On paper the electric furnace wins. It turns nearly every watt it draws into heat, while even a good gas furnace sends some of its heat up the flue. On your utility bill it usually goes the other way in Southern California, because electricity costs more per unit of heat than gas does. And for a Pasadena, CA winter, the electric option that actually competes with a gas furnace is a heat pump, not a resistance furnace. Here is how to think it through for your house.
How each one makes heat
A gas furnace burns natural gas inside a heat exchanger. The blower pushes house air across the hot metal, and the exhaust goes out a vent. It needs a gas line, a flue, and air for combustion.
An electric furnace is a set of resistance heating elements sitting in the airstream, like a very large toaster. The elements switch on in stages, the same blower moves air across them, and there is no flue. What it needs instead is a lot of electrical capacity, often a dedicated high-amperage circuit.
Both use the same ducts, the same thermostat wiring, and the same kind of blower. From the registers they feel different, and we will get to that.
What the efficiency ratings say, and what they leave out
Gas furnaces carry an AFUE rating. A Department of Energy guide defines it as the ratio of a furnace's annual heat output to the fuel energy it consumed over the year. An AFUE of 90% means 90% of the energy in the gas became heat in the house and the rest went up the chimney. The same guide's ranges:
- Older natural-draft furnaces with a standing pilot: roughly 56% to 70% AFUE.
- Mid-efficiency furnaces with electronic ignition and an exhaust fan: 80% to 83%.
- Condensing furnaces with a second heat exchanger and sealed combustion: 90% to 98.5%.
An all-electric furnace has no flue loss, so a Department of Energy guide for contractors puts its AFUE between 95% and 100%.
That looks like a clear win for electric. The catch is that AFUE measures how much of the energy you paid for became heat. It says nothing about what that energy cost. The same guide notes that electricity is still one of the most expensive heating fuels. Pasadena is not an exception.
To compare for yourself, look at your rate per kilowatt-hour on the Pasadena Water & Power bill (LADWP in the San Fernando Valley) and your rate per therm on the SoCalGas bill. One therm is roughly 29.3 kilowatt-hours of heat energy. Divide each price by the furnace efficiency and you have the cost of delivered heat from each fuel. In our area gas has usually come out well ahead per unit of heat, but rates change, so run the numbers on your own bills.
Why the gap matters less here than it would in Minnesota
Our heating season is short. Furnaces in the San Gabriel Valley and the Valley mostly run from November into March, on nights that drop into the 40s, and sit idle the rest of the year. What drives the winter bill is run hours multiplied by the price of delivered heat. Fewer run hours shrink the gap between fuels.
That is why an electric furnace can make sense in a small space with no gas service, like an ADU or a hillside cabin with an electric-only hookup, and why it rarely makes sense as the main heat for a 2,400-square-foot house that already has a gas line.
The third option, and usually the right electric one
If you want to get off gas, compare the gas furnace to a heat pump, not to a resistance furnace. A heat pump moves heat from outdoor air into the house instead of making it from scratch, so it delivers more heat energy than the electricity it uses. ENERGY STAR puts it as up to three times more heat energy delivered than electrical energy consumed.
A Pasadena winter night in the 40s is easy territory for a modern heat pump. The ratings you will see on quotes are SEER2 for cooling and HSPF2 for heating, the test standard DOE switched to on January 1, 2023. Pasadena Water & Power and LADWP have had heat-pump incentives; check the current program before you buy. If that is the direction you are leaning, start with heat pump installation.
Installation and the house you already have
- Gas furnace. Most 1950s-to-80s ranch homes in the SGV and SFV already have a gas line and a vent. A condensing furnace vents through plastic pipe and needs a condensate drain, so it may not slot into the old chimney path at all. Where the old chimney still serves another gas appliance, the venting has to be looked at as a whole rather than left as it was.
- Electric furnace. No vent needed, but the elements pull serious current. Many older homes in Reseda and Northridge still have 100-amp service, and upgrading a panel is an electrician's job, a separate licensed trade from ours.
- Either one. In California, replacing the furnace or air handler triggers a duct leakage test (HERS, now called ECC) under Title 24, and new attic ducts in our climate zones must be insulated to R-8 under the 2025 code. Leaky attic ducts waste heat no matter which fuel made it, which is why a duct repair often comes up in the same conversation.
- Craftsman bungalows with a wall or floor furnace and no ducts. Neither option applies without adding ductwork. A mini split or ducted heat pump is the usual answer there.
Safety and upkeep
A gas furnace has combustion, a heat exchanger, and a vent. It needs an annual check of the burners, flame sensor, heat exchanger, and venting, and the house needs working carbon monoxide alarms. An electric furnace has no combustion and no carbon monoxide risk; what fails are elements, sequencers, and connections, and there is less to inspect. Electric furnaces often last longer for that reason, though how long any furnace lasts depends more on airflow and filter habits than on the fuel.
Comfort
Gas furnaces push hotter air out of the registers and heat the house faster. Electric furnaces run longer with gentler air. Most people notice the blower more than the fuel: a variable-speed blower on either type is quieter and holds a steadier temperature than a single-speed one.
What you can check yourself
- Pull your last winter's PWP or LADWP bill and SoCalGas bill and note the price per kWh and per therm.
- Find the data plate on your furnace. It lists the model, and often the AFUE and the manufacture date.
- Confirm whether the house has gas service at all. Some hillside and ADU properties do not.
- Read the main breaker label on your panel for the service amperage. Reading the label is fine; leave the cover on.
- If you have a smart thermostat, check its history for how many hours the heat ran last winter.
When to call a licensed tech
- You are replacing a furnace. Sizing should come from a load calculation (Manual J), not from the size of the old unit.
- You want a written quote for a gas furnace and a heat pump side by side before deciding. A furnace installation quote and a heat pump quote from the same visit is a normal request.
- You smell gas, see yellow or flickering burner flames, or a carbon monoxide alarm has gone off. Leave the house and call SoCalGas first, then us.
- Your ducts have never been tested or sealed. The replacement is the moment to fix them.
Common questions
Is an electric furnace really 100% efficient?
Close to it at the appliance. A Department of Energy guide for contractors rates all-electric furnaces at 95% to 100% AFUE. That still leaves out duct losses and the price of electricity, which is where the electric furnace loses the comparison in most Southern California homes.
Which is cheaper to run in Pasadena, gas or electric?
Usually gas, because a therm of gas has cost less than the same amount of heat from electricity here. Check your own bills using the therm-to-kWh conversion above. A heat pump changes the answer, since it gets roughly three units of heat per unit of electricity.
Should I skip both and get a heat pump?
If you want to leave gas, yes, compare the heat pump to the gas furnace and ignore the resistance furnace. If you are keeping gas, a condensing furnace with a variable-speed blower is the efficient version of what you have. Either way, get the ducts sealed and tested at the same time.
Our diagnostic visit is $69, told to you before booking and credited toward the work. Call Boost Services Heating and Cooling at 818-277-5056 or contact us here.
Written with AI assistance by Boost Services, Heating and Cooling team, and reviewed by our licensed technicians before publishing. Boost Services Heating and Cooling, C-20 #1119892.