The pool water is typically heated by means of either thermostatically controlled heat exchangers, which use the building’s central boiler or steam system as their heat source, direct-fired pool heaters, or recovered heat from the natatorium dehumidifier or two of the above. The respective heating systems must be capable of maintaining desired water temperature.

Lochinvar are "low NOX direct fired pool heaters" - they range from 88% to 97% efficiencies and they are NSF listed with cupronickel heat exchangers and bronze headers. Lochinvar has pool heater R & D division that is ongoing.

Raypak is as a lesser pool heater option although they are not as well supported or serviced but they do maintain an NSF listing. Raypak are also not as efficient as Lochinvar, as they are only 84% efficient at the top end. The heat exchanger is standard copper as opposed to cupronickel and they don’t have bronze headers, they are steel on their pool heaters so have a limited life.

Pentair Heaters "Power Max' are also available and are NSF listed. 82% efficient with copper heat exchangers, no bi pass pump with unit.

Pentair’s Master Temp 400 heater should not be used for commercial applications due to multiple failures at Crown Valley Teaching Pool.

Pool heaters need to be initially started and adjusted by an authorized pool heater representative.

'Pool Boilers' are atmospheric hot water boilers similar to Parker Boilers and are commonly seen in Arizona - these have 24" flues and require 3'-0" of clearances on all sides and run at 65% efficiency. They require medium pressure gas hook ups and a drain sump.

If the dehumidification system is being used to supply heat to the pool, then it often necessary to provide a backup heat source as the dehumidification may not be able to handle the entire load. The backup would normally be either a heat exchanger or a gas fired heater that requires a separate set of connection tees on the pool’s return line.

If there are more than one bodies of water in the system, the dehumidification will only be able to provide heat to one of the bodies.

Occasionally, stand-alone pool heaters are recommended so that building heating system boilers do not have to operate in summer. If there is a central steam or hot water system that will operate year-round, heat exchangers may be preferred.

Normally, a side stream of 20% to 40% of recirculation is heated, and then mixed into the pool recirculation.

Unless the capacity of the pool filter system is specifically designed to accommodate the heating system, then a booster pump may be necessary for conveyance of the pool water from the filter return line, to the heat source and return.

The heating system for a spa should be designed to heat the initial fill water in a relatively short time. Because of the high bather concentration in a spa and the small amount of water, the owner may choose to empty and refill the spa several times a week, or even once a day.  Because of this, consideration should be given to designing the spa heating system for heating the initial fill water in approximately 4 to 8 hours (8 hours would typically allow the spa to heat up overnight).   A cross fill from the swimming pool to the spa will reduce both the energy demand and the time required to heat the spa.  Cross fill connections are not allowed in every state.

  • The majority of West Coast projects require direct-fired pool heaters.
    • For these projects, Lochinvar should be the basis of design because the meet the SCAQMD (Southern California Air Quality Management District) low NoX requirements and because of their stacking and venting capabilities.
    • Heater locations and piping should be shown on CH drawings.
    • Structural calculations and drawing details for the heater stacking racks need to be provided.
    • The schematic drawings should indicate all valve locations, CPVC/PVC flanges, thermostats, and detail to join main pool return lines.


Interlock heaters to the pump so they do not stay on when the pump is off and therefore do not melt the pipe.

Make sure there is sufficient fresh outside air makeup, so they do not soot (Colorado Springs).

Heaters need to be de-rated for projects at elevations above 2000 feet from sea level. Heater de-rating is 4% for each 1000 ft above sea level.

Most health codes do not allow cross connections between pool systems. Separate heat loops/heat exchangers must be provided for each pool.  If heat loops or heat exchangers are shared, water from multiple pools will be mixed.  This creates the possibility of cross contamination between the various bodies of water.  Shared heater piping also prevents the cross-connected pools from operating at different water surface elevations.

