Swimming pool air handling unit installation service and repair.

Indoor Swimming Pool Ventilation And Dehumidification

Creating a comfortable indoor swimming pool requires much more than heating the water.

Warmpools designs, supplies and installs specialist indoor pool environmental control systems that manage humidity, air temperature, fresh-air ventilation and pool-water heating as one coordinated system.

We work with Calorex Variheat and Delta air handling units to protect the pool building, improve comfort and recover valuable heat that would otherwise be lost.

Heat recovery specialists.

Indoor pool system design
Calorex Variheat and Delta specialists
Installation and commissioning
Replacement and upgrade projects
Repairs to existing units

What does an indoor pool air handling unit do?

diagram showing what a swimming pool air handling unit does. Pool heat recovery.

A Must For Indoor Pools

An indoor swimming pool air handling unit removes excess moisture from the pool hall, supplies warm dry air, introduces controlled fresh air and extracts stale air.

Heat-pump systems such as the Calorex Variheat and Delta also recover energy from the warm, humid air. This recovered heat can be reused to assist with heating the pool water and pool-hall air.

The result is a more comfortable pool environment with better protection against condensation, mould, corrosion and moisture damage.

Why specialist ventilation and humidity control is needed.

Why indoor pools need specialist ventilation and humidity control

An indoor swimming pool releases a significant amount of moisture into the surrounding air.

Every time water evaporates from the pool surface, warm humid air enters the pool hall. Without effective dehumidification and air movement, this moisture can condense on windows, walls, ceilings and colder parts of the building.

Condensation

Water forming on glazing, roof structures, walls and metalwork is often the first visible sign that the pool environment is not being controlled correctly.

Damage to the building

Moisture can penetrate finishes and building materials, creating conditions that may lead to mould, corrosion, staining and deterioration of the structure.

Uncomfortable conditions

Excessive humidity can make a pool hall feel oppressive and uncomfortable, even when the air temperature itself appears correct.

High energy use

Simply exhausting warm pool air outdoors wastes valuable heat. A purpose-designed heat-recovery system captures part of that energy and reuses it within the pool system.

Calorex describes Variheat as a purpose-built environmental control system that removes moisture with an integral heat pump while recovering latent heat for pool-water and air heating.

How indoor pool dehumidification and heat recovery works

1. Warm humid air returns from the pool hall

Moisture-laden air is drawn back to the air handling unit through the return-air ductwork.

2. Moisture is removed

The heat-pump dehumidifier cools the air below its dew point. Water vapour condenses into liquid and is discharged through the condensate drain.

3. Heat is recovered

Instead of throwing away all the energy contained in the warm humid air, the system recovers useful heat.

4. Warm dry air is returned

The conditioned air is reheated and supplied back to the pool hall. Recovered heat can also be transferred to the swimming pool water.

Where fresh-air ventilation is fitted, the system introduces outdoor air while extracting a controlled amount of pool-hall air.

Calorex indoor swimming pool air handling units

Warmpools supplies, installs and repairs two principal Calorex ranges for ducted indoor pool environmental control: Variheat Series 3 and Delta.

Both ranges provide heat-pump dehumidification and heat recovery, but they are designed for different pool sizes, ventilation requirements and plant-room conditions.

Correct selection should be based on the calculated evaporation load, pool-hall airflow, fresh-air demand, duct resistance, available heat source and building design — not simply the pool length or water volume.

Calorex Variheat and Delta Repairs

Calorex Indoor Pool Air Handling Unit Repairs

A fault with an indoor pool air handling unit can quickly lead to rising humidity, condensation, uncomfortable temperatures and loss of pool-water heating.

Warmpools diagnoses and repairs Calorex Variheat and Delta systems used in private, hotel, leisure and commercial indoor swimming pools.

We investigate the complete system rather than replacing parts without first identifying the cause. This includes the air handling unit, heat-pump circuit, fans, sensors, dampers, controls, water flow, heating circuit and connected ductwork.

