Picture the scene: the thermometer reads 27 degrees, the heat pump is running as it should, and a guest by the pool asks whether the water could be a little warmer. The owner has just paid the electricity bill and is sorely tempted to show them the meter.

As far as both are concerned, it is straightforward. The owner has a heated pool. The guest booked a heated pool. They just had different ideas about what that swim would feel like.

For one person, it means water comfortable enough for swimming. Another wants to stand in it for an hour with a drink in hand, while a third expects something close to a hot tub. Two words in a listing can become the starting point for a disagreement that would have been easier to prevent before booking.

A heated pool can be a good reason for a guest to choose a holiday home outside the peak season. But before investing, owners need to understand what is expected of it, how much it will cost and whether the chosen equipment can actually deliver.

Is 25 degrees cold or perfectly normal?

Some people find water at 25 °C perfectly comfortable. Usually, they are the ones who have already swum a few lengths. Someone easing their way down the steps and planning mostly to soak may feel differently, especially when the sun is not out or there is a breeze.

That is why “hotel pools are 25 degrees too” is not a particularly convincing response to a complaint. Hotels have different types of pools, from sports pools to children’s pools and wellness facilities, so no single temperature applies to all of them.

The recommendations of the British specialist organisation PWTAG show how much a pool’s intended use shapes expectations:

These are professional guidelines based on how a pool is used, not a uniform Croatian regulation for holiday homes. They help explain why a swimmer and a guest who wants a long soak do not necessarily want the same temperature.

For an outdoor pool at a holiday rental, a target of around 27 to 29 °C can be a reasonable compromise. It will not feel equally comfortable to everyone, but it provides a sensible starting point for explaining what guests can expect. Naturally, that range should only be advertised for periods when the system can actually achieve it.

A hot tub is a different matter. Hot tubs are often used at 34 to 38 °C and contain much less water, perhaps one to two thousand litres. Heating a 40,000-litre pool with a large surface exposed to the air is an entirely different task.

Guests expecting that level of warmth need to understand the difference. But if the listing promised 28 °C and the water is at 22 °C, saying that the guest is sensitive to the cold will not solve the problem. The next step is to find out why the advertised temperature has not been achieved.

A sunny day does not cancel out a cold night

The guests arrive in the afternoon, the terrace is in the sun and the air temperature is around twenty degrees. It looks like a perfect day for a swim. The pool, however, may have just been through several cold nights.

Water heats up and cools down more slowly than air. One pleasant afternoon cannot undo everything that happened over the previous few days, especially at the start of the season or after the pool has been filled with fresh water.

As spring progresses, conditions help the heating system: the days grow longer, the sun rises higher in the sky and the nights become shorter. At the start of the season, though, a large volume of cold water needs to be heated first. Switching the heating on in the morning and expecting the pool to be ready for guests that afternoon can be a serious miscalculation.

In autumn, the process is reversed. In early September, the pool may still benefit from heat accumulated over the summer. As the days shorten and the nights become longer and colder, it gradually loses that advantage. This is why the same pool needs different levels of heating support in June and October, even when daytime air temperatures are similar.

On Krk, exposure to wind also needs to be considered. A pool in a sheltered courtyard and one exposed to the full force of the bora can behave very differently. Wind increases evaporation, and heat is lost along with the evaporating water. The water’s surface area matters too: the same volume will behave differently in a deeper, smaller pool than in a shallow pool with a large surface area.

When planning pool heating , it is therefore important to consider conditions throughout the day and night, the pool’s location and how it will be covered. The air temperature when guests arrive is only a small part of the picture.

In summer, heating can become unnecessary

In spring, the owner works hard to gain a few extra degrees. In the middle of summer, they may want the exact opposite.

If the water is heated to a high set temperature during a warm night, followed by a long sunny day, the pool can become too warm for a refreshing dip. This is especially true when a cover retains heat well and its material also lets sunlight through or harnesses it to warm the water further.

The thermostat will stop the heating once the set temperature is reached. The sun will take no notice of that setting. So a controller set to 28 °C is no guarantee that the water will not reach 30 °C or more during the day.

In summer, owners need to monitor the actual water temperature and adjust the system’s operation accordingly. When sunshine and warm nights are already keeping the water comfortable, the heating can be reduced or switched off. Simply keeping the spring settings makes little sense.

