Are Electric Resistance Pool Heaters Worth Considering?

You can buy electric resistance heaters to suit all sizes of pools and spas but they are not as popular as gas heaters or heat pumps.

Coates offer a large range to cover virtually any residential or commercial application and are a good buy if you want this sort of heater but there are only a limited number of situations where they are advantageous compared to other types of heater.

Coates Heater Company has been manufacturing pool heaters since 1955. They still aim to build quality and reliability into every model to provide years of hassle-free performance.

If you have access to natural gas a gas pool heater will be cheaper to buy and much cheaper to run (although a propane heater will likely cost more than an electric heater).

A pool heat pump is the cheapest way of heating a pool and is the route you would normally take if you want (or need) to use electricity to heat your pool or spa.

Looking at the Coates CHP Range (24 – 30 kw) which you might use for a residential pool, these can be installed indoors or outdoors, are available for single or three phase power supplies and feature a digital thermostat for accurate temperature control. Flow rates are between 20 and 80 GPM and have a built in switch to prevent operation when there is no flow. An all stainless steel tank for long life and corrosion resistance is also standard.

The advantages of an electric resistance heater are:

  • Provides its quoted heat output regardless of the conditions – The same applies to a gas heater but a heat pump becomes less effective as the temperature drops and they may not work at all in cold conditions.
  • Pollution free – There is no need to worry about exhaust gases or air flow, which means that there is more flexibility in locating an electric resistance heater making it less obtrusive  and it may be safer if there are children about.
  • Mature Technology – the device should run reliably for many years.

The disadvantages of an electric resistance heater are:

  • Costly to run – running costs many times that of a heat pump or a natural gas heater.
  • Not as powerful as a gas heater – The Coates heaters range from 1.5 to 300 kw (for comparison purposes this is  5k – 1025k BTU) although the high powered ones are for commercial applications. The models for a residential pool are about 30kw which is about 100k BTU.
  • Environmentally unfriendly – unless the electricity is generated by renewable means.

If you have a spa that you want to use in colder weather and do not want a gas heater then an electric resistance heater may be ideal. However for heating a residential pool this sort of heater is unlikely to be a good choice.

To see the Coates pool heater range at Pool Supply World – CLICK HERE

What Size Pool Heater Do I Need?

A simple question but there is no simple answer.

Gas pool heaters typically range from 100,000 BTU/hour to 400,000 BTU/hour and all will heat your pool. Larger heaters will warm a pool faster and are slightly more energy efficient but, of course, they cost more.

The main alternative electric heat pumps are much less powerful 100,000 – 130,000 BTU/hour and cost more but they are very energy efficient  and therefore cheaper to run.

Below is a table giving some guidance based on the capacity of the pool or the surface area but this is very just a general guide. Much will depend on:

How you will use your pool heater

Will you want your heater to heat up your pool as quickly as possible at intervals or will you keep it heated all the time during the season. If the former you want the highest capacity heater you can afford so that the pool is ready for use quickly when you need it. If the latter you need a lower capacity energy efficient heater which keeps the pool ready for use at the lowest cost.

The location of your pool

Wind is the big enemy here. It will cause more evaporation which causes the pool to lose heat. So if your pool is in an exposed position your pool heater will have to work harder.  You also need to consider the lowest air temperature in the months you want to heat the pool and therefore the temperature raise required.

Your use of a pool cover

Use of a pool cover when the pool is not in use will dramatically reduce heat loss and therefore the demand on your pool heater.

Below is a simple table to give an indication of the size of gas heater that will be appropriate.  If you want to undertake a more detailed calculation have a look at this page.

Size Heater Gallons in Pool Sq. Ft. Surface Area of Pool
100 – 200 BTU heaters 1,000 gals to 10,000 gals up to 300 sq ft
200 – 300 BTU heaters 10,000 gals to 20,000 gals up to 500 sq ft
300 – 400 BTU heaters 20,000 gals to 40,000 gals up to 800 sq ft
400 BTU heaters 40,000 gals to 80,000 gals up to 1200 sq ft

In general it is best to work out what you think you need then get something slightly larger as, apart from the higher purchase price, there is no harm in having a more powerful heater than you need.

If you want to heat your pool quickly you should go for a gas heater. However, before doing so you should look at the running costs compared to a pool heat pump as it may be that using a heat pump to keep the pool heated for longer periods would be more cost effective.