Problems we investigate

High humidity or condensation

If the unit is running but humidity continues to rise, the cause may be related to refrigeration performance, airflow, incorrect settings, sensor readings, water flow, blocked filters or a change in how the pool is being used.

Unit not dehumidifying

We investigate compressor operation, refrigerant circuits, coils, condensate drainage, air temperatures, control demand and whether the system is achieving the conditions required for dehumidification.

Pool hall not heating

Poor air heating may be caused by an issue with the LPHW heating circuit, control valve, water temperature, circulation, air volume, temperature sensor or the external boiler or heat-pump system.

Pool water not heating

Calorex Variheat and Delta units can recover heat to the pool water and may also use an LPHW pool-water heat exchanger. We check water flow, control demand, valves, sensors, heat-source operation and heat-exchanger performance.

Fan or airflow faults

Fan faults, blocked filters, damaged dampers, incorrect fan settings or restricted ductwork can reduce the air volume passing through the system and prevent it from controlling the pool environment correctly.

Touchscreen, sensor or control faults

Both Variheat and Delta systems use PLC controls to manage humidity, air temperature and pool-water temperature. Their controls also provide operating and fault information that can help with diagnosis.

Calorex faults we can assess

Warmpools can investigate problems including:

Calorex unit not starting
High-humidity or low-humidity alarms
Pool hall condensation
Loss of dehumidification
Compressor or refrigeration faults
Fan failure or reduced airflow
Damper and actuator faults
Fresh-air or exhaust-air problems
Incorrect negative pressure
Pool air not reaching temperature
Pool water not reaching temperature
LPHW valve or heating-circuit faults
Temperature or humidity sensor faults
Touchscreen and control errors
Network or remote-access problems
Condensate leaks or blocked drains
Excessive noise or vibration
Filters becoming blocked unusually quickly
Intermittent operation or unexplained shutdowns

Repairs for Calorex Variheat systems

We can assess Calorex Variheat 600, 900, 1200 and 1500 air handling units, including systems fitted with optional fresh-air or negative-pressure modules.

Variheat units combine heat-pump dehumidification, heat recovery, air circulation, pool-water heating, air heating and touchscreen controls. A fault in one part of the system can therefore affect several functions at the same time.

For example, reduced airflow may appear to be a refrigeration problem, while poor water flow may prevent recovered heat from being transferred effectively to the pool.

The Variheat control system can provide fault information, operating history and diagnostic data that can assist the repair process.

Repairs for Calorex Delta systems

Warmpools can also investigate faults on Calorex Delta 2, 4, 6, 8, 10, 12, 14 and 16 systems.

Delta units include recirculation fans, exhaust fans, fresh-air dampers, heat-pump dehumidification, heat recovery, LPHW heating and integrated environmental controls.

Because the Delta controls fresh air, exhaust air and pool-hall pressure, a fault may affect more than temperature or humidity. Incorrect airflow or damper operation can also allow humid pool air to move into adjacent rooms or parts of the building.

The Delta controller provides operating, configuration and fault-status information covering humidity, air temperature and pool-water temperature control.

Repair or replace?

Not every faulty air handling unit needs to be replaced.

Repair may be appropriate where the cabinet, coils, fans, refrigeration circuit and controls remain serviceable and replacement parts are available.

Replacement may be more sensible where:

Major components have failed together
Parts are obsolete or no longer supported
The unit is badly corroded
The refrigeration system has suffered repeated failures
The system is significantly undersized
The existing ductwork or controls no longer meet the pool’s requirements
Repair costs would be disproportionate to the remaining service life

Warmpools can provide an honest assessment of whether repair, refurbishment or replacement offers the better long-term solution.

Safety note

Calorex air handling units contain electrical, rotating and refrigeration components. Manufacturer manuals state that servicing and internal work should only be carried out by competent personnel.

The equipment should be electrically isolated before panels are removed, and refrigeration repairs must be undertaken by engineers with the appropriate qualifications for the refrigerant used.