The cover also needs to be used thoughtfully. Leaving the pool uncovered on a cooler night can help it cool down, but increases evaporation and water loss. Some heat pumps can also provide cooling, although this needs to be checked for the specific model. Simply switching off the heating does not actively cool the water.

It is the heating that should be switched off, not the necessary filtration and water treatment. Sunshine and bathers still affect disinfectant consumption, so a pleasant temperature is no substitute for regular pH and water quality checks. A comfortably warm pool still needs proper maintenance.

Which heating system makes sense for a holiday home?

For a seasonal outdoor pool, a heat pump is a good option to consider first. It draws heat from the surrounding air and transfers it to the water, so it can use significantly less electricity than a direct electric heater to deliver the same amount of heat.

But the impressive figure on the front of the brochure does not tell the whole story. Performance achieved in warm air should not be expected on a cold spring night. As the air temperature falls, both available heating output and efficiency may decrease, and defrost cycles also need to be taken into account in cold conditions.

For an owner who wants the pool to be usable in April, performance data for cooler air temperatures matters more than the most impressive quoted summer rating. A statement that the unit can operate at low temperatures does not, in itself, mean that it can maintain the desired temperature in their pool under those conditions.

It is important to distinguish between heating output and electrical power consumption. A heat pump delivering 10 kW of heat does not necessarily draw 10 kW of electrical power. The ratio of heat delivered to electricity consumed is known as the COP: a value of 4 means four units of heat for every unit of electricity consumed, under the conditions in which that ratio was achieved.

Other solutions are available. A direct electric heater simply converts electricity into heat at approximately a one-to-one ratio, so consumption can be high when heating a large pool for long periods. Heating through a boiler and heat exchanger can make sense where a suitable heat source is available, but the heat exchanger itself does not generate energy.

Solar thermal collectors use the sun to heat the water. They can provide useful support, but do not offer the same reliability during cloudy, cold periods. They should not be confused with photovoltaic panels, which generate electricity: these can help power the system but do not eliminate its heat losses.

Owners should therefore ask the installer for an assessment based on their specific pool, the intended months of use and the target temperature, with a clearly stated assumption about how the pool will be covered. The plan should also account for the electrical supply, the unit’s position, water flow and noise affecting the terrace, bedrooms and neighbours. Guests notice all of these things, even if none appears in large print next to the heat pump’s name.

The pool cover: an easily underestimated part of heating

Buying a heating system while overlooking the pool cover can mean paying every night to replace heat that could have been retained.

Much of the problem occurs at the water’s surface. According to the US Environmental Protection Agency, a properly used cover can prevent up to 95 % of evaporation. For solid covers, the EPA also cites potential heating cost reductions of 50 to 70 %, depending on conditions and use.

That does not mean a 95 % reduction in the electricity bill. Evaporation and total energy consumption are not the same thing, and savings achieved with a regularly used cover cannot be expected from one that spends the entire week rolled up against a wall.

What is each type of cover for?

Practicality is particularly important in holiday rentals. A cover that one person can easily handle is more likely to be on the water when needed than heavy equipment that requires the guest to ask for help.

The term “solar” also needs to be understood before buying. Materials differ in how much solar energy they transmit or harness. What helps during the cooler months can contribute to overheating in summer. The choice should reflect the pool’s conditions and intended use.

Safety is a separate issue: an ordinary floating thermal cover does not prevent a child from falling into the water. Nor does a motorised mechanism automatically make it a safety cover. That requires a suitable product and correct installation, and children still need supervision. A thermal cover must be completely removed before swimming.

How much does pool heating cost, especially in winter?

There is no honest answer to “how much does a heated pool cost to run?” in the form of a single daily price. Raising the temperature after filling, maintaining warm water under a cover in May and keeping an outdoor pool very warm throughout winter are very different calculations.

To get a sense of the scale, take a pool containing 40 cubic metres, or 40,000 litres, of water that we want to heat from 23 to 28 °C.

Example of a single heating cycle: raising 40 m³ of water by five degrees

That €12 covers only the water heating described, in a simplified calculation that excludes heat losses. The actual bill also includes replacing lost heat, the electricity used for circulation and subsequent temperature maintenance. It also depends on the heat pump’s actual efficiency and the property’s electricity tariff.

