Here is some information to help you in your thinking and planning process.
There are so many choices on the market today that selecting the one that is right for you can be a bit confusing. What type of heater is best for your pool? What size heater do you need? Often, we only hear the "good stuff" from manufacturers and sales info, but are left to wonder about or find out the hard way some of the "not so good stuff". Typically in our area, we see GAS FIRED POOL HEATERS, POOL HEAT PUMPS, AND SOLAR POOL HEATING SYSTEMS. Each has their own advantages and disadvantages that we try to address briefly in this blog post.
The first thing you need to know is that it CAN be quite expensive to heat any swimming pool, particularly if you are counting on your heater to extend the season by a number of weeks early in the spring and later into the fall. It is usually more practical to use a heater to enhance your normal swimming season by giving you more swimmable days. How many times have you gone out on a cloudy day in the summer and wished the pool was just 5 degrees or so warmer so it would be more comfortable to get in? This is the true value of a pool heater in our Maryland climate - owning a pool heater can give you the maximum number of swimmable days in our short swimming season and used in this way can be relatively inexpensive to run. How inexpensive or expensive it is to heat your pool depends on quite a few factors that include size of the pool in surface area, capacity of the pool in gallons, environmental conditions at your particular pool location (windy, woodsy, sunny, etc), temperature differential between air and pool (how cold is it outside vs. how warm do we want the pool?), and whether we are using the pool heater for maintenance heating (heating the pool and then maintaining a constant temperature throughout the season) or demand heating (heating the pool intermittently only as needed and when desired). Most manufacturer heater sizing charts are based on “average” environmental conditions and usually include one chart for maintenance heating based on pool surface area and one chart for demand heating based on pool capacity in gallons. It is important to remember that all pools (and spas and any body of water) loose 90% or better of their heat through evaporative cooling through the surface area of the pool. Utilizing a SOLAR BLANKET with any pool heater cuts evaporative heat loss to a minimum and is the single best thing you can do to minimize energy costs with any type of heating system. Solar blankets typically are cut to fit and float on the top of the pool water.
SIZE MATTERS!! Regarding HEATER SIZING, you should always check the manufacturer charts to make sure you are never buying a heater that is simply too small to effectively heat your pool. If you select a heater that is marginal or too small for your size pool, chances are you are just throwing you money away as it can never heat your pool the way you want. BIGGER IS USUALLY BETTER!! Gas heaters and electric Heat Pumps are usually rated in bTU sizes. By way of example, assume we have two identical pools right next to each other in exactly the same environmental conditions and want to heat both pools from 60 degrees to 85 degrees. Pool #1 is heated by a gas fired 250,000 bTU heater and pool #2 is heated by a gas fired 400,000 bTU heater. In a “textbook” situation, by the time both both pools reach 85 degrees both will have used EXACTLY THE SAME AMOUNT OF GAS to do the job. Pool #2 with the larger size heater will have simply done the job in about half the amount of time. In practical (not “textbook”) application, since pools loose a great amount of heat through the surface area and this loss is constant based on time, the larger capacity heater can actually use LESS GAS over time because there is less heat loss during the shorter heat up time!
GAS FIRED POOL HEATERS, while more expensive in terms of energy cost than other alternatives, are usually the best overall choice for heating any pool in our service area. They seem to give the best balanced combination of comparatively low initial cost, quick heat up time, fuel consumption and cost, and ongoing service and maintenance. Blue Waters has technicians that are capable of repairing just about any problem you may have with your gas fired pool heater. They are available for either propane (LPG) and natural gas use, depending on what is available in your area and also available with either electronic ignition or standing pilot (millivolt) versions. While the millivolt heaters cost a little less up front, electronic ignition is usually more trouble-free over your years of ownership. If you have a pool and spa combo and/or you want to be sure, no matter what the conditions that your pool is heated when you need it, then beyond a shadow of a doubt an electronic ignition gas fired heater is the best choice for you. For the reasons above, it is usually best to choose the largest size heater available for your pool. Just remember to check with your local gas supplier to make sure they can supply the gas to feed your heater.
SWIMMING POOL HEAT PUMPS definitely win in the category of efficiency of fuel cost over gas fired pool heaters. When you read this in manufacturer information, it is not a lie. Be careful to look at the big picture, though. Heat pumps by nature heat whatever they are heating (pool or house) very slowly - usually by only a fraction of a degree per hour. For this reason, they are better thought of for “maintenance” heating rather than “demand” heating. The colder it is outside, the less heat is available to “pump” into your pool and the heat pump becomes less effective. At air temperatures too much below 50 degrees, most swimming pool heat pumps become unable to add any significant heat to your pool. They are also more costly to purchase up front (often twice the cost of a gas fired pool heater) and because they utilize a mix of technologies (they are similar to an air conditioner working in reverse to add heat to a pool) it is often difficult to know who to call to solve your heat pump service problem. Control and water chemistry and flow issues can usually be handled by Blue Waters Inc.,your pool service company, but the refrigeration aspects usually require an HVAC technician. You are a good canditate for a heat pump if you simply want the lowest energy cost to run your heater, religiously use a solar blanket or have a relatively small pool in terms of surface area, are never in any particular hurry to get the pool up to temperature, and don’t really ever have the need to extend your season too far in either direction and/or for any reason cannot get any kind of gas supply on your property. If you are considering a heat pump for your pool, remember again that BIGGER IS USUALLY BETTER. Blue Waters will be happy to recommend a quality heat pump that can best meet your needs.
WHY NOT BOTH? Adding one of each to your pool gives you the best of all worlds. The powerful, fast heating gas fired heater can be used to handle the extreme circumstances of overcoming cold air temperatures, extended seasons or needed quick “demand” heating and the much more econimical heat pump can be used to take over the “maintenance” heating to keep the pool warm at the lowest energy cost.
SOLAR HEATING SYSTEMS can be quite tempting with their promise of “free” energy to heat your pool. Usually composed of large, dark colored panels that your pool water flows through to be heated by the sun, solar heating systems need a rather large area that is exposed to constant sunshine to do their job. The larger the surface area of the solar panels, the more heat they are capable of adding to the pool. They are typically mounted on the sunny side of the roof of your home and require re-piping of the pool to divert water through the solar panels to be heated when the sun is shining. While this is a great concept, remember that solar heaters only work when it is warm and sunny outside - typically the times you need to heat your pool the least. If it is cloudy or cool outside, a solar system has the potential to work in reverse, acting like a large “radiator” that can increase the surface area heat loss of the pool if pool water is flowing through it during a non-desirable period such as a cool day or night. If you have a suitable location to mount a solar heating system, they are best used to simply keep the cost of energy used by gas heaters or heat pumps lower, but can be rather disappointing in our climate as a stand-alone heating system.