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Estimate a natural gas or propane bill
Gas utilities bill in therms or CCF; propane is sold by the gallon. One therm is 100,000 BTU; one gallon of propane is about 0.915 therms.
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Therms, CCF and propane gallons
A gas bill mixes units of volume with units of energy, which is where confusion starts.
A therm is 100,000 BTU, and a BTU is the heat needed to raise one pound of water one degree Fahrenheit. A therm measures energy, not gas.
A CCF is one hundred cubic feet, a volume. Your meter records volume, but the energy in a given volume varies with gas composition and with pressure and temperature at the meter, so utilities convert before billing. A CCF of pipeline natural gas is about 1.037 therms; the exact multiplier for the month appears on the bill as a BTU factor, therm factor or heating value. An MCF is a thousand cubic feet, or ten CCF.
A gallon of propane holds about 0.915 therms, roughly 91,500 BTU. Propane is sold by liquid volume because it arrives by truck rather than through a meter.
One consequence matters most: a price per gallon of propane and a price per therm of natural gas are not comparable numbers, and neither are a price per gallon and a price per CCF. Divide a propane price per gallon by 0.915 to express it per therm, which raises it about 9%; divide a natural gas price per CCF by 1.037, which lowers it about 3.6%. This calculator returns a cost per therm for that reason: it is the only figure here that compares across fuels.
What the lines on a gas bill are
The commodity charge — labelled gas supply, gas cost or cost of gas — pays for the molecules. Under regulated service it is passed through at cost with no markup and reconciled through a purchased gas adjustment, which is why it moves month to month when nothing about your service has. In states with gas choice, a competitive supplier bills this line.
The delivery charge pays the local utility to move gas through its pipes to your meter, priced per therm or per CCF, and applies regardless of who supplies the gas. The structure mirrors electricity; the supply versus delivery guide works through the same split.
The customer or basic service charge is fixed per month, which is why a summer bill on a gas-heated house is never zero. Around it sit taxes, franchise fees, infrastructure replacement riders and weather normalisation adjustments — individually small, collectively not.
Propane bills look nothing like this. There is no per-therm delivery charge, because propane does not arrive through a regulated pipeline. Instead a price per gallon contains fuel, truck and margin, usually tiered by annual volume and by delivery type, alongside a possible tank rental, delivery fee and minimum-drop fee. Enter the per-unit price and the fixed items separately: a tank rental belongs in the fixed field.
Why propane is a different market entirely
Natural gas from a utility is a regulated monopoly service. Rates are set in public proceedings before a state commission, tariffs are published, and the commodity is generally passed through at cost.
Propane is unregulated retail, and almost every assumption from the utility world fails there. Price is set dealer by dealer, so two houses on the same road buying identical fuel routinely pay different prices, and there is no tariff to look up. The spread is driven by logistics and volume: distance from the bulk plant, road access, gallons per stop, gallons per year.
The contract structures are worth knowing by name:
- Will-call — you monitor the tank and order. Cheapest per gallon in principle, and likeliest to leave you empty in a cold snap.
- Automatic or keep-full — the dealer schedules deliveries from a degree-day model. Convenient, and it removes your ability to time purchases.
- Pre-buy — paying in advance, usually in summer, for a fixed number of gallons at a locked price.
- Budget plans — level monthly payments with a true-up, the same idea as budget billing on a utility account.
Above it all sits the tank, which decides whether you can shop at all. If the dealer owns or leases you the tank, you buy that dealer's propane only; leaving means the tank is pumped out and removed, often with fees, and the fuel left in it is bought back at a discount or not at all. Owning your tank lets you take bids; a leased tank usually carries a lower headline price and no exit. Settle the tank question first.
January is not one twelfth of the year
In a house heated with gas, space heating dominates consumption and everything else — water heating, cooking, a gas dryer — forms a flat baseline. That makes gas the most seasonally lumpy bill a household receives. Summer months are that baseline; winter months are the baseline plus heating, and heating tracks degree days — the accumulated difference between outdoor temperature and a base indoor temperature — not the calendar.
Annualising a single bill is therefore wrong in both directions. Multiplying a January bill by twelve overstates the year badly; multiplying a July bill by twelve understates it just as badly. Neither is a forecast.