Heating is not instantaneous either. A unit continuously delivering 10 kW of heat would need almost a full day for this task, even without any losses. In practice, it may take longer. Raising the setpoint to 35 °C does not increase the unit’s maximum available output. The heating needs to be switched on early enough, with an appropriate target temperature.

In winter, the challenge grows on both sides: the water loses more heat to its cold surroundings, while the heat pump has a harder time extracting heat from the cold air. A higher target water temperature further increases the temperature difference the system must maintain. A year-round outdoor pool is therefore a much more substantial project than extending the swimming season by a few weeks.

The monthly bill can easily run into three figures. If a system consumed 100 kWh of electricity a day at the same assumed price of €0.20, that would amount to €20 a day, or €600 over 30 days. This is an example calculation, not a claim about typical winter consumption on Krk. A specific estimate requires information about the pool, equipment and operating conditions.

Heating on a cheaper night tariff is not automatically the most economical option either. Electricity may cost less, but colder air can reduce the heat pump’s efficiency. What matters is the cost of the heat delivered, while ensuring that the pool is ready when guests want to use it.

It pays off when you know what you are offering guests

Heating makes sense if it helps secure bookings during periods when comfortably warm water really matters to guests. For a holiday home aiming to attract more spring and autumn bookings, it can be an important part of the offer. For a property rented almost exclusively in summer, when the water is already warm, the benefit may be much smaller.

Before buying, it is worth opening the booking calendar first and the equipment brochure second. Which dates would you like to fill? Is there demand for them? Could an improved offer generate enough extra nights or a higher rate to cover the investment and operating costs?

The calculation needs to include the heat pump, installation, any necessary works, the cover and its storage arrangements. Then come electricity, servicing and pool maintenance over a longer season. Any additional revenue should be assessed after commissions and other costs associated with those bookings. The words “heated pool” alone do not guarantee that gaps in the calendar will fill.

The listing needs just as much care. Before booking, guests should know which months heating is available, whether it is included in the price or charged separately, whether advance notice is required and what water temperature they can realistically expect.

A target temperature, a typically achieved range and a guaranteed minimum are not the same promise. The listing should reflect what the pool can actually deliver. The phrase “depending on weather conditions” is useful alongside a specific explanation, but on its own it does not tell guests whether they will be able to comfortably enjoy the facility they are paying for.

If maintaining the temperature depends on covering the pool at night, this should also be explained in advance, and the cover must be simple and safe to use. Heating on request needs to be agreed early enough for the pool to be ready on arrival, rather than only switched on then.

Hosts can adapt the following example description to their actual operating period, charging arrangements, achievable temperature and cover use:

Heated outdoor pool: information before booking

Pool heating is available [specify months or dates]. To allow us to prepare the pool, please let us know [specify the required notice period] before arrival.

The target water temperature while the heating is in operation is 27 to 29 °C. During colder or windy weather, the actual temperature may be lower.

The pool is covered at night to retain heat. On arrival, your host will explain how to use the cover easily and safely.

And if a complaint does arrive, the first step is not a debate about who prefers warmer water. Measure the actual pool temperature, check that the system is working and compare the result with what was advertised. The electricity meter confirms that power has been consumed. The thermometer and the listing show whether the guest received what they booked.

Sources

• PWTAG: Code of Practice, poglavlje 14.1 - recommended temperatures by pool use.
• SPATA: Swimming Pool Heating and Energy Efficiency in Pools & Spas - heating methods, operating conditions and heat losses.
• SPASA: Solar Pool Heating - solar water heating.
• EPA WaterSense: Pool Water Efficiency and Jump Into Pool Water Efficiency - evaporation and the potential benefits of covering a pool.
• PWTAG: Swimming pool covers operation and safety - cover types, handling and safety.
• Zodiac Z550iQ, technical documentation and AstralPool, pool cover documentation - examples of differences in operating conditions and equipment designs.
• Government of South Australia: Swimming pools and spas - hot tub temperatures and characteristics.
• CDC: Home Pool and Hot Tub Water Treatment and Testing - pool water testing and treatment.

Sources checked on 10 September 2026. The recommendations for holiday rentals are the editorial team’s application of professional guidelines. Financial examples are our own illustrative calculations based on the stated assumptions, not consumption estimates for a specific property.