How Long Does It Take to Heat a Pool With a Heat Pump?

When it's time to purchase a heat pool pump, one of the first questions that comes to mind is:  how fast does a pool heat pump heat water?

Well, most heat pumps warm the pool gradually, by raising the temperature 1°F to 2°F per hour.  To put that into perspective, heating an average-sized pool by 10°F can take anywhere from 10 hours to a full day. However, the number isn’t fixed as the time duration may vary as per the pool size, water volume, weather conditions, and more.

In this blog, we’ll explore in detail about the pool heat pump heating time, factors that affect performance, and tips to speed up the process.

Average Pool Heating Time by Temperature Increase

The average time to heat a pool heat pump is the difference between the existing water temperature of your pool and the desired temperature. The larger the temperature increase requested, the longer the run time for your pool. Even a temperature increase of a few degrees requires a large amount of thermal energy. Besides, factors including ambient air temperature and humidity also dictate your pool heating time. The following table outlines the time taken by an average heat pump to heat the pool as per the outdoor temperature  

So, if you're wondering how long to heat pool 10 degrees, the answer is 10 to 20 hours under average conditions. For larger increases, like how long to heat pool 20 degrees, you may need 24 to 48 hours or more.

Key Factors That Affect Pool Heating Time

How fast pool heaters heat water depends on various factors listed below:

Pool Size and Water Volume

Pool size and water volume is indirectly proportional to the heating speed of a heat pump. The higher the gallon capacity (the total volume of water needed to be heated), the more energy the heat pump requires to heat the water. This means:

• Smaller pools (around 8,000–10,000 gallons) heat at a faster heating speed because the heat pump requires a low amount of energy to warm a low volume of water in the pool.

• Larger pools (15,000–25,000 gallons or more) take a longer time to heat since the heat pumps require a high amount of energy to function, which slows the heating speed. 

Heat Pump BTU Capacity

The BTU metric, which stands for British Thermal Units, measures the heating capacity of a pool heat pump. The BTU output directly impacts the healing speed and overall heating rate of a swimming pool. 

• Pumps with higher BTU ratings raise the temperature quickly. Since these units can move more thermal energy into the water, it speeds up the heating process.

• On the other hand, a unit with low BTU capacity slows down the heating speed, especially for larger pools, as it transfers less energy into the water and takes more time to heat. 

Let's compare how various BTU capacities affect the performance and speed of a heat pump.

Outdoor Air Temperature

In regions with warmer air, it is easier for the heat pump to capture and transfer heat. However, when air temperatures drop, the heat pump has less available heat to draw from, which can slow down the heating process.

• Warm air temperatures (around 70°F): When the air is warmer, the heat pump can easily capture, extract, and move more heat into the pool water. Thus, warm air helps to heat the pool faster and raise the water temperature quickly.

• Cooler air temperatures (below 50–55°F): In colder regions or lower temperatures, the heat pump struggles to perform efficiently, which in turn reduces the heating speed and overall rate. 

• Humid Air: Since damp air consists of more thermal energy than dry air, humidity can help a heat pump to function more effectively, increasing the pool’s temperature quickly.

Pool Cover Usage

Did you know? Evaporation makes up to 70% of a pool’s heat loss. To prevent this, it is advised to use a pool cover, which prevents the heat from escaping. The usage of a pool cover helps to raise your pool’s temperature at a faster rate.

Let's look at the numbers displaying the performance of a heat pump with and without a pool cover:

Wind and Weather Conditions

Many pool owners fail to realize this, but wind can be a "silent killer" of pool warmth and is the cause behind your pool’s heat loss. When a breeze blows across the surface of the water, it leads to evaporative cooling. This means the breeze carries the heat away from the water.  

For pools situated in high-wind areas without a windshield, heat pumps have to put in more effort to replace the thermal energy being carried away by the wind. It translates to low efficiency of heat pumps, thus leading to a slow heating process.

The table below displays how the wind and weather conditions have an impact on the efficiency and speed.

Example Heating Scenario

With this example, we’ll calculate how long it takes to raise the temperature from 70°F to 82°F for an average 15000-gallon pool with a 90,000 BTU heat pump raising the water from 70°F to 82°F (a 12°F or 6.7°C increase). 

• If we consider moderate conditions, that is, outside air temperature stands at 70°F, a pool cover is judiciously used, and there’s no extreme wind blowing through the area, the heat pump can deliver 0.8-1.2°F per hour. That is, in an ideal climate, it takes up to 12-18 hours for a heat pump to warm the water to 82°F. However, the desired temperature can also affect the time and heating speed. For instance:

• A modest 8°F rise (e.g., 70°F to 78°F) will require 8-12 hours.

• A higher temperature request of 16°F rise (e.g., 70°F to 86°F) may take up to 16-24 hours.

