Pool heater cost in St. Louis: gas vs. heat pump
A gas pool heater costs about $4,500–$7,000 installed in St. Louis, and a heat pump about $6,500–$9,000. The heat pump is cheaper to run at today's Ameren and Spire rates. The gas heater is faster and keeps working on the cold April and October nights when St. Louis pools most need heat.
- Gas heater, installed
- $4,500–$7,000
- Heat pump, installed
- $6,500–$9,000
- Missouri dealer average
- $6,125 (10 dealers, 2026)
- Cheapest heat to run
- Heat pump, about $8.70 per million Btu
- Works below 50°F air
- Gas yes; most heat pumps no
Gas heater vs. heat pump at a glance
| Compare | Gas heater | Heat pump |
|---|---|---|
| Installed in St. Louis | $4,500–$7,000 | $6,500–$9,000 |
| Typical size | 250,000–400,000 Btu | 110,000–140,000 Btu |
| Cost per million Btu into the water | About $13.20 natural gas; about $28 propane | About $8.70 |
| Heat-up speed | Fast; hours | Slow; a day or more for a big rise |
| Cold weather | Works in any weather | Output drops in cool air; many stop below 50°F |
| Typical life (DOE) | 5 or more years | 10 or more years |
| Needs | Gas line and a mechanical permit | 240-volt circuit and an electrical permit |
What pool heater installation costs
Equipment is only part of the price. Unit prices online in October 2026 ran about $3,800–$5,400 for a 400,000 Btu gas heater and $6,000–$7,500 for a 140,000 Btu heat pump. Manufacturers restrict online pricing, so dealer prices can differ. On top of the unit:
- Gas line. Fixr puts a pool heater gas line at about $20–$25 per foot. The equipment pad is often at the far side of the yard, so a 50-foot run adds roughly $1,000–$1,250.
- Electrical. A heat pump needs its own 240-volt circuit, typically on a 50–70 amp breaker for a 140,000 Btu unit, plus bonding. A long run from the house panel, or a full panel, raises the cost.
- Pad, plumbing and permit. A level pad, plumbing into the filter return, and the permit and inspection.
Our installed ranges include the gas line or circuit and the permit for a typical layout. The Missouri dealer average of $6,125 lands inside them.
What a pool heater costs to run in St. Louis
The fair way to compare is the cost of putting one million Btu of heat into the water. We worked it out from current rates, including the per-unit charges most guides leave out.
| Heat source | Cost per million Btu | Rate used |
|---|---|---|
| Heat pump, summer | $8.69 | Ameren 16.89¢/kWh (June–September), COP 5.7 in 80°F air |
| Heat pump, spring and fall | $8.73 | Ameren 11.91¢/kWh (October–May, first 750 kWh), COP 4.0 in 50°F air |
| Natural gas, 96% efficient | $11.55 | Spire East $1.149 per Ccf |
| Natural gas, 84% efficient | $13.20 | Spire East $1.149 per Ccf |
| Propane, 84% efficient | $28.39 | Missouri average $2.181 per gallon (EIA, October 2026) |
Ameren's rate is the base residential energy charge plus its fuel, efficiency and renewable riders. Spire's is summer delivery plus the gas charge and weather adjustment. Both exclude local taxes and fixed monthly charges. Spire's gas charge resets each November, and Ameren has a rate case pending for 2027. Heat pump efficiency (COP) is from Hayward's published ratings; gas assumes 1,036 Btu per cubic foot.
The surprise is that the heat pump keeps its edge in cool weather. It is less efficient in 50°F air, but Ameren's October–May rate is lower, so the cost per Btu barely changes. If your home has propane instead of natural gas, a heat pump costs about a third as much to run.
A worked example
Take a 16×32 pool averaging 5 feet deep, about 19,000 gallons. Warming it 15°F in spring takes about 2.4 million Btu before any heat escapes.
| Heater | Energy cost | Run time |
|---|---|---|
| 400,000 Btu gas, 84% | About $32 | About 7 hours |
| 400,000 Btu propane, 84% | About $68 | About 7 hours |
| 140,000 Btu heat pump, warm air | About $21 | About 17 hours |
| 140,000 Btu heat pump, 50°F air | About $21 | About 28 hours |
Warming the water once is cheap. Keeping it warm is what costs money, because a pool loses heat every night, mostly through evaporation. That is why the season totals below swing so much with a cover.
What a season costs
The U.S. Department of Energy published season estimates for a 1,000 sq ft pool heated May through October. Kansas City is the closest city in its tables, and its gas rate ($1.09 per therm) is almost exactly Spire's summer rate today.
| Kept at 80°F, May–October | No cover | With a cover |
|---|---|---|
| Heat pump | $1,274 | $279 |
| Gas heater | $2,552 | $567 |
DOE's heat pump figures assume a lower electric rate than Ameren's summer rate today, so add something for June through September. The bigger lesson stands either way: a cover cuts the heating bill by roughly three-quarters. See automatic pool cover cost.
Spring and fall: where St. Louis decides it
St. Louis averages above 67°F only from May through September. A heater earns its keep by stretching the season into April and October, when average highs are 68–69°F but lows are 47–49°F.
- Heat pumps lose output in cool air. Hayward's 140,000 Btu HeatPro is rated at 140,000 Btu in 80°F air but 85,000 Btu at 50°F. Pentair's UltraTemp 140 drops from 145,000 to 90,000.
- Many stop at 50°F. Hayward lists 50°F as the minimum air temperature for its heat-only models (40°F for heat-and-cool models). DOE says heat pumps work efficiently above the 45–50°F range.
- Gas does not care. DOE notes gas heaters can hold any temperature regardless of the weather, which also makes them better for an attached spa.
