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How to Choose The Right Pool Heater

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Categories: How To Guides, Hot Tubs & Spas, Energy Efficiency, Heaters, Above Ground Pools
 
The search for the perfect heater for your pool or spa is sometimes riddled with weird acronyms, strange sizings… and what the heck is a millivolt? This guide, along with our sizing guide will hopefully provide all the information needed to find the heater perfectly suited for your pool.
 
When purchasing a heater, a major consideration is the type of energy used. Your location will also play a part in the type of heater and size. Many residential customers might consider a commercial unit because they’re more heavy duty and may withstand the heavy use of a pool during peak season. If you’re heating your pool year round or use your pool more often than the average residential pool owner, a commercial unit is recommended.
 
Below is a glossary of terms and information to consider when shopping for a pool or spa heater.
 
Heater type
When it comes down to it, there are only a couple ways to heat water... The most common method is using a gas heater. These heaters will burn natural or propane gas to heat the water. There are also heat pumps that essentially work like a backwards air conditioner. Heat pumps use condensed refrigerant that heat up as it is condensed. It will use the heat from the condensing refrigerant to heat the water. Lastly, there are all electric heaters. These have an element that heats up using high voltage electricity. The water passes over the element, heating the water.
 
Gas Heaters
Gas heaters are the most popular option when it comes to heating water because they are the most versatile and most powerful. The only major consideration when it comes to gas heaters is elevation. If you are in higher altitude areas, you’ll need to consider your elevation when purchasing a heater. There are some heaters that will work from sea level all the way up to 9,000 feet without any issues. While others will require a specific heater depending on your elevation. There are two main types of gas with these heaters: natural gas and propane. When choosing the type of gas for your system, verify if you’re going to need a propane tank or if you can run a natural gas line to your heater from the source. If there are any questions about gas, your local gas provider is your best point of contact. Some heaters can be easily converted from natural gas to propane and vice versa, some cannot. We would be happy to review different options with you.

Heat Pumps
A heat pump is a great way to heat a pool with low energy costs. This option uses electricity, but not nearly as much as an all-electric heater. The primary downfall when it comes to heat pumps is that they’re not very powerful, so the option is limited based on the size of your pool. This heat pump sizing guide can help you determine if a heat pump will support your pool. Using a heat pump in the right conditions is by far the least expensive way to heat water. Not the fastest, but the most efficient. A heat pump is a great way to maintain a temperature at low costs during warmer months. Gas heaters and electric heaters are not greatly affected by outside air or water temperature but heat pumps are. Heat pumps work best in warm or humid climates For that reason, Floridians LOVE heat pumps!

Electric Heaters
Electric heaters are different from heat pumps as they use electricity to heat an element that heats the water as it passes though. These use a lot of current and voltage to heat the water and is typically used on smaller bodies of water, like spas and small above ground pools. Some of these heaters come salt compatible.

Heater Sizing
There are many variables involved with sizing a heater. In fact there is so many variables, that there is an entire blog post dedicated to it!

Low NOx
NOx (or oxides of nitrogen) is an emission that is produced in combustion where nitrogen is present (like in the air we breathe) and high temperatures occur. When shopping for heaters, Low NOx is an indicator of the emission being produced is limited. Some parts of the country, such as most of the counties in Southern California counties and certain counties in Texas, require Low NOx emission heaters for commercial applications. Some brands make some models that are Low NOx like Raypak, and others make all their heaters Low NOx like Pentair.

ASME
When purchasing a heater for commercial properties, the heater is required to pass a series of tests to be suitable for commercial applications. ASME (American Society of Mechanical Engineers) is the method and design in which we determine if the heater is suitable for commercial applications. These heaters typically come with a stronger heat exchanger and glass lined metal headers.

Cupro-Nickel
All heat exchangers for gas heaters are copper. Although copper is a great conductor for heat, they’re horrible when it comes to abrasion since it is such a soft metal. The Cupro-Nickel heat exchanger was created specifically for salt pools or pools with harsh water. These types of heat exchangers are copper that have been nickel plated to be more resistant to the abrasiveness of the salt. If you have a salt pool, these types of heaters are highly recommended for warranty purposes. Also, it’s just a great investment overall for a heavier duty heat exchanger.
 
Automation Compatibility
Most heaters are compatible with most automation systems regardless of brand. When a heater is installed, the temperature is set at the heater (typically 100-104 F for spas and 75-85 F for pools). Once the heater is connected to automation, the system will tell the heater to turn by a sensor. Depending on your heater, pool set up, and automation system, functionality will be a little different, but the main benefit is being able to set the temperature using the automation system.

Millivolt Standing Pilot
New heaters are turned on electronically with their own electric ignition. Similar to how your gas stove turns on when you hear that clicking sound. Before this technology was available, all we had was a standing pilot. That is nothing more than a flame that is constantly on which turns the system on when the gas runs through the burners. This is now an obsolete technology, and for good reason. These were difficult to keep on during windy seasons, and if the standing pilot remained on while gas was being pumped through your heater, and it suddenly caught ignition, that would equate in a nice little (or large and not so nice) bang!

Above Ground Pools and Spas
When shopping for heaters for your above ground pool, the largest obstacle that you’re going to face is the type of plumbing that is used. Most above ground pools are going to be using a flex hose type plumbing which most heaters are not compatible with. Make sure your plumbing is compatible with your preferred heater when looking to add a heater to your above ground pool system.

One of the primary things to consider for spas is the capacity of the heater. Typically spa heaters are oversized to quickly heat the spa within a reasonable time frame. A large spa that is a 1,000 - 2,000 gallons can do just fine with a 125,000 BTU rated heater, which will be about a 45 minute – 1.5 hour heat up time depending on your location. Increasing the BTU rating, to 250,000 – 350,000 BTU will drop that time down to as little as 20-30 minutes. Choose the capacity of your heater according to your preferred heat up time.

Gas Line
When sizing your heater, make sure you have the proper gas line size for the distance you’re running to supply the size of the heater. Below is a chart that will help you size your heater according based on the length and size of the gas line. There’s a ratio of size of heater in BTU to length of run. Without this proper sizing, your heater will not function properly or function at all.
 
Natural Gas Through Iron Pipe:

Distance in Feet
100-150k BTU
200k BTU
250k BTU
300k BTU
350k BTU 400k BTU
500k BTU
0 - 50
0.75"
1"
1"
1.25"
1.25"
1.25"
1.25"
50 - 100
1"
1"
1.25"
1.25"
1.25"
1.25"
1.5"
100 - 200
1.25"
1.25"
1.25"
1.5"
1.5"
1.5"
2"
200 - 300
1.25" 1.25"
1.5"
2" 2"
2"
2"
 
Liquid Propane Gas Through Iron Pipe: 
 
Distance in Feet
100-150k BTU
200k BTU
250k BTU
300k BTU
350k BTU 400k BTU
500k BTU
0 - 50
0.75"
0.75"
1"
1"
1"
1"
1"
50 - 100
0.75"
1"
1"
1"
1.25"
1.25"
1.25"
100 - 200
1"
1"
1.25"
1.25"
1.25"
1.25"
1.25"
200 - 300
1" 1.25"
1.25"
1.25" 1.25"
1.5"
1.5"
 
No matter which heating method makes sense for you, it's important to consider your heating purchase as an investment. Our pool experts are always available via phone or email to help you make this purchasing decision.

Finally, it's important to remember that using additional methods to keep the pool warm (solar covers, solar panels, etc.) is another key way to maintain a consistently comfortable pool. Check our out blog article on additional heating methods for your pool.
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