Proper installation
The key to a properly installed and performing gas pool heater begins with selecting an appropriately sized heater (in British thermal units [BTUs]), which aligns with the fuel source available. Then, the heater must be positioned to achieve proper clearances for performance, maintenance and safety.
Whether installing a gas heater on a new equipment pad or replacing an existing system, a thorough understanding of the fuel source is necessary to ensure meters and fuel lines are sized properly for the gas heater being considered. When replacing an existing heater installation, it may be necessary to downsize to a smaller heater, as today’s more efficient fan-assisted combustion heaters require exact gas pressure to operate properly.
A smaller heater, which aligns with the gas source available, will almost always result in improved heater performance and swimming pool and hot tub heating due to its more efficient combustion process. Again, always evaluate the existing or planned gas line and meter to ensure the heater being installed will operate correctly and efficiently.
Before starting any gas heater installation, it is imperative that the installation and operating instructions supplied with the chosen heater be thoroughly read and understood. Additionally, all gas heaters must be installed in accordance with all local and provincial/state codes. Installation must also conform to the latest edition of the National Fuel Gas Code (American National Standards Institute [ANSI] Z223.1/National Fire Protection Association [NFPA] 54) and with the requirements of the authority having jurisdiction.
Size selection
Selection of a specific gas heater, after gaining an understanding of the available fuel source, requires two basic considerations: size and cost of operation. Size of the gas heater should be maximized to provide the most rapid heating of the pool or hot tub as possible. An undersized gas heater will surely result in complaints from the owner with regards to the pool or hot tub not heating up fast enough.
To estimate heater size use 10 Btus every hour for every 0.1 m2 (1 sf) of pool surface area for every one-degree temperature rise. For example, a 4.5 x 9.1-m (15 x 30-ft) swimming pool yields 42 m2 (450 sf). To increase this pool’s temperature by one degree would require a 4,500 Btu heater. Assuming a 20 degree temperature rise is desired, 90,000 Btus per hour would be required to hold the temperature. In a 24-hour day, that would equate to a total of 2,160,000 Btus. In dividing this by the pool pump’s eight-hour per day circulation time, it shows a gas heater capable of 270,000 Btus per hour is required. It is important to note gas pool heaters are rated in Btus per hour of input. Therefore, a heater at 400,000 Btu per hour input with a thermal efficiency of 82 per cent will generate an output of 328,000 Btus.
The cost to operate this type of natural gas heater can be determined based on the cost of a therm (100,000 Btu/hour of heat) of gas.
Continuing with the example, dividing 400,000 Btus/hour by 100,000 Btus/hour results in four therms/hour. This result is then multiplied by the circulation pump’s eight-hour-per-day run time to determine 32 therms/day are required to run the heater. Assuming a cost of $1.10 per therm, it will cost $35.20 per day to operate.
