Pool Heating Load Calculator

Calculator Inputs

Unit System

Environment

Volume Input Mode

Pool Length (m)

Pool Width (m)

Average Depth (m)

Current Water Temperature (°C)

Target Water Temperature (°C)

Time to Reach Target (hours)

Air Temperature (°C)

Relative Humidity (%)

Wind Speed (m/s)

Use Pool Cover

Ground U-Value (W/m²·K)

Lower is better insulation.

Ground Temperature (optional) (°C)

If blank, air temperature is used.

Heater Efficiency (%)

Safety Factor (%)

Covers weather swings and uncertainties.

Example Data Table

Scenario	Surface Area	Volume	Temps (Now→Target)	Air / RH / Wind	Cover	Warmup Time	Result (Approx.)
Outdoor residential	50 m²	75 m³	26°C → 30°C	20°C / 60% / 2 m/s	Yes (60%)	8 hours	~35–55 kW
Indoor small pool	30 m²	45 m³	27°C → 29°C	26°C / 55% / low	No	6 hours	~12–25 kW
Outdoor windy day	60 m²	90 m³	24°C → 29°C	18°C / 50% / 5 m/s	No	10 hours	~45–80 kW

Values above are illustrative. Use the calculator for project-specific inputs.

Formula Used

Warmup power: P_warm = (m · c_p · ΔT) / t
Evaporation loss: Q_e = 0.1 · A_ft² · (P_w−P_a) · (25 + 19V_mph)
Convection loss: Q_c = h · A · (T_w − T_a), with h ≈ 2.0 + 2.5V
Radiation loss: Q_r = εσA (T_w⁴ − T_sky⁴)
Ground conduction: Q_g = U · A · (T_w − T_g)
Total heater input: P_in = ((P_warm + Q_loss) · (1+SF)) / η

Notes: vapor pressures use a standard saturation correlation, radiation uses an approximate sky temperature, and cover reduces evaporation and radiation by a user percentage.

How to Use This Calculator

Select unit system and pool environment.
Enter dimensions or switch to direct volume mode.
Set water temperatures and desired warmup time.
Provide air temperature, humidity, and wind speed.
Enable a cover and its reduction percentage if used.
Enter efficiency and a safety factor, then calculate.
Download CSV or PDF for project documentation.

Tip: Wind strongly affects evaporation losses outdoors. A cover can reduce heater size and operating cost substantially.

Technical Article

Why heating load matters during planning

Pool heating capacity affects electrical demand, gas sizing, plantroom ventilation, and operating budgets. Underestimating load leads to slow warmups and unstable setpoints, especially in cool nights or windy conditions. Overestimating load increases capital cost and can reduce efficiency at part load. This calculator provides a structured estimate using warmup energy and steady losses.

Warmup energy and scheduling strategy

Warmup power is based on water mass, specific heat, and required temperature rise over a selected time window. Shorter schedules need larger heaters, while longer schedules reduce peak power and may allow smaller utilities. For commercial sites, scheduling warmup before occupancy can reduce peak demand charges and improve comfort predictability.

Heat loss drivers at operating temperature

Evaporation is usually the largest loss for outdoor pools and increases with wind and low humidity. Convection scales with air–water temperature difference and airflow. Radiation depends on sky conditions and water temperature. Ground conduction depends on construction and insulation quality. Using a cover can sharply reduce evaporation and radiation.

Design factors and equipment selection

Efficiency converts required delivered heat into input power. A safety factor accounts for weather swings, measurement uncertainty, and operational events such as frequent bather load or splash-out. Select heaters with adequate modulation, corrosion resistance, and compatible control integration. Use the loss breakdown to evaluate covers and insulation upgrades.

Example data for a quick check

The following example reflects a common residential scenario and helps validate inputs before final sizing.

Length	Width	Avg Depth	Now → Target	Air / RH / Wind	Cover	Time
10 m	5 m	1.5 m	26°C → 30°C	20°C / 60% / 2 m/s	Yes (60%)	8 h

Use site conditions and construction details for final design decisions.

FAQs

1) Should I size the heater for warmup or for steady losses?

Size for the larger of warmup demand and steady losses, then add a safety factor. If warmup time is flexible, you can reduce heater size by allowing longer heat-up schedules.

2) Why does wind increase the required heating load so much?

Wind increases evaporation and convective heat transfer at the water surface. Evaporation carries large latent energy, so even small wind changes can significantly raise heating requirements.

3) How does a pool cover affect the calculation?

A cover mainly reduces evaporation and radiation losses. Enter a reduction percentage that matches your cover type. This can lower the required heater input and reduce ongoing operating cost.

4) What ground U-value should I use?

Use project insulation details if available. Higher U-values mean more heat loss to the ground. If uncertain, use a conservative value and include an appropriate safety factor.

5) Can I use this for indoor pools?

Yes. Select the indoor option to limit wind effects. For indoor pools, humidity control and ventilation rates still influence evaporation, so use realistic air temperature and relative humidity inputs.

6) Why is heater efficiency included?

The model estimates heat needed by the water. Efficiency converts that delivered heat into input power. Lower efficiency requires higher input capacity for the same delivered heating performance.

7) What safety factor is reasonable?

Many projects use 5–15% depending on exposure, data confidence, and operational variability. Use higher values for windy sites, uncertain construction, or tight warmup schedules.