Solar, gas or heat pump: which pool heating?

The requirement most comparisons leave out

Here is the fact that ought to lead every article on this subject and rarely appears in any of them.

The Building Code of Australia sets energy efficiency requirements for swimming pools and spas at Volume One J7.3 and J7.4, and Volume Two parts 3.12.5.7 and 3.12.5.8. It permits heating of pools other than a spa pool by a solar heater not boosted by electric resistance heating, a gas heater, a heat pump, a heater using reclaimed energy, or a combination of these. And then:

“Where the heating is by a gas heater or heat pump, the swimming pool must be provided with a cover and a time switch to control the operation of the heater.”

Read that as a pricing fact rather than a compliance one. If you are comparing a solar quote against a gas or heat pump quote, the gas and heat pump options carry a mandatory cover and a mandatory time switch. If those are not in the quote, the quote is incomplete — and since a cover is the single biggest determinant of how much heat you lose overnight, a heating comparison that omits it is comparing the wrong things.

It also quietly answers a question people ask separately. “Is a pool cover worth it?” is a genuine question for an unheated pool. For a gas or heat pump heated pool it is not a question at all, because you are required to have one. What a pool cover saves covers the payback arithmetic.

One related rule: a spa pool with a capacity of 680 litres or more is required to have a time switch to control the operation of the circulation pump. And a spa sharing a reticulation system with a swimming pool can be heated by one or a combination of the permitted methods.

What each one actually costs to run

Over a six-month season, on an assumed 33 cents per kilowatt hour, the ranges break down like this:

• Solar: $96–$240. You are not paying for heat at all. The sun is free and the cost is the electricity to run the booster pump that pushes water through the roof collectors.
• Heat pump: $300–$1,020. A heat pump does not make heat, it moves it — taking warmth from the air and transferring it to the water. That is why it beats gas on running cost by a wide margin, and why its efficiency falls as the air gets colder.
• Gas: $600–$1,500. You are buying the energy outright and burning it. Gas is the most expensive to run and the only one that does not care what the weather is doing.

These are wide ranges because they must be. The variables are pool size, target temperature, how long the season is, whether the pool is covered, how sheltered the yard is, and local energy prices — and published estimates disagree with each other substantially. Treat the range as the answer and a single figure as a warning sign. Our pool running costs page sets out the full annual picture, of which heating is the swing factor.

The comparison people find hardest to believe is gas against heat pump, because gas is cheap per unit of energy and electricity is not. The resolution is that a heat pump is not buying energy, it is buying transport for energy that already exists in the air. That is also its weakness: on a cold night there is less heat in the air to move, so the gap narrows exactly when you most want heating.

Choosing on how you will actually use the pool

The running cost table only answers the question once you know which pattern of use you are buying for. There are three, and they map cleanly onto the three technologies.

“I want a longer summer.” You want the pool usable from October to April instead of December to February, and you do not need a guaranteed temperature on any given day. Solar. It is by far the cheapest to run, it works best exactly when you want to swim, and its unreliability in cold weather does not matter because you were not going to swim in July anyway. The constraint is roof area and aspect, not money.

“I want the pool at a set temperature for most of the year.” Heat pump. It is designed to hold a temperature rather than to reach one quickly, and over a long season it is dramatically cheaper than gas. It heats slowly — over hours, not minutes — which is fine when the pool is always warm and useless when it is not.

“I want the pool warm this weekend, occasionally.” Gas. It is the only one that heats fast and the only one indifferent to weather. Used as intended — a few weekends, a party, a cold snap — the running cost never materialises, because you are not running it. Used continuously, it is the most expensive option on this page by a factor of several.

And a combination is permitted. The BCA expressly allows a combination of the permitted methods, and solar plus gas is a sensible pairing: solar does the season, gas covers the weekend you need it warm now. What is not permitted is solar boosted by electric resistance heating.

The time switch, and the thing it protects you from

The mandatory time switch deserves a sentence of its own, because it is the cheapest component on any of these quotes and it is doing the most work.

The failure mode with any heater is not the technology, it is the running hours. A gas heater left to hold temperature continuously will produce a bill nobody forecast, and a heat pump running through the coldest hours of the night is working at its least efficient exactly when it costs most. A time switch confines the heater to the hours where it is useful — and where, on a time-of-use tariff, it is cheapest.

This is also why the cover and the time switch are required together rather than separately. The cover reduces the heat you lose overnight; the time switch stops you replacing that heat at three in the morning. Neither alone does much; the pair changes the running cost materially. That the code requires both is the clearest signal available that the running cost figures people quote for gas and heat pumps assume a covered pool on a timer.

So when comparing quotes, three questions settle it: is the cover in this price, is the time switch in this price, and what running hours is your cost estimate based on? The third is where two heat pump quotes with identical hardware produce different cost forecasts. Getting several quotes makes that difference visible quickly, because the assumptions only stand out when you can compare them side by side.

Where heating meets the rest of the build

Two practical points that only appear once heating is part of a real pool rather than a comparison table.

Solar heating adds a suction point. Under AS1926.3-2010, suction points must be not less than 600mm apart, including solar suctions. A pool designed with compliant spacing can be made non-compliant by adding solar heating later with its suction in the wrong place. If solar is a maybe rather than a yes, say so at design stage so the hydraulics allow for it. Pump and suction rules covers the standard.

Plant is a climbable object. Heaters, heat pumps and pumps sit outdoors near the pool, and anything climbable near a barrier is a problem. For an above-ground pool the barrier must be 300mm clear of the ladder, pump, filter or any other climbable object. Plan the equipment position and the barrier line together. Non-climbable zones explained covers the general rule.

Finally, a note on what this page does not do. We have not named a brand, a model or a price for any specific unit, because we cannot verify vendor performance claims at an independent source and heating marketing is full of efficiency figures with no published method behind them. The running cost ranges here are from our own running costs research; the code requirements are from the BCA as restated by the Victorian Building Authority. Where a figure could not be verified independently, it is not on this page.

Common questions

Sources

• VBA Practice Note 05-2018 — Swimming Pool & Spa Safety (BCA energy efficiency for pools)
• National Construction Code — Volume One and Volume Two
• Australian Standard AS 1926.3-2010 — Water recirculation and filtration systems
• VBA Practice Note 05-2018, as published by Mornington Peninsula Shire

General information only, current at 2026-09-16. Pool rules differ by state and by council, and penalty amounts are updated regularly. Confirm your own obligations with your council or a registered inspector before acting.