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What Size Pool Heater For 18000 Gallons

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Sizing The Pump For Your Swimming Pool

DIY Pool Heater – $50 Solar Heater

You might think bigger is better in terms of pump size, but a pump that is too big can cause serious problems.

The first step in sizing your pool is to know the volume of water in your pool, which is the average depth:

Calculation Example

Measure the shallow end depth. 4 feet

Measure the deep end depth. 12 feet

Add them together. 16 feet

Divide by two. 16 ÷ 2 = 8 feet

In the example above, the pools average depth is 8 feet.

Now use the formulas below to determine the volume of water in your pool.

  • Circular Pools: Diameter x Diameter x Average Depth x 5.9 = Total pool capacity in gallons
  • Oval Pools: Length x Width x Average Depth x 6.7 = Total pool capacity in gallons
  • Rectangular Pools: Length x Width x Average Depth x 7.5 = Total pool capacity in gallons

Once you know the volume of water in your pool, youre ready to calculate the flow rate and turnover required to circulate the water in the number of hours you want.

Let A Pool Heating Professional Do The Work

A trained pool heating professional can perform a proper sizing analysis for your swimming pool to determine the correct pool heater size that you need. Well provide you with product features and details on our complete line of heat pumps and heaters. If you have questions, please feel free to call us at 1-800-741-9956. Our team of friendly pool experts will answer any questions you may have and offer technical advice in selecting the model that is right for your pool.

Pool Heater Sizing Calculator And Rules

The core guidelines for sizing your heat pump pool heater are as follows:

  • Determine the desired temperature of water in °F.
  • Determine the average air temperature for the coldest month in which you plan to use your swimming pool in °F.
  • Subtract the average air temperature from the desired water temperature to get the required temperature rise.
  • For size at 4 BTUs per gallon or 1 BTU per liter of water to heat water in normal summer conditions when the ambient air temperature is about 70°F in a 24-hour period.
  • For size at 5 BTUs per gallon or 1.3 1.5 BTUs per liter of water to heat in the normal spring and fall conditions when the ambient air temperatures average 60°F in a 24-hour period.
  • For size at 6 BTUs per gallon or 1.5 BTUs per liter of water to heat in the normal spring and fall conditions when the ambient air temperatures have an average of less than 60°F in a 24-hour period.

The surface area of a swimming pool in feet2 can be calculated as follows:

  • Circular pools: radius x radius x 3.14
  • Oval-shaped pools: x x 3.14
  • Kidney-shaped pools: length x width x 0.75
  • Rectangular pools: length x width
  • The required BTU output per hour is calculated as follows:

    Surface area x temperature rise x 12

    If you cant directly get these measurements and calculations by yourself, you can ask the suppliers of your pool heat pump to do it for you. Chances are high that you already have these measurements from the people who sold or built your pool.

    Pool Heat Pumps/Filters

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    How To Save Money On Pool Heater Operation

    One of the best ways to save money on pool heater operating costs is to purchase a pool cover. A pool cover costs around $650 to $2,350 to install. Installing a pool cover will reduce heating costs anywhere from 50% to 90%. They also have no operating costs.

    Solar blankets are another type of pool cover used to help pools retain heat. The cost of a solar blanket will fall between $50 to $500.

    You could also opt to build a pool enclosure. The cost of building a pool enclosure will fall between $5,300 and $15,600 on average. While the pool is still technically outside in a non-climate controlled area, putting the pool in a glass enclosure will help the inside maintain heat similar to a greenhouse.

    Compare Pool heater Installation Quotes

    How To Calculate The Volume Of Your Pool

    ComforTemp 95,000 BTU Heat Pump

    To calculate the volume in cubic feet you multiply the surface area by the average depth.

    example : 800 x 3 = 2400 cubic feet.

    Convert to gallons

    Volume = 7.5 x the calculated pool volume.

    7.5 is a constant used to covert the volume to gallons. )

    Using our example of a square pool: 7.5 x = 18,000 Gal.

    Calculate the BTUs required

    For these calculations, lets consider an outdoor pool of 40 x 20 with an average depth of 3. We want to heat it from 60°F to 80°F in about 48 hours while the outside air temperature is 60°F. The wind speed is moderate. We will calculate the total required heat to increase and maintain the temperature:

    First, we calculate the BTUs needed to heat the pool to the desired temperature . Next, we estimate the BTUs that are used to contain the temperature losses due to evaporation .

    Total BTU = Heat up BTU + Surface BTU


    Total BTU = Total heat load in BTU/hr.

