Convert Natural Gas Furnace to Propane Safely and Efficiently

Converting a natural gas furnace to propane requires careful planning, correct parts, and adherence to safety codes. This guide explains the technical steps, costs, permits, and professional considerations to help homeowners understand what the conversion involves and whether it is the right choice for their home heating needs.

Factor	Natural Gas	Propane
Energy Content	~1,030 BTU/ft³	~91,500 BTU/gal
Supply Method	Piped Utility	Onsite Tank
Pressure	Low (0.25–7 inches WC)	Higher For Tank Delivery (2–14 inches WC)
Typical Conversion Needs	Original	Orifice, regulator, possible burner adjustment

Why Convert A Natural Gas Furnace To Propane

Homeowners consider conversion when natural gas service is unavailable, when moving to rural properties, or when cost and supply factors favor propane. Propane offers high energy density and widespread availability via delivered tanks, but conversion is not simply swapping fuels — it involves mechanical and regulatory changes to ensure safe and efficient operation.

Key Differences Between Natural Gas And Propane

Understanding the fundamental differences helps explain why conversion involves hardware changes. Propane burns hotter and has a different air-fuel ratio and required gas pressure.

• Energy Density: Propane contains more energy per volume than natural gas, requiring smaller orifices to reduce fuel flow.
• Pressure And Regulation: Propane systems typically require a pressure regulator designed for liquid petroleum gas and different manifold pressures at the burner.
• Combustion Characteristics: Burner adjustments and sometimes different burners or valves are necessary to maintain proper flame and CO emissions.

Permits, Codes, And Safety Considerations

Almost all jurisdictions require permits and inspections for fuel conversions. Local building codes, the International Fuel Gas Code (IFGC), and NFPA 54/58 provide standards for safe installation.

• Obtain a permit before starting work and schedule inspections after installation.
• Work by a licensed HVAC or gas contractor is often required and recommended due to safety and liability.
• Carbon monoxide and combustion air requirements must be re-evaluated after conversion.
• Propane storage tanks must meet setback, anchoring, and venting standards per NFPA.

Components Required For Conversion

Successful conversion requires the correct parts and calibration. Key components include:

• Conversion Kit: Manufacturer-specific kit containing orifices, instructions, and sometimes a new gas valve.
• Orifices/Nozzles: Smaller orifices reduce propane flow to match its higher BTU density.
• Pressure Regulator: A regulator sized and rated for propane to ensure the correct manifold pressure.
• Gas Valve: Some older valves need replacement if not rated for propane or adjustable.
• Burner Adjustments: Burner ports may require tuning or replacement to achieve proper flame shape and combustion.

Step-By-Step Conversion Process

The following outlines the usual sequence performed by a professional technician. Homeowners should not attempt gas work without licensing.

1. Verify Furnace Compatibility: Check the furnace nameplate and manual for a convertible model and locate the manufacturer conversion instructions.
2. Obtain Manufacturer Kit: Use the exact conversion kit from the furnace manufacturer to maintain warranty and safety compliance.
3. Shut Down And Isolate Gas: Turn off the gas supply and electrical power to the furnace before any service.
4. Replace Orifices And Adjust Burners: Remove natural gas orifices and install propane orifices; adjust air shutters and mixing for correct combustion.
5. Install/Adjust Regulator: Fit a propane-rated regulator and set manifold pressure to the manufacturer’s propane specification (commonly 11 inches WC but varies).
6. Check Gas Valve Compatibility: Replace the gas valve if it is not approved for propane or not adjustable within required ranges.
7. Leak Test And Purge Lines: Pressurize the system with nitrogen or propane and test all joints with approved methods; purge any air from lines where necessary.
8. Combustion Analysis: Use a combustion analyzer to measure CO, CO2, O2, and stack temperature; adjust for optimum efficiency and safe emissions.
9. Labeling And Documentation: Affix conversion labels, update service stickers, and leave documentation for future technicians and inspectors.
10. Inspection And Approval: Schedule local inspection; the inspector will confirm compliance with codes and proper combustion performance.