Calorex Variheat

Calorex Variheat Series 3 Flexible indoor pool dehumidification, heating and ventilation

The Calorex Variheat Series 3 is a packaged environmental control system designed specifically for indoor swimming pools.

It combines heat-pump dehumidification, air circulation, heat recovery and pool-water heating within a single unit. Optional fresh-air and negative-pressure modules allow the system to provide controlled pool-hall ventilation where required.

Variheat is particularly useful for private pools, smaller commercial pools and projects where plant-room space or access is restricted.

Designed around the plant room

The modular Variheat design is available in a wide range of vertical, horizontal, upflow, downflow and side-outlet configurations.

Supply-air outlets can be arranged in different positions, while plumbing and ventilation connections can be configured to suit the available plant-room space. Bottom-outlet models can connect to underfloor ductwork.

This flexibility allows the equipment to be adapted to the building rather than forcing the entire plant room to fit one cabinet arrangement.

Variheat key features

Heat-pump dehumidification for indoor pool halls
Heat recovery to pool water and pool-hall air
Optional fresh-air ventilation module
Optional negative-pressure module
Air heating and pool-water heating through LPHW heat exchangers
Low-temperature air-heater option for suitable renewable and condensing heat sources
Constant-flow or variable-speed fan technology, depending on the model
Air filtration
Multiple supply-air and service configurations
Touchscreen PLC control
Remote monitoring and selected BMS connectivity
Occupied and unoccupied temperature settings
Diagnostic information and operating history

The Variheat touchscreen system can provide remote monitoring, control of air, water and humidity set points, air-temperature setback and diagnostic information.

Variheat model range

ModelRated dehumidificationMain airflowVariheat 6004.6 litres per hour2,000 m³/hVariheat 9006.5 litres per hour2,500 m³/hVariheat 12008.5 litres per hour3,500 m³/hVariheat 150010.5 litres per hour4,300 m³/h

Technical note: Manufacturer dehumidification figures are measured at 30°C and 60% relative humidity. The optional fresh-air module is rated at up to 900 m³/h. Actual performance and model selection depend on the design conditions and available external static pressure.

Is Variheat suitable for your pool?

Variheat may be suitable when:

The project is a domestic or light-commercial indoor pool
A compact, configurable plant-room arrangement is needed
The pool requires combined dehumidification, air heating and water heating
Fresh-air ventilation is required but does not need to be permanently provided at the scale of a larger Delta system
The equipment must connect to overhead, side or underfloor ductwork
Remote control or BMS integration is required

Calorex Variheat installation service and repair.

Calorex Delta

Pool Air Handling Systems Integrated fresh-air ventilation and dehumidification, larger pool halls.

The Calorex Delta is a hybrid fresh-air dehumidification and ventilation system designed for indoor swimming pools.

It combines recirculated pool-hall air, automatically controlled fresh air, exhaust ventilation, heat-pump dehumidification and heat recovery within one packaged system.

The range includes models for private pools as well as larger hotel, leisure, health-club, school and commercial swimming pool facilities.

Controlled fresh air and negative pressure

Delta units introduce a variable volume of fresh air while extracting a slightly greater quantity of pool-hall air.

This creates a small negative pressure within the pool hall, helping to reduce the movement of warm humid air into adjacent rooms and the surrounding building fabric.

During colder weather, heat can be recovered from the exhaust-air stream and used to warm the incoming fresh air. Delta models 4 and above can also reject excess heat through the exhaust air to provide pool-hall cooling when the air temperature rises above the set point.

Delta key features

Heat-pump dehumidification and heat recovery
Automatically regulated fresh-air ventilation
Dedicated exhaust fan and fresh-air damper
Slight negative pool-hall pressure
Heat recovery to pool water and pool-hall air
Heat recovery between exhaust and incoming fresh air
Pool-hall cooling on Delta 4 and above
Fully controlled LPHW air and pool-water heat exchangers
Air filtration
Direct-drive EC fans
Automatic humidity, air-temperature and pool-water control
Night or unoccupied temperature setback
Network, remote-control and BMS options
Multiple supply-air configurations

Delta model range

The current Delta range consists of models 2, 4, 6, 8, 10, 12, 14 and 16.