One of the major manufacturers Raypak has an interesting program for sizing a heat pump and showing the savings you will make. Click Here to visit this program,

Pool Heat Pumps – The Best Option?

Pool heat pumps are an increasing popular way for heating a pool. They are cheap to run and environmentally friendly but do have some disadvantages.

What is a Heat Pump?

A heat pump is a device for moving heat from one location to another. In the case of pool heat pumps heat is taken from the surrounding air and transferred to the pool water. The efficiency of air source heat pumps, like pool heaters, declines with the air temperature and ice formation is a problem at low temperatures.

A heat pump providing heating for a house is likely to be a ground source heat pump where the heat is taken from the ground using a length of well buried pipes. These have the advantage of being able to work at low temperatures but are expensive to install.

There are also water source heat pumps which take heat from one body of water and transfer it to another. These are rarely suitable as pool heaters but there are models available designed to take heat from a swimming pool to heat a spa.

How do Heat Pumps work?

We are all used to refrigerators and air conditioning units which work in the same way except they are used for cooling rather than heating. In fact the top of the range pool heat pumps usually have a reverse mode in which they cool the pool.Heat Pump

Heat pumps transfer heat by circulating a refrigerant through a cycle of evaporation and condensation. An electrically powered compressor pumps the refrigerant between the two heat exchanger coils. In one coil, the refrigerant is evaporated at low pressure and absorbs heat from its surroundings. The refrigerant is then compressed en route to the other coil, where it condenses at high pressure. At this point, it releases the heat it absorbed earlier in the cycle.

With any other type of heater it is impossible to have an efficiency in excess of 100% because energy output cannot exceed energy input. In practice, for example, most gas pool heaters are 80-90% efficient. The key point about a heat pump is that because it does not actually generate heat, the amount of energy (heat) produced is much greater than the energy (electricity) used. So even though a pool heat pump is powered by electricity it is still much cheaper to run than a gas heater.

How efficient are Pool Heat Pumps?

The efficiency of pool heat pumps is measured by their COP (Coefficient of Performance). This is a measure of how many units of heat energy are produced for every unit of electricity used. For a residential pool heat pump a value in excess of 5 is good. However a word of warning, the COP varies depending on the air and pool water temperature and relative humidity. It is normally measured at 80 degrees for air/water and 80% RH but this is not a defined standard.

Pros and Cons of Pool Heat Pumps


  • Cheap to run
  • Eco Friendly
  • No emissions


  • More expensive to buy
  • Less powerful than gas heaters
  • Not so good in cold conditions

Should you buy one?

If you want to extend the season during which your pool is usable and you heat the pool most of the time then a heat pump will be your best option. If you only want to heat your pool occasionally then you might be better with a gas heater because it will be able to heat the pool faster and its lower purchase cost will offset the higher running cost.

Click this link for information on Pool Heat Pumps that are available.

Raypak Pool Heaters

Raypak pool heaters are produced by Raypak inc. a California based company specializing in water heating systems including commercial boilers, water heaters and control systems, pool and spa heaters, and residential boilers. Founded in 1947 the company has grown rapidly and now supplies its products worldwide. Its goals have always been to achieve high quality, reliability and energy efficiency. The company was pleased to become the first boiler manufacturer to achieve ISO 9001 registration in 1996.

The current range includes:

  • Raypak Digital Heater – This is often referred to as the RP2100 although that is actually an older model. With models ranging from 200 to 399 BTU/hr, theRaypak Digital Heater Raypak digital heater is designed to minimize condensation and provide rust free waterways. It will provide years of trouble free use and be unaffected by all except the most extreme weather conditions. It is microprocessor controlled with electronic ignition and on-board diagnostic controls. Basically you just have to set the required temperature and the heater does the rest. There is also a low NOx version of this heater which exceeds all NOx emission requirements.
  • Raypak Millivolt Heater – This is very similar to the Digital heater except that it has a standing pilot light to provide ignition, uses a mechanical thermostat and has no diagnostics.raypakpool heaters
  • Raypak Heat Pumps – For 2019 Raypak have revised their lineup of heat pumps (details on the Raypak Heat Pump page) but most of those on sale are still the 2018 models – the Compact Series, the Classic Series, the Specialty Series and the Quiet Series. All feature a titanium heat exchanger to withstand corrosion. There is a choice of analog or digital controls but in both cases you can control pool and spa temperature separately. Some of the Specialty models can be switched into reverse to provide pool cooling in summer and also feature a defrost mode to prevent ice forming on the condenser.

