Frequent
Questions

You’ve Got Questions. We’ve Got Answers.

Have questions about solar and heat pump swimming pool heating? Or high efficiency home water heating? Here are the questions we are most often asked. If you don’t see a particular question that you are interested in, please use our contact form to ask your question and we’ll get back to you with an answer. We try to answer all questions within a day or so.

How much of the year can we expect to swim if we don’t heat our pool?

Generally speaking, you can double the number of days of pool use per year up to 290 days along Florida’s Treasure Coast.

A lot depends upon how you use your pool and your tolerance for colder temperatures. Residents of northern climates are completely comfortable swimming in 78°F water and this is usually the temperature required for competitive swimming events. On the other hand, Florida residents usually like their pool water a bit warmer; at least 80°F or more. And if you are heating your pool for therapeutic reasons, you will want at least 85°F water and possibly as warm as 90°F.

A screened pool in South Florida will typically be at least 80°F or warmer for about three-and-a-half to four months and may reach 83–85°F from mid August to early September. Open pools are a bit warmer because the pool surface receives more direct solar energy, and may stay comfortable for an extra month or more.

What are the health benefits of heating my pool?

Doctors and physical therapists regard swimming as a very beneficial form of exercise because it works the entire body without impact stresses on the joints. A heated pool can safeguard your health and contribute to your well-being by allowing you to exercise throughout the year.

And while children love to swim and can often tolerate lower temperatures, pediatricians caution that repeated chilling can make young children more susceptible to respiratory infections. This can also be true for elderly swimmers. A heated pool prevents chilling and problems associated with excessive body heat loss.

Compared with a gas heater, how long does it usually take for a solar pool heater to pay for itself with savings?

After subtracting the installed cost of a gas heater and propane storage tank, you will usually recoup the additional cost of a solar pool heater within about one year for propane and less than two years in the case of natural gas.

This assumes keeping a pool at least 80°F or so during the spring and fall and at least 76°F or so during the winter, at current fuel costs, and keeping the pool continuously heated to at least the desired minimum temperature throughout the heating season. An additional financial benefit of solar is that the leading solar pool heating collectors have useful lives of 20 years or more. Even the highest quality gas heaters have to be replaced every 10 years or so, and the average is probably closer to seven years.

How automatic is a solar pool heater?

Completely. All you do is set your pool pump’s time clock or automation system to run during the daylight hours, then set the solar pool heater’s automatic control temperature indicator to your preferred temperature. The control system takes care of the rest. Sensors compare the temperature at the solar collectors with you pool water temperature. Whenever the solar collector temperature is at least four degrees warmer than your pool water, the control system adjusts a motorized valve to divert pool water through the solar collectors if your pool is not at the desired temperature.

And even if your pool cannot reach your preferred temperature setting during the coldest winter weather, your pool will always be warmer than a neighbor’s similarly situated unheated pool, without you spending a penny on expensive fuel.

How can I determine what size and type of pool heater is best for me?

Every situation is different and relying upon simple “rules-of-thumb” can lead to unrealistic expectations and unhappy cusotmers. Among the many factors we consider when sizing a pool heater are:

desired swim season length
preferred water temperature
type of pool use (exercise, kids playing, casual dips, etc.)
therapeutic requirements
screen enclosures and other direct shading of pool surface
open space and windbreaks, especially along northwest to northeast exposures
waterfront location
distance between pool equipment pad and pool heater
for solar, availability of sufficient unshaded roof or other installation location
for solar, direction best available roof area faces
willingness to use a pool blanket
ability and willingness to pay increasing energy costs

I keep reading about the pool’s surface area. Why don’t you use the number of gallons in my pool for sizing?

Your pool’s water volume (gallons) does matter, especially if your system is installed during the winter, because the water temperature of an unheated pool during the winter months can be as much as 20 degrees below the desired temperature. In this case, dividing the estimated average daily Btus of heat input from the heating system by the pounds of water in the pool (water weighs 7.5 pounds per gallon) tells us how fast we can bring the pool up to the desired temperature.

On the other hand, in normal operation we are simply trying to replace the two to four degrees of water temperature lost overnight, and most heat loss occurs through evaporation at the pool’s surface. This is why we size pool heating systems in relation to the pool surface area.

How well do solar collectors work during cloudy weather?

A solar pool heating system will typically collect about half the solar energy of a clear, sunny day on an overcast day. If you have ever had the experience of going to the beach on an overcast day and still getting a sunburn, you understand this phenomenon. Clouds block many of the visible wavelengths of sunlight, but much of the heat energy still gets through.

