How Do You Convert a Furnace From Natural Gas to Propane? The Complete Step-by-Step Guide
In this guide: Everything you need to know about how do you convert a furnace from natural gas to propane - covering pre-conversion assessment, the conversion process step by step, required parts and kits, costs, safety requirements, when to hire a professional, and the complete FAQ for 2026.
How Do You Convert a Furnace From Natural Gas to Propane? Quick Answer
You convert a furnace from natural gas to propane by obtaining a manufacturer-approved propane conversion kit for your specific furnace model, replacing the natural gas orifices with propane orifices, adjusting or replacing the gas valve and regulator, setting the correct manifold pressure, adjusting the air shutter for propane's different air-to-gas ratio, and having a licensed HVAC technician perform and document the conversion. The most critical step is using the correct manufacturer-approved conversion kit - not generic parts. Attempting to convert a furnace by simply swapping orifices without a proper kit is dangerous and often illegal under NFPA 54 and the furnace's UL listing. A factory-authorized natural gas to propane conversion costs approximately $200–$600 for the conversion kit plus $150–$400 for professional installation, totaling $350–$1,000 in most cases. The conversion must be performed by or supervised by a licensed HVAC professional, and the conversion must be documented and re-certified for propane use before the furnace is returned to service.
Before You Begin: Can Your Furnace Be Converted?
The Pre-Conversion Assessment
Not every natural gas furnace can or should be converted to propane. A proper pre-conversion assessment determines whether conversion is feasible, safe, and economical:
Furnace conversion eligibility checklist:
| Assessment Item | Requirement | If Not Met |
|---|---|---|
| Manufacturer offers approved conversion kit | Must have manufacturer kit for exact model number | Do not convert; consider replacement |
| Furnace is <15 years old | Conversion investment should be recoverable | Replacement more cost-effective |
| Furnace is in good working condition | No cracked heat exchangers; no major component failures | Replace - conversion is not worth it |
| Gas pressure at property supports propane | Propane requires 10–14" WC at appliance | May require tank and regulator upgrade |
| Adequate propane supply infrastructure | Propane tank sized for heating load | Install properly sized tank first |
| Local code permits field conversion | AHJ approval required for fuel conversion | Must use certified propane unit if not permitted |
The manufacturer's kit is always required: Natural gas furnaces are designed, tested, and UL-listed for natural gas at specific pressures and flow rates. Converting to propane without the manufacturer's certified conversion kit voids the furnace's UL listing, violates the furnace's warranty, may not meet local building codes, and creates serious safety hazards. No exceptions apply. If the manufacturer does not offer a conversion kit for your furnace model, the furnace cannot be legally or safely converted to propane.
Understanding the Key Differences: Natural Gas vs. Propane
Why the Two Gases Require Different Components
Converting from natural gas to propane requires specific component changes because the two gases have fundamentally different combustion properties:
Natural gas vs. propane - the key differences affecting furnace conversion:
| Property | Natural Gas | Propane | Conversion Requirement |
|---|---|---|---|
| BTU per cubic foot | ~1,000 BTU/cu ft | ~2,500 BTU/cu ft | Orifices must be smaller for propane |
| Required manifold pressure | 3.5" WC (inches water column) | 10–11" WC | Gas valve must be adjusted or replaced |
| Orifice drill size | #42–#56 (large) | #73–#52 (small) | Orifice replacement required |
| Air-to-gas ratio | 10:1 | 23:1 | Air shutter adjustment required |
| Gas valve type | Natural gas valve | Propane valve (or adjusted) | Valve adjustment or replacement |
| ** regulator** | Low-pressure natural gas regulator | Propane regulator | May need regulator swap |
Why simply swapping orifices is dangerous: If you install propane orifices on a natural gas furnace without also adjusting the gas valve pressure and air shutter, the furnace will receive propane at natural gas pressure settings - approximately one-third of what propane needs to burn correctly. This creates a dangerously rich fuel mixture that produces carbon monoxide, causes soot buildup in the heat exchanger, and can cause the furnace to overfire or fail. The manufacturer's conversion kit addresses all of these variables together - not just the orifices.