Of these Raypak pool heaters which is best for you? Well the first thing to decide is whether you want a gas heater or a heat pump. Assuming that getting electricity to the pool location is not a problem, a heat pump will be best if you keep your pool heated most of the season. Although the purchase price is higher than a gas heater, a heat pump has much lower running costs. You might prefer a gas heater if you only heat your pool occasionally because gas heaters are more powerful and can get a pool up to the required temperature more quickly. They are also cheaper to buy and if they are not used a great deal then this advantage will not be wiped out by the higher running costs.

Assuming you are looking at a gas heater then you would go for the digital heater (or the low NOx version) if you can provide an electricity supply to the heater. If not you will have to go for the Millivolt heater.

Either way you will find that one of the Raypak pool heaters meets your needs.

Gas Pool Heaters – The Best Choice?

Gas pool heaters are very popular but these days might be considered environmentally unfriendly when there are more energy efficient ways of heating a pool.

However gas pool heaters are popular because they have a number of advantages:

  • Relatively cheap to buy and install – Obviously the cost depends on the size of your pool but gas pool heaters for above ground pools are available under $1000 and for in-ground pools under $1500. You will have to pay to have the gas and electric side of things professionally installed but the rest of the installation should be within the capability of someone who is reasonably handy.
  • Powerful – A key advantage of gas pool heaters is that they are powerful and can heat up a pool quickly (although we are still talking hours rather than minutes). Therefore they are ideal if you only heat your pool from time to time.
  • Energy Efficient – Gas heaters are much more efficient that they used to be with most falling in the 80-85% range. However you can buy gas heaters with an efficiency rating of 95% but they are expensive.
  • Reliable – Although gas heaters are improving all the time this is a tried and tested technology. A properly maintained heater should give you many years of worry free pool heating.
  • Not affected by the weather – A gas pool heater will operate in all weather conditions.

Gas heaters usually are available for either natural gas or propane. In terms of performance it does not matter which you use but in terms of cost there is a major difference. Propane is much more expensive and you would only use it if natural gas is not available.

Gas pool heaters are available in both electronic and millivolt versions. The former are more popular as they feature electronic ignition and electronic controls. However to power these functions they need an electricity connection. Millivolt heaters, on the other hand, use a pilot light ignition system (which wastes energy) and have more basic controls but have the advantage of not needing an electricity connection.Pool Heater

Popular heater ranges include the Raypak Digital Heater, Pentair MasterTemp and Hayward H Series.

The main competition these days comes from pool heat pumps. These cost considerably more, are less powerful, are electrically powered and don’t work in very low temperatures. However, they can be several hundred percent efficient so that they are cheaper to run than a gas heater.

If you heat your pool constantly during the season then you should certainly consider a heat pump. If you do not heat your pool all the time then a gas heater will be your best option giving you the best balance between purchase/installation costs, heating power and running costs.

The table on this page gives approximate running costs for a gas heater by city.

Hayward Pool Heaters

Hayward pool heaters are manufactured by Hayward Pool Products, a division of Hayward Industries, Inc., who have been manufacturing pool equipment for over 80 years. They are one of the large pool equipment producers and their range includes pumps, filters, pool cleaners, lighting, salt chlorine generators and pool heaters. The length of time they have been in the business indicates that they know what they are doing.

Their current range includes:

Hayward pool heaters for In ground pools

Hayward H SeriesUniversal H Series– A range of heaters powered by either natural gas or propane. Power levels range from 150K to 500K BTU/hr. The key benefit of these heaters is that they are energy efficient (84%) and produce emissions of NOx low enough to meet the most demanding local requirements including those of California and Texas. These heaters feature electronic ignition and a digital LED control panel, they are designed for ease of installation as connections can be made on either side.

Hayward H250H Series Millivolt – Again a range of heaters powered by either natural gas or propane. The available power levels range from 150 – 400k BTU/hr with the Hayward H250 being the most popular. Their energy efficiency is 81% and there is no claim as to low NOx. Millivolt heaters have a pilot light for ignition and to generate a small amount of electricity for the controls. The benefit is that they do not need an electricity supply so there is more flexibility in choosing a location.

HeatPro Heat Pump – A range of heat pumps rated at 95 – 140 BTU/hr. They all feature electronic temperature control and dual thermostat, so you can heat both a pool and spa. In addition they they are specially designed to operate quietly and reliably whilst being extremely energy Hayward Heatproefficient.

