Quick answer: The cost of an indoor pool dehumidification system is set mainly by one number: how much water evaporates from the pool. That depends on the water area, the water and air temperatures, the humidity you hold and how busy the pool is. Calculate it first; it fixes the equipment size, the power supply, the ducting and most of the running cost. The two biggest savings are a pool cover when the pool is closed and recovering the heat the dehumidifier releases back into the hall.
Quick answer
- Size from evaporation (kg/h), not floor area. A 100 m² hotel pool can evaporate around 400 L/day at peak.
- Hold the hall at about 50–60 % RH with air 1–2 °C warmer than the water.
- Covering the pool when closed can save 50–70 % of pool heating costs (US DOE).
What makes up the cost
| Cost line | What decides it |
|---|---|
| Dehumidifier | Capacity needed at the hall condition, corrosion protection, heat recovery options |
| Air distribution | Ducts, supply grilles along cold glazing, return location, insulation, corrosion-resistant materials |
| Ventilation | Outdoor air required by code, its heating in winter, exhaust |
| Electrical and drainage | Supply size, protection, condensate route |
| Controls | Humidistat or BMS link, staging, alarms, cover-mode setback |
| Installation and commissioning | Access, lifting, plant room, testing |
| Running cost | Hours, power input, electricity price, heat recovered, maintenance |
Every line depends on the evaporation load, so calculate it before collecting quotes.
Step 1: Calculate the evaporation
The ASHRAE Handbook—HVAC Applications (Natatoriums) gives an empirical equation for pool evaporation. In SI units:
W (kg/h) ≈ 0.144 × A × (p_w − p_a) × F_a
- A = pool water surface area, m²
- p_w = saturation vapor pressure at the water temperature, kPa
- p_a = vapor pressure of the hall air, kPa
- F_a = activity factor
| Pool type | Activity factor F_a |
|---|---|
| Residential | 0.5 |
| Condominium, therapy | 0.65 |
| Hotel | 0.8 |
| Public, school | 1.0 |
| Whirlpool, spa | 1.0 |
| Wave pool, water slides | 1.5 or more |
Worked example: 100 m² hotel pool
- Water at 28 °C: p_w = 3.78 kPa
- Hall air at 30 °C, 55 % RH: p_a = 0.55 × 4.25 = 2.34 kPa
- Difference: 1.44 kPa
- W = 0.144 × 100 × 1.44 × 0.8 ≈ 16.6 kg/h, about 400 L/day if the pool were busy all day
Then add:
- outdoor air: in summer it can add moisture; in winter it removes some, but must be heated;
- people and wet decks: included in the activity factor for typical use; add extra for large deck areas or splash features;
- margin: for peak periods and future use.
Most pools are not at peak all day. A schedule with busy and quiet hours, and a cover at night, cuts the daily total.
Step 2: Pick the hall condition
| Setting | Typical range | Effect on cost |
|---|---|---|
| Air temperature | 1–2 °C above water temperature (ASHRAE guidance) | Warmer air reduces evaporation; much warmer is uncomfortable |
| Relative humidity | 50–60 % | Lower RH increases evaporation and running cost; higher RH risks condensation on glazing and structure |
| Water temperature | Set by use: competition pools cooler, leisure and therapy warmer | Warmer water evaporates more |
Holding 40 % RH instead of 55 % does not make the hall "safer"; it pulls more water out of the pool and costs more to run. Protect cold surfaces instead: supply dry air along windows and skylights, and insulate the envelope.
Step 3: Choose the system type
| Option | When it fits | Cost notes |
|---|---|---|
| Refrigerant dehumidifier with heat recovery | Most hotel, school, club and residential pools | Returns condensation heat to the hall air or pool water; lowest energy per litre at pool conditions |
| Ducted refrigerant dehumidifier | Halls where air must reach glazing and corners evenly | Duct cost rises with hall size; check fan external static pressure |
| Ventilation only (outdoor air with heat recovery) | Climates and seasons when outdoor air is dry | Low equipment cost; fails in humid weather and heats a lot of air in winter |
| Combined ventilation + dehumidification | Large public pools | Highest first cost; each part does the job it is best at |
Step 4: Estimate the running cost
Daily energy cost = power input (kW) × running hours × electricity price
Example: a dehumidifier with a maximum power input of 8.4 kW running 12 hours at full load, at €0.20 per kWh, costs at most about €20 a day. The real figure is usually lower because the unit cycles on its humidistat.