A dehumidification unit has only one influent and effluent connection, therefore each dehumidification unit should only be used to provide heat to one pool system in order to prevent a cross connection between multiple pools. (Additional heat exchangers can be added to the dehumidification unit effluent piping to deliver heat to other pools if required.)


  • Heaters should be connected to the swimming pool system with CPVC with the possible use of short sections of stainless steel or copper piping to serve as heat sinks if the heat source is of a high enough temperature to adversely affect the pipe.
  • Copper piping has been used throughout the construction industry for sixty years as an interface with hot water heaters and steam heat. CPVC was developed in the 1960s and 70s for exceptionally high pressures and temperatures.  With regard to pool heating systems it is believed that the copper piping has the advantage of creating a heat dissipation line that is beneficial should there be a malfunction in the heater valving which permits hot water to siphon back into the pipes should the pressure system (filter pump or inline pump) fail.
  • While CPVC will not dissipate the heat like copper, the inverse of that statement is that it will not lose as much heat in the water flowing back to the pool.
  • CH does not suggest the use of copper piping for the entire length of pool heating recirculation. Copper piping, over a period of time, can sometimes lead to elevated levels of copper in the pool water and the eventual staining of some pool finishes. The swimming pool drawings typically show by-pass tees in the return line for a flanged connection to the heater loop.  Mechanical is to provide service valves and thermometers at the point of connection.
  • Even when chlorine gas escapes into a space that has copper piping, the copper will oxidize creating a green patina, which usually stabilizes with minimal advancement of this oxidation. Should the environment be especially aggressive over a long period of time the sweated fittings are the first to fail and then the piping will need to be replaced.  Failures of this type frequently occur for both copper and CPVC at the threaded male-to-female connection at the heat exchanger.

Solar Heating


  • Passive solar heating systems where the building itself serves as a solar collector and heat storage device, should be considered; South facing glazed areas, protected from the summer sun by overhangs will admit heat and light during the winter months.
  • The concrete pool deck, masonry walls of the interior wall of the natatorium and swimming pool itself may be designed to be the needed thermal mass for providing energy storage and to dampen temperature fluctuations.



  • In general, active systems employ hardware and mechanical equipment to collect and transport heat.
  • Condensing Boilers
  • Rice University wanted the design team to investigate using a condensing boiler method for heating their outdoor 50-meter and 2500 SF leisure pool. The primary driving force behind this was the pursuit for a more efficient and “green” pool heater.
  • Lochinvar does not offer a condensing boiler. Raypak manufactures an Advanced Design Boiler (ADB) which has been around for a few years.  The big difference between boilers and pool heaters is that Lochinvar puts chemically treated water through the pool heaters.  Boilers do not see water that is chemically treated.  Lochinvar has a high efficiency unit called the Intellifin which if used as a pool heater would be 97% - 98% efficient, but because of the chemicals in pool water, they never put that product in their pool lineup.  Raypak’s ADB picks up some of its efficiency from a secondary heat exchanger that captures heat from the flue.  This is a condensing heater which requires a condensate line and limestone pit.  The life expectancy for this heater will only be as good as the water chemistry.
  • The Intellifin 1500 from Lochinvar retails for approximately $37,000. The ADB 1001 from Raypak retails for approximately $31,500 and the ADB 1501 goes for about $39,000.  The ADB 1501 is Raypaks largest model.  Lochinvar makes a 1.7 and 2.0 million BTUH models.  The Lochinvar CPN1801 costs approximately $20,000 and is capable of 1.8 million BTUH.
  • The only realistic option that was discussed to have the condensing boiler last more than a year or two was to add a heat exchanger so that the pool water does not come in contact with the unit that is really not designed for the corrosive water found in pools. However, the cost for such a system would be significant.  Lochinvar is currently doing research on such a system for testing and evaluation.  They are using a copper-fin boiler and shell and tube hex.  The pool water never comes in contact with the boiler and the efficiency of this system will be in the 94% to 96% range.
  • In the end, the cost comparison was $40,000 for two pool heaters and around $147,000 for three condensing heaters with heat exchangers.

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