    Surface BTU = Heat loss from the pool through the surface mainly through evaporation of water in BTU/hr.ef

    Heat up BTU = Heat load required to increase the pool temperature

    VIDEO | Watch this informative video Pool Heaters vs Heat Pumps

    To heat the pool from cold

    To heat one gallon of water by 1°F, you need 8.34 BTU. Therefore:

    Heat up BTU = 8.34 x Volume x dTw ÷ H time

    dTw = difference between the initial temperature and the final temperature of the pool water

    H time = Time to heat the pool we use 48 hours, but a longer period will enable us to use a smaller unit

    e.g. 5 x x = 80000

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    Is An Electric Pool Heater Worth It

    The overall cost of ownership of an electric pool heater is less than that of a gas heater if you live in a relatively warm climate. In cooler climates, there may be more financial costs in the long run for energy use. In terms of reliability and flexibility though, an electrical pool heater has advantages that gas heaters cant often match.

    A Swimming Pool Chemical Calculator

    Adjust sliders to calculate the time needed to heat the pool.

    This calculator is approximate because it doesnt account for the many factors that impact heat loss in the swimming pool. The exact time needed to change the pool temperature will vary based on evaporation rate, convection losses, thermal radiation losses and conduction losses . One of the easiest ways to reduce heat loss is by using a pool cover it can reduce convection losses between 15%-25%. Always oversize when purchasing a pool heater. An undersized pool heater takes longer to heat and cost more money to operate.

    More About Pool Heat

    Pool Heat Evaporative Losses:

    Swimming pool water on the surface is continually transitioning to water vapor. The heat energy used during the transition to water vapor is lost from the body of water reducing the overall temperature. Evaporative losses can account for 50% of swimming pool heat loss.

    Convection Losses

    Convection losses are similar to evaporative losses in that they are both related to environmental conditions impacting the surface area of the pool. Convection losses occur when air contacts the surface area and heat energy is transferred. This effect is similar to the chill felt on the skin from the breeze when exiting the pool. Convection losses can be responsible for 15%-25% of heat energy loss. These losses can easily be reduced with the use of a pool cover.

    Thermal Radiation Losses

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    How Long To Run Your Variable Speed Pool Pump

    When people upgrade from a single speed pool pump to a variable speed pool pump they often continue to run their pump from eight to 10 hours a day, just as they did with their single speed pump. However, it is important to note that a variable speed pool pump should ideally be running 24 hours a day to ensure proper and optimal water circulation.

    When your pool pump is not running, the water is sitting stagnant in your pool allowing bacteria to survive and grow. Additionally, any method of water disinfection you use is not able to work properly when your water is not circulating. This can lead to health hazards because even if you turn the pool pump off only when you are not using the pool, once you turn the pump back on it will take some time before that stagnant water is fully disinfected.

    While running your pool pump 24 hours a day may subtract from some of the energy savings you gain by switching to a variable speed pool pump, it will be worth doing in order to have peace of mind that your pool water is healthy.

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    How Large Should My Heat Pump Be

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    Without getting too much into the scientific computations, the easiest way to do this is to assume that it takes 1.16 Wh to heat one litre of water up by one degree. Taking this number, we know that it takes 11.6kWh to heat up a 10,000 litre pool by one degree Celsius in an hour.

    To further simplify things, we have created a table that can give you an idea of how fast different sized pool heat pumps can raise the temperature of your water so that you can have a rough idea of the size youll need for your pool before going to look at the specific models.


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    Is 40000 Btu Good For A Patio Heater

    Patio heaters that are freestanding have an output of 40,000 BTUs per hour on average. This can heat a room with a circumference of 20 feet, which can accommodate a medium-sized gathering. If you want to heat a room with a circumference of 10 feet or less, get a unit with an output of 20,000 BTUs per hour. This can be used for small gatherings.

    How Much Does A Pool Heat Pump Cost

    They can cost less to run than gas heaters, but may also cost more upfront because of their unique heat-generating ability. They also last longer than gas heaters, too.

    Pool heat pump prices range from $2,000 to $3,000 and can go as high as $4,000 to $5,000.

    Of course, the cost to run it will depend on where you live. For example, if you live in a warmer climate, it will cost less to run.

    Maintaining an outdoor pool in Florida at 80°F year-round can cost about $1,400 annually, but only about $300 if you use a solar cover.

    In the Northeast United States, maintaining an outdoor pool at 80°F from May to August costs about $1,100 annually, but only around $120 with a solar cover.

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    Best Inground Gas Pool Heater: Hayward Universal H

    The Hayward Universal H-Series Gas Heater comes as either a natural gas or propane pool heater. Its available in a variety of sizes, ranging from 150,000 BTU to 400,000 BTU. And its an environmentally-friendly option for those in locations where low-NOx emissions are required. Keep in mind that youll likely have to pay to install it: professional installation is recommended to ensure plumbing and gas lines are handled correctly.

    With a properly sized heater for your pool, you can expect the temperature to increase by one to two degrees an hour. A 40,000 BTU heater will warm a 33,000-gallon pool from 77 to 86 degrees in eight hours. Once it arrives at the set temperature, it will kick on a few times a day to maintain it.

