Best Pool Heaters & Heat Pumps

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Heat pump vs gas heater: the real trade-off

This is the single biggest decision in pool heating, and most buying guides gloss over exactly what you're trading away with each choice. Both raise pool temperature — how they do it, what they cost to run, and what they're actually good at are genuinely different.

Heat pumps

Pull heat from the surrounding air (like a reverse air conditioner) and transfer it into the water. Much cheaper to run per degree of heating, but slow — typically 1–3°F per day — and effectiveness drops sharply below around 50°F ambient air temperature, becoming essentially non-functional below 45°F.

Gas heaters

Burn propane or natural gas to heat water directly and fast, regardless of air temperature. Can raise a pool several degrees in hours rather than days, but running cost per hour is substantially higher than a heat pump doing the equivalent job.

The practical upshot: a heat pump suits an owner maintaining a consistent swim temperature across a full season, run continuously and left to do its slow, efficient job. A gas heater suits an owner who wants the pool ready on demand — heating it up for a weekend, an event, or unpredictable use — where running cost matters less than speed. Some owners with the budget for it run both: a heat pump for baseline temperature maintenance, gas for a fast boost when needed.

What running each one actually costs

Exact numbers vary heavily by local electricity/gas pricing, pool size, climate, and how consistently the pool is used — but the relative gap between the two technologies is consistent enough to plan around.

Heat pump running cost

Typically $50–150 a month to maintain a consistent swim temperature through a moderate-climate season, for an average residential pool with reasonable coverage/shade. Inverter models (which modulate output rather than running full-blast or off) run noticeably more efficiently than older single-speed heat pumps.

Gas heater running cost

Often 3–5 times higher than an equivalent heat pump for the same heating job, since it's converting a more expensive energy source directly to heat rather than moving already-present ambient heat. A gas heater run continuously all season, rather than used for occasional fast boosts, gets expensive quickly.

What actually moves the number most

A pool cover, used consistently. Evaporation is the single largest source of heat loss from an uncovered pool — a solar or thermal cover cuts that loss dramatically and is the cheapest, highest-impact addition to any heating setup. See our pool covers guide for options.

Sizing a heater correctly

Undersizing is the most common heater-buying mistake we see — an undersized unit runs constantly, struggles to hold target temperature against wind and evaporation, and shortens its own working life from the extra strain. Sizing depends on pool volume, climate, wind exposure, and desired temperature rise, but as a rough baseline for heat pumps:

Mild climate, well-sheltered pool

Roughly 3,500 BTU per 1,000 gallons is often sufficient.

Cooler climate or exposed, windy location

Budget closer to 5,000+ BTU per 1,000 gallons to hold temperature reliably against faster heat loss.

Gas heaters

Sized differently — around 100,000–400,000 BTU depending on pool size and how fast you want it to heat, since gas heaters are generally chosen specifically for speed rather than efficient continuous maintenance.

When in doubt, size up rather than down — an oversized heat pump costs a little more upfront but runs less continuously and lasts longer; an undersized one never fully catches up on cooler days.

Understanding efficiency ratings

Heat pump efficiency is usually expressed as COP (coefficient of performance) — the ratio of heat output to electricity consumed. A COP of 5 means the unit delivers roughly 5 units of heat energy for every 1 unit of electrical energy it uses, since it's moving existing ambient heat rather than generating heat directly the way a gas heater or electric resistance heater does. Most modern residential heat pumps sit somewhere between COP 4 and COP 7 depending on model, ambient temperature, and water temperature differential — the number is genuinely useful for comparing two heat pumps of similar output, since a higher COP model will cost less to run for the same heating job. Gas heaters don't use COP; their efficiency is usually expressed as a percentage (how much of the fuel's energy converts to usable heat), typically 80–95% for a modern unit, but this doesn't change the underlying cost gap versus a heat pump, since gas itself is a more expensive energy source per unit of heat than the ambient air a heat pump draws from for free.

