Aquatic Facility Maintenance

Delivering healthy indoor air quality

By James Hogan

elieve it or not, at least half of the recreational indoor pool facilities in North America are not delivering the kind of indoor air quality (IAQ) that is considered healthy. Poorly operating facilities can lead to many problems, including asthmatic conditions, poor indoor air comfort and ultimately, poor attendance.

Recreation managers aren't expected to be architects, engineers or HVAC technicians, but they should know enough about the basics of indoor pool operation to determine if their facilities are operating correctly. For proper IAQ, a natatorium must have synergy between the building envelope, the air distribution (ductwork), mechanical dehumidification equipment and water chemistry. If any of these important components break down, the facility will not function properly.

Ongoing neglect of a dysfunctional natatorium goes beyond impacting general health. Numerous instances of untamed humidity within natatoriums have led to collapsed roofs or resulted in building demolition or complete reconstruction.

Poor natatorium IAQ might require only a quick fix of pool-water chemistry or routine mechanical equipment service and calibration. Unfortunately, in many cases major reconstruction of the building or air distribution is needed to remedy poor IAQ problems.

Dehumidifier basics

Almost all indoor pools have some type of mechanical HVAC equipment. Most modern pools have a commercial dehumidifier that, depending on its size, is specially designed to eliminate up to several hundred pounds of moisture per hour from the natatorium air. Besides dehumidifying the natatorium to approximately 50 percent relative humidity (RH), many dehumidifiers also provide air conditioning for the space and can use heat recovery to heat the pool water.

Keeping the space relatively dry at 50 percent RH is critical not only for the integrity of the building structure, but also for the general health of the occupants. Some older facilities might have conventional air-conditioning equipment, which can't handle the excessive humidity of indoor pools. Depending on the season and geographical location, conventional air conditioning typically can't provide 50 percent RH all year long.

Modern dehumidifiers from as early as the 1980s have a microprocessor controller with a read-out that indicates room and pool conditions, plus the diagnostic operating status of the unit. Daily monitoring and recording will indicate any abnormal operating conditions such as high RH, temperature variances, etc. This controller is mounted either on the unit, in the mechanical room, near the pool or located remotely in an administrator's office.


  • Remove moisture
  • Distribute air on windows
  • Prevent moisture migration in the structure
  • Reduce chemical off-gassing in pool water

HVAC service contractors don't necessarily see dehumidifiers regularly. Therefore, a facility manager shouldn't automatically assume that the dehumidifier has been installed properly or maintained correctly. For example, many dehumidifiers are designed to recover heat and thus provide free pool-water heating. However, there are many incidences where the pool-water circulation system was never connected to the unit. This can cost tens of thousands of dollars in pool-water heating costs because the backup boiler becomes the primary pool heater.

While a dehumidifier should be serviced by a certified refrigeration technician, a recreational facility manager should keep a maintenance checklist. Some manufacturers supply maintenance checklists as part of the machinery manual.

A general checklist is:

  • Air filters should be replaced monthly.
  • Fan belts should have proper tension because loose belts can diminish air flow. Overly tight belts can result in blower damage.
  • The condensate drain pan should be cleaned semi-annually.
  • Older-model dehumidifiers have motor bearings or blower bearings that should be greased annually. Newer models may have permanently sealed assemblies that need no lubricants.

Attentive eyes, ears and noses are the best deterrent to emerging IAQ problems. Problems may be indicated by mechanical equipment noises, unusually uncomfortable IAQ, atypical chemical odors, condensation on windows or visible building damage such as crumbling brick and discolorations on walls or ceilings.

Another natatorium rule-of-thumb is maintaining a one- to two-degree differential between water and space temperature. For example, a pool-water temperature of 82 degrees would dictate keeping the space temperature at about 84 degrees. These temperatures and set points should be accessible via the dehumidifier controller readout.

Building and airflow problems

While the dehumidifier typically is blamed for any condensation problems, 80 to 90 percent of these problems are due to poor architectural and airflow designs or installation mistakes.

For example, the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) has established standards indicating that vapor retarders-plastic films or other materials that reduce the amount of pool area moisture migrating through the walls, ceiling or floors of the structure-should envelope the natatorium without any breaks. But many retrofits of dysfunctional natatoriums have revealed gaps, tears or improper seals in vapor retarders. It's not rare for this essential natatorium building material to be completely missing. Uncontrolled moisture migration can cause dampness within the structure and possible biological IAQ issues, such as mold and mildew.

Airflow problems are very common in natatoriums. Fogged or wet windows are leading indicators of airflow problems. Supply air diffusers should be within a foot of all windows with exterior exposure. The air should cover the entire surface of the glass. Overhead ductwork may not be sufficient when windows span a wall from the deck to a high ceiling. Smart architects use under-floor ductwork along with overhead ductwork aimed at the bottom and top of the window surfaces, respectively.

Improper ductwork installation, especially near the dehumidifier, can reduce both supply and return airflow.


Paul Richards suspected something was wrong with the indoor air quality (IAQ) when his swim team members kept developing asthmatic and other breathing conditions. Inhaler use was as common as swim goggles.

Richards, the swim coach and manager of the Dickinson College natatorium in Carlisle, Pa., finally convinced school officials that the lack of proper dehumidification was not only harmful to students, but was taking a toll on the space's infrastructure and an adjacent 80,000-square-foot fieldhouse.

Richards, who has a master's degree in sports sciences with a specialization in aquatics maintenance, management and design, reversed the downward IAQ trend with a new dehumidifier and ductwork.

Today, Richards reports that the facility has a healthy IAQ and it's a lot easier to recruit prospective swimmers.

Water chemistry

Perhaps the easiest precaution a facility manager can exercise is storing pool chemicals in a separately ventilated space away from mechanical equipment. Whether covered or uncovered, these chemicals can cause IAQ problems and prematurely corrode most metal. Therefore, chemicals should be stored in their own designated space and not in a mechanical room.

Many pages could be allotted to proper water chemistry, and most pool facility managers already understand chemical balances and the dangers, especially chloramines production, that exist when this important category is neglected.

Besides health risks to occupants, equipment can be severely damaged by prolonged exposure to chloramines. Typically, all dehumidifiers and other equipment manufactured for indoor pool applications have protective coatings and other safeguards protecting them against moisture and corrosives. However, no mechanical equipment can withstand prolonged exposure to excessive chloramines resulting from poor water chemistry.

The parts of the natatorium must work together. A recreation manager can prevent most IAQ problems by controlling the building construction, the mechanical systems and the pool-water chemistry.


James Hogan is product development engineer at Dectron Internationale, a manufacturer of indoor air quality equipment. In his eight years at Dectron, Hogan has advised hundreds of natatorium building owners with IAQ problems. He also is the director of the Dectron Installation & Service School in Niagara Falls, N.Y. For more information, visit

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