Indoor Swimming Pool Heating & Ventilation

Designing effective heating and ventilation (H&V) for indoor swimming pools requires a specialized approach due to high humidity, chemical fumes, and the need for a stable, comfortable environment. Poor H&V design can cause condensation, mould, and structural damage.

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Main types of H&V system options for indoor pools are:

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1. Ducted dehumidification and air handling systems

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This is the most comprehensive and effective solution for larger or heavily used indoor pools, such as those in commercial or leisure centres.

 

• How it works: A central air handling unit (AHU) performs dehumidification, air heating, and heat recovery. The treated air is distributed evenly throughout the pool room via a network of ducts, and stale, humid air is exhausted.

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• Pros:

  • Superior climate control: Provides the most even air distribution and effectively prevents condensation on all surfaces, including windows.

  • Excellent air quality: Introduces fresh outdoor air while exhausting stale air rich in corrosive chloramines.

  • High energy efficiency: Recovers heat from the humid exhaust air to pre-warm the fresh incoming air, minimizing heating costs.

  • Versatile installation: The main unit can be placed in an adjoining plant room, reducing noise in the pool area.

• Cons:

  • Expensive: These systems typically have the highest initial cost.

  • Complex installation: Requires careful duct design and professional installation. 

 

2. Wall-mounted dehumidifiers with integrated heating

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Ideal for smaller, private indoor pools and hot tubs, these self-contained units offer a cost-effective solution. 

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• How it works: The unit is mounted directly on the wall and pulls moist air in, condenses the water vapor, and returns warm, dry air to the room. Many models include an integrated air heating coil and can recover latent heat from the moisture to help warm the pool hall.

• Pros:

  • Lower cost: Much cheaper and simpler to install than ducted systems.

  • Space-saving: The self-contained unit takes up minimal space.

  • Good for smaller pools: Offers effective humidity control for smaller-scale environments.

• Cons:

  • Uneven air distribution: Since it's not ducted, air distribution can be uneven, potentially leading to condensation on surfaces far from the unit.

  • Noise: The unit's noise is located directly within the pool room. 

 

3. Air-source heat pumps

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Heat pumps can be used for both heating the pool water and the air in the pool room. 

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• How it works: An air-source heat pump extracts warmth from the outside air and transfers it to the pool water or the air in the pool hall. Some advanced units can perform dehumidification as well.

• Pros:

  • Energy-efficient: A very cost-effective way to heat both the pool water and the air.

  • Versatile: Some models can be reversed to provide cooling in the summer.

• Cons:

  • Humidity control limitations: May not provide the same level of precise, dedicated dehumidification as a system designed specifically for it. 

 

Regardless of the system type, the best H&V solutions for indoor pools will include these essential features:

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• Dehumidification: This is the primary function, removing excess moisture to prevent condensation, mold, and damage to the building.

• Heat recovery: Recovers wasted energy from the moist exhaust air to pre-heat incoming fresh air or pool water, drastically reducing energy costs.

• Corrosion resistance: All components, especially air inlets, grilles, and diffusers, must be made of materials resistant to corrosion from pool chemicals. Aluminum is often an ideal choice.

• Precise controls: Allows you to set the optimal air temperature and relative humidity (ideally 50–60% RH) for bather comfort and building protection.

• Adequate ventilation: Ensures a sufficient amount of fresh air is introduced to maintain good indoor air quality and disperse airborne chloramines. 

 

The right choice depends on your specific needs:

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• For residential pools: A wall-mounted heat pump dehumidifier is often a practical, cost-effective solution for smaller spaces.

• For large residential or commercial pools: A ducted environmental control system provides the best performance for air quality, energy efficiency, and preventing long-term structural damage.

• For maximum energy efficiency: Choose a system with advanced heat recovery and consider incorporating a separate heat pump for water heating.

 

Design conditions and calculations

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• Temperature control: Maintain the air temperature 1 to 2°C warmer than the pool water temperature. This minimizes evaporation, which lowers humidity and heating costs. A common range is 28°C to 30°C air temperature and 25.5°C to 28°C water temperature.

• Humidity control: Keep relative humidity (RH) between 50% and 60%. Too high can lead to mould and corrosion, while too low increases evaporation and costs. A setback mode can lower temperature and humidity when the pool is covered and unoccupied, significantly saving energy.

• Prevent condensation: Condensation forms on surfaces cooler than the air's dew point. A high dew point is common in pool rooms, making effective insulation and strategic airflow crucial. To combat this:

  • High-quality insulation: Properly insulate all walls and the roof.

  • Vapor barrier: Install a continuous vapor barrier on the warm side of the ceiling and walls to prevent moisture from reaching cooler surfaces within the building structure.

  • Thermal breaks: Use thermally broken windows and door frames to stop cold spots.

  • Blanket windows with air: Direct supply air across windows and other cold exterior surfaces to raise their surface temperature and prevent condensation. 

 

Air quality and distribution

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• Ventilation and exhaust: Proper ventilation removes harmful airborne chloramines, which can cause respiratory and eye irritation.

  • Fresh air: Introduce outside air per local codes and ASHRAE Standard 62 to dilute contaminants.

  • Negative pressure: Keep the pool room under slight negative pressure relative to adjacent areas (typically 0.05–0.15 in. w.g.) to prevent humid, chemically laden air from migrating.

  • Source capture exhaust: For spas and hot tubs, install exhaust grilles directly above the water surface to remove the highest concentrations of pollutants at the source.

• Air changes: Aim for 4 to 6 volumetric air changes per hour for regular natatoriums, or 6 to 8 for spectator areas, to avoid stagnant air.

• Air velocity: Minimize air velocity over the pool surface (below 30 feet per minute) to avoid excessive evaporation.

• Duct design and materials:

  • Corrosion-resistant materials: Choose aluminum or high-grade PVC ductwork and components, as the chlorine-rich environment will corrode untreated steel.

  • Distribution layout: A U-shaped ductwork layout with supply vents along exterior walls and return grilles on the opposite interior wall is highly effective.

  • Acoustics: Use large, well-insulated ductwork and flexible connectors near the equipment to minimize noise and vibration transfer. 

 

Equipment and energy efficiency

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• Integrated HVAC system: Use a dedicated pool dehumidifier (often called a pool climate control system) that combines dehumidification, air heating, and pool water heating into a single unit.

• Heat recovery: The most energy-efficient systems use heat recovery, which captures waste heat from the dehumidification process and transfers it back into the pool water or air.

• Automated controls: Use advanced controls, like sensors for humidity and volatile organic compounds (VOCs), to optimize energy usage based on occupancy and air quality needs.

• Energy-efficient components: Look for systems with variable-speed fans, high-efficiency heat pumps, and modern automation to reduce running costs.

• Plant room: Ensure the equipment plant room is properly sized, insulated, and positioned away from occupied spaces to reduce noise. 

 

Strategic planning and execution

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• Early collaboration: Involve architects, engineers, and pool specialists at the design stage to ensure seamless integration and avoid problems later.

• Consider construction: Use construction materials resistant to moisture damage and corrosion. Insist on quality glazing with thermal breaks to manage condensation.

• Maintenance plan: Put a plan in place for regular inspections and maintenance to ensure the longevity of the HVAC system.