Gas Type Adjustment Guide: Safely Convert Natural Gas Furnaces to Propane

Why switch to propane? Let’s set the scene

Maybe your street doesn’t have a gas main… or your cabin’s miles from town. Propane is a solid option because it’s stored on-site and packs a lot of energy. A gas-type adjustment is the safe, code-compliant process of converting a furnace built for natural gas so it runs on propane. We’ll walk this like neighbors on the job: clear steps, real numbers, no fluff.
What you’ll learn here: the right BTU math, why orifices matter, which pressures are safe, and what a licensed tech actually does. If you’re weighing equipment choices, keep our Furnace Sizing Guide handy. And if you’d rather send photos, try Quote-by-Photo we’ll sanity-check your plan.

BTU 101: the energy difference in plain English

BTU is just heat math how much warmth your home needs. The fuel types deliver different punch per volume:

• Natural gas: ~1,030 BTU per cubic foot

• Propane: ~2,516 BTU per cubic foot

Put simply, propane has ~2.5× more energy per cubic foot. When you compare by container size, propane is about 91,452 BTU per gallon, while natural gas is about 85,098 BTU per “gallon-equivalent.” The key takeaway isn’t to change your home’s BTU target, it's to understand how much fuel flow it takes to reach it.

Why this matters: Higher energy density means smaller fuel openings and different pressures for propane. That’s where orifices and regulators come in (we’ll get there). For background reading, bookmark our HVAC Tips blog.

Does your furnace size change? (Short answer: No.)

If your home needs 100,000 BTU/h to stay comfortable on a design-cold night, that target does not change just because you switch fuels. The house load is driven by insulation, windows, air-sealing, and climate, not the fuel.
What does change is how much fuel the furnace must draw to hit that same heat output.

Remember:

• Keep the same output BTU target when comparing furnaces.

• Choose a model whose input BTU and efficiency deliver that output.

• Use our Sizing Guide to cross-check tonnage and BTU for your region.

Real-world fuel use: how fast each gas burns

Here’s the “flow” difference you can picture:

• A 100,000 BTU natural gas furnace burns roughly ~97 cubic feet per hour.

• A 100,000 BTU propane furnace burns about ~40 cubic feet per hour.
  That’s close to a 2:1 reduction in flow for propane at the same heat output, thanks to its higher energy density.

What this changes for you:

• Meter vs. tank: Natural gas is metered; propane comes from a storage tank your supplier will size deliveries based on your hourly and seasonal usage.

• Piping & regulators: The appliance sees different pressures and needs the correct orifice sizing for clean, safe burn (coming next).

• Budgeting: Propane usage per hour is lower by volume, but price per unit differs. Track seasonal consumption after conversion to set refill reminders.

Orifice kits 101: small parts, big safety

Orifices are precision holes that meter fuel into the burners. Because propane is “hotter” per cubic foot, propane orifices are smaller than natural-gas orifices (often about half the size). Example from cooktop land that illustrates the idea: a 0.125" natural-gas orifice vs. 0.082" propane for the same burner output. Furnaces follow the same principle model-specific orifice sizes matched to BTU rating.

Do not DIY drill or swap orifices. A licensed tech uses manufacturer-approved conversion orifice kits and verifies sizing with numbered twist drills (as gauges, not for drilling new holes).

Keep the conversion label that comes in the kit on the furnace jacket. Future techs need to know it’s on propane at a glance.

Need parts or a new matched furnace/coil set? Browse Furnaces.

Gas pressure: the quiet force you must get right

Fuel type changes manifold pressure:

• Natural gas: typically ~3.5" W.C. (inches of water column)

• Propane: typically ~11" W.C.

Because propane runs at higher pressure at the appliance, the system must be adjusted accordingly: gas valve spring, regulator setting, and orifices must match the fuel.

Why it matters: Wrong pressure or orifice size can cause sooting, yellow flames, overheating, CO risk, or burners that won’t stay lit. A tech sets pressure using a manometer and confirms flame shape and combustion numbers.

If you hit a snag, our Help Center has checklists you can reference while talking with your installer.

What a licensed tech actually does during conversion

A proper gas-type adjustment is more than swapping orifices. Expect a licensed HVAC pro to:

1. Shut off fuel & power; verify zero gas at the appliance.

2. Install model-specific orifices and replacement gas-valve spring for propane.

3. Adjust regulator/manifold pressure to spec (around 11" W.C. for propane).

4. Leak test with electronic detection and bubbles at all disturbed joints.

5. Clock the input (confirming BTU flow).

6. Perform combustion analysis (CO, O₂, CO₂, flue temp, efficiency).

7. Inspect flame pattern and burner carryover.

8. Label the appliance as converted; document settings.

What’s inside a proper conversion kit

Quality, manufacturer-approved kits generally include:

• Correctly sized orifices for your model and BTU rating

• Gas-valve spring for propane regulator pressure

• High-altitude pressure switches (when required)

• Hardware, gaskets, and instructions

• Safety documentation & conversion labels

How to use this info:

• Match the kit part number to your furnace model and serial.

• Verify the BTU input on the data plate matches the orifice chart in the instructions.

• Keep all paperwork with your furnace manual.

If your existing unit is past its prime, a modern setup can be simpler: browse Package Units or ask our Design Center for a propane-ready recommendation.

Safety hazards to respect no scare tactics, just facts

Attempting a DIY conversion can lead to:

• Fire or explosion hazards from oversized or mis-threaded orifices

• Carbon monoxide from poor combustion or blocked venting

• Equipment damage (warped exchangers, fouled burners)

• Voided warranties and code violations

Why people get into trouble: using natural-gas orifices on propane (over-fueling, overheating) or using propane orifices on natural gas (under-fueling, unstable flames and raw gas buildup). The right kit + pressure + verification prevents all of this.

Need a hand choosing gear the right way? Ping us at Contact Us—friendly humans, no upsell.

Sizing sanity check (and when to up/downsize)

Before you keep your old size, do this quick check:

• Age & efficiency: Older 60–80% units replaced by 95%+ may allow lower input BTU for the same output.

• Rooms feel uneven? Could be duct or blower setup, not size.

• Additions or air-sealing upgrades? Heat loss changed—recalculate.

If you’re pairing with cooling, explore R-32 residential packaged systems so everything is matched.

Budget, permits, and smart add-ons

Budget line items to expect:

• Conversion kit + labor (includes leak, pressure, and combustion tests)

• Permit/inspection where required

• Tank/regulators and line if adding propane service

• Optional: CO detectors, new venting (if needed), filter cabinet, programmable thermostat

Smart add-ons we like:

• CO alarms near sleeping areas

• Condensate neutralizer on high-efficiency units

• Fresh filter media and a sealed filter rack

Shopping? See Furnaces if you’re updating the whole system. 

Your action plan for a clean, code-safe gas-type adjustment

1. Document your current setup: model, serial, input BTU, altitude.

2. Confirm the BTU goal stays the same (house load).

3. Line up the right propane kit for your model (or price a new unit).

4. Schedule a licensed HVAC tech for: orifices, gas-valve spring, 11" W.C. manifold pressure, and full combustion/leak testing.

5. Label and file the conversion docs.

6. Track usage your first cold month; adjust delivery schedule with your propane supplier.

If you want a second set of eyes, send photos via Quote-by-Photo or chat with our team through the Help Center.