Gas vs Electric Furnace: The Ratio That Decides It

If you have a gas line, a gas furnace is almost certainly the cheaper machine to run in California. If you are looking at electric because you want off gas, the comparison to run is not gas-versus-electric-furnace at all — it is gas-versus-heat pump, because a heat pump is also electric, is roughly three times as efficient as an electric furnace, and is the only electric option that competes with gas at 33 cents a kilowatt-hour.

What each one actually is

Three different machines end up pushing warm air through the same ductwork, and the differences are the whole decision.

A gas furnace burns natural gas or propane in a sealed heat exchanger, which transfers that heat to the air stream without mixing combustion products into it while a flue carries the exhaust outside. Efficiency is AFUE — Annual Fuel Utilization Efficiency, the share of fuel that becomes usable heat. Roughly 80% for a conventional furnace, 90–99% for a condensing one.

An electric furnace has no burner, no heat exchanger, no flue and no gas line. It is a cabinet of electric resistance heating elements and a blower. All of the electricity becomes heat, so its efficiency is 100% — a number that does more damage than any other figure in this comparison.

A heat pump is not a furnace and does not generate heat at all. It moves heat from the outdoor air into the house using refrigerant, which is why it can deliver two to four units of heat per unit of electricity. It belongs here because it is the direct competitor to the electric furnace, and it wins outright.

The 100%-efficient trap

An electric furnace is 100% efficient; a good gas furnace is 95%. It is easy to read that as “the electric one is better,” and it is wrong, because efficiency percentages only compare machines burning the same fuel at the same price. What you pay for is heat delivered, which depends on the price of the energy going in as much as on the fraction that survives the conversion.

Put it this way: 100% is not a floor, it is a hard ceiling — no electric furnace can return more than one unit of heat per unit of electricity, and none ever will. A heat pump on the same electricity routinely returns three. Among electric options, “100% efficient” describes the worst one available.

Running cost: the only comparison that matters

Here is the arithmetic in full, so you can re-run it on your own bills. Inputs: US residential electricity 18.44 cents/kWh, California 33.25 cents/kWh (EIA Electric Power Monthly, Table 5.6.A, May 2026 data, released July 23, 2026); US residential gas about $1.46 per therm January–March 2026 and California $2.00–$2.21 per therm, call it $2.10 (EIA, release July 31, 2026). Conversions, which are ours: one million Btu is 10 therms of gas input or 293.07 kWh of electricity. The input prices are federal figures; the per-million-Btu results are our arithmetic, not a published EIA result.

Our derivation from EIA electricity and natural gas prices, dated above. Both EIA series update monthly, so re-run these before acting on them.

The bottom row is the finding. In California an electric resistance furnace costs roughly 4.4 times as much to run as a 95% AFUE gas furnace, and about three times as much as a heat pump. Nationally it is about 3.5 times the gas furnace. There is no version of this arithmetic in which an electric furnace is the cheap option.

Express it as a ratio — never as a gas price

You will find pages offering a threshold gas price: “if gas is below X per therm, gas wins.” Ignore them. A threshold in dollars goes stale the month it is published, and it hides the thing that actually matters — the relationship between two prices. The rule that survives a price change is simple:

That second number matters, because the widely repeated “3.5 to 1” rule of thumb is too generous to the heat pump for the equipment most people are actually quoted. A 7.5 HSPF2 unit breaks even at about 2.3 to 1, not 3.5.

Now put California’s real numbers in. Electricity at $97.45 per million Btu of input against gas at $21.00 is a ratio of about 4.6 to 1 — above 3.16, above 2.31, and still above the break-even for a heat pump holding a COP of 4. Gas currently wins on running cost in California, and it wins because electricity there is extraordinarily expensive, not because gas is cheap. Nationally the ratio is about 3.7 to 1 against the same 3.16 break-even, so gas wins there too, but narrowly enough that a heat pump holding a seasonal COP above about 3.7 flips it.

Two honest limits. Seasonal COP describes a season, not a moment — efficiency falls as the outdoor temperature falls, and a mild inland Central Valley winter favours the heat pump more than a national average implies. And running cost is one input among several, alongside install cost, rebates, and whether the house has gas at all.