COP drops as ambient air temperature drops, which is the underlying reason heat pumps lose effectiveness in cold weather — there's simply less ambient heat available to extract. A published COP figure is normally measured at a specific reference air and water temperature, so real-world performance on a cooler day will be lower than the headline number suggests. This is worth keeping in mind when comparing published specs between models, rather than assuming the number applies unchanged across every condition.

Warranty and expected lifespan

A well-maintained heat pump typically lasts 8–12 years, and a gas heater somewhat less on average given the more demanding combustion environment — though both figures vary a lot based on climate, water chemistry (especially for salt pools without a titanium exchanger), and how consistently the unit is run within its rated capacity. Most heat pumps carry a compressor warranty in the 5–10 year range separate from a shorter warranty on the rest of the unit — check both figures rather than assuming the longer compressor warranty covers everything. Registering the warranty promptly after installation and keeping installation/service records is worth doing, since warranty claims on major components can require proof of professional installation and regular maintenance.

Other factors that matter

Installation considerations that affect the buying decision

Electrical supply

Most residential heat pumps need a dedicated 220–240V circuit, and larger units draw enough current that an electrician needs to confirm your panel has capacity before installation — factor this into total project cost, not just the unit price.

Placement and airflow clearance

Heat pumps need open airflow on at least three sides to work efficiently — boxing one into a tight enclosure or against a wall on multiple sides reduces performance and can trip the unit's own safety cutoffs. Manufacturers publish minimum clearance specs; leave more room than the bare minimum if space allows.

Gas line or propane supply

A gas heater needs either an existing natural gas line sized correctly for its BTU draw, or a propane tank and regulator sized appropriately — undersized gas supply is a common cause of a gas heater underperforming its rated output, and it's a licensed-installer job, not a DIY one.

Bypass valve plumbing

Both heat pumps and gas heaters are typically installed with a bypass valve so water flow through the heater can be adjusted independently of total pump flow — this protects the heater from excessive flow rates and is worth confirming is part of the installation, not an optional extra.

Most owners buying a heater have it professionally installed rather than DIY, given the electrical and plumbing work involved — factor installation cost into the total budget, which can add several hundred dollars on top of the unit price depending on how much existing infrastructure (gas line, electrical circuit, plumbing) is already in place.

Mistakes that waste money on heating

Buying advice by climate

Hot, consistently warm climate

A heat pump alone is usually all you need — ambient air rarely drops low enough to meaningfully hurt efficiency, and the low running cost lets you maintain a comfortable temperature essentially year-round without a large ongoing bill.

Mild climate with a defined swim season

A heat pump extends the usable swim season on both ends (spring and fall) at reasonable running cost, without needing gas backup for most owners — this is the most common scenario where a heat pump alone covers the whole need well.

Cold climate or short swim season

A heat pump's effectiveness drops sharply below 50°F ambient and stops working below around 45°F, meaning it can't extend the season into genuinely cold shoulder months on its own — a gas heater, used for shoulder-season boosts specifically, fills that gap where a heat pump alone can't.

Unpredictable or occasional-use pool

If the pool sits unheated most of the time and gets heated for specific occasions rather than maintained continuously, a gas heater's fast heat-up time suits that pattern better than a heat pump, which is built for slow, continuous maintenance rather than heating on demand.

Five heaters worth considering

Spanning efficient heat pumps for season-long maintenance through to a fast gas option for on-demand heating.

Our verdict by scenario

Mid-size inground pool, best value

The FibroPool FH255 covers most residential inground pools well without overpaying.

Large pool, warm climate, frequent use

The AQUASTRONG 80,000 BTU inverter unit has the output and efficiency for consistent season-long running.

Salt pool, mid-size, want inverter efficiency

The TURBRO Beluga's titanium exchanger and inverter compressor suit salt systems well.

Above-ground or smaller pool, tight budget

The FibroPool FH122 is sized and priced appropriately without overbuying capacity.

Want the pool ready fast, cost is secondary

The Pentair MasterTemp 400 gas heater is built for exactly that job.

Common questions