Pool Heater Basics

Need to Hire a Plumber?
Get a free estimate online from top local home service pros in your area.
Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.

Pool heaters are essential equipment for swimming pools. They provide warmth to the water, keeping it at a comfortable temperature. This helps prevent algae growth and keeps swimmers safe from hypothermia.

Pool heaters come in three main types: gas, electric, and solar. Each type has its advantages and disadvantages. But what else do we need to know about them? And how can you find this information out quickly and easily? 

Well, by sticking with us! In this article, we’ll explain the differences between them and give you some helpful tips on choosing the right pool heater for your home.

What Is A Pool Heater?

A pool heater is used to keep water warm in indoor or outdoor swimming pools (see also ‘How To Put A Swimming Pool In Your Basement‘). 

It uses electricity or natural gas to generate hot air that circulates through pipes or tubes placed around the perimeter of the pool. The heated water is then circulated back into the pool as needed.

The most common way of using a pool heater is called direct circulation. When this method is used, the circulating water carries away excess heat from the pool.

The primary function of a pool heater is to maintain a constant body temperature in the water. 

For example, if a person stands in cold water for an extended period of time, their core temperature lowers. Heat is required by the body to raise the temperature back up to normal levels.

If someone were to stay outside for several hours without wearing enough clothing they would feel uncomfortable due to hypothermia – low body temperature, resulting from exposure to cold weather.

By contrast, if one were to stand inside a hot tub of 90 degrees Fahrenheit the body’s thermostat would kick in and cause the blood flow to redirect itself around the lower extremities towards the heart. 

As long as the core body temperature remained above 98.6 F, there would be no risk of harm.

The same principle applies to people who swim regularly in cool waters; the body can adapt to tolerate the warmer temperatures. A properly functioning heater can help manage this process.

Different Types Of Pool Heaters And How They Work

There are several different ways of heating water in a pool or spa. Direct-circulating heaters use electrical resistance to transfer heat from the heater to the water in contact with it. 

These units are the cheapest option because they require virtually no maintenance. However, their efficiency can vary greatly depending on how old the unit is and how well maintained it is.

In a single pass system, the water passes directly over the heating element once, absorbing energy and warming it before returning to the pool/spa. 

Because the water only goes past the heater once, there are fewer moving parts than indirect systems. Single-pass heaters also produce more consistent results.

When heat is added in multiple passes, the energy is absorbed and transferred throughout the pool water, but less efficiently.

If the heater develops leaks or the water absorbs too much energy, those areas will need replacing at great expense.

Since the water never touches the heater, there are not many moving parts to wear down or fail. Indirect heaters take longer to heat the water, so they typically cost more per hour of operation.

Solar pool heaters work much like the sun does, capturing the energy present in light waves. Photovoltaic panels convert sunlight into DC (direct current) power, which is stored in batteries. 

Once charged, these cells create AC (alternating current) power when the cell receives another charge of sunlight.

This converted power powers a pump that circulates warm water through copper tubing embedded in the walls of your swimming area. 

In warmer climates, solar heating systems require less electricity to operate and are more efficient than other methods. But solar heaters cannot provide heat during cloudy days or periods of prolonged darkness.

Choosing A Pool Heater

Choosing A Pool Heater

If you’re ready to buy a new pool heater, consider a few things first: How often do you have guests? What size is the pool? 

Is the pool heated year-round, or just in the summer? Do you already have a gas line? If not, where could you tap into natural gas services? Would you prefer an electric heater, or possibly both?

Electric and gas pool heaters (see also ‘Electric Pool Heaters Buying Guide‘) offer a wide range of options. Electric heaters come in a variety of sizes and styles.

Gas heaters tend to be more popular, especially in older pools built before the introduction of electronic controls. 

For example, some older homes may have had a gas-fired boiler mounted outdoors, then piped in later to the home’s plumbing system. You may find it easier to repair a gas system if a pipe breaks.

Electric heaters are typically more expensive than gas heaters, although they don’t require any major repairs compared to a broken boiler. 

Electric heat pumps run more quietly and consume far less space than traditional heaters. They also heat the entire body of water as opposed to just the surface.