How well will my solar pool heater work during cold weather?

Solar pool heating collectors typically deliver excellent performance in Florida during cold weather because the sky is very clear during winter high pressure waves. On the other hand, increased evaporation from your swimming pool surface can significantly reduce your pool temperature during cold fronts. A pool blanket can help keep heat from escaping.

How long will it take for my pool to heat up after my installation is completed?

This depends upon what time of your system is installed and will be greatly accelerated if you use a pool blanket to keep the added heat in the pool. For most solar pool heaters and with a pool blanket in place, an unheated pool will usually come up to temperature within three days or so during the spring and fall.

We have an installed pool heater. How can we tell how well the system is working?

Of course, if your next door neighbor’s pool is unheated and has similar site factors (screen enclosure, windbreaks, etc.), you can simply compare water temperatures.

If you don’t happen to have such a convenient comparison point, or if you simply want to better understand your pool’s temperature dynamics, the method described below will provide you with a pretty good approximation of what your pool’s current 24-hour average temperature would be without supplemental heat.

Go to www.Weather.com and enter your zip code into the search box at the top of the page.
When the results page for your local weather appears, look in the left column for the list of links for different types of local weather data (“Yesterday,” “Today,” “Hourly,” “Weekend,” etc.). Select “Monthly.”
Record the daily high and low temperatures for each of the preceding six days. You should have 12 temperature points. If you are within the first six days of the month, use the “Previous” link at the top left corner of the calendar table to see the last few days of the previous month.
Calculate the average for the 12 temperatures (the high and low for each day). The result will be a good estimate of the current day’s temperature of an unheated pool in your locale.

Remember that on a sunny day, a solar heated pool is usually at least three degrees warmer during the afternoon than during the early morning hours. So your unheated pool might be a degree or two cooler than the average temperature for the previous six days, first thing in the morning, and a degree or two warmer late in the afternoon.

Also, keep in mind that www.Weather.com often publishes the same weather data for every zip code within a single county or large metropolitan area. However, actual air temperatures within the same county or metro area will vary: a bit warmer in urban surroundings and a bit cooler in rural surroundings. This is called a microclimate difference. You can get a good estimate of any microclimate difference applicable to your pool by comparing the Weather.com current local air temperature for your zip code with an outdoor thermometer reading. Just make sure the sun isn’t shining directly on the thermometer.

Can my solar pool heating system also be used to heat hot water for my home?

No. This requires two different systems. Home water heating water temperatures of 125°F to 140°F call for solar collectors constructed with metals like copper that conduct heat well, and insulation and glass cover plates to keep the extra heat from being dissipated into the air. Swimming pool solar collectors typically operate at temperatures of just 75°F to 95°F, so they can be constructed of polypropelene plastic and do not require insulation or cover plates.

How long will polypropylene solar collectors last before I need to replace them?

Millions of square feet of polypropylene solar pool heating collectors have been operating in the field since the late 1970s. You can expect 20 to 30 years of service from high quality solar pool collectors before replacement is recommended. This is far better than a gas pool heater, which loses efficiency each year and usually requires replacement after seven to 10 years.

Should my solar collectors be removed from the roof if a hurricane is approaching?

No. The mounting systems for all solar collectors approved for installation within Florida are engineered to withstand hurricane windloads. It is not unusual to see completely intact banks of roof-mounted solar collectors on a heavily damaged house following a hurricane. If solar collectors are detached from the roof after a hurricane, either (1) the system was not installed in accordance with the approved installation mounting and fastening specifications; or (2) the house was destroyed, as happened with thousands of homes during Hurricane Andrew.

Should I be concerned about roof penetrations? Is it possible that expansion and contraction of the solar collectors over time might cause the roof penetrations to leak?

No. First, polypropylene solar pool heating collectors do indeed expand and contract throughout the day, so our mounting systems are designed to allow the solar collectors to “float” inside the roof mounting straps, free to expand and contract as needed without putting any strain on the mounting hardware roof penetrations.

Second, conventional sealants can lose elasticity over time. This is not a significant issue for applications like window and bathtub caulking, but the extreme temperatures experienced on a roof surface are a different story. So our roof mounting penetrations are sealed with a special high technology sealant, originally developed for the aerospace industry. This sealant has been proven to maintain its elasticity over several decades.

Will expansion and contraction of the solar collectors damage my roof?

No. Solar collector expansion and contraction occurs so slowly that it is not apparent to the naked eye. And such a slow rate of movement has no effect on your roof surface.

