner, typically measures between 3.5 and 5.0 inches of water column. Propane systems operate at more than double that pressure, usually between 10.0 and 11.0 inches of water column.

If you run natural gas through a propane water heater without changing the hardware, the tiny orifice chokes the fuel flow. The burner produces a faint flame that cannot heat water, along with heavy soot and carbon monoxide. Running high-pressure propane through a natural gas orifice is worse: it creates a massive fireball that can melt internal controls and cause a house fire.

Follow the manufacturer steps if your heater allows a kit

If your water heater rating plate confirms that conversion is allowed, buy the exact kit supplied by the manufacturer. Never buy generic brass parts online, and never try to drill out an orifice with a handheld drill bit. A regular drill leaves rough ridges inside the hole, disrupting gas flow and flame quality.

Turn the water heater off, let the tank water cool, and shut off the main gas valve upstream from the appliance. Once the gas is off, follow these steps:

1. Disconnect the burner tube and wiring: Locate the gas control valve, which is the box regulating gas flow and temperature mounted on the lower side of the tank. Unscrew the main burner tube, the pilot gas tube, and the thermocouple wire from the base of the valve.
2. Remove the burner assembly: Remove the screws on the combustion chamber access door. Carefully slide the burner assembly out of the chamber, taking care not to bend the copper pilot tube or thermocouple tip.
3. Replace the main burner orifice: Locate the orifice, which is the tiny brass nozzle that sprays gas into the burner. Use a socket to remove the propane orifice. Thread the new natural gas orifice into place by hand first, then tighten it snugly with your wrench.
4. Swap the pilot assembly orifice: The pilot assembly, which is the small starter flame mechanism that lights the main burner, also has its own fuel orifice. Loosen the pilot tube fitting, remove the propane nozzle, and install the natural gas pilot nozzle from your kit.
5. Convert or replace the gas control valve: Natural gas requires lower internal valve pressure. On units with convertible valves, remove the regulator cap and install the natural gas spring included in the kit. If your heater has non-convertible controls, replace the entire gas control valve box with a factory natural gas valve.
6. Reinstall the burner and attach new labels: Slide the burner assembly back into the chamber and secure the door. Reconnect all tubes to the gas control valve. Stick the conversion label from your kit directly over the old propane label on the rating plate.

Inspect for gas leaks and check proper draft before lighting

Do not light a flame right after assembling the parts. You must verify that your gas fittings are airtight and that exhaust gases escape cleanly outside. Gas leaks cause explosions, while poor exhaust venting fills homes with deadly carbon monoxide.

Check for leaks along every pipe connection you touched. Mix equal parts liquid dish soap and warm water, or use commercial leak detection fluid. Brush the soapy liquid generously around the gas pipe joints, the fittings under the gas control valve, and the pilot line connections.

Turn the main gas supply valve on to pressurize the line. Watch the soapy fittings carefully for several minutes. If you see growing bubbles, gas is leaking out. Turn the main gas valve off immediately, apply fresh gas-rated thread sealant paste, tighten the joint, and retest. Never use a match or lighter to check for leaks.

Next, check your burner manifold pressure. Connect a digital manometer to the pressure tap port on your gas control valve. Turn on the burner and verify that the manifold pressure matches the natural gas specification in your conversion instructions. Adjust the regulator screw until it matches the target.

Finally, check the draft. Hot exhaust gases must flow up through the central flue and out the roof vent. Let the burner fire for five minutes, then hold a lit match or smoke pencil one inch from the draft hood at the top of the tank. The draft should pull the smoke smoothly up into the chimney. If your water heater sits in a chilly garage, cold air can push down an exterior flue; while using an auxiliary electric heater for garage with thermostat controls can protect exposed water pipes from freezing, the flue itself must draft freely. If smoke blows back into the room, shut the heater off and call a heating technician.

Compare the total conversion cost against a new water heater

Many homeowners consider converting a propane water heater to save money after utility gas lines arrive in their neighborhood. But when you add up the cost of parts, permits, and professional labor, conversion rarely delivers significant savings.

An official manufacturer conversion kit usually costs between $75 and $250. If your model requires an entirely new gas control valve rather than just a regulator spring swap, that valve can cost an additional $150 to $300.

Labor adds to the expense. Working on gas lines carries serious safety and legal risks. Most municipalities require gas conversions to be performed by a licensed plumber or gas technician, along with a mechanical permit. A professional service call to handle the orifice replacement, valve tuning, and safety checks generally runs between $200 and $500.

Equipment age also matters. Storage water heaters last between 8 and 12 years. If your propane heater is already 6 or 8 years old, spending $300 to $600 to convert it is a poor investment. Mineral scale has formed on the bottom of the tank, and the internal steel lining is wearing thin. The tank could spring a leak shortly after you pay for the conversion.

Special home types have additional rules. If you live in a manufactured home, heating equipment must meet strict federal safety standards. As covered in our guide on choosing a heater for mobile home spaces, appliances in these homes need closed-combustion air intakes and specific certifications that generic conversion kits do not provide.

Compare those expenses to a brand new water heater. A standard natural gas storage unit typically costs between $600 and $1,100. Buying a new heater gives you a fresh warranty, clean components, and complete peace of mind. For standard tank heaters, buying new is almost always the smarter financial move.

FAQs

Can I drill out my propane water heater orifice with a regular drill bit?

No, you should never drill out a propane orifice with a handheld drill. Hand drilling leaves jagged metal ridges inside the nozzle, which disrupts gas flow and creates incomplete combustion. Incomplete combustion produces high levels of dangerous carbon monoxide gas and heavy soot. Always buy a factory-machined orifice specifically designed for your water heater model.

What should I do if my water heater has no factory conversion kit?

If the manufacturer does not offer an official conversion kit for your model, you must replace the water heater with a dedicated natural gas unit. Attempting an unapproved conversion with aftermarket parts violates building codes, voids your warranty, and can cause house fires. Replacing the entire unit guarantees proper combustion and preserves your home insurance coverage.

Do I need a permit to convert a water heater from propane to natural gas?

Yes, nearly all cities and counties in the United States require a mechanical or plumbing permit for fuel conversions. Gas lines operate under strict safety codes to prevent leaks, fires, and carbon monoxide poisoning. Having a licensed professional pull a permit ensures that an official inspector verifies your gas pressures, connections, and venting before you use the heater.

How can I tell if a water heater was already converted to natural gas?

Look closely at the rating plate on the side of the tank. An official conversion requires the installer to place an updated conversion sticker directly on or next to the original factory rating plate. This sticker states the conversion date, the kit part number used, the new manifold pressure, and the technician or company who performed the work.