Gas heaters aren’t without advantages either. They can be installed quickly without having to dig trenches or drill holes. 

And a properly maintained gas heater won’t develop problems until its life ends, unlike a boiler that must be taken apart and repaired every time it fails. 

On the flip side, gas heaters can be pricey to install. And replacing a blower motor or a heating element would likely void your warranty.

Since most people spend a lot of time in the pool, it pays to get one that fits the needs of your household and lifestyle. 

Take into account how long you plan on keeping the pool heated, whether you’ll use it all year round, and what size and shape your family prefers for comfort and safety.

Pool Heater Features

When selecting a pool heater, keep in mind that the following terms describe features common to all types of pool heaters:

Warm-Up Time

The amount of time it takes before the temperature reaches a steady state. Also known as “off-time”. Warm-up times vary based on the type of heater and the initial conditions of the pool.

Heat Output 

Wattage produced by the heater; is measured in watts per hour. It is important to know this information since higher wattages mean a smaller unit will need fewer amps to maintain stable temperatures. 

As a general rule, however, lower wattages produce hotter water while higher wattages give off cooler air.

Watts Per Hour 

Unit of measurement is used to determine the number of hours required for the pool to reach the desired temperature. The formula is Watts Per Hour Total Watts / Hours in Minutes.

Volts Required

Measurement of electricity that goes through a circuit breaker to activate the pool heater. Most pool heaters sold today run between 12 and 20 volts.

Amps Required 

Size of the electrical transformer needed to handle enough electricity to supply the pool heater unless it’s solar. When determining required amps, calculate amps as amperes multiplied by volts.

Appliance Efficiency 

How much energy (watts) an appliance consumes over some time (hours). Generally speaking, efficiency increases with wattage. This means increasing numbers of watts will result in lower percentages of efficiency.

Pool Heater Sizing

Like other appliances, there’s no magic number when it comes to sizing a pool heater. However, here are several guidelines that can help narrow down the choices:

Power Consumption 

To ensure adequate battery capacity, measure the total power consumption of the heater during normal operation. 

Remember that the batteries need to last throughout the summer months, so choose a model with high wattage ratings and ample battery capacity.

Size Requirements 

Consider the size of the pool itself. If you have a small pool, a small heater might suffice. But if you’ve got an expansive pool that requires multiple zones, consider investing in a large heater.

Other Pool Heating Considerations

There are many other things to take into consideration when purchasing a pool heater including:


Look for a model with automatic shut-offs or adjustable thermostats that automatically turn the heater off after a set amount of time has passed. 


Check out a pool heater’s rating for heat output. You’ll want to be sure that enough space exists above the heater to allow circulation of warm and cool air between the two surfaces.


Some manufacturers offer warranties ranging from 2 to 10 years along with warranty cards that specify specific parts covered under the warranty. 

Other factors to consider include serviceability of the product, ease of servicing, quality customer support, and cost of repair/replacement.

It’s important to remember that selecting a residential pool heater should match your needs, budget, and lifestyle. 

After all, the best-designed pool heater may not meet your expectations. So make sure you’re fully informed about your options before making a decision.

Pool Heater Efficiency

Electric Pool Heaters Buying Guide

Pool heating equipment rated at a higher kilowattage generally produces less heat than models rated with lower kilowattage.

For example, a 25 kW pool heater would likely produce roughly 3,000 BTU per hour while a 15 kW heater would produce about 600 BTUs per hour.

However, both units will work with the same sized battery pack. What’s more, these estimates only reflect the efficiency of the particular unit being considered.

The actual BTU outputs for a given heater depend largely on the type of gas used and its efficiency.

The other major factor affecting heater efficiency is the surface area of the tank. Larger tanks tend to require less energy to achieve the same degree of heating.

On average, a 50-gallon hot tub uses approximately 35 watts of electricity (about 1/2 the energy required by a typical 75-watt pool light fixture). 

Thus, if you plan to use a smaller heater in addition to an existing heater, you could potentially eliminate that second element.

Because the output of some pool heaters cannot exceed 110°F, they cannot be placed near air conditioning vents. 

