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How To Determine Pool Heater Size

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How To Determine The Heaters Btu

How To: Size a Gas Heater for Your Swimming Pool

You can also determine the heaters BTU required for your in-ground pool or above-ground pool to figure out the size of your solar heater system. Keep in mind that you need a heater that is capable of not just heating your pool but of heating it to your desired temperature and as fast as possible. BTU, or British Thermal Units, measure the heating capacity of solar pool heaters.

It only takes 8.33 BTU for the pool heater to heat one gallon of water one degree higher. This basis can already be used to calculate just how many BTUs will be needed to heat your entire pool.Calculations can go like this.1° First, you need to gauge how many gallons of water are in your pool.2° Then set a desired temperature level for your pool water.

Using the standard value given above, you then need to calculate the number of BTUs necessary to heat up all the gallons of water in your pool. Next, look for a solar heating system that meets your requirements and enjoy well-heated water in your pool.

What Else Do You Need To Know About A Heat Pump

The choice of location is also very important because the heat pump needs very large amounts of air to function properly! For this, a suitable place for the fresh air must be found in most cases indoor operation does not work.

The heat pump itself is then integrated directly into the filter circuit, after the filter system and before the chlorinator if fitted.

High-quality heat pumps are equipped with corrosion-protected heat exchangers and can thus heat any swimming pool water, whether it is cared for with chlorine, bromine, ozone or chlorine-free products. The use for pools with sea water is also possible.

With all pools other factors including solar gains, wind factors and evaporation losses need to be taken into consideration. This article is to give a bit of insight on one way of sizing.

Ways To Size Your Solar Pool Heater

Solar pool heaters are must-have for every pool owner. After all, what good is a pool if you cant jump into it because your pool water is not the right temperature?

This is why investing in a solar pool heater system is a wise move. Using solar heaters is also an efficient way to utilize solar energy. But one of the biggest considerations in getting a solar pool heater is the size of the heater you will need.

To figure out the ideal size of your solar pool heater, you need to consider several factors, but the most important of these is the size of your pool.

The bigger your pool, the bigger your heating requirements are, which means you also need a larger pool heater. Some small pools can enjoy sufficient heating from affordable heating systems under $300, but larger pools require bigger investments.

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Swimming Pool Heater Size Calculator

To help estimate the pool heater size, enter all of your information regarding your pool.

Use the swimming pool heater size calculator below. Click calculate to get your

Please note that heat rise varies when dealing with different heaters. The usual recommendation is an increase of 1 to 1 and a half degree per hour.


  • Calculations are rough estimates as to which size pool heater you may need.
  • Consult with a certified pool installer to verify the minimum heater size required
  • Most newer heaters are at least 83% efficient.
  • Heaters manufactured prior to 1996 are 78% efficient.

We recommend you size your heater one size larger than required. Shop swimming pool heaters from our online store. Get Free Shipping!

Size Really Does Matter

Hayward H400FDN Natural Gas Pool Heater

Contrary to what women say, size really does matter at least, as far as swimming pool heaters go.

Correct pool heater sizing can be slightly tricky, but it mainly comes down to this: large heaters will heat quickly, whereas smaller heaters take more time to distribute heat throughout the pool. The choice is yours.

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Pool Heat Pump Sizing: How To Size Your Heat Pump

  • |February 24, 2021

Heating the water in a pool makes swimming more enjoyable for everyone.

With different types and sizes of heaters available, heat pumps are an energy efficient and effective solution to warming up pool water.

But if youve decided to go electric, youll need to figure out how to get the correct pool heater pump sizing for your pool.

Important: This article is about sizing electric pool heat pumps, not gas pool heaters. If youre looking for the latter, please read our article on sizing a pool heater.

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Sizing Your Pool Heater

When I first started working in the pool industry, one of the areas I always tried to avoid was helping customers size their pool heaters. Im not sure what made me uncomfortable about sizing heaters but I avoided it like the plague. One thing I did know was that when it came down to heaters and heat pumps, the bigger the better. Although true, I learned that some pool owners actually prefer efficiency over size. Eventually, I realized that my bigger is better line wasnt always the best advice for every pool set up and sooner, rather than later, Id have to learn how to size a heater for a pool owner.

So, exactly how do you size a heater for your pool? Lets do this together.

