Heat Pump vs Gas Heater Selection
Why this matters
A customer asking "should I get a gas heater or a heat pump for my pool?" expects a 30-second answer. The right answer depends on five variables: their climate, their actual use pattern, their natural gas availability, their electric rate, and how often they want fast heating. A pool tech who asks the right questions and quotes both options closes the heater install at a higher rate than the one who installs whatever the customer asked for. Getting the choice wrong costs the customer thousands of dollars over the heater's life and creates a relationship complaint when the wrong technology underperforms in their specific situation.
The two technologies
Gas heater (natural gas or propane)
A combustion heater burns natural gas or propane to heat water directly. Common brands: Hayward H400, Pentair MasterTemp, Jandy LXi, Raypak P-R-407, Sta-Rite Max-E-Therm.
| Property | Detail |
|---|---|
| Heat output | 150,000 to 400,000 BTU/hour typical residential |
| Temperature rise per hour | 10 to 25 F (depends on pool size and heater size) |
| Run pattern | On-demand; heats fast |
| Climate sensitivity | None; works in any ambient |
| Fuel source | Natural gas (preferred) or LP propane |
| Equipment cost | varies by market |
| Install labor (with gas line) | varies by market |
| Service life | 5 to 12 years |
| Annual fuel cost (typical) | varies by market (depends on use) |
Heat pump
An electric heat pump extracts heat from outdoor air and transfers it to pool water. Common brands: Hayward HeatPro, Pentair UltraTemp, Jandy AquaPure, AquaCal Heat Wave.
| Property | Detail |
|---|---|
| Heat output | 100,000 to 140,000 BTU/hour typical residential |
| Temperature rise per hour | 1 to 3 F (slow) |
| Run pattern | Continuous; long runs |
| Climate sensitivity | Significant: efficiency drops as ambient temperature drops |
| Fuel source | Electric |
| Equipment cost | varies by market |
| Install labor | varies by market |
| Service life | 10 to 15 years |
| Annual electric cost (typical) | varies by market |
The fuel economics
Heat-pump cost per BTU delivered (heat extracted from air, not from fuel):
- COP (Coefficient of Performance) varies with ambient: typically 4.0 at 85 F outdoor, 2.5 at 50 F outdoor
- Higher COP = more BTUs delivered per kWh of electric
Cost per BTU:
| Source | Relative cost per million BTU |
|---|---|
| Natural gas (80% heater efficiency) | low-to-mid baseline |
| LP propane (80% heater efficiency, 91,500 BTU/gal) | highest of the four; roughly 3x natural gas |
| Electric heat pump (COP 4.0, warm-season) | lowest in this comparison; well below natural gas |
| Electric heat pump (COP 2.5, cold-season) | roughly comparable to natural gas |
| Solar (passive) | zero marginal fuel after install |
In the warm season (heat pump at COP 4.0) with natural gas at typical pricing, the electric heat pump is roughly 40 percent cheaper per BTU. With propane vs heat pump, electric is more like 75 percent cheaper. With cold-season heat pump (COP 2.5), natural gas and electric are roughly comparable; propane is still 2x more expensive. Plug in the customer's actual utility tariff (gas therm rate, kWh rate, propane gallon delivered price) to get the live numbers for their decision.
Climate matters
Heat pumps work by extracting heat from outdoor air. Below approximately 50 F ambient, residential heat pumps efficiency drops dramatically; below 40 F, most stop working at all.
In southern climates (USA Zones 1 to 3 - FL, southern GA, southern TX, south CA, AZ):
- Pool season is 8 to 12 months
- Ambient stays above 50 F most of the time
- Heat pump is the clear winner for most uses
In northern climates (USA Zones 5 to 7 - upper Midwest, Northeast, Mountain States):
- Pool season is 4 to 6 months
- Ambient is variable; cold mornings limit heat pump
- Gas heater is more reliable for extending the season
In moderate climates (Zones 3 to 5):
- Pool season is 6 to 8 months
- Heat pump works most of the season; gas useful for season extension or cold-snap fast warmup
- Both technologies have a place
Use-pattern matters
| Use pattern | Best heater |
|---|---|
| Resort-style: maintain temperature 24/7 all season | Heat pump (slow, continuous, cheap) |
| Weekend-only: heat from 70 to 84 F every Friday | Gas (fast warmup; heat pump can't catch up) |
| Spa-only use: maintain spa at 102 F | Gas (heat pump doesn't deliver enough BTUs for spa) |
| Daily use; consistent: maintain 80 to 84 F | Heat pump |
| Seasonal extension: warm to 80 F in shoulder seasons (Apr, Oct) | Gas (heat pump's COP drops in cool season) |
| Vacation house used occasionally: warm 1 to 2 weekends per year | Gas (faster recovery from cold pool) |
The math: a heat pump heating a 20,000 gallon pool from 70 F to 84 F (14 F rise) takes 8 to 16 hours of continuous run depending on ambient. A gas heater does the same job in 2 to 4 hours. For weekend users, this difference is the deciding factor.
Sizing the heater
For gas heater, the rule of thumb:
| Pool size (gallons) | Heater BTU/hr recommended |
|---|---|
| 10,000 to 15,000 | 150,000 |
| 15,000 to 25,000 | 200,000 to 250,000 |
| 25,000 to 35,000 | 300,000 to 400,000 |
| Over 35,000 | 400,000+ or two heaters |
For heat pump, the rule:
| Pool size (gallons) | Heat pump BTU/hr |
|---|---|
| 10,000 to 15,000 | 90,000 to 110,000 |
| 15,000 to 25,000 | 110,000 to 130,000 |
| 25,000 to 35,000 | 140,000+ |
| Over 35,000 | Two heat pumps or hybrid system |
A pool cover dramatically reduces the heater size requirement (or improves the existing heater's performance). A typical solar cover reduces heat loss by 50 to 75 percent.
Hybrid approaches
For customers who want both fast recovery and ongoing low cost:
- Gas + heat pump: gas for initial warmup and shoulder season; heat pump for ongoing maintenance during the main season
- Solar + heat pump: solar panels for free daytime heat; heat pump for evening / cold-day backup
- Solar + gas: solar for free heat; gas for evening / cool season
Pentair MasterTemp Hybrid combines a gas heater and heat pump in one unit; UltraTemp Hybrid same. Premium (per the application); good for customers who want both.
Installation considerations
Gas heater
- Verify gas supply: meter-side pressure and capacity
- Gas line sizing: 200,000 BTU/hr heater on 30 ft of 3/4 inch black iron line is borderline; many installs need 1 inch line
- Combustion air: minimum free area for cabinet ventilation
- Exhaust: vent termination clearances to property line, openings, etc.
- Local code may require permit
For propane:
References
- ANSI Z21.56 (Gas-fired pool and spa heaters).
- DOE 10 CFR 431 Subpart Y (related pool equipment efficiency standards).
- ASHRAE Handbook, HVAC Applications, Pool and Spa Heating chapter.
- Manufacturer literature: Hayward, Pentair, Jandy, Raypak, AquaCal, Sta-Rite.
- ENERGY STAR Pool Heater Specification.
- Manuall internal: PoolService Heater Service, PoolService Heater Fuel Comparison, PoolService Equipment Sizing.