Every indoor pool has its own microclimate. The below terms explain what’s happening in the air above the water and why it matters for comfort and health.

The amount of moisture (water vapour) held in the air. Indoor pools naturally produce a lot of moisture as water evaporates from the pool surface, so pool halls need to manage humidity carefully to stay comfortable and protect the building.

A measurement of how much moisture is in the air compared to the maximum it could hold at that temperature, shown as a percentage. Most indoor pools are kept between 50–60% relative humidity which is high enough to be comfortable for swimmers but not so high that it causes condensation or a stuffy atmosphere.

Water droplets that form when moist air comes into contact with a cooler surface, such as a window, ceiling or steel beam. Persistent condensation is usually a sign that humidity levels are too high or that ventilation isn’t working effectively. Over time this can cause damp, mould and damage to the building structure.

The chlorine-like smell often noticed above indoor pools. It isn’t caused by too much chlorine, it’s actually a sign of by-products (called chloramines) forming when chlorine reacts with sweat, urine and other organic matter in the water. Good ventilation clears these by-products from the air before they build up, so a well-ventilated pool shouldn’t have a strong smell.

Outdoor air that is drawn into the building to replace stale, humid air from inside the pool hall. Bringing in a steady supply of fresh air is one of the main ways pool halls keep air quality and humidity under control.

The general term for moving air into and out of a building. In a pool hall, ventilation removes moist, stale air and replaces it with fresh, conditioned air, helping to control humidity, temperature and air quality throughout the day.

The main piece of equipment responsible for treating and moving air around the pool hall. It draws in fresh air, removes moisture from the air already in the building, and delivers air back into the space at the right temperature, usually housed in a plant room or on the roof.

A dedicated room or enclosure that houses the mechanical equipment for the pool hall, such as the air handling unit, pumps and controls. Plant rooms are required in order to keep noise, heat and aesthetically displeasing equipment away from swimmers.

The conditioned air delivered into the pool hall by the ventilation system, usually through grilles or diffusers in the ceiling or walls. Supply air is warmed and dried before it enters the room, helping to keep the space comfortable.

The warm, moist air that is extracted from the pool hall and removed from the building. Because this air holds so much heat and moisture, well-designed systems recover as much energy from it as possible before it’s expelled (see Heat Recovery).

How often the entire volume of air in the pool hall is replaced with fresh air, usually described as a number of “air changes per hour.” Pool halls typically need a higher air change rate than most other buildings because of the amount of moisture and chemical by-products produced by the water.

The movement of air within the pool hall itself, as opposed to air being brought in from outside. Good air circulation ensures fresh, conditioned air reaches all areas of the pool hall, including down at water level where swimmers breathe, rather than just collecting near the ceiling.

The process of removing excess moisture from the air. Pool ventilation systems dehumidify continuously to stop the air becoming saturated with moisture, which would otherwise lead to condensation, mould and an uncomfortable, muggy atmosphere.

How effectively a system uses energy to achieve the desired result, in this case, comfortable temperature, humidity and air quality. A more energy-efficient ventilation system uses less electricity and gas to maintain the same conditions, saving money and reducing carbon emissions over time.

The way a ventilation system automatically manages itself, i.e. deciding when to bring in more fresh air, run heating or step up dehumidification based on readings from sensors around the pool hall. A good control strategy responds to actual conditions (such as how busy the pool is or the season) rather than running everything at full output all the time, keeping the pool hall comfortable while avoiding unnecessary energy use.

The target temperature or humidity level that the system is set to maintain. For example, a pool hall might have a temperature setpoint of 28°C and a humidity setpoint of 55%RH; the system will then automatically work to keep conditions close to these targets.

Regular inspection and upkeep of the ventilation system by a qualified engineer to keep it running efficiently and catch small issues before they become bigger, more costly problems. Recotherm recommend scheduled servicing through our fixed price maintenance plan to protect performance, fix your costs and give you the option of additional warranty cover.

Components within the air handling unit that remove dust, debris and other particles from the air before it’s supplied into the pool hall. Filters need to be checked and replaced periodically as a blocked filter can reduce airflow and make the whole system work harder than it needs to.

The network of metal or fabric channels that carry air between the air handling unit and the pool hall. Ductwork should be inspected periodically to check for damage, blockages or condensation, all of which can affect how well air is delivered around the space.