Pool Heating Compared: Heat Pump, Solar, Heat Exchanger
Heat pumps, solar absorbers and heat exchangers warm the pool water in very different ways – with markedly different purchase, operating and connection costs. This comparison ranks the three systems by cost, realistic season extension and space requirements, and works through the costs over ten years using a worked example.
The Three Systems and How They Work
All three systems are integrated into the flow in the same way: as a bypass after the filter and before disinfection. However, they differ fundamentally in their energy source.
- Heat pump: Draws heat from the ambient air and transfers it to the pool water via a titanium heat exchanger. Depending on the outside temperature, around 1 kWh of electricity becomes roughly 4 to 5 kWh of heat – this ratio is stated as the coefficient of performance (COP) and drops in cool air.
- Solar absorber: Black plastic mats or tubes on a roof or open area, through which the pool water is pumped. The energy is free but depends on the time of day and the weather. Only minor pump-electricity costs arise.
- Heat exchanger: A plate or shell-and-tube exchanger transfers heat from the home’s existing gas, oil or pellet heating to the pool circuit. It has no energy source of its own but uses the existing central heating.
This already points to the key decision: a heat exchanger is only worthwhile if a suitable home heating system with spare capacity is available; solar requires sufficient, well-sunlit space; the heat pump is the most universally usable option.
Investment and Operating Costs per System
The purchase price alone says little – what matters is the sum of unit, installation and running costs. The following figures are typical market ballpark values for a pool of roughly 8 x 4 m (around 50 m³) and serve only as a guide; the actual prices depend on output, design and installation effort.
| System | Purchase (approx.) | Operating costs | Requirement |
|---|---|---|---|
| Heat pump | medium to high | electricity costs, cushioned by the COP | electrical connection, outdoor installation space |
| Solar absorber | low to medium | almost only pump electricity | sunlit roof or open area |
| Heat exchanger | low (unit), plus installation | fuel costs of the home heating | existing heating with spare capacity |
In day-to-day operation, solar is by far the cheapest because the heat itself costs nothing. Thanks to its coefficient of performance, the heat pump is well below purely electric heating. The heat exchanger often has the lowest purchase cost, but its operating costs fluctuate widely with the fuel price and the boiler’s efficiency.
Season Extension – What Is Realistically Possible
How much a system extends the swimming season depends on its heat output and, above all, on a cover. Without a cover, a large part of the heat added is lost again overnight through the water surface – this applies to all three systems.
- Solar absorbers raise the water temperature noticeably on sunny days but largely fail in dull weather and in the shoulder months. A realistic gain is an extension of a few weeks and a more comfortable summer level, not dependable spring or autumn warmth.
- A heat pump heats regardless of the weather and maintains a set target temperature. With a cover, this makes use from roughly April to October achievable; however, its efficiency falls the colder the outside air becomes.
- A heat exchanger delivers constant heat all year round – provided the boiler output is sufficient – and is therefore the most reliable choice for a long season or year-round indoor pools.
For every system, a cover is the most cost-effective single measure because it substantially reduces the heat demand and therefore the operating costs.
Space and Connection Requirements
On all three systems, the connection to the pool pipework is made via a bypass with shut-off and control valves. The pipe size follows the existing pipework; d50 (DN40) or d63 (DN50) are common.
- Heat pump: Needs a frost-free outdoor installation site set away from walls for air flow and requires its own power connection – 230 V or 400 V depending on the output. The electrical connection and equipotential bonding belong in the hands of a qualified electrical contractor. Take care regarding noise emission towards the neighbouring property.
- Solar absorber: Requires the largest area – as a rough guide, an absorber area in the region of half to the full water surface is assumed. The pipework should be planned so that it can be drained in order to avoid frost damage.
- Heat exchanger: Needs the least space and sits in the plant room. It additionally requires a circulation pump and control system in the heating circuit as well as a connection to the home heating. With salt water or a salt chlorinator, make sure to use a corrosion-resistant heat exchanger (e.g. titanium).
Plan the heating connection into the initial pipework wherever possible – adding a bypass later is more involved than a branch provided for from the outset.
Sensible Combinations
The systems are not mutually exclusive; in many cases they complement each other well:
- Solar plus heat pump: Solar covers the base demand for free on sunny days, while the heat pump steps in as a dependable reserve in bad weather and during the transitional periods. This is the most common combination for long, comfortable seasons.
- Heat exchanger plus solar: Anyone who already has a powerful home heating system uses solar to ease the load on summer days and the heat exchanger as the base load.
- Photovoltaics plus heat pump: If the heat pump runs preferentially on self-generated PV electricity, the operating costs fall further – here a time-controlled release of the filter pump and the heating pays off.
In every combination the rule is: only one system actively heats at any one time; switching and prioritisation are handled by a solar or heating controller with temperature sensors.
Payback over Ten Years
Over ten years, the balance shifts markedly compared with the purchase price alone, because the running costs dominate. The following worked example for a covered pool of around 50 m³ shows the tendency – it is no substitute for an individual calculation using your energy prices and your usage.
| System | Purchase | Operating costs/year | Trend after 10 years |
|---|---|---|---|
| Solar absorber | low to medium | very low (pump electricity only) | lowest total cost, but limited output |
| Heat pump | medium to high | moderate, cushioned by the COP | higher purchase cost, good operating figures – a strong overall package for dependable heat |
| Heat exchanger | low | depends on the fuel price | cheap entry cost, total cost highly price-dependent |
As a rule of thumb: if a suitable, well-sunlit area is available and summer comfort is enough, solar pays for itself the fastest. Anyone wanting dependable heat over a long season is usually most economical with a heat pump. The heat exchanger is attractive when an efficient home heating system with spare capacity is running anyway. Include the cost of a cover in every calculation – it shortens the payback of every system.
Bill of materials
Example – please verify with a specialist. Parts and quantities depend on the installation; sizes shown are examples.
| Component | Size | Art. No. | KLN No. | Qty |
|---|---|---|---|---|
| Heat pump (air/water) | – | – | – | Outdoor installation, dedicated power connection by a qualified electrician; titanium heat exchanger for salt water |
| Solar absorber (mats/pipes) | – | – | – | Absorber area roughly half to the full water surface; pipe so it can be drained frost-safe |
| Plate heat exchanger | – | – | – | Connection to the existing house heating with power reserve; corrosion-resistant version with salt electrolysis |
FAQ
Which pool heater is cheapest to run?
The solar absorber, because the solar energy is free and only minor pump-electricity costs arise. The heat pump comes next thanks to its coefficient of performance, while the cost of the heat exchanger depends on the fuel price of the home heating.
How much does a heat pump extend the swimming season?
With a cover, use from roughly April to October is realistic because the heat pump maintains a target temperature regardless of the weather. Its efficiency does fall, however, the colder the outside air is.
Can I combine solar and a heat pump?
Yes, that is a common combination. Solar covers the base demand for free on sunny days, while the heat pump steps in as a dependable reserve in bad weather and during the shoulder months.
What pipe diameter does the heating connection need?
d50 (DN40) or d63 (DN50) are common, matching the existing pool pipework. The connection is made as a bypass after the filter with shut-off and control valves.
Does a pool heat pump need a special power connection?
Depending on the output, 230 V is enough; larger units require 400 V. The electrical connection and equipotential bonding must be carried out by a qualified electrical contractor.
This guide provides general technical orientation and does not replace professional planning. Safety-, electrical- and permit-relevant work must be carried out by qualified specialists.