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How To Size A Pool Heater

Whenever I talk to another pool professional about calculating heater size, I usually see their eyes glaze over. Not that sizing a pool heater is super difficult, but if you want to do it right, you need to do some calculations first.

Similar to pumps, sizing heaters isnt usually calculated. Its usually a matter of picking a model youve used in similar applications. For example, if youre working on a pool with an attached hot tub, most installers would suggest a 400,000-Btu heater, which is the largest available in most residential applications.

In that case, a pro might not feel he or she needs to run the calculations because they know the attached hot tub, circulated at pool temperature, will need to be heated before use. And the higher the Btu output of the heater, the faster the heater will raise the water from pool temperature to spa temperature.

Nobody wants to turn on their spa two hours in advance just for it to warm up. With a giant 400,000-Btu heater, an average 8-by-8-foot spa could go from 80 degrees up to 104 degrees in about an hour.

Similarly, when a homeowner asks what size heater they should use, most installers just pick their favorite heater that is between 200,000 and 350,000 Btu, knowing from experience that it will work on a pool approximately the size of the one in question.

Calculate Your Surface Area

What size electric heat pump should you get for your pool?

When you are determining which size pool heater to buy, the first step is calculating your pools surface area. A lot of pool owners assume that you use your pools gallon size to determine your heater size. In fact, there are some websites that DO use the number of gallons. If you have a pool with a large surface area, the heat has more space to escape and subsequently, more water to heat. As a result, the heater needs to be large enough to compensate for surface area and the pool size.

To calculate the surface area of your pool, multiply the length times the width.

For example: If your pool is 15 x 30, then your surface area is 450 square feet.

Related:Pool volume calculator.

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Residential Gas Heater Sizing Calculator

Raypak has a gas heater calculator that configures your city and state with your desired water temperature, average air temperature, and desired temperature rise. Raypaks online calculator allows pool owners to input specific information about their pool and location and configure what size heater is best, not only for their pool but taking your physical location into consideration as well.

View the calculator here.

The calculator also can calculate the cost of an electric heat pump versus direct fire propane or natural gas heaters. This tool allows customers to compare energy costs by showing their regions average temperatures and the cost to heat the water to your desired temperature, broken down for each month of the year. Its a really useful tool I use to explain to pool owners the costs of heating their water and a realistic plan for which months they might want to close the pool, if at all. Once you review the different options you will understand that heat pumps are more efficient in milder climates where there is less temperature increase required. And propane is more expensive than natural gas. I will review solar and geothermal options in another article. If you prefer to look at averages vs. using this calculator, I wrote a guide on average pool heater costs by type that should help. And if youre experiencing trouble with your current heater, read my pool heater troubleshooting guide. Hopes this helps, reach out to us with any questions!

Tips On How To Properly Size A Gas Pool Or Spa Heater

Replacing a defunct pool or spa heater for a customer on your route? Adding a heater to an equipment pad that previously lacked one? Welcome to the world of heater sizing and the art of finding the right unit to provide your customer with a cost- and energy-efficient source of heated pool or spa water. Doing the job right means the water will heat to the desired temperature in the desired time frame. An undersized heater will heat too slowly and, although heater manufacturers advise that bigger is always better when choosing a heater, a significantly oversized unit will do the job, but also will boost the cost of the installation.

Choosing the right heater will please your customers and provide you a trouble-free heating system on your service route.

Warming up

Before selecting a heater, you must determine the customers needs. For example, is the heater going to warm a pool or a spa? Although many units can be used for either vessel separately, the thought process behind selection differs for pools and spas.

Take a pool: One of the primary factors used in calculating heater size is heat loss from the surface. In a spa, however, surface area is far less a factor because so many spas are covered, which greatly reduces surface heat loss. Instead, heat-up time relative to the spas gallonage is the critical factor.

Defining the variables

To properly size a heater, you need to know the following information.

Rectangular pool: length x width

Rectangular pool with rounded ends:

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Choosing The Optimum Heat Exchanger Calculate With Our Program For Heat Exchangers

Pahlén has an extensive experience in dimensioning and heat calculation. Our calculation program for heat exchangers can be used to assist in decision making. The heat requirement for each pool is unique and is a ected by a variety of factors such as isolated/non-isolated pool, above ground pool/inground pool, pool cover, etc.

Pool Heating Pump Systems: How To Calculate Heat Loss And Heater Size

I need help sizing a natural gas pool heater for a ...

