How to Find Out What Fuel Serves the House

Why this matters

"Gas heat" on a listing or a customer's call can mean utility natural gas, a propane tank in the side yard, or, from someone who does not know the difference, an oil boiler. Each one changes which equipment you can offer, how it is vented and piped, what the conversion kit costs in hours, who has to be called before the fuel is shut off or restored, and what the customer's operating cost looks like afterward. A furnace quote written for natural gas on a propane house is wrong in its equipment, its gas piping and its schedule. Getting the fuel right is a five-minute check that most often happens after the quote instead of before it.

Before anything: if there is a gas or fuel odor

If anyone smells gas (natural gas and propane are both odorized with a sulfur smell), or smells heating oil strongly indoors, the research stops. Everyone leaves the building. Nobody operates a light switch, an appliance, a phone or a garage door opener inside, and nobody starts a vehicle in an attached garage. From outside and well away, call the gas utility's emergency line or the propane supplier, and 911. Do not go back in until the utility or supplier says it is safe. Propane is heavier than air and collects in basements, crawlspaces and low spots, so "it smells less upstairs" is not an all-clear.

Step 1: Find the delivery point outside

Walk the exterior before you walk the mechanical room. The fuel has to arrive somewhere:

• Natural gas: a meter on a riser coming out of the ground, with a service regulator ahead of it, usually on a side wall near the front. Many meters carry the utility's name and a meter number.
• Propane: an above-ground tank, usually a horizontal cylinder on a pad or blocks, or vertical cylinders in a pair against the wall. A buried tank shows only a dome lid in the yard, often 10 ft or more from the house, plus a regulator at the house wall. There is no utility meter on most propane systems.
• Heating oil: a fill pipe and a vent pipe on an exterior wall, often with a cap and a small whistle vent, and a tank in the basement or garage. A fill and vent with no indoor tank can mean a buried tank.
• Electricity only: no gas meter, no tank, no fill pipe.

Reason: the delivery point is unambiguous in a way the appliances are not, and it tells you who supplies the fuel.

What breaks if you skip it: you read a furnace rating plate that says natural gas on a house where someone converted it to propane, or left it unconverted and misfiring.

Step 2: Read every fuel-burning appliance's rating plate

Find each appliance's rating plate and read the fuel line: natural gas or LP (propane). An appliance converted in the field should carry a conversion label stating the fuel it was converted to, the date, and who did it. Check the furnace, water heater, range, dryer, fireplace, generator, pool heater and space heaters.

Reason: one house can run three fuels. A propane range and fireplace, an oil boiler and an electric water heater is a common mix in rural areas. Your quote touches one appliance, but the fuel system's capacity is shared by all of them on that fuel.

What breaks if you skip it: a new appliance gets sized against a propane system that is already carrying loads nobody listed.

Step 3: Ask who supplies it and who owns the tank

For utility gas, note the utility. For propane, ask for the supplier's name and whether the customer owns or leases the tank. Leased tanks are common, and in many states the lease, state law or both bar anyone but the owning supplier from filling it. For oil, ask for the supplier and the tank's age if known.

Reason: on propane, the supplier controls the tank, the regulator and often the first-stage piping, and most states' propane rules, built on NFPA 58, require a leak check of the system before gas is restored after an interruption of service, which the supplier normally performs. That puts the supplier on your schedule for any job that shuts propane off at the tank. On oil, tank age matters because an old tank near its end of life is a separate conversation from the burner.

What breaks if you skip it: the new equipment is set, and nobody can light it until the supplier comes out.

Step 4: Look for abandoned fuel systems

Note any capped gas line, an unused propane regulator, a removed oil tank, or a fill pipe with nothing behind it. Ask the owner for documentation of any tank removal or closure.

Reason: abandoned systems cause real incidents. An oil fill pipe left in the wall after the tank was removed has received deliveries that went straight into a basement. A buried oil tank left in place can leak; residential heating oil tanks used on the premises are excluded from the federal underground storage tank rules (40 CFR Part 280), so removal and closure requirements come from the state and sometimes the locality, and they vary widely. A buried tank found during an equipment change is something the customer's insurer, a buyer's inspector and possibly the state environmental agency will care about.