Will the heat generated by the black solar collectors damage my roof?

No. Quite the opposite. Solar pool heating collectors actually protect the portion of roof they cover because the sun’s energy is being absorbed and carried away by the pool water circulating through the collectors. Also, because a bank of solar pool heating collectors typically covers a fairly large area of roof, it can keep your attic a bit cooler whenever the system is operating.

Are there meaningful differences in efficiency between different brands and models of solar pool heating collectors?

Yes, but the differences are not easy to understand if you are only shown published performance ratings. All solar pool heating collectors are unglazed—that is—the plastic absorber surface is exposed directly to the air. This means the performance of all unglazed pool heating collectors falls off rapidly with colder daytime air temperatures. This isn’t that important for pool heating because most of us have no desire to swim during the winter, when the outside air temperature is cold. But one popular type of pool heating collector—called a loose tube collector—can experience much greater performance losses even during comfortable swimming weather—during the spring and fall—when the wind picks up.

Loose tube collectors—primarily the FAFCO® Sunsaver® ST and all Heliocol® collectors—have air spaces between the flow tubes. This allows air to flow freely between the tubes.

Dealers for loose tube solar collectors market their solar collectors as better for handling Florida’s occasional hurricane force winds because loose tube collectors have no wind resistance—the “wing” effect—during hurricances. But all solar collector fastening systems installed in Florida are required by law to meet hurricane windloads, so this claim is a solution to a non-existent problem.

The problem with loose tube solar collectors is that their heat loss in five to 10 mph winds is much worse than for solid absorber type pool heating collectors. This increased heat loss is not apparent in the “instantaneous” thermal performance ratings published by Solar Rating and Certification Corporation (SRCC) or the Florida Solar Energy Center (FSEC), which assume only a minimal wind speed. However, the rapid performance decline of loose tube collectors is quite clear in the thermal performance equations published on the rating certificates published by these independent testing agencies. And while it’s true that you may not be swimming during a windy, chilly day, solar pool heaters do not have high recovery ability. So a pool with a loose tube solar collector system like the FAFCO® Sunsaver® ST or Heliocol® will cool down faster in windy conditions than a solar collector without air spaces between the flow tubes, and will take extra days to return to a given heated temperature once the wind dies down.

And this suggests that loose tube solar pool heating collectors should never be installed at a location near the beach, which will experience more consistently windy conditions.

I’ve heard the U.S. Department of Energy determined that loose tube collectors are best for pool heating, when they selected this type of solar pool heater for the Atlanta Olympic Games. Is this true?

No. This particular system was actually selected to cool the Olympic venue pool.¹ Here’s what happened. The swimming and diving competitions of the 1996 Summer Olympic Games were held at the Georgia Tech Aquatic Center, which was designed as an outdoor facility in order to increase spectator seating capacity from 2,000 to 15,000. (The Aquatic Center was converted to an indoor facility about five years after the Atlanta Summer Games.)

Pool water temperature for competitive swimming events must be maintained between 25°C and 28°C (77°F and 82.4°F).² An outdoor pool’s temperature tends to match the 24-hour average air temperature for the preceding week, and Atlanta’s average daily air temperature in late July is 88°F (31°C). It isn’t unusual for temperatures to climb into the high 90s.

This meant the Aquatic Center pool water would be at least 10 degrees too warm for competition. So the primary goal of the architects and engineers was to come up with an effective method of cooling the pool.

If you read the previous question and answer, you know where this is going. Most non-metal solar pool heating collectors, including loose tube designs, radiate energy to a clear night sky at about the same rate. However, loose tube collectors have much greater convective heat transfer rates than flat plate designs because air is able to flow freely around and between the fluid passageways.

This is a really bad thing when you’re trying to heat a pool and the surrounding air is cooler than the water circulating through the collector’s fluid passageways. And even worse when the wind picks up. On the other hand, a higher rate of convective heat transfer is great if your primary goal is to cool a pool at night. Thus, a loose tube heat exchanger design was a perfect choice to cool the Atlanta Olympic pool during the hot Georgia summer.

The manufacturer and dealers of this particular loose tube collector system promote the Georgia Tech Aquatic Center project as their flagship large-scale “solar heating” installation, and often point to the Department of Energy selection process for this project as evidence of the product’s solar heating superiority. Nevertheless, the fact remains that the loose tube collector array installed at the Georgia Tech Aquatic Center was specifically designed for cooling. The pool has a steam heat exchange system for primary heating.