Recirculation airflow increases from approximately 2,600 m³/h for the Delta 2 to 12,000 m³/h for the Delta 16. All models are supplied as packaged pool air handling systems with integral controls and a 5.7-inch touchscreen.

Is Delta suitable for your pool?

Delta may be the preferred option when:

The pool hall has a high moisture or ventilation demand
The pool is used commercially or has frequent occupancy
Regular fresh-air ventilation is an important part of the design
The pool hall needs to operate under controlled negative pressure
The building has large areas of glazing or significant solar gain
Summer pool-hall cooling is required
Higher recirculation airflow is needed
The system must integrate with wider building controls

Warmpools expertise

Why choose Warmpools for your indoor pool air handling system?

An indoor pool air handling unit cannot be considered in isolation.

Its performance depends on the pool, ductwork, air-distribution grilles, heat source, pipework, electrical supply, controls, pool cover and building construction all working together.

Warmpools takes a complete-system approach to indoor pool environmental control.

Pool-specific system design

We assess the actual pool surface area, water temperature, air temperature, humidity target, cover use, occupancy and operating hours.

Equipment selection

We compare the required moisture-removal duty, airflow, ventilation rate and heating demand against the available Variheat and Delta models.

Ductwork planning

We consider duct dimensions, static pressure, air velocity, insulation, grille positions, fresh-air intake, exhaust discharge and service access.

Heating-system integration

The pool-water and air-heating circuits must be matched to the available boiler, heat pump or other LPHW heat source.

Controls and interlocks

Pool pumps, heat sources, pool covers, occupied settings, temperature setback, remote monitoring and BMS connections can all affect system performance.

Commissioning and handover

Airflow, water flow, sensors, set points, dampers and operating modes must be checked and commissioned as part of the completed installation.

Warmpools are expert engineers and can cover all aspects of the calorex variheat and delta heat reco

Design information

How we size an indoor pool ventilation and dehumidification system

A professional system design should consider all of the following.

Pool information

Pool length and width
Water surface area
Water temperature
Pool depth
Spa pools or water features
Pool-cover type and expected use
Typical number of bathers
Daily and weekly operating hours

Pool-hall information

Required air temperature
Required relative humidity
Room dimensions and volume
Glazing area and type
Wall, roof and floor construction
Insulation standards
Cold bridges and known condensation areas
Doors connecting to other parts of the property

Plant-room information

Plant-room dimensions
Delivery and lifting access
Required service clearances
Existing ductwork
Available electrical supply
Existing pool-water flow rate
Boiler or heat-pump flow temperature
Condensate drainage
Network and BMS requirements

Why the pool cover matters

Covering the pool when it is not in use can significantly reduce evaporation.

The expected use of the pool cover therefore affects the calculated moisture load, heating requirement and operating schedule of the air handling system.

The cover position can also be connected to the environmental controls so that the pool hall moves automatically between occupied and unoccupied operating conditions.

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Installation process

From initial survey to commissioned pool environment

1. Initial consultation

We discuss the pool, the building, the intended use and any existing problems with humidity, condensation, noise or running costs.

2. Site survey

We inspect the pool hall, plant room, existing equipment, duct routes, heat source, pipework and electrical services.

3. Design and equipment selection

We calculate the required moisture-removal duty, airflow, ventilation rate and heating requirements before selecting the appropriate Variheat or Delta model.

4. Installation planning

We coordinate the equipment position, delivery route, duct connections, water connections, condensate drain, controls and service clearances.

5. Installation

The air handling unit, ductwork, pipework, electrical services and controls are installed and connected.

6. Commissioning

Air volumes, temperatures, water flow, sensors, dampers and operating modes are checked and adjusted.