The Conversion Kit: What It Contains
Components in a Factory-Authorized Kit
A manufacturer-approved natural gas to propane conversion kit contains all the components needed to safely convert your specific furnace model:
Typical propane conversion kit contents:
| Component | Function | Natural Gas Spec | Propane Spec |
|---|---|---|---|
| Orifices (one per burner) | Restricts gas flow to burners | Large (0.045–0.080") | Small (0.010–0.030") |
| Gas valve orifice insert / conversion label | Converts valve to propane pressure | 3.5" WC | 10–11" WC |
| Pilot orifice (if applicable) | Restricts pilot gas flow | Natural gas pilot | Propane pilot |
| Manifold pressure spring (if applicable) | Sets correct outlet pressure | 3.5" WC spring | 10–11" WC spring |
| Conversion label / sticker | Documents the conversion | Applied to furnace | Required by code |
| Installation instructions | Step-by-step conversion procedure | Model-specific | Required for compliance |
How to find the correct conversion kit: The correct conversion kit for your furnace is identified by your furnace's exact model number and manufacturing date - not by the furnace brand alone. Locate the model number on the furnace's rating plate (a metal label on the furnace cabinet, typically near the gas valve). Search the manufacturer's website using that model number, or call the manufacturer's technical support line. Use only the exact kit listed for your model. Do not substitute components from similar kits - even slight model variations may require different parts.
Step-by-Step: How to Convert a Furnace From Natural Gas to Propane
The Complete Conversion Process
For experienced HVAC technicians with the correct kit. This process must be performed by or under the direct supervision of a licensed HVAC professional in most jurisdictions:
Step-by-step natural gas to propane furnace conversion:
| Step | Task | Key Details |
|---|---|---|
| 1. Turn off gas supply | Shut off gas at the meter or gas valve | Close the main gas supply valve before beginning |
| 2. Turn off electrical supply | Shut off power at the furnace disconnect switch | Prevents accidental ignition during conversion |
| 3. Disconnect and remove gas line | Loosen the gas line from the furnace gas valve | Have a catch pan ready; residual gas may drip |
| 4. Remove burner access panel | Access the burners and gas valve | Remove screws; set panel aside carefully |
| 5. Remove natural gas orifices | Unscrew each orifice from the manifold | One orifice per burner; note positions |
| 6. Install propane orifices from kit | Screw in each propane orifice | Torque to manufacturer spec (typically 9–12 in-lbs); do not over-tighten |
| 7. Convert the gas valve | Install propane pressure spring or valve conversion component | Follow kit instructions exactly |
| 8. Set manifold pressure | Adjust regulator to propane pressure: 10–11" WC | Use a manometer - never estimate |
| 9. Adjust the air shutter | Set air shutter per manufacturer instructions | Propane requires less primary air (10:1 vs 23:1 ratio) |
| 10. Reconnect gas line | Reconnect and check all fittings | Use new Teflon tape or pipe sealant on threads |
| 11. Pressure test the gas line | Check for leaks at all connections | Apply soap solution; watch for bubbles |
| 12. Restore power and light the furnace | Ignite burners and verify proper flame | Flame should be crisp, blue, and stable - no yellow tipping |
| 13. Check flame color and behavior | Verify clean combustion | Yellow flame = too rich; adjust air shutter |
| 14. Check heat rise | Measure temperature differential across the furnace | Should match manufacturer specifications |
| 15. Apply conversion label | Affix the propane conversion sticker to the furnace | Documents conversion; required by code |
| 16. Document the conversion | Record the conversion in the furnace documentation | Include date, technician name, kit part number |
Critical safety notes: Always use a manometer to verify manifold pressure - never set pressure by feel, sound, or flame appearance alone. Never convert a furnace without a manufacturer-approved kit. Never leave the furnace unattended during initial startup after conversion. If the flame is yellow or the furnace does not light properly, shut off gas immediately and recheck the conversion steps.
