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water as a by-product. If ….

water as a by-product. If the heat exchanger is too cool, the humid flue gases will condense on the fins of the heater. Condensation on the heat exchanger causes carbon to stick to it. Specifically, water collects and then drops onto the burners. The combustion is then impeded as a sprinkling of water interferes with the flame pattern. That poor combustion turns into soot, which collects on the fins, causing the flue gasses to be impeded. The condensation will not only result in heater function inefficiency, but will also cause oxidation on copper.

Low gas pressure: Low gas pressure can lead to damage of the internal parts of the heater. Low gas pressure leads to build-up that blocks the heat exchanger.

Lack of proper ventilation: Proper ventilation prevents sooting, which does not allow the heater to work at its maximum efficiency because the soot insulates the heat exchanger and heat does not transfer to the water as well.

Costs of Reduced Efficiency

Let’s take a 25,000-gallon pool as an example of how old, inefficient heaters affect operating costs. (Note that 1 Btu will raise 1 lb of water 1 degree Fahrenheit) Heat Up Time and Cost

Let’s say you have a 25,000-gallon pool that requires a 30-degree temperature rise.

NOTE: 1gal of water weighs 8.33 lbs

25,000 gal x 8.33 lbs = 208,250 lbs of water in the pool to be heated 208,250 lbs x 30-degree rise = 6,247,500 Btu’s required

(Btu’s is a measurement / hour) So, you need 6,247,500 Btu’s to raise the water 30 degrees or 260,313 Btu’s per hour.

(3,332,000 ÷ 24 hours = 260,313 output Btu per hour required)

A new 400,000 Btu heater that is 95% efficient has a 380,000 Btu output.

With at 380,000 Btu output it will take about 16 hours to raise that 25,000-gallon pool by 30 degrees.

6,247,500 Btu’s ÷ 340,000 = 16.4 Hours

As we all know, gas companies charge by the Therm.

To figure out how much it will cost to heat, note that 100,000 Btu’s = 1 Therm.

If we know that it takes 16.4 hours to heat a 25,000-gallon pool with a 30-degree temperature rise using a 400,000-Btuheater that is rated at 95% efficient (i.e. 380,000 Btu output), then to figure out the cost of the gas required to heat that pool with that heater:

Hours of heat up time x input Btu’s ÷ by 100,000 x cost of a Therm 16.4 X 400,000 = 6,560,000 total Btu’s 6,560,000 ÷ 100,000 = 65.6 Therms used If the cost of a Therm of gas is $1.20/Therm then: 65.6 Therms x $1.20 = $78.72

It will cost $78.72 to raise that 25,000-gallon pool by 30 degrees in a 16.4-hour period.

But if we had a 10-15 year old 400,000 Btu heater that was originally rated 78% efficient but is now probably only operating at 65% efficient, then you are looking at a heater that outputs only 260,000 Btu’s so:

6,247,500 Btu’s required ÷ 260,000 = 24 Hours 24 x 400,000 = 9,600,000 Btu’s 9,600,000 Btu’s ÷ 100,000= 96 Therms 96 Therms x $1.20 = $115.2

This means that it costs the facility 32% more to heat the same body of water with their older heater.

Propane Example

Consider a similar example for propane use:

1 Gallon of propane = 92,000 Btu 16.4 hours of run time x 400,000 Btu input = 6,560,000 Total Btu’s required 6,560,000 ÷ 92,000 Btu = 71.3 Gallons of Propane If the cost of 1 Gallon of propane = $3.00 71.3 gallons x $3.00 per Gallon = $213.9 But if it takes 24 hours to increase the temperature then: 24 x 400,000 = 9,600,000 Btu 9,600,000 ÷ 92,000 = 104.35 Gallons 104.35 x $3.00/ gal = $313

Again, it will cost the facility 32% more to heat their pool with their older, less efficient heater.

Choosing a heater for a particular pool

Once you can explain how the heater works and why older heaters don’t operate as efficiently, dramatically increasing operational costs, it’s time to figure out what kind of heating unit is appropriate for your customers’ swimming pools.

To calculate an approximate heater size for a pool, pool professionals need to: a) Determine the desired swimming pool temperature (average is 82 degrees for competitive swimming). b) Determine the average temperature for the coldest month of pool use, if the pool is outdoors. c) Subtract the average temperature for the coldest month from the desired pool temperature. This will give the temperature rise needed. d) Calculate the pool surface area in square feet. e) Use the following formula provided by the U.S. Department of Energy:

Pool surface area x Temperature Rise x 12 = the Btu/ hour output required

Based on this information, you can decide which heater is appropriate for your pools.

Additional benefits to heater upgrades

In addition to energy and money savings, there are a few additional reasons to upgrade to a new heater: 1. Lower Emissions: Today’s heaters are cleaner burning heaters (or Low NOx) heaters which have minimal emissions.

In most of California, as well as Texas, these are required and have a regulated emission standard.

More states are sure to follow in the coming years.

2. Easier Maintenance: Newer heaters are much easier to install and maintain, because they are designed to be more “plug and play,” including such features as sealed combustion, reducing the chance for internal issues to occur such as condensation.

Modern units are also ultra-quiet, have faster heat-up times, and are easy to install both indoors and out.

3. Sealed Combustion: Many new heaters today have sealed combustion units. These are safer because: a) Pool heaters installed indoors are frequently located next to stored chemicals, and sealed combustion presents much less of a fire hazard. b) Adequate combustion air is guaranteed when outside air is ducted with a sealed combustion unit.


Armed with all such facts, pool professionals may find it easy to sell and upgrade customers to a newer, more efficient heater that will immediately reduce the pool’s energy bills. With so many families at home and hoping to extend their swim season, updating the heater will surely make customers happy, especially when they see how it lowers their monthly bills.

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