An indoor swimming pool is one of the most ambitious home projects a homeowner can take on. The idea is easy to fall in love with. A private pool, usable 365 days a year, completely sheltered from the British weather. The reality, done well, is genuinely extraordinary. But it comes with a level of complexity that catches a lot of people off guard.
This isn’t a reason to be put off. It’s a reason to go in with your eyes open. A home swimming pool of this kind requires careful planning across a range of disciplines – building, engineering, ventilation, heating, waterproofing, and design. The decisions you make at the outset will determine how well the finished space performs for the decades that follow.
Here’s what you actually need to think about before you build an indoor pool.
The Building Itself Comes FirstÂ
Before a single decision is made about the pool, the structure that will house it needs to be right. Whether you’re converting an existing building, a barn, a garage, an outbuilding, or commissioning a purpose-built pool house from scratch, the envelope matters enormously.
Indoor pools generate a significant amount of moisture. Without the right structural approach, that moisture will find its way into walls, ceilings, and roof structures, causing damage that is both serious and expensive to put right. Vapour barriers, correct wall construction, and appropriate drainage all need to be built into the fabric of the building from the start – not retrofitted after the fact.
The Petham Project is a case in point. What had been an empty barn was transformed into a pool building of genuine architectural distinction, housing a full indoor pool, spa, sauna, and indoor kitchen. The building sits within the grounds of a 12th century Chantry and 16th century manor house, which meant every design decision had to work in harmony with the historic surroundings. The result is a space that is as considered as it is extraordinary.
Heating and Ventilation: The Most Critical Decisions You’ll Make
Get the heating and ventilation right and your indoor pool will be a pleasure to own. Get it wrong and you’ll be dealing with condensation, damp, poor air quality, and spiralling running costs for as long as you own it.
Pool Water Heating
The water itself needs to be kept at a consistent, comfortable temperature year-round. Ground source heat pumps (GSHPs) are increasingly the preferred solution for indoor pools at the higher end of the market. They’re efficient, environmentally sound, and operate quietly. The Petham Project uses a deep bore ground source heat pump system to heat both the pool and the pool building, delivering consistent year-round performance with state of the art monitoring.
Air source heat pumps are a more accessible alternative for projects where ground source isn’t viable. Both significantly outperform traditional gas or electric heating in terms of running costs over time.
Pool Hall Ventilation and Dehumidification
This is the part of an indoor pool project that homeowners most frequently underestimate. A body of heated water in an enclosed space produces a continuous volume of water vapour. Without a properly specified dehumidification system, that moisture will saturate the air, condense on cold surfaces, and begin to degrade the building fabric and everything in it.
A well-designed pool hall ventilation system does several things simultaneously. It controls humidity levels within a safe range, maintains comfortable air temperature for swimmers, manages air quality, and prevents condensation on glazing, walls, and structural elements. This is specialist engineering. It needs to be specified by someone who understands the thermal dynamics of indoor pool environments, not adapted from a standard HVAC design.
Setback Systems
A setback system allows the pool’s heating and ventilation to operate at reduced capacity when the pool isn’t in use, typically overnight or during extended periods away. This keeps the environment stable without running the system at full output around the clock, reducing energy consumption meaningfully over time. For a home swimming pool used by a family rather than a commercial operation, a well-configured setback system can make a significant difference to annual running costs.
Pool Covers Are Non-Negotiable Indoors
Outdoors, a pool cover is highly advisable. Indoors, it’s essential.
An uncovered indoor pool evaporates water continuously into the surrounding air, placing constant pressure on your dehumidification system and increasing both heating and ventilation costs. A quality automatic pool cover, deployed whenever the pool is not in use, reduces evaporation by up to 98%. Dramatically cutting the load on the building’s mechanical systems and extending the life of the pool hall fabric.
An automatic cover also improves safety and keeps the water cleaner between uses, reducing chemical consumption. For an indoor home swimming pool, it’s one of the highest-return investments you can make.
Ducting, Drainage, and the Infrastructure Nobody Sees
The infrastructure behind an indoor pool is substantial, and it needs to be planned before construction begins, not accommodated afterwards.
Ducting for the ventilation system needs to be routed through the building fabric in a way that is both effective and unobtrusive. Getting this wrong means either compromised performance or visible ductwork that undermines the finished aesthetic. Good ducting design is invisible in the finished space.
Drainage needs to account not just for the pool itself but for the surrounding wet areas – poolside, changing facilities, shower areas, and plant rooms. Surface water management in an indoor pool environment needs more careful thought than most people anticipate.
Plant room space is another consideration that gets underestimated. The heating, filtration, dehumidification, and chemical dosing equipment required for an indoor pool takes up meaningful space. A dedicated, accessible plant room with sufficient floor area, headroom, and drainage needs to be built into the design from the outset.
Glazing, Skylights, and Natural Light
An indoor pool without natural light can feel institutional. Glazing and skylights transform the experience of the space, but they also introduce thermal and condensation challenges that need to be managed carefully.
Single or poorly specified glazing in a pool hall creates cold surfaces that attract condensation. Triple glazing with thermally broken frames is the standard for a well-built indoor pool environment. Roof lights and skylights need to be specified with the same rigour. Both for thermal performance and to handle the cleaning and maintenance access they’ll require over time.
The payoff is significant. A well-glazed pool hall with considered natural light is a genuinely beautiful space to spend time in, and it reduces the reliance on artificial lighting during daylight hours.
Splash Barriers, Finishes, and the Wet EnvironmentÂ
Every material used in and around an indoor pool needs to be appropriate for a permanently wet, humid environment. This sounds obvious but it’s easy to overlook in the excitement of choosing finishes.
Splash barriers, glazed or solid panels that contain water movement around the pool, are both a practical and an aesthetic decision. They protect surrounding surfaces and define the pool zone within the wider space. The Petham Project uses the pool building’s architectural features, including its remarkable hammerhead oak beam, as design elements in their own right, creating a space where the functional and the beautiful are inseparable.
Wall and floor finishes need to be fully waterproof, slip-resistant where appropriate, and resistant to the chemical environment that pool water creates. Timber, plaster, and standard paint have no place in a pool hall unless specifically treated and sealed for the application.
What Does an Indoor Pool Actually Cost to Run?
Running costs for an indoor home swimming pool are higher than for an outdoor pool, and it’s worth being realistic about this from the start. Heating, dehumidification, filtration, chemical dosing, and lighting all run continuously or near-continuously in an indoor environment.
The good news is that the gap between a well-specified indoor pool and a poorly specified one, in terms of running costs, is enormous. Investing properly in the right heating system, a quality pool cover, a well-designed ventilation system, and setback controls will reduce annual running costs significantly compared to a pool that cuts corners on any of these elements. The specification decisions made at the design stage have a direct and lasting impact on what the pool costs to own.
Thinking About an Indoor Pool? Talk to XL Pools First
Indoor pools are complex, and the number of decisions involved can feel overwhelming without the right guidance. XL Pools has designed and built indoor pool projects across Kent and the South East, including projects of the ambition and complexity of the Petham Project, and we understand what it takes to get every element right.
If you’re at the early stages of thinking about a home swimming pool and want an honest conversation about what’s involved, get in touch with our team. We’ll help you understand what’s realistic for your property, your budget, and your brief, before any commitments are made. You can also browse our completed pool projects and find out more about us on our about us page.