Which to choose – A gas heater will be cheaper to buy but will cost more to run. A gas heater will also warm the pool quicker. If you are going to heat the pool constantly during the season then a heat pump will be best, however if you are only going to heat it occasionally then a gas heater will be the better buy. If going for a gas heater you would go for the Universal H Series unless getting electricity to the heater is a problem. In this case the H Series Millivolt provides a good alternative.

Hayward H Series (Universal H Series)

The Hayward Universal H Series is a series of pool and spa heaters ranging from 150K to 500K BTU/hr with versions for either natural gas or propane. The key benefit of these heaters is their energy efficiency and low NOx emission levels which comply with all current California and Texas air quality emission standards.

To purchase from the Hayward Universal H Series range at Pool Supply World – Click Here.

The Hayward Universal H-Series heaters feature an industry leading 83%-84% thermal efficiency and this plus the low NOx emissions make these heaters about as environmentally friendly as a gas heater can be (unless you pay considerably more). This energy efficiency is achieved through the use of an insulated fire tile combustion chamber which minimizes heat loss and maximizes the heat output for every BTU used.

These heaters also save energy through their industry leading hydraulic performance which reduces the time the pump needs to be running.

Hayward H series pool heater

In addition to their environmental credentials the Hayward H Series heaters also have a number of other significant benefits (see Hayward H Series Brochure):

  • Heat Exchanger – “Finn Plate” heat exchanger specially designed for fast heating and longer life. In addition the use of cupro nickel provides exceptional corrosion resistance even with salt based chlorination systems.
  • Exclusive Silicon Nitride ignition system – provides dependable lighting and reliable operation.
  • Digital LED Control Panel – which makes it easy to see the water temperature and  monitor heater performance.
  • Dual Voltage – Can be installed with a 110 or 220 volt electricity supply.

The Hayward Universal H Series heaters are easy to install thanks to their low profile, light weight and CPVC plumbing capability. In fact the electric, gas and water connections can be on either side and only front panel access is needed for servicing.

The Universal H-Series heater combines advanced technology with universal-fit, for easy installation. This together with the range of models available means that it is a good choice for just about any pool.

These heaters are widely available and get good user reviews. Our favorite supplier is Pool Supply World. They offer competitive prices, which include shipping, and feedback from their customers is very good.

See other Hayward Pool Heaters.

The Types Of Swimming Pool Heater You Can Choose From

Having decided that you want a heater for your swimming pool you then need to decide which type. The main types are gas, solar and electric (mainly heat pumps) but even within these there are a number of choices to be made.

Gas Powered Heaters
These are the most common type and they have the advantage of being able to provide heat faster than other options as they are more powerful. Units designed for above ground pools (such as the Pentair MasterTemp 125) typically supply around 100k BTU, on the other hand a heater designed for an in ground pool (such as the Hayward H series) can provide up to about 400k BTU. This is particularly useful if you heat the pool intermittently and therefore need to raise the temperature quickly.

Gas pool heaters are available to use natural gas or propane. Clearly natural gas would be the best choice if it is supplied on site or LPG might be a good option if you already store it for home heating. If there is no existing supply of gas it may be best to look at some other form of pool heater.

Gas pool heaters also come in Electronic or Millivolt versions. Electronic versions are like a modern gas boiler and feature electronic spark ignition and micro processor control. Millivolt models use an older technology which uses a permanent pilot light and therefore is slightly less efficient. As well as being used as an ignition source the heat from the pilot light is used to produce a small voltage (where the name comes from) to power the controls. The former is the preferable option but it requires an electricity supply, if this is not possible a Millivolt heater is appropriate.

The major negative with gas heaters, especially those using LPG, is that they can be costly to operate.

Electric Heaters  
You can buy direct electric heaters but these are expensive to run and so are usually only appropriate when heating small above-ground pools.

These days the electric heat pump is becoming an increasing popular choice (such as the Hayward HeatPro range). Heat Pumps work by transferring heat from the surrounding air into the pool water, rather than generating heat themselves. This means that in terms of energy used to heat output they can be several hundred per cent efficient. As a result they are cheaper to run than gas heaters and are more environmentally friendly. They are also expected to have a longer lifetime than gas heaters.

Heat pumps do have some disadvantages. They are not as powerful as gas heaters and are best run continuously, to maintain the pool temperature. In addition the air temperature should be at least forty-five degrees if they are to work efficiently.