Typical Costs And Timeframe

Costs vary depending on furnace age, region, and whether parts require replacement. Typical ranges:

• Professional Conversion Labor: $300–$800 depending on complexity and local labor rates.
• Parts: $50–$400 for orifices, regulator, and conversion kit; $300–$800 if a new gas valve or burners are needed.
• Propane Tank Installation: $800–$2,500 for aboveground tank and installation; underground tanks cost more.
• Permits And Inspection Fees: $50–$300 depending on locality.

Most conversions take 2–6 hours for a straightforward job; complex systems or additional modifications extend time.

When A Furnace Can’t Be Converted

Some furnaces are not convertible due to valve design, combustion chamber geometry, or manufacturer restrictions. If the manufacturer explicitly states no conversion, replacing the furnace with a propane-specific model is the safest option.

• Older or obsolete models may lack available kits or parts.
• High-efficiency condensing furnaces may require special venting or controls for propane.
• If combustion testing shows unsafe patterns that cannot be corrected, replacement is recommended.

Venting, Exhaust, And Condensing Furnaces

Conversion affects venting requirements. Non-condensing furnaces usually vent similarly for both fuels, but condensing units may have different flue gas condensate properties when burning propane.

• High-efficiency furnaces produce acidic condensate; materials must be resistant to corrosion.
• Propane combustion can slightly change flue gas temperature and moisture; verify vent material and slope.
• Ensure adequate combustion air to prevent spillage or incomplete combustion after conversion.

DIY Versus Professional Conversion

While some technically skilled homeowners may be tempted to perform the conversion, working with gas fuel requires expertise. Hiring a licensed HVAC technician minimizes safety risks, ensures code compliance, and protects warranties.

• Professionals have the proper tools, combustion analyzers, and knowledge of local codes.
• DIY attempts may void equipment warranties and expose the home to carbon monoxide or fire hazards.
• Some jurisdictions legally prohibit unlicensed individuals from altering gas systems.

Checklist For Hiring A Contractor

When selecting a contractor, use this checklist to ensure competence and transparency.

• Verify state and local licensing and insurance.
• Request manufacturer-certified conversion experience and references.
• Get a written estimate listing parts, labor, permit fees, and timelines.
• Confirm use of manufacturer conversion kit and provide equipment model numbers.
• Ensure combustion testing and written results will be provided upon completion.

Energy Efficiency And Operating Costs After Conversion

Conversion itself does not significantly change furnace efficiency if properly performed, but fuel cost and delivery logistics affect operating costs.

• Propane typically has a higher per-BTU price than natural gas but pricing varies regionally.
• Tank refill logistics add periodic costs and require monitoring to avoid runouts.
• Proper tuning after conversion is essential to maintain rated AFUE and safe emissions.

Safety Tips And Best Practices

Follow these safety practices before and after conversion:

• Install and maintain carbon monoxide detectors near sleeping areas and mechanical rooms.
• Schedule annual inspections for the furnace and propane tank, including leak checks and regulator maintenance.
• Keep a written service history and conversion documentation with the furnace.
• Know emergency shutoff procedures and tank valve locations.

Common Questions And Troubleshooting

Will The Furnace Burn Propane Exactly Like Natural Gas?

No. Flammability, flame temperature, and required fuel flow differ. Proper orifices and adjustments are required to replicate safe combustion and maintain efficiency.

Can Any Gas Furnace Be Converted?

Not any furnace. Compatibility depends on the manufacturer’s design and available conversion kits. If the manual disallows conversion, replacement is necessary.

Will Conversion Affect Warranties?

If done per manufacturer instructions and using approved kits, warranties typically remain valid. Unauthorized modifications or DIY work may void warranties.

Resources And Where To Find Parts

Manufacturer websites and authorized distributors are the safest sources for conversion kits and replacement parts. National associations and code guides provide regulatory context:

• American Gas Association (AGA)
• NFPA (National Fire Protection Association)
• Contact the furnace manufacturer for model-specific kits and documentation.

Conversion Decision Flow Summary

Step	Action
1	Check furnace nameplate and manual for conversion allowance and obtain kit if allowed
2	Get local permit and hire licensed technician
3	Install orifices, regulator, and any required valve/burner changes
4	Perform leak tests and combustion analysis; adjust for safe performance
5	Schedule inspection and keep documentation

This guide equips homeowners with the technical background and practical steps for converting a natural gas furnace to propane. For safety and compliance, engaging a licensed HVAC professional and following manufacturer and local code requirements is strongly recommended.