On running cost alone, a 95% AFUE natural gas furnace beats a heat pump in Hawaii by $3.97 per million Btu of heat delivered, using EIA average prices. That is a narrow margin on a very small job. Honolulu’s reference station logs about 0 heating degree days a year, so the cooling side of a heat pump often outweighs the fuel math.
The short answer for Hawaii
Start with the numbers. Using average residential prices from the U.S. Energy Information Administration (EIA), ENERGY STAR efficiencies and standard EIA energy conversions, one million Btu of heat delivered to the house costs $135.64 with electric resistance baseboard, $57.14 with a heat pump at 8.1 HSPF2, and $53.17 with a natural gas furnace at 95% AFUE. The gas furnace is cheapest to run, $3.97 less per million Btu than the heat pump. Resistance heat sits far behind both.
Read that carefully, though. It is a running-cost comparison on the same unit of heat. It is not a yearly bill, because a bill depends on the house, its insulation and how many hours the system runs. It is not the price of equipment or installation either. And the gas figure assumes a house that can actually get gas service, which is something to confirm with the local gas utility before it enters any plan.
The part that shapes the decision is the climate. Hawaii has no real heating season, so the fuel burned for warmth in a typical year is small, and a $3.97 edge on a small quantity is a small edge. A heat pump also cools, and cooling is where Hawaii homes spend their energy. If you need both heating and cooling, price the heat pump first; the gas furnace only pulls ahead when the house already has gas service and air conditioning is not a factor.
What each option costs to run in Hawaii
The table below copies the computed figures. Each one is the cost of delivering one million Btu of heat at the state’s average residential prices.
| System | Efficiency used | Cost per million Btu delivered |
|---|---|---|
| Electric resistance (baseboard) | 100% efficient | $135.64 |
| Heat pump | 8.1 HSPF2 (seasonal COP about 2.4) | $57.14 |
| Natural gas furnace | 95% AFUE | $53.17 |
Electricity is the input behind two of those rows. EIA’s Electric Power Monthly (Table 5.6.B) puts the average residential price at 46.28 cents per kWh, year-to-date through July. That is a statewide average, and utilities and rate plans differ, so use it for comparing fuels rather than predicting a bill. The gas row comes from EIA’s average residential natural gas price, converted at about 1,037 Btu per cubic foot. Check your own utility’s rate before trusting any of these figures for a specific house.
Efficiency matters as much as fuel price because the same dollar buys very different amounts of heat. Resistance heating turns each kWh into exactly one kWh of heat. A heat pump moves heat rather than making it, which is why a seasonal COP of about 2.4 makes electricity competitive with gas even at 46.28 cents per kWh. HSPF2 is the heating yardstick, and the details of the rating are covered in What HSPF2 Measures, and Why Ductless Asks for More. ENERGY STAR sets the bar at 8.5 HSPF2 for non-ducted split systems and 8.1 for ducted ones. A ductless unit has no duct losses, so it starts with an advantage and has to perform better to earn the same label.
Do not compare an HSPF2 number with a SEER2 number. SEER2 measures cooling (ENERGY STAR asks for at least 15.2), HSPF2 measures heating. Match the letters when you compare two units. The 8.1 used in the table is a label minimum, not a typical value, so a better unit would cost less to run than the figure shown.
How cold it gets, and what that does to a heat pump
Honolulu International Airport, the reference station here, shows about 0 heating degree days a year (base 65°F) in NOAA’s 1991-2020 normals. It also shows about 4,767 cooling degree days. The coldest month still averages a daily minimum of 66.8°F. By these measures, no heating season exists at that station. There is no starting month to name, and the usual northern worries (frozen ground, deep-cold performance drops) do not apply there.
That matters for the heat pump figure. The 2.4 seasonal COP behind the $57.14 is an average across a heating season, and in deep cold a heat pump’s efficiency falls. Colder climates then lean on resistance strips or a furnace to carry the coldest nights. At a station where the coldest month’s average low is 66.8°F, a heat pump barely leaves its efficient range. Backup heat is much less of a design question than it would be in Minnesota or Maine. For the opposite end of the spectrum, How Cold Is Too Cold for a Heat Pump covers what happens when temperatures drop.