7. Handover

The owner or facilities team is shown how to operate the touchscreen controls, change approved settings and identify routine maintenance requirements.

Replacement systems

Replacing an existing indoor pool dehumidifier or air handling unit

Older pool air handling systems may become unreliable, inefficient or difficult to maintain.

However, replacing the cabinet alone does not guarantee that the new system will perform correctly.

A replacement survey should check:

The original design duty
Current pool temperatures and usage
Changes made to the pool or building
Existing supply and return duct sizes
Air distribution around glazing and external walls
Fresh-air and exhaust arrangements
Available static pressure
Pool-water and LPHW flow rates
Electrical supply
Condensate drainage
Plant-room access and service clearance
Existing controls and interlocks

Warmpools can assess the existing installation and recommend whether the project requires a direct replacement, a redesigned duct arrangement or a broader plant-room upgrade.

Replacement calorex variheat and delta units available. Supplied and installed.

Indoor pool ventilation and dehumidification FAQs

Please reach us at info@warmpools.co.uk if you cannot find an answer to your question.

Does every indoor swimming pool need dehumidification?

Every enclosed indoor pool needs a planned method of controlling moisture.

In most permanently enclosed pool halls, a purpose-designed dehumidification and ventilation system provides more dependable control than relying on extract fans or opening windows.

What relative humidity should an indoor pool hall have?

Approximately 60% relative humidity is a common design target for indoor swimming pools.

The correct setting depends on the pool temperature, air temperature, glazing, insulation and building construction. Reducing humidity excessively can increase evaporation and energy consumption.

Should pool-hall air be warmer than the water?

We offer a 25-year warranty on our in-ground and semi-ingroundPool-hall air is commonly maintained approximately 1–2°C warmer than the pool water while the pool is uncovered.

This can improve bather comfort and help reduce evaporation. The final temperatures should be established during the system design and commissioning process.

Can the system heat both the pool water and the air?

Calorex Variheat and Delta systems can recover heat from the dehumidification process and transfer it to the pool water and pool-hall air.

They can also include heat exchangers connected to a suitable external LPHW source for supplementary heating.

Can these systems work with an air source heat pump?

Potentially, yes.

Calorex offers upgraded air-heater options intended to provide suitable output at lower LPHW temperatures. The heat source output, water temperature, flow rate and hydraulic design must be checked before the equipment is specified.

Do Variheat and Delta units need ductwork?

Yes. These are packaged ducted air handling systems designed to connect to supply and return air ductwork.

Fresh-air and exhaust ductwork will also be required where ventilation is included.

Can the air handling unit be installed inside the pool hall?

These units are normally intended for installation in a suitable internal plant room, with ductwork connecting the equipment to the pool hall.

The plant room must provide adequate access and clearance for maintenance. The Delta manual describes the unit as a packaged system designed for an internal plant room and requires access to controls, service panels and connections.

Can the system be controlled remotely?

Variheat and Delta systems include touchscreen PLC controls and can provide network, remote-monitoring or BMS connectivity, depending on the selected controls and project requirements.

How do I know which Variheat model I need?

The correct model is calculated from the pool’s evaporation load and required airflow.

Pool surface area, water temperature, pool-hall temperature, humidity, cover use, occupancy, fresh-air requirement and duct resistance all affect the result.

Does Warmpools replace older Calorex units?

Warmpools can survey existing Calorex and other indoor pool environmental control systems to determine the correct replacement duty and any changes required to the ductwork, controls, plumbing or electrical services.

Talk to Warmpools about your indoor pool environment

Pool Heating And Ventilation Experts

Whether you are planning a new indoor swimming pool, replacing an older air handling unit or trying to solve an existing condensation problem, the first step is to understand the complete pool-hall system.

Send us your pool dimensions, intended temperatures, pool-cover details and photographs of the plant room. We will advise what additional information is required to specify the correct ventilation, dehumidification and heat-recovery solution.

WarmPools

England, United Kingdom

07720928585

Experienced and qualified swimming pool heating and ventilation engineers.