Upfront cost and installation

The installed-cost picture runs opposite to the running-cost picture, which is exactly why electric furnaces keep getting sold.

An electric furnace is the cheapest heating box to install, for structural reasons rather than shopping around: no flue to run or reline, no burner, so no combustion air and no gas piping, and no condensate. It is a cabinet, a blower and some elements. We do not publish an installed figure for one, because we have no defensible source and would rather leave a gap than invent a number.

A gas furnace carries all the costs the electric one avoids. Contractor cost guides put a full gas furnace replacement across a $3,500–$10,000 span depending on tier and size; our furnace replacement cost guide is the canonical page for that detail.

Two lines get left out of quotes, one on each side, and both are worth asking about by name:

• The venting conversion, on the gas side. Stepping from 80% AFUE to a 90%+ condensing model means abandoning the old flue and running new PVC intake and exhaust — roughly $500–$2,500 per contractor guides. The missed line: if the old furnace shared a masonry chimney with the gas water heater, removing it orphans that water heater on a flue far too large for it, and relining or re-venting runs roughly $1,000–$3,000 more. Ask it in these words: “If I go condensing, what happens to my water heater’s vent?” This is a safety line as much as a money line — a water heater that cannot draft properly can push combustion products back into the house.
• The electrical service, on the electric side. A resistance heat bank draws serious current on dedicated circuits, and a 20 kW bank is not something you add without looking at the panel first. Contractor guides put a 100A-to-200A service upgrade at roughly $1,500–$4,500 — enough to swallow the electric furnace’s entire installed-price advantage in one line. Repeated trips on a heat strip circuit are a defect, not a nuisance: ESFI notes that equipment which “repeatedly blows a fuse or trips a circuit breaker could indicate a defect that may cause a fire or electrical shock.”

Price ranges on this page are contractor-reported market estimates. No government body or standards organisation publishes installed residential HVAC prices; we label these rather than dress them as sourced facts.

One part of this is federal. The Bureau of Labor Statistics Producer Price Index for warm air furnaces stood at 253.005 in March 2026 against 227.268 in March 2025 — up 11.3% year over year on our arithmetic on the published index. Two caveats travel with it: the index measures what manufacturers charge at the factory gate rather than what a homeowner pays installed, and April through July 2026 are flagged preliminary, so March is the last firm reading. It records the movement; it does not explain it, and we will not speculate about why.

Comfort, compared

Supply air temperature. A gas furnace delivers the hottest air of the three, with an electric furnace close behind; a heat pump delivers cooler air over longer runs. If someone wants that blast of heat, both furnaces give it and the heat pump does not.

Winter humidity. Neither furnace adds moisture. Dry winter air is a function of heating cold outside air, not of which appliance heats it — combustion products from a sealed furnace do not enter the air stream. Any page claiming a gas furnace dries a house out more than an electric one is describing something that does not happen.

Noise. Both are blower-dominated and the blower type matters more than the heat source. A gas furnace adds a short sequence of sounds at each start — inducer, ignition, burners lighting — that an electric furnace does not have.

Safety and maintenance, compared

A gas furnace is a combustion appliance, and combustion appliances produce carbon monoxide when something goes wrong. EPA describes CO as “an odorless, colorless and toxic gas” and warns that “because it is impossible to see, taste or smell the toxic fumes, CO can kill you before you are aware it is in your home.” Its household source list includes “leaking chimneys and furnaces,” “back-drafting from furnaces, gas water heaters, wood stoves and fireplaces,” and a flue that is “improperly sized, blocked or disconnected.”

The mechanism that matters most is a cracked heat exchanger — the wall between the flame and the air you breathe. Crack it and combustion products, carbon monoxide included, can enter the supply air. A confirmed cracked heat exchanger is not a repair-or-replace decision until the furnace is off: shut it down at the gas shutoff and the electrical disconnect and do not run it, including for heat, until it is repaired or replaced. There is no “run it carefully until spring” answer.

Know the symptom pattern. EPA lists, at low concentrations, “fatigue in healthy people and chest pain in people with heart disease”; at higher concentrations “impaired vision and coordination; headaches; dizziness; confusion; nausea.” The clause worth memorising: CO “can cause flu-like symptoms that clear up after leaving home.” That is how CO poisoning is caught in a household.