A salesman told me that solar collectors with two-inch header pipes are better than models with 1-1/2 inch headers. Is this true?

No. The argument is that a two-inch solar collector header improves efficiency by allowing more water per minute to flow into the fluid passages of the heating surface. While it is true that two-inch pipe has a higher saturation (maximum) flow rate than 1-1/2 inch pipe, a single bank of solar collectors is never installed with more than about 480 square feet of total solar collector surface area. (Larger solar systems are broken into multiple banks.) solar collectors designed for swimming pool heating temperatures function best at a water flow rate of about 1/10 gallon per square foot of solar collector surface area per minute. So for the best thermal performance, we would never want to flow more than about 48 gallons per minute (1/10 gpm per square foot x 480 square feet; the surface area of ten 4-foot x 12-foot collectors) through a single bank, regardless of the pipe size. 48 gallons per minute is well below the saturation flow rate of 1-1/2 inch pipe.

Some solar collectors require larger headers to partially offset the increased back pressure created by a plenum chamber design (see below). Unfortunately, some of the companies that sell plenum chamber collectors teach their salespeople to compare the costs of 1-1/2 inch and two-inch Schedule 40 PVC pipe at building supply outlets like Home Depot and Lowes, to justify higher prices for their solar pool heaters. But this is a meaningless comparison because headers comprise only a fraction of the material in a polypropylene solar collector.

Is it true that solar collectors with “flow-balancing” plenum chambers perform better than other solar collector designs?

No. The idea is that flow-balancing plenums—secondary water chambers between a solar collector’s headers and the flow passageways of its heating surface—provide more balanced water flow throughout a bank of solar collectors, and thus more efficient heat transfer.

But this is a solution to a non-existent problem. A basic rule of fluid hydraulics is that flow rates will vary in parallel pipes so that the head losses are equalized through each flow path. In plain English, if the diameters and lengths of the individual parallel flow passages in a solar collector are identical, the flow rates through these passages will be identical. This is always the case in a correctly installed solar pool heating system.

The only practical effect of additional flow restriction in a properly installed solar pool heating system is increased workload for the pump.

Here’s how this idea got started. During the 1970s, a solar collector manufacturer developed a process for heat-welding the heating surface of a polypropylene solar collector to the collector’s header pipes. The patented³ process involved fusing strips of plastic—called flanges in the patent application—along the length of each header pipe, encasing the the ends of the heating surface. The flange design cut manufacturing costs by reducing the number of steps needed to attach the heating surface—and its many individual fluid passageways—to the headers. Unfortunately, the new process created a secondary water chamber along the length of each header, which significantly increased flow restriction through the collector.

An old saying holds that you should find ways to turn your weaknesses into strengths. Someone came up with the idea of claiming that the additional flow restriction would ensure that water spread out more evenly among all of the fluid passageways in the solar collector’s heating surface. And so it was that the drawback of substantially increased flow restriction was magically transformed into “flow metering” and “flow balancing.”

Only one major solar pool heater manufacturer uses the plenum chamber design in their solar collectors today. Their dealer salespeople sometimes use the example of house central air conditioning ducts to illustrate the need for a flow-balancing plenum chamber. But this is a poor analogy because there is usually great variation in the length and size of air conditioning ducts branching to the different rooms within a house, so there is indeed a need to balance the air flow between the rooms. This variation does not exist within a bank of solar collectors.

But perhaps the best indicator of the need for “flow balancing plenums” is that the patent in question has long since expired and not a single competing manufacturer has copied the design.

Is an electric heat pump pool heater less expensive to operate than a gas heater?

Yes. A an electric heat pump pool heater uses a chemical refrigerant, just like the refrigerant in your refrigerator and your home air conditioning system, and a mechanical compressor to produce four to six times more heating energy than the electrical energy required to run the compressor. On average, the electricity to run a swimming pool heat pump costs about one-third of the cost of propane gas; about half the cost of natural gas; and about one-sixth the cost of direct resistance electric heating. (Direct resistance heating with a heating element is sometimes used for small spas, but is impractical for swimming pools. Some affluent homeowners combine a heat pump pool heater to maintain their pool’s temperature during the spring and fall months, with a gas heater to provide an extra boost during the coldest winter weather.

How does a swimming pool heat pump work?

A swimming pool heat pump works just like your home air conditioning heat pump works during the winter heating months. The only difference is that instead of absorbing heat from the outside air into a refrigerant, and then transferring that heat into the indoor air, the refrigerant transfers heat into the swimming pool water. Your home air conditioning heat pump sends the heated refrigerant through a coil inside an air handler, while the swimming pool heat pump has a heat exchanger with two liquid coils in contact with each other—one coil for the refrigerant and the other for the swimming pool water.