Solar Pool Heaters
In these systems the pool water is pumped through solar collectors which are designed to trap solar energy. Although each location is different, a good rule of thumb is that the area of solar collectors should be the same as the pool area. Solar heating will probably be more expensive to purchase and install than other types but should have a longer lifetime and be less costly to operate. It is certainly the best option if you want to be environmentally friendly.

There are more things that you need to address with a solar system if it is to work satisfactorily. These include the local climate, finding the best location, heeding local building codes and making sure the system is safe. Solar systems are dependent on the local climate so the most important thing is to ensure that the system will heat the pool for the period you wish to use it.

Spa Pool Heaters

Spa pools are mainly used for relaxation purposes and therefore it is common to have a heating system installed in them. Spa pool heaters not only provide a comfortable soothing experience that is perfect for unwinding after a long day, they also extend the season of the spa pool so that they can still be used during a cold weather.

The normal range to which a spa pool is heated is 97 to 102 degrees.  This is considerably higher than the normal temperature of a swimming pool but spa pools are much smaller, typically not more than eight square feet and less than four feet deep. As a result the requirements for a heating system are less than those of a swimming pool.

There are four main types of spa pool heaters that are available today. These are:

Small gas heaterhot tubs like the Pentair MasterTemp 125 which are designed for an above ground pool and/or spa. These are relatively cheap to buy and will be able to heat up a spa quickly. If you can use natural gas they are reasonably cost effective. Disadvantages are that they are not small and because of the need for ventilation and safety cannot be out of sight.

Direct Electric Heaters such as these made by Coates are small and effective. They can be installed out of sight and should offer trouble free operation for many years. However they cost more than a gas heater to buy and much more to run.

Lower capacity heat pumps like the AquaCal TropiCal Heat Pump are another option. This model is designed specially for above ground pools and spas and has low running costs. You probably can’t hid it but there are less issues with installation than with a gas heater and it is the most environmentally friendly of these three options. The disadvantage is the purchase cost which is more than an electric heater and considerably more than a gas heater. Also a heat pump becomes less effective as the temperature goes down.

A solar heating system can also be considered. In the right location solar power is quite practical during the summer but is not much use on cold evenings at other times of year.

In the end it depends on how often you want to heat your spa. If it is only occasionally a gas heater is likely to be the best option but if it is used regularly it might be worth investing in a heat pump.

Above Ground Pools – Buying & Heating

Installing above ground pools is clearly cheaper and less work when compared to in ground pools however it requires considerable commitment (usually your site turns out not to be as level as you thought). The good news is that there is a large range of pools available for sale in varying sizes shapes and depths. To see what you can buy CLICK HERE. Tips on installing your pool can be found HERE.above ground pools

When it comes to heating your pool you have a number of models to choose from which are made specially for the purpose. These differ from in ground pool heaters as they are lower powered, and hence cheaper, as the volume of water to be heated is smaller.

When looking at above ground pool heaters there are a number of options. As the volume of water is relatively small it is possible to use an direct electric pool heater. These are cheaper than gas heaters and easier to install. However, they are not cheap to run as they use a significant amount of electricity which is more expensive than gas.

Gas heaters made for above ground pools (such as the Pentair Mastertemp 125) are lower powered than those for in-ground pools (such as the Raypak 2100). Since an above ground pool is usually relatively small you don’t use up that much energy as the heater only needs to maintain the temperature of a relatively small volume of water.

Another option when looking at above ground pool heaters is a solar pool heater. You can buy small cheap solar panels but it is generally agreed that the solar panels need to cover the same area as the surface of the pool to be heated. They also need to be sited at the right angle, facing south and in an unshaded position. Since most above ground swimming pools are not that big, you don’t need to have a very large space for the solar panels. However, proper solar pool heater systems can be expensive to buy and setup, do have running costs and of course depend on the weather – that’s why most people opt for gas or electric heaters.Above Ground Heat Pump

Today a good energy efficient way to heat a pool is to use an electric heat pump (like the AquaCal TropiCal Heat Pump). Heat Pumps are very efficient because they don’t produce heat they just “pump” heat from the air into the water.

When using a pool heater you can greatly increase its efficiency, and reduce your costs, by using a pool cover when the pool is not being used. Pool covers insulate the pool and minimize evaporation so limiting heat loss. As a result the pool heater will not use as much energy to keep the pool temperature steady.

If you are looking at above ground pool heaters keep the above points in mind so that you can maximize your enjoyment of the pool whilst minimizing the cost. Click this link to see the above ground pool heaters reviewed on this site