The pool heater’s primary function is to maintain the water temperature in the pool vessel — approximately 82 to 84 degrees Fahrenheit, for regular activity pools and 102 to 104 degrees Fahrenheit for whirlpools. Its secondary use is to heat the water during a start-up phase after the pool has been drained.

Typically each pool vessel requires a dedicated source of heat because codes require that water cannot be mixed between vessels.

There are two primary pool-heating systems and two supplemental heating systems. System selection is important because maintaining constant pool water temperatures leads to guest satisfaction. Water that’s too cold will generate complaints and water that’s too hot raises safety concerns. Following are the different options.

  • Primary System No. 1: Dedicated gas-fired pool heater

Dedicated gas-fired pool heaters are available at standard efficiency condensing (80 to 88 percent) or high efficiency (90 to 96 percent). Pool water is directly circulated through the heater and warmed using natural or LP gas as the fuel source.

  • Primary System No. 2: Boiler system

This type of system generally uses the facility boiler as the common heat source, with a dedicated heat exchanger for each pool vessel, but a dedicated boiler system also may be used. Typically, these systems are designed modularly so the available capacity can change. Generally, excess capacity is built in, so the operator can still maintain a warm pool, even if one boiler fails. This feature makes a boiler-based system very suitable for meeting start-up and maintenance heating requirements.

  • Supplemental System No. 1: Energy recovery system

An energy recovery system utilizes “waste heat” that is transferred to water circulated through a dedicated heat exchanger for each pool. The “waste heat” is generally recovered from a source such as the facility’s central cooling system, laundry or kitchen, and because the source of heat is essentially free, this is typically a very low operating cost system. The drawback is that the heat source must be consistently available when the pools need it, and for that reason, an energy recovery system typically cannot be the primary heating system.

  • Supplemental System No. 2: Active solar systems

Solar pool heating systems use solar collectors to absorb the available solar radiation and transfer that heat directly to pool water circulating through the collector. A dedicated system for each pool vessel or a central system with dedicated heat exchangers for each pool vessel is required.  Because of the low temperatures involved in pool heating this can be one of the most effective uses for solar heating available, with the best payback. As with energy recovery systems, solar is generally not suitable for use as the primary pool water-heating source. A separate primary system must be installed.


When it comes to maintenance, a dedicated gas-fired pool heater system provides no redundancy in operation, so if there’s a heater problem, no heat is available to the pool. Proper installation is critical to maximize heater life and reliability. Also, systems should always be vented properly according to manufacturers’ recommendations, with adequate combustion air available. If your heating equipment is located in the pool equipment room, it is especially critical to eliminate any corrosive fumes from the atmosphere. If it smells like a pool environment, you’re asking for maintenance and service life problems.

With boiler heating systems, required maintenance is generally minimal, from a pool operator standpoint — assuming boilers are already being maintained by the heating plant operator. The control valve becomes the primary point of maintenance for the system.


Pool heating systems are generally reliable, as long as certain parameters are monitored regularly. The most important are efficient combustion and correct water flow. On a regular basis, verify that the venting system is clear and continuous, the combustion air inlets are unobstructed and no contaminants exist. Also verify that there are no gas or water leaks, and check the pool water temperature rise through the boiler to ensure proper flow exists.  If any of these items are not correct, shut the system down and address the issue immediately.

Heat exchanger systems are a more trouble-free option, but as with pool heating systems, certain items should be verified regularly.If you’re having trouble maintaining water temperature, verify smooth, continuous operation of the control valve and that the sensor is clean and providing an accurate control signal. Check the performance of the heat exchanger, verify the temperature and flow of boiler water through the heat exchanger and the temperature difference of pool entering and leaving water. If the heat exchanger is not performing as specified, there may be a fouling problem. This will generally occur on the pool-water side and may require cleaning of the heat exchanger.


In choosing a heating system, selection should be based on a life cycle cost analysis, comparing the expenses of equipment, maintenance, operation and future replacement over a 20-year period. Don’t fall into the “first cost” trap of buying a system that will stress your operating budget for the life of the equipment and the life of your facility.  If “first cost” is your only option now, plan for the future so that when replacement time comes (it will come soon), your options to upgrade to a low life cycle cost system will remain open.

It’s also important to define the required system priorities early in the design process so the desired needs are evaluated and designed in. System reliability should be the top priority, with maintenance (life cycle) and operating costs in a close second position.

Dedicated gas-fired pool heaters are generally lowest in initial cost, but have the shortest life span, five to 10 years, on average. There are high-efficiency options, but as efficiency increases, so do installation and maintenance costs.

Boiler systems are highly reliable, lasting between 20 and 30 years, and efficiency is dependent on the design of boiler plant and circulating loop.

Energy recovery equipment requires a significant capital investment. For that reason, it’s recommended that planning for this type of system begins during the initial design phase. But implementation often occurs later, after facility cash flow has stabilized. Life span can vary quite a bit. Usually there is a heat exchanger involved that may have a lifetime of approximately 25 years. The actual source of the heat recovery may be chillers, heat pumps that give off waste heat. This type of equipment typically has a lifetime of about 20 years. 

With solar, some additional items that must be addressed during system design include freeze protection and choosing either variable speed or constant speed pumping and control. Expect solar heaters to last 15 to 20 years and in-line circulating pumps, 10 years.

About the Instructor

Dan Dehnert is the chief mechanical and production engineer for Iconica, based in Madison Wis. Dehnert has more than 30 years of experience doing MPE and design, and more than 15 years experience designing mechanical and electrical systems for indoor waterparks.