How noisy are swimming pool heat pumps?

A swimming pool heat pump has the same noise-generating components as the outdoor compressor and condenser coil unit for your home air conditioning system (compressor motor, condenser fan motor and fan blades), so the outdoor noise level is about the same.

I have heard that swimming pool heat pumps stop operating once the air temperature falls below a certain point. Is this true?

Yes. Remember that heat pump pool heaters take heat out of the outside air to heat your pool. Once the air temperature falls below about 50°F, a heat pump loses most of its rated efficiency, and most models have automatic shutoff switches that are triggered when air temperature reaches 35–45°F. Heat pumps are an ideal solution for pool owners who want to swim during the winter in between cold fronts when the daytime air temperature is above 60°F or so because they have much greater recovery rate than the typical solar pool heating system. That is, the heat pump can put far more heat into the pool in much less time than a solar pool heating system.

I am considering a heat pump instead of solar so I can avoid having to use a pool blanket. Will a swimming pool heat pump allow me to do this?

It is true that a reasonably sized swimming pool heat pump will give you a longer swimming season without the use of a pool blanket than a solar pool heating system. However, as a general rule, you can cut the cost of electricity to run a swimming pool heat pump in half by using a pool blanket at night during cold winter weather. Using a pool blanket at night during the winter months also reduces the heat pump’s recovery time to bring the pool back up to a comfortable temperature after a cold front passes.

How often does the refrigerant in a heat pump pool heater need to be recharged?

Unless a leak develops, the factory charge of refrigerant should last for the life of the unit. If your unit stops heating as a result of low refrigerant pressure, the most likely reason is a leak that will require repair. Most refrigerant leaks result from shipping or handling damage and are readily apparent following installation.

Do some heat pumps use more environmentally safe refrigerant chemicals than others?

Since January 1, 2010, all manufacturers have been required to use more environmentally friendly refrigerants. Most heat pumps today all use the same refrigerant: R-410A.

Do pool blankets work?

Absolutely. Most of your pool’s heat loss occurs through evaporation at the surface. A pool blanket blocks this evaporation, which keeps your pool warmer than a similarly situated pool without a blanket. A pool blanket supercharges the performance of a solar pool heater, and it can reduce the cost of running a gas heater or electric heat pump by more than half.

Most people use pool blankets during the coldest months of the year when a pool’s heat loss is the greatest. Pool blankets can greatly increase the efficiency of solar pool heating systems during the winter months, when pool surface heat loss is the greatest and the sun’s energy is the least intense. Without a pool blanket in place during the colder months, heat loss at the pool surface is more than a solar pool heater can offset.

Yes, pool blankets can be difficult to handle, especially for freeform swimming pools. You may want to keep this in mind if you are building a pool. One product that can make the job more pleasant is a pool blanket reel.

You might also experiment with a patented product called a “liquid pool blanket.” This is a liquid solution that is added to your pool water. The solution forms a thin layer across the pool’s surface that blocks evaporation and heat loss. This solution is completely invisible and non-toxic; in fact, the active ingredient is used in cosmetics and toothpastes. While a liquid pool blanket isn’t as effective as a conventional plastic pool blanket, it is much easier to use and does offer significant savings.

If you are using a conventional pool blanket without a reel, here’s what we recommend:

Avoid an “all or nothing” mentality. start by using the pool blanket at least during the two to three days when a severe cold front passes through, and during the winter months when trying to heat a pool without a pool blanket is like trying to cool your house with all the doors and windows open.

Finally, practice folding and storing your pool blanket with two people. You are more likely to use your pool blanket if you become comfortable handling it.

What is a pool blanket?

The most popular pool blankets are similar to blue plastic air bubble packing material. To increase durability, a pool blanket’s plastic contains UV inhibitors and is two to three times thicker than the plastic used in the air bubble packing material. A pool cover, on the other hand, is typically a much heavier, rigid structure. Rigid pool covers are typically used to close pools for the winter, up North. Florida’s mild climate allows pools to stay open year-round.

Will a solar pool blanket heat my pool?

Yes, and no. The term “solar” pool blanket is actually a bit of a misnomer. A pool blanket keeps heat in your swimming pool by stopping evaporation at the pool’s surface. Evaporation is by far the greatest cause of heat loss from a swimming pool. If evaporative heat loss is reduced, an unheated pool will stay warmer longer and a heated pool will need less solar energy, electricity or gas to maintain a given temperature.

