How to Convert a Gas Range from Natural Gas to Propane
Why this matters
A range built for natural gas and fed propane without a complete conversion burns rich: tall lazy yellow flames, soot on every pan and the oven walls, and carbon monoxide in the kitchen. A half conversion is worse than none because it looks done. The top burners get their new orifices, everyone is satisfied with the cooktop flames, and the oven orifice and the appliance regulator stay in their natural gas settings, out of sight. The conversion has seven or more parts to it on a typical range, and every one gets touched and proven, then the manifold pressure gets read on a manometer, before you call it done.
Gas, carbon monoxide and power first
Gas smell on arrival. If the kitchen smells of gas, nothing gets converted. Everyone leaves, no switches, lights or phones are used inside, and the call to the gas supplier or the fire department is made from outside.
Gas off at the range shutoff, power off at the cord. Close the appliance shutoff valve and unplug the range before removing a single orifice. The 120 V cord feeds the igniters and the control, and a spark module firing while an orifice is out puts a spark next to an open gas path. Confirm the shutoff is closed by trying a top burner: no gas, no flame.
Fire it with a carbon monoxide monitor on you. Every time you light a burner during the conversion, a personal CO monitor clipped near your breathing zone is on and the kitchen has a window or the hood running. An oven burner fired on the wrong orifice can push CO into the room in minutes. If the monitor alarms, turn the burner off and ventilate before going on.
Leak tests use solution, never flame. Every joint you disturbed gets a noncorrosive leak-detection solution after gas is restored, and a bubble that grows over a minute is a leak. 'Gas Range Connection and Leak Check Standard' owns the method.
Your side of the line, and the supplier's
The appliance tech's work starts at the outlet of the existing shutoff and ends at the burners. The tank, the first- and second-stage regulators, and the house piping belong to the propane supplier or a licensed gas fitter, per 'The Gas-Side Boundary for an Appliance Tech'. Before you open the kit, confirm the supply is propane and that the supplier has set the house regulation; a propane line regulated to the low pressure a natural gas house runs at will fail every test below. Some states and localities require conversions to be done by a licensed gas fitter or propane dealer; where yours does, the conversion is theirs.
What the conversion changes
Propane carries roughly two and a half times the heat of natural gas per cubic foot and is delivered at higher pressure. So a propane burner needs a much smaller hole at a higher pressure to make the same rated output, and the appliance regulator has to hold that higher pressure. Flow through an orifice rises with the hole's area and with the square root of the pressure across it; leave a natural gas orifice in place and propane pours through it.
APPLIANCE REGULATOR, CAP REMOVED (one common type)
NAT position LP position
+------------+ +------------+
| insert end | | insert end |
| "NAT" out | | "LP" out |
+-----+------+ +-----+------+
| less spring force | more spring force
| outlet set low, | outlet set high,
| often 4 in WC | 10 in WC on many
v v
manifold manifold
BURNER ORIFICE SPUD
valve outlet --[ hex body | bore ]--> burner throat
size stamped on the hex
Regulators differ: some caps reverse, some hold a reversible plastic insert, some use a pin, and a few ranges ship with a regulator already set and a separate part in the kit. The rating plate states both manifold pressures for that model; read it, not the drawing. The orifice spud is a brass fitting with a drilled bore and its size stamped on the hex; the kit chart lists which stamp goes in which position.
Two other parts move with the gas. Each top burner valve carries a simmer (low flame) screw, turned in for propane so the low flame is not too large. The oven and broil burners carry an air shutter that sets how much primary air mixes with the gas before it burns.
The conversion
Match the kit to the model. The kit number on the rating plate or in the installation instructions, and the chart inside it, must match the range. An orifice that threads in is not proof it is right. Lay the new orifices out against the chart before removing any old ones.
Convert the appliance regulator. Remove the cap, reverse or flip it or its insert so the LP marking faces out, and reinstall it with its gasket seated. Skip it and every new orifice runs at the natural gas pressure: the top burners run small, and any orifice you miss runs rich. The regulator is usually behind the storage drawer or the back panel; it is the one part a quick conversion forgets.
Top burner orifices. Lift the grates, caps and burner heads, remove each spud with the nut driver the kit specifies, and install the matching LP spud, snug, not cranked. Bag and tape the natural gas spuds inside the range near the rating plate for a future reconversion. Check the stamp on every one as it goes in; two sizes on one cooktop is normal and swapping them puts a large burner on a small hole.