One caution: this is a single station. Higher elevations in the islands can run colder than Honolulu’s airport, and a home there would see more heating hours than the figures suggest. Even so, those colder hours still sit in a mild range for a heat pump, and the gas furnace’s advantage depends on how long the system actually runs. With so little heating demand, the gap between $53.17 and $57.14 per million Btu adds up to very little money over a year.
What homes in Hawaii already heat with
The Residential Energy Consumption Survey (RECS) 2020 state tables report that electricity is the main heating fuel for 5% of Hawaii homes. For furnaces, central heat pumps, steam or hot-water boilers, natural gas and propane, the survey does not publish a figure, because the estimates were suppressed as unreliable. For fuel oil or kerosene, none was reported, meaning too few households to publish. None of that means zero. It means the data are thin.
A thin dataset still says something. Heating equipment is not a big part of the picture in a state with no real heating season, so the figures that do exist are small and the rest are suppressed. These shares also describe what was installed, which reflects what was cheap when houses were built. They are not a recommendation, and they are state shares from a national survey, not a count for your county.
Two practical points follow. A house without a gas line changes the comparison completely: the gas furnace’s $53.17 only exists if gas service reaches the property, and connecting a new line is a cost the per-Btu figure does not include. In that case the real contest is heat pump against resistance heat, and the heat pump wins by a wide margin. A house with a boiler is a different conversion again, because hot-water radiators have no ducts to reuse. Switching to a heat pump there means adding ductwork or ductless heads, not just swapping a box. More on the local picture sits in Heating a Home in Hawaii.
When the other choice wins
The gas furnace is the cheaper option to run, so the exceptions favor the heat pump. The biggest is cooling. With about 4,767 cooling degree days a year at the reference station, air conditioning does far more work here than heating ever will. A heat pump handles both jobs with one system, while a furnace plus a separate air conditioner means two pieces of equipment. When a home needs cooling anyway, the heat pump usually wins, even though gas is a few dollars cheaper per million Btu of heat. The choice between ductless and ducted layouts is laid out in Ductless or Central.
No gas service is the second case. Without a gas line, the furnace’s running cost is irrelevant, and the heat pump’s $57.14 against resistance heat’s $135.64 settles it. A dual-fuel setup, a heat pump paired with a furnace that takes over in deep cold, makes sense where winters are hard. At a station with a coldest-month low of 66.8°F, there is little cold for the furnace half to handle, so paying for two systems is hard to justify.
An old system with years left is the last exception, and it can favor the furnace. A working furnace that still heats the house costs nothing to keep, and a $3.97 per million Btu difference rarely justifies replacing it early. If it starts failing, Repairing a Furnace or Replacing It walks through when repair stops paying off. Rebates and installed prices vary, so get local quotes before deciding.
Common questions
Is a heat pump cheaper to run than a gas furnace in Hawaii?
No, not by the per-Btu math. At average residential prices, a gas furnace at 95% AFUE costs $53.17 per million Btu delivered and a heat pump at 8.1 HSPF2 costs $57.14, so gas is $3.97 cheaper. The figure compares fuels on the same unit and says nothing about a yearly bill.
Why does the heat pump come out so close to gas?
Because it moves heat instead of making it. The seasonal COP of about 2.4 means each unit of electricity delivers more than twice its own heat, which offsets electricity’s higher price per Btu at 46.28 cents per kWh.
Does Hawaii get cold enough to need backup heat?
At the Honolulu reference station, the coldest month averages a daily low of 66.8°F, with about 0 heating degree days a year. Higher elevations can be colder, but a heat pump stays in its efficient range across most conditions the station records.
Is electric baseboard worth considering?
It is the most expensive of the three to run, at $135.64 per million Btu. It can make sense for a small, rarely used space where the heating hours are few and equipment cost matters more than running cost.