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Pool Heaters

What They Do, How they Work, Choosing the Right One & Much More!

Pool Heaters are a great way to warm your swimming pool water to your perfect temperature during times when cool days, evenings or nights would normally make your pool too cold to enjoy. Pool Heaters are a great way to extend your swimming season, and provide heat on demand when you need it most. In fact, no other piece of pool water heating equipment – be it a solar heating application, or even a heat pump – has the ability to heat your pool water as fast a pool heater!

How Does a Pool Heater Work?

A swimming pool heater works by burning fuel to create heat, which is then passed through a heat exchanger and on to water drawn from your swimming pool. The water, now considerably warmer, is then reintroduced to the swimming pool, raising the overall temperature.

How Do You Size a Swimming Pool Heater? (or “Why Bigger IS Usually Better”)

Swimming pool heaters are rated according to their BTU output (a measurement also known as British Thermal Units). 1 BTU is capable of raising the temperature of 1 lb of water by 1 degree Fahrenheit. Therefore the more BTUs a pool heater produces, the faster it will heat the water in your swimming pool. Because swimming pools come in all shapes and sizes and are located in many different climates, you’ll need to calculate the number of BTUs needed to heat your swimming pool according to your specifications in order to select the right pool heater. This can be accomplished once the following variables have been determined:

1. Surface area – The main job of any pool heater is to heat the pool water at a faster rate than heat is being lost from the surface of the swimming pool. Once the ideal temperature has been reached, your pool heater only needs to run enough to compensate for the heat that escapes from the surface of the water. Therefore, we strongly suggest using a quality Solar Blanket in conjunction with your pool heater (or with any piece of pool water heating equipment for that matter), in order to maximize efficiency.

The more surface area your pool contains through which heat can escape, the more BTUs your pool heater will need to produce to heat your pool water. Calculating the surface area of your swimming pool is relatively easy, and some common calculations are provided here:

  • Round pools: radius (1/2 diameter) x radius x 3.14
  • Rectangular pools: length x width
  • Oval pools: 1/2 length x 1/2 width x 3.14
  • Rectangular pools w/ rounded ends: length x width x 0.8
  • Kidney-shaped pools: length x width x 0.75

2. Temperature rise – The temperature rise of your pool water is a calculation of your desired water temperature minus the average ambient air temperature. The desired water temperature is simply the final temperature you’d like your pool water to reach. The average ambient air temperature is the average daily outdoor air temperature and should be figured on the basis of the coldest month you plan on using your pool. For instance if you live in an area where the average outdoor air temperature in May (the month you would like to start using your pool) is 60 degrees and your desired water temperature is 80 degrees, your temperature rise would be 20 degrees (80 – 60).

With both surface area and temperature rise now calculated, you can refer to the chart below to find just how many BTUs will be necessary for the desired heating effect on your swimming pool:

Temp Rise (in ° F)
5 ° 10 ° 15 ° 20° 25 °
Surface Area of Your Swimming Pool (in sq. ft)

Required Heater Output / Hour (in BTUs):

200 21,000 31,500 42,000 52,500 63,000
300 31,500 47,300 73,000 78,800 94,500
400 42,000 63,000 84,000 105,000 126,000
500 52,500 78,800 105,000 131,000 157,000
600 63,000 94,500 126,000 157,000 189,000
700 73,000 110,000 147,000 184,000 220,000
800 84,000 126,000 168,000 210,000 252,000
900 94,500 142,000 189,000 236,000 284,000
1,000 105,000 157,000 210,000 263,000 315,000

Chart is based upon an assumed wind velocity of 3.5 mph. Totals should be multiplied by a factor of 1.25 or 2.0 for wind speeds of 5 and 10 mph respectively.

After finding the required number of BTUs / hr you will need from the above chart, you can compare pool heater models based upon the BTUs they produce. This number can be found by multiplying a pool heater’s input (measured in BTUs) by the pool heater’s efficiency rating. An explanation of pool heater efficiency follows here:

3. Heater efficiency – Pool heater efficiency is provided by the manufacturer, and is expressed as a percentage that represents the amount of energy a pool heater transfers to the water for each unit of energy (BTU) used to generate that heat. The US Department of Energy has mandated that all pool heaters have an efficiency rating of at least 78%. So, as an example, a 300,000 BTU pool heater with an efficiency of 85% would produce 255,000 BTU/hr.