A pool blanket does not help the pool surface absorb more solar enegy. In fact, a blanket actually blocks and reflects a small amount of the solar energy that would normally be absorbed by the pool surface.⁴ But this effect is small and insignificant compared to the pool blanket’s dramatic ability to stop heat loss off the pool surface.

Are there any other benefits to using a pool blanket?

Yes. By blocking evaporation from a pool’s surface, a pool blanket also conserves water and reduces consumption of pool chemicals by 30 to 60 percent. The precise amount naturally depends upon how many hours each day the pool blanket is in place.

What is the best way to handle and store a pool blanket?

Pool blanket reels offer convenience; however, many pool owners do not want the reel assembly sitting on their pool deck. For a typical residential pool, two people can very easily remove and fold a pool blanket in about two minutes.

To remove the blanket, each person stands at an opposite corner of the same end of the pool. Pull the corners of the blanket out of the pool, then step back and set the blanket down so that about three to four feet of the blanket is overlapping the pool deck. Next, each person should step forward along his or her side of the pool to a point roughly twice the length of the section of blanket resting on the pool deck (six to eight feet). From this point forward, simply repeat the process of pulling six to eight foot sections of the blanket back out of the pool and folding each section accordion-style on the pool deck.

With the blanket folded at one end of the pool, repositioning it on the pool surface takes less than one minute and is a simple matter of each person grabbing a corner of the blanket and walking forward to the far end of the pool.

I have heard about something called a liquid pool blanket. Is this for real?

Yes. A liquid pool blanket is a patented solution that, when spread across the surface of a pool, reduces evaporation from a calm pool surface by about 40 to 50 percent. Of course, a swimming pool is not always calm, and actual reported savings on heating costs range from 15 to 35 percent.⁵

The liquid solution, marketed under the brand name Heatsavr®, is a mixture of alcohol and aluminum salt. Aluminum salt is a white flaky substance commonly used in cosmetics, soaps and toothpaste. It is safe, clear, tasteless, odorless and biodegradable. Alcohol is lighter than water, which allows the solution to form a thin film at the pool surface. A very useful property of the alcohol and aluminum salt mixture is that the molecules tend to rearrange themselves back into a thin sheet across the pool surface after pool activity, as the water calms. Also, the aluminum salt particles used in the Heatsavr® product are so tiny that they will not clog pool filters.

Liquid blankets are especially useful for larger residential and commercial pools and for unusually shaped pools, situations where handling a plastic blanket may be impractical. The Heatsavr® liquid solution is dispensed automatically, either from a metering pump dispenser or from a plastic container that floats in the pool. The most popular containers are shaped like tropical fish; the solution dispensed by one “fish” may cover up to 800 square feet of pool surface for two months.

While a liquid pool blanket is only about two thirds as effective as a plastic pool blanket, it may actually deliver better performance than a plastic blanket in real world situations, if the inconvenience of removing and replacing the plastic blanket leads to inconsistent use.

I tried one of those liquid pool blanket “tropical fish” this winter. It didn’t heat my pool and I ended up with a white residue on my pool walls. What’s going on?

First, as we explain above, a pool blanket does not heat your pool. A pool blanket allows your pool to stay at a higher temperature by stopping heat loss from the water surface. It will not add heat to your pool. For that, you need a pool heater.

As for the white residue, that’s aluminum salt (see the previous question). If you add Heatsavr® solution to pool water that is colder than 70°F (21°C), the aluminum salt will solidify and collect at the water’s edge. This may also occur if you add too much liquid pool blanket solution in relation to your pool’s surface area. Don’t worry, though. It’s completely harmless, biodegradable, and will go away on its own.⁶

Is there anything I can do to increase the performance of my solar water heater?

Yes. The energy savings produced by your solar water heater are strongly influenced by the time of day when most of your hot water use occurs. Ideally, if you take your showers, run your dishwasher, etc. during the evening or when you first wake up in the morning, colder water will be circulating through your solar collector(s) each morning. This is because the cold water that flows into the bottom of your water heater storage tank, to replace the hot water you use, tends to not mix with the hotter water at the top of the tank. This phenomenon is called stratification. The plumbing in a solar storage tank is designed to circulate this colder water at the bottom of the tank through the solar collector.

Why is this important? Well, the solar control system will only circulate water through your solar collector(s) when the temperature inside the solar collector(s) is warmer than the temperature of water in the bottom of the water heater. Colder water in the bottom of the tank in the morning means that the solar collector(s) will start heating your water earlier in the morning. This means you will collect more solar energy during the day. And save more electric energy.

