Indoor Pools: Humidity and Ventilation

The main challenge in an indoor pool is not the water itself but the moisture rising from it. Uncontrolled humidity leads to streaming windows, mould on ceilings and corroded metal.

An indoor pool in a villa basement or a separate pavilion lets you swim all year. Yet in the first winter owners often see the same picture: water running down the windows, black patches in ceiling corners, a heavy chlorine smell in the air and swollen doors in adjoining rooms. All of this has one root cause: moisture constantly evaporating from the water surface and not being properly managed.

Where the moisture comes from

Heated water evaporates continuously. How much depends on water temperature, air temperature, relative humidity, surface area and movement on the surface. Evaporation rises when people swim or water features run, and falls sharply once a cover is pulled over the water.

The classic principle for limiting evaporation is to keep the air slightly warmer than the water. When the air is cooler than the water, evaporation speeds up. Relative humidity is also kept within a set range: air that is too dry increases evaporation and chills swimmers, while air that is too humid leads to condensation.

Condensation and dew point

When humid air touches a cold surface, it turns to water droplets on that surface. In an indoor pool these cold surfaces are usually:

window glass and frames, especially the edges of profiles;
thermal bridges at external wall corners and wall-to-ceiling junctions;
uninsulated sections of ventilation ducts;
roof structure elements that cool from the inside.

By the time condensation is visible, the problem has already begun. Moisture accumulating out of sight inside walls or ceilings is more dangerous still, as it soaks insulation and surfaces years later as structural damage.

Ventilation and dehumidification

Ordinary domestic ventilation is not enough for an indoor pool. Purpose-built pool dehumidifiers or ventilation systems with heat recovery are used instead. They remove humid air, warm the fresh air and often recover heat from the exhaust. The capacity of the system is set by engineering calculation; a unit chosen by guesswork either cannot remove the moisture or wastes energy.

Air distribution is decisive too. Dry, warm air is supplied in front of the windows, usually through floor-level grilles, to warm the glass and prevent condensation. Humid air is extracted high up, above the water surface.

Vapour barrier and materials

Walls and ceilings of an indoor pool room need a continuous vapour barrier on the warm, inner side of the insulation. Its joints and every cable and pipe penetration are carefully sealed: even a small hole lets moisture into the structure.

Materials are chosen differently in this environment:

moisture-resistant boards or dedicated suspended ceiling systems for ceilings;
corrosion-resistant steel and protective coatings for metal elements;
moisture-resistant ceramics and natural stone;
lighting and electrical equipment that tolerates chlorinated air.

Links to adjoining rooms

The air in the pool room is kept at slightly negative pressure so that humid, odorous air does not spread into the rest of the house. Doors between the pool and living areas should close tightly, and changing and shower areas are planned as a buffer in between.

Everyday habits affect humidity as well. Drying wet towels in the pool hall, leaving doors open for long periods or switching the dehumidifier off completely overnight pushes the system out of its design conditions. It is worth watching the temperature and humidity readings on the control panel, changing filters at the intervals the manufacturer specifies and looking out for the first traces of condensation in window corners. A small sign spotted early is far easier to deal with than moisture that has built up inside the ceiling.

Questions to ask at design stage

What water and air temperatures will be maintained?
Will the water surface be covered when not in use?
Where will the dehumidification unit and its ducts go?
Is warm air supply provided in front of the windows?
How will the continuity of the vapour barrier be ensured?

In private house and villa projects, Zaferoğlu İnşaat determines the location of plant rooms and building services together with the architectural plan. If you are planning an indoor pool, we can discuss ventilation and humidity with you from the first sketches.

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