Oven and broil orifices. Behind the oven burner or the broil drawer. Some ranges use a replaceable spud here, some use an adjustable hood that is turned down onto an internal pin for propane until it seats, snug and no further, per the kit. Either way, this orifice gets touched. An oven orifice left in its natural gas setting is the most common cause of a sooted oven after a "converted" range is installed.
Restore gas and power, and leak-test. Open the shutoff, plug the range in, and put solution on every spud thread, the regulator cap, and any fitting you moved. A bubble that grows over a minute gets the gas shut off, the joint tightened or reseated, and the test repeated.
Read manifold pressure. With the shutoff closed while you open the port, connect a manometer at the regulator test port or the manifold tap the instructions name, or at a top-burner position using the adapter the instructions describe, and fire the burners they specify. The reading must match the LP figure on the rating plate. Read the supply pressure at the inlet as well: the plate states a minimum supply pressure, and a regulator cannot deliver its outlet setting from an inlet below that. When the manometer comes off, refit the test port plug and leak-test it like every other disturbed joint.
Set the simmer screws. Light each burner, turn it to its lowest setting, and turn the simmer screw in the valve stem until the flame is small, steady, and completely around the burner. Then turn the knob from high to low quickly: the flame must stay lit. A simmer left at its natural gas setting gives a propane low flame too big to simmer.
Set the oven and broil air shutters. Fire the oven with your CO monitor on and the door open as the instructions allow. Yellow tips mean too little air: open the shutter a little. A flame that lifts off the ports or roars means too much: close it a little. You want blue flames with defined inner cones. Lock the shutter screw and repeat for broil.
Fill in and attach the conversion label. The kit includes a label stating the range was converted to propane, the date, and by whom. Fix it beside the rating plate. Without it, the next tech reading the plate sees a natural gas range.
Worked example: a range moved to a propane house
A range bought in a natural gas town moved to a rural house on propane. Rating plate: natural gas 4 in WC, propane 10 in WC, minimum propane supply 11 in WC. Four top burners in two sizes, a replaceable broil spud, and an adjustable oven hood: six orifice positions plus the regulator.
- Supply inlet, static with no burner lit, before any conversion: 11.4 in WC. The supplier's regulation was in place and above the plate minimum, so the conversion could proceed; the reading under load comes after the conversion, not with propane fired through natural gas orifices.
- Regulator insert reversed to LP. Four top spuds and the broil spud replaced against the chart, oven hood turned down until it seated.
- Leak test: a slow-growing bubble at the left rear spud. Gas off, spud snugged about an eighth of a turn, retested clean over a full minute.
- Manifold, two top burners on high: 10.1 in WC against the plate's 10. Inlet held at 11.3 in WC under that load.
- Simmer screws turned in on all four burners; each held a steady low flame through a quick high-to-low turn.
- Oven first fired with short yellow tips; shutter opened slightly, flames blue with defined cones. Broil blue as set. Personal CO monitor read 0 ppm through the oven run with the hood on.
- Label filled in and attached beside the rating plate.
Where the answer changes
Supply pressure below the plate minimum. If the inlet reads, say, 9 in WC with burners firing, the manifold cannot reach 10 in WC no matter what you do inside the range. Stop, leave the range off with the shutoff closed, and route it to the propane supplier; it is their regulator or their line.
No kit for the model. Do not drill or improvise orifices. The conversion parts are part of how the range was certified to ANSI Z21.1/CSA 1.1, the standard that binds the manufacturer for household cooking appliances, and an improvised orifice voids that.
High altitude. Above the elevation the instructions name, makers call for smaller orifices still or a derate. That comes from the installation instructions, not from the chart for sea level.
How to verify you got this right
- Every orifice position touched: count them against the kit chart, oven and broil included.
- Regulator marked LP, manifold within the rating plate's propane figure on a manometer, inlet above the plate minimum under load.
- Every disturbed joint bubble-free over a full minute.
- Blue flames with defined cones on every burner, no yellow tips, no lifting, simmer flames stable on a quick turn-down.
- Personal CO monitor holding at the room's baseline through an oven run (0 ppm in the example), and the conversion label on the range.
References
- See related: The Gas-Side Boundary for an Appliance Tech; Gas Range Connection and Leak Check Standard; The Propane Conversion That Sooted Every Pan
- ANSI Z21.1/CSA 1.1, Household Cooking Gas Appliances (binds the manufacturer; conversion parts are part of the certified design)
- Manufacturer installation instructions and conversion kit chart for orifice sizes, regulator setting and manifold pressures
- Range rating plate for natural gas and propane manifold pressures and minimum supply pressure