This Blog post goes in a bit of detail the complex calculations we provide for you with our instant online pool heater calculator.

This report is the gold standard of pool heater sizing and heating evaluation and will provide you with all you need to know to get your pool heated.

Continuing from last weeks post where I explained how pool heat pumps being the most efficient way of heating a pool, I mention to speak to experts on how to calculate the heating requirement. This week I delve a little deeper into the technical aspects of pool heating pump Explaining COP, heat up times and kW required. So put your thinking cap on and continue reading, maybe you’ll be an expert by the end.

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Above The Ground Pools

In case of above ground pools, you can refer to some sizing charts to make sure you get the right heating level for your pool size. If you have an above ground swimming pool, it would be better for you to invest in a solar heater that already ships with a pool diverter value and a mounting kit for the roof or for a rack to help you with your setup.

The calculations for the size of solar pool heater are basically the same for above ground pools and in ground pools.

In fact, some in-ground pool heaters can also be used for above-ground pools with no difference at all. To be sure, you can also ask your provider for a free sizing and free quotation. Some brands also offer their own sizing charts that fit their products and all you have to do is pick out the solar pool heating system appropriate for your swimming pool and your needs.

What Size Pool Heater Do I Need An Easy Guide To Sizing

Would you like to extend the swimming season in your swimming pool? Maybe open it a month or two earlier and close it a month or two later? Wouldnt it be great to have it available for more than just a few months in the summer?

Well, you can. But no one wants to swim in ice water unless youre a member of the Coney Island Polar Bear Club and you like torturing yourself in freezing cold water so, to extend the swimming season, you need to heat the water. But what size what heater do you need?

Thats what were here for. Weve already done all the hard work for you, so just sit back, receive our words of wisdom, and youll be able to make an informed decision on the heater thats best for you.

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Pool Heater Sizing: What Size Of Pool Heater Do I Need

The right size of pool heaters is crucial in ensuring their optimal functionality. If it is too small for the size of your pool, it will be ineffective in warming the water. On the other hand, if it is too powerful compared to what your pool requires, you will end up unnecessarily wasting energy.

Curious about the right pool heater sizing? Keep on reading and learn from the things well talk about in this short guide.

Divide The Pools Surface Area By 3

How to Select an Inground Pool Heater

The pools surface area divided by three gives you the minimal BTU size recommended for that particular surface area. Continuing the example above with the 15 x 30 pool, after dividing by 3, you get 150. Therefore, the minimum size heater that is recommended for a 15 x 30 pool is 150,000 BTUs.

This is simply the recommended minimum size. I always go higher. Especially when it comes to gas heaters, you always want to oversize the unit. The job of a pool heater is to replenish the heat loss at the surface of your pool. Most heat loss happens overnight. Without a solar cover, there is no way to make up for the loss. Thats when having a higher BTU size comes in handy.

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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

    How To Properly Size A Gas Heater For A Hot Tub:

    Multiply length x width x average depth x 7.5 to determine spa gallonage.

    Besides the amount of time you can wait for your spa to heat up, other factors come into play that could affect the size of spa heater.

    • Will the spa be covered to prevent heat loss?
    • Is the spa located indoors or outside?
    • If outdoors, will it be operating year round?
    • Are there other competing appliances using the gas supply?

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    Why Is Pool Heater Sizing Important

    Weve all heard the saying bigger is better. When it comes to gas pool heaters, this is mostly true. However, it really depends on your pool size, and budget.

    Generally speaking, the amount of BTUs required to heat pool water will be the same, no matter the size of the heater. But a larger one will work quicker than a smaller heater, especially if you have a large body of water youre warming.

    Note: BTU is a unit of measurement that measures thermal energy. Gas pool heaters are rated for BTU input/output and range from 100,000 400,000 BTUs.

    Current pool heaters are 85% to 90% efficient. This means if you have a heater with an input of 400,000 BTUs, youll be getting 340,000 BTUs of output based on 85% efficiency, though this drops over time due to normal wear and tear. Understanding BTUs helps you determine the necessary heater size for the volume of water in your pool.

    A smaller heater means youll have to run it longer, which means youll be paying more in operational costs. But once it reaches the desired temperature, it can easily maintain it.

    When it comes to minimum size, the general rule is 1 BTU will raise 1lb. of water by 1 degree Fahrenheit. You can then determine the minimum BTU size of the heater you require when heating your pool by X amount of degrees.

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