Converting the Furnace: DIY vs. Hiring a Professional
When You Need a Licensed Technician
While a skilled DIYer with HVAC experience can perform the physical conversion steps, most jurisdictions legally require a licensed HVAC technician or gas fitter to perform the conversion, test for leaks, and document the work:
DIY vs. professional conversion considerations:
| Task | DIY Feasible? | Professional Required? | Notes |
|---|---|---|---|
| Obtain correct conversion kit | Yes - order online or from supplier | No | Must be exact manufacturer kit for model |
| Shut off gas and power | Yes - straightforward | No | Basic safety step |
| Remove and replace orifices | Experienced DIYers - Yes | Recommended | Requires HVAC knowledge; easy to damage orifices |
| Adjust gas valve / install conversion components | No | Yes - strongly recommended | Valve adjustment requires manometer and expertise |
| Manifold pressure verification | No - requires manometer | Yes - mandatory | Manometers cost $50–$200; not standard homeowner equipment |
| Air shutter adjustment | Experienced DIYers - Yes | Recommended | Affects combustion quality and efficiency |
| Leak testing | Yes - with soap solution | Yes - documented by professional | Documentation required for permit sign-off |
| Furnace ignition and flame verification | No | Yes - mandatory | Certified start-up required for warranty and code |
| Applying conversion label and documentation | Yes - with professional guidance | Yes - for permit records | Must be submitted to local AHJ in many jurisdictions |
The permit requirement: In most U.S. jurisdictions, converting a gas appliance from one fuel type to another requires a permit from the local authority having jurisdiction (AHJ), which is typically the city or county building department. The conversion must be inspected by a city inspector, and the work must be documented by a licensed gas fitter or HVAC technician. A DIY conversion without a permit and inspection may create liability issues with homeowner's insurance and complicate future home sales.
Cost to Convert a Furnace From Natural Gas to Propane
What to Budget
The total cost of converting a furnace from natural gas to propane includes the conversion kit, professional labor, permit fees, and any propane infrastructure costs:
Natural gas to propane furnace conversion cost breakdown:
| Cost Component | Low End | Average | High End | Notes |
|---|---|---|---|---|
| Manufacturer conversion kit | $50 | $100–$200 | $400 | Must match exact furnace model |
| Professional installation labor | $100 | $150–$300 | $500 | 2–4 hours at licensed technician rates |
| Permit and inspection fees | $50 | $75–$150 | $300 | Varies by municipality |
| Manifold pressure test equipment | $0 (included in labor) | $0 | $200 (if renting) | Professionals have their own equipment |
| Propane tank installation (if not already present) | $800 | $1,200–$2,500 | $3,500 | Separate cost if no propane infrastructure exists |
| Propane gas line installation (if needed) | $200 | $300–$800 | $1,500 | From tank to furnace location |
| Total conversion cost | $200 | $325–$650 | $1,200 | Assumes propane infrastructure is already in place |
| Total cost (with new propane tank) | $1,000 | $1,500–$3,300 | $5,000 | If new tank and gas line are required |
After the Conversion: What to Check
Post-Conversion Verification Steps
Once the furnace is converted and running, these verification steps confirm the conversion was performed correctly:
Post-conversion checklist:
| Check | What to Look For | Correct Result |
|---|---|---|
| Flame appearance | Color and stability of burner flames | Clean, crisp blue flames; no yellow tipping |
| Flame lift | Flames should not lift off burner ports | Stable flame attachment at all ports |
| Heat rise | Temperature differential across heat exchanger | Matches manufacturer spec (typically 30–60°F rise) |
| Manifold pressure | Verified with manometer | 10–11" WC (propane standard) |
| Gas leaks | All fittings checked with soap solution | No bubbles at any connection |
| CO levels | Measured with combustion analyzer | <100 ppm in flue; <10 ppm in living space |
| Thermostat response | Furnace cycles on and off correctly | Ignites, heats, and shuts off at setpoints |
| Short-cycling | Furnace does not short-cycle | Normal 10–15 minute run cycles |
Annual post-conversion maintenance: After converting a furnace to propane, schedule annual professional maintenance (combustion analysis, flame inspection, pressure verification) to ensure the conversion continues to operate safely and efficiently. Propane combustion produces slightly different byproducts than natural gas, and the heat exchanger and burners should be inspected annually for any soot buildup or corrosion that could indicate incomplete combustion.
Frequently Asked Questions
Q1: How do you convert a furnace from natural gas to propane?
You convert a furnace from natural gas to propane by following these steps in order: first, obtain the manufacturer-approved propane conversion kit for your exact furnace model number - this is non-negotiable and must be the exact kit listed for your model; second, have a licensed HVAC technician perform the physical conversion: replace the natural gas orifices with propane orifices from the kit, adjust or replace the gas valve to propane pressure settings (10–11" WC instead of 3.5" WC), adjust the air shutter for propane's different air-to-gas ratio, and verify manifold pressure with a manometer; third, pressure test all gas connections for leaks; fourth, light the furnace and verify proper flame characteristics (clean blue flames, no yellow tipping); fifth, apply the conversion label to document the conversion; and sixth, have the conversion documented and submitted to the local authority having jurisdiction for permit sign-off if required. Never attempt to convert a natural gas furnace to propane by simply changing the orifices - this is dangerous and illegal without the complete manufacturer-approved conversion process.