The U.S. Consumer Product Safety Commission (CPSC) specifically lists pool heaters among the products prohibited for use near a forced air central air conditioning system.

Pools With Pool Hovers

When purchasing a pool heater, many consumers are drawn to those with a hover feature.

If you aren’t familiar with pool hovers, here’s what they do: They move small amounts of water back and forth across the bottom or side of the pool. 

This movement creates a current through which heated water travels toward the wall, generating additional heat.

Although this technology offers convenience, it can also cause problems like increased algae growth due to the warmer temperatures created by the flow, excess chlorine build-up, and overheating of the water. 

These adverse conditions limit their use to shallow pools where temperature fluctuations are minimal.

Heat Pump Vs. Steam Heaters

A heat pump is designed to draw in cold outdoor air during the winter and expel warm indoor air. It consists of coils situated between two chambers separated by a refrigerant.

As the outdoor air passes over the coils, the air gets cooler until it reaches the desired temperature inside your home. Heat pumps have been around for decades, but they weren’t very popular.

Today they’re gaining popularity as homeowners continue to look into ways to reduce energy costs. 

Unlike traditional boilers, heat pumps don’t create steam as a means of producing heat. Instead, they rely on electricity from the grid for power and then convert the electrical energy into thermal energy.

But it must be said that although electric heat pumps are much more efficient than traditional boiler systems, they still consume a considerable amount of fossil fuel.

In contrast to heat pumps, the majority of pool heaters use natural gas or propane. A pool heater requires significantly smaller volumes of fuel than a furnace.

 By using less fuel, the cost associated with using a pool heater tends to be lower than the cost of running a standard boiler system.

How Much Does A Pool Heater Cost?

The average price for a residential electric pool heater ranges between $1,800 and $4,000.

The initial costs associated with installation vary depending on how big the pool is and where the pool heater is placed in relation to the water pump and filter.

The most common estimate for installation is around $300-$600. In some cases, an electrician with proper training can do this work alone.

How To Install A Pool Heater

To install a pool heater, follow these steps:

  1. Turn off all pool equipment including filters, pumps, lights — anything that could potentially interfere with a functioning pool heater. If you plan to add a pool heater to the same circuit as other appliances, turn them both off first.
  2. Remove any cover plates, if necessary, so you’re able to access the pool heater’s wiring connections. Locate the breaker box or fuse panel where the circuit will be installed and turn off the power supply.
  3. Check the pool heater manufacturer’s instructions before beginning the installation process. They should guide you on how to safely connect the heater to the power source.
  4. Some installers may require you to start checking wires individually, while others will show you how to locate a particular wire and properly splice it onto the correct terminal.
  5. Start at one end of the pool and remove the old terminals. Remove the old pool heater wires and replace them with new ones. Make sure you leave good margins of space between each wire.
  6. Insert the screwdriver that came with the unit along with the base plate and into the receptacle. Once put into place, tighten the screwdriver down. This helps prevent the screwdriver from slipping out.
  7. Next, insert the screwdriver into the outlet connector next to the pool pump. Once inserted, rotate the screwdriver to firmly secure it in place.
  8. You’ll know when the connection has been made because the light switch should illuminate. If not, try tightening the screwdriver further.
  9. Once the connections are made correctly, simply reconnect everything back to its original location.
  10. Finally, ensure that all the pool equipment, such as pumps, lighting, and filtration are turned back on.

Remember to check the user manual that comes with your pool heater to ensure that you are installing it correctly.


A pool heater is an important part of maintaining your swimming pool.  Electric pool heaters help keep your pool warm during cold months. 

Installing a pool heater shouldn’t take too long. Just remember to read the manufacturer’s manual thoroughly.

Also, remember to never operate a pool heater when it is plugged in and unattended. Doing so can cause serious damage to your system.

Need to Hire a Plumber?
Get a free estimate online from top local home service pros in your area.


On Key

Related Posts

Is Drano Bad for Pipes? The Truth Revealed

Need to Hire a Plumber?Get a free estimate online from top local home service pros in your area. Note: This post may contain affiliate links. This means that at no cost to you, we may