Two effects make a refrigerant pool dehumidifier cheaper to run than the electricity alone suggests:
- Heat recovery: condensing 1 kg of water releases about 0.68 kWh of heat. At 16.6 kg/h, that is around 11 kW returned to the hall, plus the compressor and fan power, which also ends up as heat. In a heated hall this offsets space or water heating.
- Less ventilation heating: every cubic metre of outdoor air you do not need for humidity control is a cubic metre you do not heat in winter. Outdoor air is still required for air quality; see Step 6.
See dehumidifier power consumption for how to calculate litres per kWh.
Step 5: Cut the load before you buy
| Measure | Why it lowers cost |
|---|---|
| Pool cover when closed | The US DOE notes that covering a pool when it is not in use can cut pool heating costs by 50–70 %, and reduces evaporation and ventilation needs (US DOE Energy Saver) |
| Night setback of activity, not of RH | With the pool covered, the dehumidifier can run at low duty |
| Correct air/water temperature difference | Air 1–2 °C warmer than the water reduces evaporation |
| Turn off splash features when not needed | Fountains and slides multiply the activity factor |
| Seal and insulate the hall | Fewer cold surfaces, less condensation risk, less infiltration |
Related: US DOE Energy Saver.
Step 6: Ventilation and water chemistry
A dehumidifier controls moisture; it does not replace outdoor air. Indoor pools need ventilation for air quality and to dilute chloramines from the water; ASHRAE Standard 62.1 sets minimum outdoor-air rates, and local codes may set more. Keep the hall slightly negative to the rest of the building so humid, chlorinated air does not spread. Water chemistry is controlled by the water treatment system.
Step 7: Protect against corrosion
Pool air is warm, humid and contains chlorine compounds. Ask for:
- coated or corrosion-resistant coils;
- stainless or coated casing and fixings;
- ducts and grilles in materials suited to pool air;
- the unit placed in a plant room where possible, with ducts into the hall.
What to send for a quote
- Pool water area, depth profile and water temperature
- Pool type and opening hours (hotel, school, public, private)
- Hall dimensions, glazing area and outdoor climate
- Target air temperature and RH
- Cover use, splash features, deck area
- Ventilation equipment already planned
- Power supply, plant room location and drain route
We will calculate the evaporation with you, show the dehumidifier capacity at your hall condition (not only at the 30 °C/80 % RH rating), and propose the layout. Compare our floor-standing industrial dehumidifiers and ceiling-mounted and ducted units.
FAQ
Frequently asked questions
How much does it cost to dehumidify an indoor pool?
It depends on the evaporation load, the system type and your electricity price. Calculate evaporation first; then the equipment size, installation scope and running hours can be priced. Running cost = power input × hours × electricity price, minus the value of heat recovered.
What size dehumidifier do I need for an indoor pool?
Use the evaporation equation above. A 100 m² hotel pool at 28 °C water and 30 °C/55 % RH air evaporates around 16–17 kg/h at peak. Choose a unit whose capacity at the hall condition covers that load.
What humidity should an indoor pool be?
About 50–60 % RH, with air 1–2 °C warmer than the water.
Can I use ventilation instead of a dehumidifier?
In dry, mild weather, yes. In humid weather, outdoor air cannot dry the hall, and in cold weather heating the extra air is expensive. Most pools use both.
Does a pool cover really save money?
Yes. Covering the pool when closed cuts evaporation, ventilation and pool heating; the US DOE puts heating savings at 50–70 %.
Sources
- ASHRAE Handbook—HVAC Applications, Natatoriums.
- ANSI/ASHRAE Standard 62.1, Ventilation and Acceptable Indoor Air Quality.
- US Department of Energy, Energy Saver: Swimming pool covers.
- ASHRAE Handbook—Fundamentals, Psychrometrics.