    Looking for another natural gas option? We recommend the Raypak Natural Gas Pool Heater.

    Why Is Pool Heat Pump Sizing Important

    ComforTemp 95,000 BTU Heat Pump

    A heat pump works by drawing in warm air from the outside environment and injecting it into the pool water.

    Measuring output in BTUs, it runs on electricity and therefore takes a longer time to heat your pool when compared to a gas heater.

    Note: The British Thermal Unit is a unit of measurement that measures thermal energy. Electric heat pumps have BTU ratings in the range of 50,000 to 150,000. Calculating the amount of BTUs required will help you determine the size of the heater for your pool.Smaller inground pools and above ground pools can get away with using a 50,000 BTU heat pump, but if you have a large pool youll need something bigger. A small pump on a large pool means it will be very slow to heat and might not even reach the desired temperature youre aiming for.

    Generally speaking, you should oversize the heat pump as much as possible. Youll never regret going too big, as doing so means warming the pool at a faster rate without running the heater as much.

    With that being said, there are still some things you should consider when sourcing a heater for your pool, so lets talk about those.

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    How Does The Pool Heater Work

    Pool heaters use a gas that burns the water that the pump filters from the pool. The gas then starts heating up the filtered water in the combustion chamber. As a result, hot water will return to the pool.

    However, the pool heater is not the primary source of the heating process. There are a lot of things happening in the system before hot water is produced.

    See below for what happens in the pool heating process.

    Hayward W3sp2303vsp Maxflo Pool Pump

    One of the most energy efficient units available, this pump from Hayward is made for you if youre looking to reduce your energy costs. It includes a large strainer basket, making it easy to clean, and it can be installed on a variety of pools. You can install it on systems and set it in stand-alone mode or you can connect it to competitive control systems to really take control of your pools filtration systems.

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    Your Climate And Swim Season

    The local climate and the length of your swim season influence the type and size of the pool heater you need. For a warmer climate, any type of pool heater will work. You could also purchase a smaller unit since the heater doesnt have to work as hard to maintain your ideal pool temperature.

    If, however, you want a year-round swimming season, even in a warmer climate, you may need a more powerful heater like a gas heater.

    How To Properly Size A Pool Heat Pump

    How to make a pool heater under $100

    Heating or warming up a swimming pool with a pool heat pump is different from heating or warming it up with a traditional pool heater. What are traditional pool heaters? These are your electric pool heaters and heaters that use natural gas. The main difference for these types of heaters is that with your traditional pool heaters, theyre actually actively producing heat to warm up your pool, which is why their output is measured by BTUs . Pool heat pumps on the other hand simply transfer the heat from the air to your water, so computations and numbers like BTUs can be a little bit off as it is directly affected by the temperature of the air. The colder the air surrounding your heat pump, the less heat is being transferred to the water and vice versa.

    Before we dive on to the details of how to properly size a pool heat pump, here’s our pool guru Tom with a quick overview of our best-selling pool heat pump, the Water TechniX Paradise Pool Heater!

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    The Best Natural Gas Pool Heater

    Its compact size makes it ideal for both inground and above ground pools. The Raypak features a digital thermostat dial.

    A soft opening gas valve makes lighting the pilot easy and safe, and the system delivers reliable and fast heat. The thick-walled copper heat exchanger is corrosion resistant and features a built-in bypass valve that balances the flow and adjusts for a wide range of pump sizes and flow rates. It comes with a one-year warranty.

    Water Volume And Time

    This is a very popular method for measuring pool heater size, it takes the volume of the pool in gallons and also factors in loss from surface through evaporation.

    First, we need to know how many BTUs it takes to heat one gallon of water. One gallon of water weighs 8.34 pounds, and we know that a single BTU is the amount of heat energy required to raise the temperature of 1 pounds of water by 1 degree. So, to heat 8.34 pounds of water we need 8.34 BTUs, which is the amount of heat energy needed to raise the temperature of one gallon of water by 1 degree. Now, we need to calculate the number of gallons in our swimming pool which measures 40 x 30 x 6. The volume is 7200 cubic feet, and when converted to gallons it is 7200 x 7.48 = 53,860 gallons.

    We need 8.34 BTUs of heat to raise the temperature of one gallon by 1 degree. Taking our example of a swimming pool in Detroit during September, we need to go from a temperature of 65°F to 80°F which is a 15 degree rise. So, we need 15 x 8.34 = 125.1 BTUs per gallon of water for a 15 degree rise in temperature. Now accounting for the entire volume of our pool, the total heat energy required is 125.1 x 53860 = 6,737,886 BTUs. Thats a whole lot of heat energy, right? Clearly there is no company on Earth which will sell you a 7 million BTU/hr. pool heater. So, lets do this over a 48- hour period which sounds reasonable- 6,737,886 BTU spread across 48 hours is 140,372 BTU per hour.

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