Something To Remember When Selecting Your Swimming Pool Heater

When selecting your pool heater, always to select a heater rated somewhat higher than your actual pool surface area and desired temperature rise require. There is no such thing as “oversizing” a pool heater. The larger the BTU output of the pool heater you buy, the quicker it will heat your pool water. This means less run time on the heater and a longer overall heater life span. You will always be glad you opted for the larger pool heate

Different Types Of Swimming Pool Heaters

Swimming pool heaters come in various makes and models. The four main differences in pool heater models have to do with (1) the type of fuel the heater uses (natural gas or liquid propane), (2) the style of ignition your pool heater will employ, (3) the level of emissions the pool heater produces, and (4) the elevation for which the pool heater is rated.

Natural Gas or Liquid Propane – What Will Your Pool Heater Run On?

When selecting your pool heater, you’ll need to decide between a natural gas or liquid propane model. The type of fuel you use will be based on the difference in availability and the price of fuels in your area. The price of the pool heater model you choose should not be affected by the fuel type you decide to use.

The Difference Between Millivolt & Electronic Start Pool Heaters

A millivolt swimming pool heater utilizes a standing pilot light that must constantly stay lit to initiate the pool heating process. An electronic start pool heater eliminates the need for this pilot light, by electronically initiating the heating process. The drawback to the millivolt model is that you may find yourself having to re-light the pilot light if it goes out. This sounds easy enough but anybody who has ever needed to re-light the pilot on a gas stove knows that this process needs to be performed VERY CAREFULLY so as to avoid injury.

Low NOx vs. Normal Emissions Pool Heaters

A “Low NOx” pool heater is a heater designed to release fewer emissions than a regular pool heater. Recently, California mandated the use of these pool heaters in certain counties. Due to their design, low NOx pool heaters are by and large more efficient than traditional pool heaters. This higher efficiency means a higher heat transfer and faster heating of your swimming pool water.

Pool Heaters Designed for Altitudes 2,000 Feet Above Sea Level

If you live at an altitude 2,000 feet or more above sea level, you will need a special model pool heater designed for that altitude. The difference in the oxygen level in the air necessitates this special model. Just one more thing to think about before purchasing a swimming pool heater!

Swimming Pool Heater Installation Basics

Swimming pool heaters should always be installed after the filter system and before any chlorinators or chemical injection systems in your swimming pool’s plumbing. This will ensure the heater receives a strong flow rate of clean water, without any highly concentrated and potentially corrosive chemicals. It will probably be necessary to enlist the help of a professional electrician and/or natural gas professional in installing your pool heater. This will not only ensure proper installation but is vitally important so as to avoid injury. Different heater models will contain varying specifications with regard to clearance and appropriate ventilation. ALL MANUFACTURER SPECS SHOULD BE RIGIDLY ADHERED TO in order to ensure maximum safety and heater efficiency (which will save you money).

Avoiding Problems With Pool Heaters – A Few Reminders

Swimming pool heaters are a wonderful addition to the swimming pool area, due to their ability to warm pool water to an inviting temperature, allowing you to utilize the swimming pool comfortably more than ever before. Follow these tips to avoid common problems and get the maximum life out of any pool heater you buy:

Size your Pool Heater appropriately. Remember a pool heater can never be too big, but buy a pool heater that isn’t big enough and you’ll never be satisfied.

Monitor pH closely. pH is probably the single biggest problem pool owners face with regard to pool cleaners and pool equipment in general. A pH level that is too low (acidic) will cause corrosion, and a pH level that is to high (base) will cause mineral deposits that could potentially clog your pool heater’s plumbing.

Maintain correct flow rate. Backwashing your swimming pool filter or washing out the cartridge occasionally will ensure that enough water gets to your pool heater for it to function efficiently.

Protect your investment. We recommend use of a pool heater cover to keep the heater protected from the elements.

Allow appropriate clearance around the Pool Heater. This will be specified in your owner’s manual.

Make sure your Heater’s gas pressure is adjusted appropriately. This step should be performed upon installation BY A PROFESSIONAL.