Natural Gas vs Propane Conversion: What You Need to Know About Weil-McLain Conversion Kits

Why Fuel Conversion Even Matters

You might be wondering, “Why would I need to convert my boiler’s fuel source in the first place?” There are a few reasons—and they’re more common than you might think:

• No access to a natural gas line in rural areas

• Rising utility costs, where propane becomes more affordable short-term

• Energy independence goals or off-grid living

• Switching home heating systems during a remodel or home purchase

• New appliance installation where fuel type doesn’t match existing infrastructure

Whatever your reason, it’s important to know that switching between natural gas (NG) and liquefied petroleum (LP)—a.k.a. propane—isn’t as simple as flipping a valve. Gas appliances are calibrated to burn one specific type of fuel, and converting a boiler requires specific orifices, gas regulators, air shutters, and sometimes even updated burners.

The good news is that Weil-McLain makes this easier with OEM-approved fuel conversion kits for many of their most popular gas boilers.

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Understanding the Difference Between Natural Gas and Propane

Before we talk kits, let’s go over how these two fuels differ.

Natural Gas (NG):

• Delivered via underground utility pipelines

• Low pressure (typically 3.5” WC)

• Lighter than air (rises if leaked)

• Clean burning, low emissions

• Often cheaper in urban/suburban areas

Propane (LP):

• Stored in onsite pressurized tanks

• Higher pressure (up to 11” WC)

• Heavier than air (settles if leaked)

• Higher energy content per cubic foot

• Ideal for rural/off-grid homes

These pressure and combustion differences are exactly why gas appliances aren’t interchangeable without modification. Feeding propane through an NG boiler without a proper conversion isn’t just inefficient—it’s dangerous.

The U.S. Consumer Product Safety Commission (CPSC) warns that improper gas conversions can lead to carbon monoxide leaks, system failures, and fire hazards. Always use a certified conversion kit and qualified installer.

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How Weil-McLain Fuel Conversion Kits Work

Each Weil-McLain conversion kit is built specifically for the model and series of the boiler. A kit will usually include:

• Gas orifices calibrated for the new fuel

• Pressure regulator springs or valves

• Air shutters or adjustment plates

• Instruction manuals with step-by-step guidance

• Safety stickers and labels to update fuel type

Here’s a quick table with examples of conversion kits and their applications:

Important: These kits are not universal. You must match the conversion kit to the exact model and series of your boiler. Mismatching can cause combustion issues or invalidate your warranty.

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How to Know If Your Boiler Can Be Converted

Not every boiler is convertible. The best way to find out?

1. Check the rating plate on the side of your boiler—look for approved fuel types.

2. Review your owner’s manual—if conversion is allowed, it will be mentioned there.

3. Look up your model on the Weil-McLain Product Catalog and search for conversion compatibility.

4. Talk to a licensed HVAC contractor with experience in boiler systems.

Also check local code—some jurisdictions require permits and inspections after a fuel conversion. For example, Massachusetts has specific rules for LP gas installs and requires licensed gas fitters.

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Key Steps in the Fuel Conversion Process

Here’s how a typical conversion goes when done right:

1. Turn off gas and power to the boiler. Safety first.

2. Remove the existing burner assembly and regulator parts.

3. Install new orifices and burner components from the conversion kit.

4. Adjust the gas pressure regulator to match fuel specs (e.g., 10” WC for propane).

5. Modify or set the air shutter for correct combustion.

6. Apply new fuel type labels on the boiler housing.

7. Use a combustion analyzer to verify safe, efficient operation.

8. Perform a gas leak check and ignition safety test.

Warning: If you’re not experienced with gas lines and combustion tuning, don’t DIY this. Call a pro. Even one mistake could result in an unsafe system.

To understand the technical side better, you can explore this detailed fuel conversion guide from Licensed NC that explains the science behind gas pressure and orifice sizing.

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Does It Make Sense Financially?

Here’s the breakdown of fuel cost vs. system efficiency:

• Natural gas is cheaper per BTU in most metro areas.

• Propane is more expensive per gallon but packs more energy per unit.

• Conversion kits usually cost $100–$300, depending on model.

• Installation labor adds $300–$600 more unless bundled with boiler replacement.

• Condensing boilers (90%+ AFUE) reduce your fuel use enough to justify either fuel if installed and tuned correctly.

Want to compare fuel prices in your region? The U.S. Energy Information Administration (EIA) tracks weekly propane and gas prices by state. You can plug those into the Heating Fuel Comparison Calculator to see what works best.

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What to Watch Out for During Conversion

Here’s a checklist of potential pitfalls and how to avoid them:

✅ Wrong Kit for the Model
➡ Double-check boiler model and series before ordering. A Series 2 kit won’t work for a Series 3.

✅ Improper Gas Pressure
➡ Use a manometer to test incoming gas pressure and match it to the manufacturer’s specs.

✅ Missed Label Updates
➡ The fuel type on your boiler must match what it’s running. Update the plate with the provided stickers.

✅ Skipping Combustion Testing
➡ Use a combustion analyzer to ensure the air-fuel mix is balanced. You’re aiming for correct CO2 and O2 levels.

✅ No Permit or Inspection
➡ Always check with your city or township. Some require post-conversion inspections for insurance and safety.

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When to Consider Conversion vs. Replacement

Sometimes, you’re better off just replacing the boiler.

Choose conversion if:

• Your boiler is under 10 years old

• Your unit is designed for dual-fuel capability

• Your heating load hasn’t changed

• You’re simply switching fuels to save money

Replace the boiler if:

• The unit is 15+ years old

• You’re upgrading to a high-efficiency condensing model

• You’re adding more zones or radiant heating

• Parts and labor for conversion are close to the cost of a new system

If you’re replacing, you can find new Weil-McLain boilers with the correct fuel type already installed—and many come with pre-mounted conversion components for flexibility down the line. One reliable place to shop for these is The Furnace Outlet, which carries genuine boilers, conversion kits, and accessories all in one place.

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Final Thoughts from Mike

Fuel conversion is one of those projects that seems simple on the surface—but if you don’t use the right parts or skip a step, it can cost you more in fuel, comfort, and safety. The good news? Weil-McLain makes it as painless as possible with model-specific conversion kits that are tested, approved, and built to last.

Whether you’re flipping your system from natural gas to propane, moving into a rural property, or trying to save on winter bills, always use a certified kit, follow the manufacturer’s instructions, and get the system tested before firing it up for the season.

And if you’re still not sure which kit you need or whether your boiler can be converted safely, take it from me—it pays to talk to someone who knows these systems inside and out.