The correct method takes ten minutes: sum twelve months of therms from your bills — most utilities print a twelve-month usage graph on the statement — then apply the current price to that total.
Two things follow. A rate increase hurts disproportionately in winter, when far more units are exposed to it. And budget billing is not a discount: it is the same annual cost in twelve equal payments with a reconciliation at the end, a cash-flow tool rather than a saving.
Comparing gas heat with electric heat
Fuels can only be compared on cost per unit of delivered heat; a price per gallon, a price per therm and a price per kilowatt-hour are three different things.
Start with a common energy unit. One therm is 100,000 BTU; one kilowatt-hour is 3,412 BTU, so a therm carries the energy of about 29.3 kWh. At the US average residential price of 18.44 cents per kWh, that much electricity costs about $5.40, so electricity delivered as heat costs roughly $5.40 per therm-equivalent before efficiency.
Then apply efficiency, which decides the comparison:
- A gas furnace delivers the fraction of the fuel's energy given by its AFUE rating — modern condensing units are rated in the high 90s, older atmospheric ones far lower. Cost per delivered therm is your price per therm divided by that efficiency.
- Electric resistance heat — baseboards, strip elements, portable heaters — is essentially 100% efficient at the point of use, so it cannot beat $5.40 per delivered therm at the national average rate, and no upgrade changes that.
- A heat pump moves heat rather than making it, delivering more heat energy than the electricity it consumes — a coefficient of performance above one. At a COP of 3, that $5.40 becomes about $1.80 per delivered therm, which is why a heat pump draws 3,000 to 5,000 W to warm a house where an electric-resistance furnace draws 10,000 to 25,000 W for identical comfort.
Three caveats keep it honest. A heat pump's COP falls with outdoor temperature, and when it reverts to backup resistance strips in severe cold it is no better than a baseboard. Fixed charges survive a fuel switch — keeping a gas meter for a range keeps the customer charge. And the cheapest fuel per therm can still lose once new equipment is priced in. To cost the electric side at your own rate, the appliance energy cost calculator handles heating equipment alongside everything else.
Frequently asked questions
How many therms are in a CCF of natural gas?
About 1.037 therms, though the precise figure changes slightly from month to month. A therm is a fixed quantity of energy — 100,000 BTU — while a CCF is a fixed quantity of volume, one hundred cubic feet, and the energy content of that volume depends on the composition of the gas and on pressure and temperature at your meter. Utilities publish the multiplier they used on each bill, labelled BTU factor, therm factor or heating value. If your bill states usage in CCF and a rate in therms, that factor is what reconciles them. Divide a price per CCF by 1.037 to express it per therm.
Is propane cheaper than natural gas?
Almost never, once both are expressed in the same units, but the comparison has to be done properly. Divide your propane price per gallon by 0.915 to get a price per therm, then set it beside your natural gas price per therm including delivery. Propane also carries costs that pipeline gas does not: tank rental if you do not own the tank, delivery and minimum-drop fees, and the risk of running out. The reason propane exists is availability, not price — it serves houses no gas main reaches. Where both are available, run the conversion with your own numbers rather than trusting a general claim.
Why did my gas bill triple in January?
Because space heating dominates gas use and it is not spread evenly across the year. A summer bill is water heating and cooking; a January bill is that same baseline plus heating driven by degree days, so a tripling is ordinary rather than alarming. Three factors compound it: colder weather means more therms, the commodity portion of the rate is often higher in winter, and any rate increase applies to far more units in a cold month. Check the therms used against the same month last year before assuming a pricing problem — if therms rose and the rate did not, the answer is weather.
Should I pre-buy propane in the summer?
Pre-buying locks a price for a set number of gallons paid for in advance, and it is a bet rather than a saving. You win if winter prices rise above your locked price and lose if they fall below it, and nobody knows which will happen. Three questions decide whether the bet is reasonable: how the dealer treats gallons you do not use by the end of the season, what happens to your money if the dealer fails, and whether the locked price is actually below what you would likely have paid on your normal volume tier. A price cap programme costs a fee but leaves the downside open.