Of course, for this approach to work best, your backup heating element should be turned off as soon as practical after your evening hot water use, or it will simply reheat the tank with electric energy at the end of the evening. Many of our customers leave the circuit breaker for their water heater electric element turned off except when very cloudy or rainy weather occurs during the middle of the day.

What about cloudy weather?

Good question. Actually, a solar water heater collects about half the solar energy of a clear, sunny day on an overcast day. If you have ever had the experience of going to the beach on an overcast day and still getting a sunburn, you understand this phenomenon. Clouds block some solar energy wavelengths, but much of the energy still gets through.

Will my water be hot enough?

Yes. Solar heated water is often hotter than the thermostat setting on your water heater. In fact, for safety reasons our systems include mixing valves to make sure the hot water going into your house isn’t too hot. On the other hand, sometimes we may have extended periods of very cloudy and rainy weather. During these periods, a backup electric heating element in your water heater / storage tank will automatically heat water to the water heater’s thermostat setting.

Will I have hot water during cold weather?

Yes. Solar water heating collectors typically deliver excellent performance in Florida during cold weather because the sky is very clear during winter high pressure waves. The glass cover plate and insulation inside the collector prevent collected heat from escaping to the outside air.

Can you use my existing water heater as the solar storage tank?

Usually, no. Solar water heating systems are designed to heat and store 24 hours worth of hot water during the daylight hours, so the tank has to be large enough to store 24 hours’ worth of hot water. Most conventional electric water heaters in Florida homes have a capacity of about 52 gallons. Standard solar storage tank sizes are typically 80, 100 and 120 gallons, with 80 gallons being appropriate for most three- to four-person households. Also, solar storage tanks typically have better insulation than conventional electric water heaters, to minimize overnight heat loss.

Does a tankless (instantaneous) water heater make more sense than a solar water heater?

We don’t think so. Even with a tankless water heater, the water you use still has to be heated with electricity or gas. The tankless water heater only eliminates energy costs for maintaining the temperature of water that has been heated and is sitting in the storage tank awaiting use. A tankless water heater is about 15–20% less expensive to operate than a conventional electric or gas water heater.

Tankless water heaters do have drawbacks. According to the U.S. Department of Energy, “Sometimes … even the largest, gas-fired model cannot supply enough hot water for simultaneous, multiple uses … taking a shower and running the dishwasher at the same time can stretch a (tankless) water heater to its limit.”

Naturally, you can overcome this problem by installing multiple tankless water heaters. On the other hand, the total installation cost for more than one tankless water heater can quickly approach the cost of a single solar water heating system.

What about an electric heat pump water heater?

An electric heat pump—which uses a compressor and heat exchanger to take heat out of the air and transfer it into your hot water—can cut your water heating cost by about half. Frankly, the theoretical return on investment can beat the return on a solar water heater. But there are some practical concerns to consider:

Noise. Think about the noise produced by your home air conditioner. Forget about installing the HPWH indoors. And even if your water heater is in the garage, the noise will be an issue, especially when amplified by the enclosed space.
True efficiency. Just like heat pump swimming pool heaters, a heat pump’s efficiency falls off dramatically as the air temperature falls. HPWH manufacturers and dealers tend not to mention the fact that their energy savings estimates are based upon 80°F air temperatures. Performance falls off rapidly for every 10 degree decline in air temperature. the performance with 60°F source air often isn’t even half of the published performance. And a heat pump will usually have a cutoff switch when the air temperature reaches 45–50°F. That said, for a heat pump water heater installed in South Florida, you will have great savings for nine months a year, especially if your heat pump water heater is installed in the garage (and it may even cool the garage by a few degrees).
False economy. A heat pump water heater installed in air conditioned indoor space will to some degree be a false economy. While the HPWH would remove some heat from your home interior during the summer, it would canibalize the air conditioning system’s energy during the heating season.
Space limitations. Have you ever read that your home air conditioner’s outdoor condenser coil housing needs a well-ventilated air space of a few feet on each side for adequate heat transfer? Well, the same is true for a HPWH to work efficiently. the compressor and the air heat exchange coil are typically mounted on top of the tank. While the manufacturer and dealer may not tell you this, cramming the unit into a recessed corner in the garage or in an indoor closet will have a substantial negative impact on the unit’s performance.

What about a heat pump water heater tied to a solar electric (PV) system?