An electric furnace has none of that — no combustion, no flue, no heat exchanger, no CO from the furnace. That is a real advantage. What it is not is a reason to remove CO alarms: a house with a gas water heater, gas range, fireplace, gas dryer or attached garage still has CO sources, and the alarms stay.

Annual maintenance is the one heating recommendation carrying full authority. EPA advises: “Have a trained professional inspect, clean and tune-up central heating system (furnaces, flues and chimneys) annually.” CPSC, quoted on that same EPA page, “urges consumers to have an annual professional inspection of all fuel-burning appliances… to detect deadly carbon monoxide leaks,” and NFPA says to have such equipment inspected every year before cold weather. Ask one question when booking: “Will you run a combustion analysis and show me the CO reading?” A tune-up that never puts an analyser in the flue has not measured carbon monoxide. An electric furnace needs none of this.

Where an electric furnace genuinely makes sense

The case is narrow but real, and it is not “you cannot afford a heat pump.”

• No gas at the property and no heat pump going in — a cabin, a workshop, a rarely occupied second home where annual runtime is small enough that a 4.4× running cost applies to almost nothing.
• As the backup, not the main system. By far the most common legitimate use: the resistance elements inside a heat pump’s air handler, covering the coldest hours and the defrost cycles. Contractor guides put a 5 kW heat kit at roughly $300–$700 installed and a 10–20 kW bank at $500–$1,200, plus electrical.
• A very small conditioned area where anything better cannot be justified against a handful of therms a year.

If your reasoning is “the gas furnace quote was higher,” price the heat pump before you sign. The install saving is one-off; the running cost is every winter for fifteen years.

The heat pump case, briefly

A heat pump is the electric option that actually competes. At a seasonal COP of 3.0 it delivers a million Btu for about $32 in California against $97 for resistance heat — the same electricity, a third of the cost, because it moves heat instead of making it. Against gas at $22 it still loses on running cost in California today, but it is in the same conversation, and it replaces your air conditioner, which no furnace does.

The incentives point that way too. There is no federal credit in 2026, but several California utility programs pay specifically for gas-to-electric conversion. SMUD, verified August 20, 2026, offers up to $3,000 with a variable-stage heat pump system and $2,000 with a qualifying two-stage system at 15.2 SEER2 or better, plus a $2,000 panel-upgrade bonus tied to that conversion — all requiring a contractor in the SMUD Contractor Network. Our California HVAC rebate guide maps the programs by utility with a verification date against every amount.

For the full climate, comfort and equipment comparison including cold-climate performance and dual-fuel, go to heat pump vs furnace; for pricing, heat pump cost by size and type.

The federal position in 2026, in three sentences

There is no federal residential tax credit for a furnace or a heat pump in 2026. Under Public Law 119-21, Section 25C is terminated for property placed in service after December 31, 2025, and Section 25D is terminated for expenditures made after that same date (IRS Fact Sheet FS-2025-05, August 21, 2025). If you installed in 2025 and are claiming it now, the two sections differ in one way that decides real money: excess 25C credit cannot be carried forward to a future tax year — the IRS states plainly that you can’t apply any excess credit to future tax years — while excess 25D credit can be. Our page on what ended and what is left covers the federal picture properly; this page does not restate it.

Run it on your own bill

Everything above is an average. Yours is on two pieces of paper in a drawer. Five steps:

1. Your effective price per kWh. Total electricity bill, every fee and tier included, divided by kilowatt-hours used, not the headline rate.
2. Your effective price per therm. Same method on the gas bill. If it is billed per Ccf, one Ccf is about one therm.
3. Convert both to cost per million Btu of input. Multiply the electricity price by 293.07; multiply the gas price by 10.
4. Divide electricity by gas. That is your ratio.
5. Compare it to COP ÷ AFUE for the equipment you are being quoted. Below break-even the heat pump is cheaper to run; above it, gas is. An electric resistance furnace loses at any ratio above 1.0 ÷ AFUE — essentially always, where gas exists.

Take that number into the quoting conversation. A contractor who can discuss it is worth listening to; one who answers with a rule of thumb is quoting from a script.

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