• In regions with lower temperatures (50°F or less) or no cover, the best-case scenario is 18 to 27 hours. However, the time taken may increase by an additional 30 to 50% time due to heat loss.

• Units with higher BTU capacity, like 125,000, can increase the heat pump pool heating rate upto 1.5°F/hour and cut down the time taken to heat the pool pump by 8 to 12 hours.

Heat Pump vs Gas Heater Heating Speed

There exists a significant difference between the speed of heat pumps and gas heaters. Gas heaters, recognized for delivering "on-demand" warmth, raise a pool’s temperature by 2°F to 5°F per hour. This is because they use a strong fuel combustion process that creates heat directly from scratch. Owing to this process, these units can warm the pool quickly, in a matter of a few hours. 

On the other hand, a heat pump is widely known for warming the pool temperature consistently. These units deliver a steady rise in temperature of 0.5°F to 1°F per hour, taking up to 24 to 72 hours to heat the pool. However, in the long run, heat pumps tend to be more cost-effective and consistent. 

Tips to Heat Your Pool Faster With a Heat Pump

To increase the efficiency of your heat pump so that it can warm your pool faster, follow the tips listed below:

• Make daily use of a pool cover: A pool cover prevents heat loss by 40-50%. The usage can shorten the gap of 24-hour heat-up to 12-16 hours. 

• Match the size of your heat pump to the size of your pool: The size of your heat pump should be adequate and appropriate to the size of your pool. It is advised to choose a 100-150 BTU capacity of a heat pump per gallon to increase speed by 50%. For instance, a 125k BTU capacity heat pump for 15k gallons will warm the pool at 1.5°F/hour vs. 0.8°F.

• Make use of a heat pump during the warmest hours: For faster heating, use your heat pump when the temperature is above 20°C as it can raise the speed by 20-30%. Avoid the use of a pool heat pump during nights because the efficiency drops.

• Place the pump in a good airflow:  With good airflow around the heat pump, it can improve the COP (coefficient of performance) by 10-20%. To further boost the speed, clear two to three feet of area around the side of the pump. 

• Clean filters, refrigerants and other components: A properly maintained heat pump with clean filters, refrigerant, and non-clogged pipes can function at 1-2°F/hour. Besides, the efficiency in neglected units can drop upto 25%.

• Target 26-28°C as desired temperature: the optimum temperature for the heat pump should be between 26- 28°C, as it avoids the overuse of the pump and saves 15-25% time.

Is a Pool Heat Pump Worth the Heating Time?

Yes. The heat pump pool temperature increases by 0.5-2°F per hour to 0.5-2°F, taking up to twelve to forty-eight hours to warm the swimming pool. In mild climates, these systems work at maximum efficiency, saving 60-80% energy as compared to gas heaters or other units.  Though the heating time may seem long, it suits most residential owners, due to low operating cost, which amounts to $0.05-0.15 per hour. Besides, with a lifespan of five to ten years, the maintenance cost is also minimal. All in all, investment in a heat pump is worth the cost, time, and all the fun you’ll have swimming. 

Final Thoughts

If you’re considering purchasing a heat pump, it's better to set your expectations straight from the start. Ask yourself these questions: do you want to use pools on a weekly basis, throw last-minute parties or spontaneous gatherings? Your answer will ultimately determine how much heating time you’re willing to work with.

Find the right system for your pool with Varminpool’s range of energy-efficient heaters. 

Frequently Asked Questions

How many degrees per hour does a pool heat pump heat?

Pool heat pumps can heat water temperature around  0.5-2°F per hour, when the conditions are normal. However, the temperature may vary depending on the BTU capacity, pool size, air temperature, etc. For instance, the rate at which a 15k gallon pool with 100k BTU capacity in 70°F outside temperature, will heat is 1-1.5°F per hour. In colder climates (below 50°F) , you can expect these rates to be halved. Meanwhile, when the temperature exceeds 80°F, the rate speeds up to 2°F.

Can a heat pump heat a pool overnight?

Yes. A heat pump can pool overnight. However, the heating speed and temperature is less efficient during nighttime. It is advised to use a pool cover to prevent the heat from escaping during these hours, as the temperature drops and the heat loss is higher. 

How long does it take to heat a pool 10 degrees?

To heat a pool by 10°F with a heat pump will take around 10 to 20 hours. However, the time duration still varies as per the pool size, water volume, outside air temperature, windy conditions, and other factors.

Does pool size affect heating time?

Yes, the size of the pool is directly proportional to the heating time. The larger the pool size, the more time is required to heat the pool, and vice versa.  Therefore, a heat pump must be bought only after considering the size of the pool.

Can you run a heat pump continuously?

Yes, the best part about heat pumps is their usage for extended hours. With continuous operation, they heat the pool at a steady and consistent rate, raising the pool’s temperature slowly. However, many systems now come up with built-in thermostats or automation controls. Once the pool is warmed up to the desired temperature, these features will switch off the pump.