Some Internet bloggers who have absolutely no idea what they are talking about recommend this as an ideal approach for water heating. It is a bad idea. Using solar PV panels to provide the source electricity does not eliminate any of the practical problems described above. But the numbers don’t make sense either. Today’s premium solar photovoltaic (PV) panels turn about 20% of the solar energy that strikes the PV panels into direct current (DC) electricity and have a net efficiency—in terms of usable AC power—of about 17%. By comparison, a solar water heater converts about 50% to 60% of the solar energy that strikes the solar collector into usable heat. This means that to provide the hot water needed by a typical family of four with a solar PV-driven HPWH, you would need about 120 square feet of PV panels to do the same job as one 40 square foot solar water heating collector, assuming a HPWH efficiency of 50%, a solar PV panel rated efficiency of 20% and net usable AC power efficiency of 17%.

The solar water heater will cost between $5,800 and $7,500 installed. Even at a cost of just $2 per peak watt installed (current installed PV system costs are around $3 to $4 per peak watt), for extra PV system capacity just to heat your water would cost about $13,700, plus another $1,400 to $2,100 for the HPWH.⁷

Anyone who reads and understands the numbers in this short explanation will also understand that a solar water heater is a much better investment than a solar electric power (PV) system, per dollar invested, and that installing a PV system for your home without first installing a solar water heater is just plain silly.

What about the risk of solar collector damage from freezing?

Both active and passive solar water heating systems come with a 100% lifetime warranty against freeze damage. The active and the passive solar water heating systems are both approved by the Florida Solar Energy Center for use in North Florida. Active solar systems have a conventional electric heating element to heat water on the few days that it might be needed. Passive solar systems act as a pre-heater to heat water before it is drawn into the cold inlet of the standard gas or electric water heater. All solar water heating systems deliver both higher temperature water and more water volume than conventional water heaters. Typically 40 to 80 gallons more hot water than conventional water heaters.

What about the appearance of a solar collector on our roof?

Today’s solar collectors are usually installed flush with the roof slope. This method of installation gives the solar collectors the appearance of a quality, opaque, glass skylight. In most cases, since the piping is not seen, it actually improves the appearance of the home because it looks like an elegant, expensive skylight. Tryon Pool Heating & Solar offers a free solar site survey to determine the location of the solar collector, and to verify that you will not have any collector shading problems. You typically need only about 4 hours of direct sun (between 9am to 4pm) per day.

What about the environmental benefits of going solar?

Any time you use solar energy to offset the amount of fossil fuels that are burned, you contribute to everyone’s health and welfare. Operating one solar water heater instead of an electric water heater saves the equivalent of nine barrels of oil every year, reduces carbon dioxide emissions (a greenhouse gas) by 1,600 pounds per year, and reduces sulfur dioxide emissions (which contribute to acid rain) by 12 pounds per year. Multiply those emissions per household by all the homes in your neighborhood, town, county, or state, and the benefits become even more clear.

So does the air we breathe and the water we drink.

Notes

Rigsby, G.G. “Its Olympic goal is a cool pool,” , March 13, 1996.
Federation Internationale de Natation (FINA) Rule 2.11.
United States Patent No. 3,934,323, “Solar heat exchange panel and method of fabrication,” January 27, 1976.
This is why “floating solar pool heaters” you may find on the Internet don’t really do anything to heat a pool. If anything, they just block solar energy that might have been absorbed directly by the pool surface.
United States Patent No. 6,943,141, “Process for making a liquid evaporation retardant solution,” September 13, 2005. The Heatsavr® patented mixture of alcohol and aluminum salt is based upon the science of Langmuir monolayers, materials that tend to form into one-molecule thick sheets when spread onto an aqueous surface.
Aluminum salt is an ingredient in many toothpaste products.
The price of $2 per peak Watt assumes that the inverter(s) and other solar power system components are already installed and the only cost is for the extra solar PV modules necessary to drive the HPWH. 80 gallons per day × 8.34 pounds per gallon x (122°F − 75°F) water temperature rise = 31,358 Btuh per day. 31,358 Btuh ÷ 3.412 Btuh per Watt-hour = 9,190 Watt-hours. 9,190 Watts heat energy would be required. 9,190 Watts × 50% HPWH efficiency = 4,595 Watts of HPWH power use. 4,595 Watts ÷ 67% derating factor for line losses and conversion of DC power output from the solar PV modules to net usable AC power × $2 = 6,858 peak rated Watts of required PV output. 6,858 Watts × $2 per Watt = $13,716.