Q2: Can any natural gas furnace be converted to propane?
No - not every natural gas furnace can be converted to propane. A furnace can only be converted if the manufacturer offers an approved propane conversion kit for that specific model. If no kit exists for your furnace model, the furnace cannot be legally or safely converted. Additionally, furnaces older than 15–20 years are generally not good candidates for conversion - the cost of the conversion plus repair needs of an aging furnace often exceeds the cost of replacing with a new propane furnace. Furnaces with damaged heat exchangers, cracked cast-iron components, or significant corrosion should not be converted and should be replaced instead.
Q3: How much does it cost to convert a furnace from natural gas to propane?
Converting a furnace from natural gas to propane costs approximately $200–$650 for the conversion itself (kit + professional labor + permit) if propane infrastructure already exists at your property. This includes: the manufacturer conversion kit ($50–$400 depending on the furnace brand and model), professional installation labor ($100–$400), and permit and inspection fees ($50–$200). If you do not already have a propane tank and gas line, budget an additional $800–$3,000 for propane tank installation and $200–$800 for gas line routing, bringing the total to $1,000–$5,000. Compare this to the cost of a new propane furnace ($3,000–$6,500 installed) to determine whether conversion or replacement makes more financial sense for your situation.
Q4: Do I need a professional to convert my furnace from natural gas to propane?
Yes - in most jurisdictions, converting a gas furnace from natural gas to propane must be performed by a licensed HVAC technician or gas fitter, and the conversion must be inspected by the local building department. While an experienced DIYer can perform some physical steps (swapping orifices, shutting off utilities), the critical steps - setting manifold pressure with a manometer, adjusting the gas valve, verifying combustion safety, and documenting the conversion - require professional expertise, specialized equipment, and licensing. A DIY conversion without a permit and inspection may void the furnace warranty, violate local building codes, create liability issues with homeowner's insurance, and - most importantly - create serious safety hazards from improper gas pressure settings or combustion.
Q5: What is the difference between converting a furnace and replacing it?
Converting a furnace from natural gas to propane modifies the existing furnace's components to operate on propane, keeping the existing equipment in place. Replacing a furnace means removing the existing natural gas furnace and installing a new furnace that is certified from the factory for propane use. Conversion costs $200–$650 (plus infrastructure if needed) and makes sense when the existing furnace is in good condition, less than 10–15 years old, and a manufacturer-approved conversion kit exists. Replacement costs $3,000–$6,500 installed but provides a factory-certified propane unit with a full new warranty, higher efficiency (if upgrading to a modern 95–98% AFUE condensing unit), and no risk of conversion errors. When the existing furnace is aging, repair-prone, or a manufacturer conversion kit is not available, replacement is the better choice.
The Bottom Line
Converting a furnace from natural gas to propane is a viable, cost-effective option when your furnace is in good condition, is less than 15 years old, and the manufacturer offers an approved conversion kit for your specific model. The conversion process involves replacing the orifices, adjusting the gas valve and manifold pressure, setting the air shutter for propane's combustion characteristics, pressure testing, and professional verification. The total cost is $200–$650 for the conversion itself - significantly less than the $3,000–$6,500 cost of a new furnace. The single most important requirement: use only the manufacturer-approved conversion kit for your exact model, and have the work performed by a licensed HVAC technician. No exceptions. If the furnace is aging, if no conversion kit exists, or if the furnace has underlying problems, replacement with a factory-certified propane furnace is the safer and more reliable long-term choice.
Last updated: July 2026
Disclaimer: This guide provides general information about converting a furnace from natural gas to propane for educational purposes. Gas furnace conversions must comply with NFPA 54, local building codes, and the furnace manufacturer's specific instructions. All conversions should be performed by licensed HVAC professionals. Never attempt to modify a gas furnace without proper authorization and professional supervision. Obtain required permits from your local authority having jurisdiction before beginning any fuel conversion. This guide is not affiliated with, endorsed by, or sponsored by any propane equipment manufacturer.