The practical result: a heat pump in St. Louis runs cheapest from May to September and on mild spring and fall days. If you want to swim in early April or in late October, or heat a spa quickly in cold weather, gas is the reliable choice.
What size pool heater you need
DOE's sizing rule is pool surface area × temperature rise × 12. The rise is your target temperature minus the average air temperature of the coldest month you will swim. For an 82°F pool in St. Louis:
| Pool | Swim from May | Swim from April or into October |
|---|---|---|
| 16×32 (512 sq ft) | About 89,000 Btu | About 150,000 Btu |
| 20×40 (800 sq ft) | About 139,000 Btu | About 235,000 Btu |
Those are minimum heat outputs. A 400,000 Btu gas heater covers either pool. A 140,000 Btu heat pump covers a 16×32 from May, but in 50°F air it delivers only about 85,000 Btu, so for April and October it is undersized for most pools. Some owners pair a heat pump with a cover, or add a gas heater for a spa.
Permits and where the heater can go
- Permits. A gas heater generally needs a mechanical permit and a heat pump an electrical permit. Webster Groves lists a mechanical permit for fuel-fired appliances such as a gas pool heater. Ballwin lists mechanical, electrical and plumbing permits at $75–$175 plus a $30 processing fee.
- Placement. Town and Country keeps pool equipment at least 20 feet from a side lot line and out of required front and rear setbacks. Wildwood requires equipment in a side yard to be screened for noise and looks. Heat pumps have a fan, so ask about noise if the pad sits near a neighbor's patio.
- Clearances. Pentair's heat pump guide calls for a level pad, 24 inches of clear space in front and 12 inches on the other sides, 5 feet of clearance overhead, and at least 5 feet from the pool wall unless a fence separates them.
See pool permits by city for who issues permits where you live.
Gas or heat pump: which to choose in St. Louis
- Choose a heat pump if you swim mostly May through September, want the water warm all season, and will cover the pool. It costs more up front and less every month after.
- Choose gas if you heat only for weekends or parties, want early April and late October swims, or have an attached spa. It costs less up front, heats in hours and works in any weather.
- Propane only? A heat pump is usually the better buy, because propane costs about three times as much per Btu.
- Both is common on pools with a spa: a heat pump for the pool all season and a gas heater for quick spa heat.
Rebates will not tip the decision. We found no Ameren or Spire rebate for a residential pool heater, and the federal energy credits ended after 2025.
Pricing a heated pool?
The cheapest time to run a gas line or a 240-volt circuit is while the pool is being built. Get matched with a local builder who can price the pool, heater and cover together.
Get matched with a local pool builder Estimate a heated pool
Common questions about pool heaters
How much does a pool heater cost in St. Louis?
A gas pool heater typically costs $4,500–$7,000 installed in St. Louis, including the gas line and permit. A heat pump typically costs $6,500–$9,000 installed, including a 240-volt circuit. A survey of 10 Missouri pool dealers averaged $6,125 for a heater.
Is a heat pump or gas heater cheaper to run in St. Louis?
A heat pump. At current Ameren and Spire rates, a heat pump puts heat into the pool for about $8.70 per million Btu, against about $13.20 for an 84% efficient gas heater and about $28 for propane. That holds even in cool spring air, where the heat pump is less efficient but electricity is cheaper.
Will a heat pump heat my pool in April or October?
Only on mild days. A typical 140,000 Btu heat pump puts out about 85,000 Btu at 50°F air, and Hayward's heat-only models stop below 50°F. St. Louis averages lows of 47–49°F in April and October, so a heat pump will struggle on cold nights. A gas heater works in any weather.
How long does it take to heat a pool?
Raising a 16×32 pool (about 19,000 gallons) by 15°F takes about 2.4 million Btu. A 400,000 Btu gas heater can deliver that in roughly 7 hours of run time. A 140,000 Btu heat pump needs about 17 hours in warm air and closer to 28 hours at 50°F. Heat lost overnight makes real times longer, especially without a cover.
How much does it cost to heat a pool for a season?
DOE's estimate for a 1,000 sq ft pool in Kansas City, the closest city it lists, is about $1,274 a season for a heat pump and $2,552 for gas at 80°F without a cover, and $279 and $567 with one. Those tables use rates close to St. Louis's, but your pool, target temperature and months of use will move the number a lot.
Are there rebates for pool heaters in Missouri?
Not that we found. Ameren Missouri's residential rebates do not include pool heat pumps or pool pumps, Spire's gas rebates cover equipment in living spaces only, and the federal energy tax credits ended after 2025 and excluded pools anyway.
Do I need a permit for a pool heater?
Usually. A gas heater generally needs a mechanical permit and a heat pump needs an electrical permit. Webster Groves and Ballwin, for example, list mechanical permits for gas pool heaters. Your builder or installer should pull them.
Sources
- Hayward HeatPro heat pump sell sheet (2023)
- Pentair UltraTemp heat pump installation guide (2023)
- Pentair gas pool heater brochure (August 2024)
- Hayward Universal H-Series brochure (2023)
- U.S. DOE: heat pump pool heaters (archived January 2026)
- U.S. DOE: gas pool heaters (archived January 2026)
- Spire Missouri rate schedule (March 2026)
- Missouri PSC: Spire weather adjustment, effective September 2026
- Missouri PSC: Ameren fuel adjustment, June 2026
- Missouri PSC: Ameren energy efficiency charge, 2026
- Missouri PSC: Ameren renewable energy charge, February 2026
- EIA: Missouri residential propane price (weekly)
- EIA: British thermal units and heat content
- Thursday Pools: fiberglass pool cost in Missouri (updated July 2026)
- Federal pool heater efficiency standard (May 2023)
Published October 27, 2026. Rates checked October 2026. Planning ranges, not quotes.