Step 5: Check what other fuel is available at the street

If the customer is considering a fuel change, ask the gas utility whether natural gas is available on that street and what the utility requires to extend a service. Many utilities publish service territory maps; most will answer by address.

Reason: "convert to natural gas" is only an option where a main is close enough, and the extension rules decide whether it is a small job or a large one. The answer also sometimes runs the other way: a house on propane on a street with gas service is a common case after a main extension.

Step 6: Read the electrical service

Note the main breaker rating and the meter. A 100 A service with a full panel is a different starting point for a heat pump, heat pump water heater or induction range than a 200 A service with open spaces.

Reason: every fuel decision is now also an electrification decision. Even a customer staying on gas may want a heat pump with gas backup. The service size decides whether all-electric options need a service upgrade, which brings the electric utility into the schedule.

Step 7: Write the fuel profile into the record

Record for the address: fuel by appliance, supplier and tank ownership, tank size and location if propane or oil, any abandoned system, gas availability at the street, and service size.

Reason: the next call on that house starts with this, not with Step 1.

Worked example: "gas heat" on a rural listing

A homeowner calls for a furnace replacement and wants to add a tankless water heater at the same time. They say the house has gas heat.

• Step 1. No meter on the house. A horizontal tank sits 15 ft off the side wall, labeled by a propane supplier, with a regulator on the house wall.
• Step 2. Furnace rating plate: 80,000 Btu/h input, LP. Range: 65,000 Btu/h total input, LP. Water heater: electric tank. Fireplace: none.
• Step 3. The tank is leased from the supplier. The owner does not know its size; the data plate on the tank shows its water capacity, and the tech reads it.
• Step 4. No abandoned systems found.
• Step 5. The gas utility says no main within a mile.
• Step 6. 200 A service, several open spaces.

The tankless unit the customer wants is rated 199,000 Btu/h input. Add up what could fire at once: 80,000 (furnace) plus 65,000 (range) plus 199,000 (tankless) is 344,000 Btu/h. Propane carries about 91,500 Btu per gallon, so at simultaneous full fire the house would draw 344,000 divided by 91,500, about 3.8 gallons an hour.

Three things follow, and each changes the quote:

• Tank and regulator capacity. A propane tank delivers vapor by boiling the liquid inside, and how fast it can do that falls as the weather gets colder and the tank gets emptier. Whether this tank and its regulators can carry 344,000 Btu/h on a design-temperature morning is the supplier's determination, not yours. The tech calls the supplier before quoting and asks that question with the combined load in hand.
• Piping. The existing gas line was sized for 145,000 Btu/h (80,000 plus 65,000). Adding 199,000 more than doubles the load, so the house piping has to be re-sized from the propane sizing tables in the fuel gas code as adopted (the International Fuel Gas Code or NFPA 54), using the propane supply pressure the supplier sets.
• The alternative. With 200 A service and open spaces, a heat pump water heater avoids the propane load entirely. The quote offers both, with the propane tankless option marked "subject to supplier capacity confirmation."

The supplier answers that the tank can carry the combined load in mild weather but not reliably at the coldest design conditions without a larger tank. The customer chooses the heat pump water heater, and the furnace replacement proceeds on propane with the supplier booked for the leak check before relight.

What changes the answer: if Step 1 had found a natural gas meter, the tankless option would turn on the utility meter's capacity and the house piping only, and the utility, not a supplier, would decide whether the meter needs upsizing.

How to verify you got it right

• You saw the delivery point, and it agrees with every appliance rating plate or conversion label.
• You know who supplies each fuel and who owns any tank, and you have their number.
• Every fuel-burning appliance on the same fuel is in your load total, by its rated input.
• Any job that shuts off propane has the supplier's leak check on the schedule before relight.
• The record names the electrical service size for the next electrification conversation.

References

• NFPA 58, Liquefied Petroleum Gas Code, in the edition your state has adopted, which binds propane suppliers and installers through state rules.
• International Fuel Gas Code or NFPA 54, as adopted by your jurisdiction, for gas pipe sizing.
• 40 CFR Part 280, federal underground storage tank rules, and its exclusion of heating oil tanks used on the premises; your state's tank rules.
• See related: Reading the Place Before the Quote; How Altitude Changes Combustion.