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Pool Heater FAQ

Frequently Asked Questions About the FPH Heat Recovery Pool Heater

Why is it necessary to heat a swimming pool?
Studies show that most people prefer a swimming pool to be between 84-86F, about 13F cooler than human body temperature.  As water evaporates from the large exposed surface area of a pool, a thermodynamic  effect called evaporative cooling occurs. This is where the vast majority of pool heat loss occurs and it's the reason why a pool can lose heat even on a hot sunny day.  Of course whenever ambient air temperatures fall below the pool temperature, convective, conductive and radiant heat transfer occurs, however since the temperature delta is minimal this amount is very small and is usually replaced by solar radiation so it does not need to be closely calculated. Even in warm and sunny locations like Key West, Florida, pools require a heat source nearly all year to remain at a comfortable temperature due to evaporative cooling. See US Department of Energy pool heating cost data.

How does the HotSpot FPH heat recovery pool heater work?
Basically, it’s a geothermal heat exchanger system added to your normal air conditioner, which allows the AC to become a water cooled unit when the pool needs heat and lets the system run normally when the pool does not need heat. It takes the waste heat that the AC throws away, and puts it into the pool. The operation of the AC is improved, electrical draw is reduced, and the outdoor AC fan unit doesn't need to run. Heating the pool is free. Here is a high-level diagram.

pool heater diagram of a swimming pool heating system

What kind of air conditioner will it work with?
We offer standard FPH (free pool heater) systems preconfigured for 134a, R410a, and R22 AC units between 1.5 and 5 tons utilizing single-stage, single speed compressors. Dual-stage and variable speed compressors can be used when the FPH is installed by an expert installer that is highly familiar with the customers AC unit as certain communications issues must be resolved by the installer. HotSpot offers limited installer support on these types of units.  We can custom-configure systems for larger air conditioners up to 200 tons or other types of refrigerant. The FPH pool heating system can also connect to multiple air conditioners. We can provide FPH for air conditioners and heat pumps. You must tell us if you have a heat pump. We cannot always tell from the model number. NOT GENERALLY USED FOR VARIABLE SPEED COMPRESSORS - CONTACT US FOR THIS APPLICATION.

How big can my pool be? (or, How large must my air conditioner be?)
We estimate that on average, a full sun, low wind pool needs a net heating capacity of about 650 BTU per day, per sq. ft. of surface area. A typical 16 x 32 pool (512 sq. ft.) will need about 332,800 BTU per day of heating capacity.  A little more, if in a windy or shady location. A heat recovery pool heater can deliver about 15,000 BTU per hour into the pool per ton of AC capacity. Therefore an average pool would need up to 22 “ton hours”, meaning a 5 ton AC unit would need to be running for 4.4 hours per day, or a 3 ton AC running for 7.4 hours per day, and so forth. For extra large pools, or when using small air conditioners, we can provide a dual system that will use two AC units together on one pool.

How do you calculate the surface area of a pool?
Rectangle: length x width 
Round: radius(1/2 diameter) x radius x 3.14
Oval or Roman: 1/2 length x 1/2 width x 3.14
Kidney shape: length x width x 0.75

How do I determine the size or capacity of my AC?
It's not going to be listed on the AC unit. If you don't have the paperwork, you can give us the model number from the outdoor unit and we can look it up for you.

How hot can the FPH make the pool?
The pool temperature can be set and operate up to 94F depending on the AC size, pool size, and operating conditions.

When can the FPH pool heater be used?
The FPH pool heater can be used during the air conditioning season, it will not operate unless the AC is running. It is recommended for use only when the pool is between 62F and 94F.

How is the FPH installed?
There are two parts to the installation. Part one, connecting the FPH to the air conditioner, must be done by a licensed HVAC technician, this takes about 5-6 hours. The second part, connecting the FPH to the pool pump, can take two hours and up, depending on distances and complexity. The "water side" connections can be completed by the HVAC technician, a handyman/home owner, or hired out to a pool company, etc. The water-side components are standard schedule 40 PVC parts available through Lowe's or Home Depot.

How do the FPH controls work?
The FPH system includes an automatic programmable thermostatic controller with a user-defined temperature set point, it monitors the pool temperature and the operating state of the AC compressor. When the compressor comes on and the pool does not need heat, nothing happens and everything works normally. When the compressor comes on and the controller sees that the pool needs heat, heat recovery is engaged and all of the normally wasted heat goes into the pool until such time as the pool is above the set point, or until the AC unit goes off. At that point the system is reset automatically to normal operation. When the system is in heat recovery mode, the outdoor condenser fan is off. The FPH system controller will turn the pool pump on when heat recovery is engaged regardless of the timer settings, it releases the pump back to control by the normal pump timer when heat recovery is disengaged. Control hysteresis of 2F keeps the system from cycling.

Can I also connect it to my Hot Tub/Spa?
No, not really. If you are an engineer and need a titanium desuperheater give us a call. Otherwise, we do not support Spas.

Will it work with above-ground pools?
Yes, both above-ground and in-ground pool installations are supported.

Does the FPH work with salt pools?
Yes. Actually the end-result pool chemistry of a normal "salt" pool is the same as a chlorine pool, it is just arrived at differently. With a salt pool you are using salt and the process of electrolysis to create hypochlorous acid and sodium hypochlorite, which are the same chemicals produced by the breakdown of chlorine tablets. If your system uses actual salt water, that's OK too - titanium heat exchangers are perfect for salt pools or ocean water pools.

What if my AC unit is far away from the pool pump equipment?
The heat exchanger always installs next to the AC unit. The distances allowed really depends on the horsepower of your pool pump with PVC runs up to 300 ft. supported when the pump is large enough. We can help calculate the pump size needed if you are in doubt. If our standard system won't work at your distance, you could consider a pump upgrade or we can provide our L-model (low flow) heat exchanger which will work in nearly every situation.

What kind of pumps can be used?
We recommend a single speed pool pump of sufficient size for your pool, and large enough to handle the pumping disctances. VSD (Variable Speed Drive) pool pumps can be used as long as they can be controlled by a 24vac dry contact relay (check with your manufacturer to see if you have this or if a relay module can be added). If your VSD pump cannot use a relay there are various work-arounds, contact our support department. A VSD pump saves energy for people who do not use pool heaters, but when using a pool heater (ours or any other type like gas, heat pump, or solar) the extra cost of a VSD pool pump is often wasted.

Can I use a Heat Recovery Pool Heater and a Heat Recovery Water Heater on the same AC unit?
Yes, it is normal to do this when there is sufficient capacity. It will depend on your AC unit size, size of the pool etc. Our tech support staff can calculate it for you.

My local HVAC guy said that with the newer scroll and/or high-SEER compressors, the discharge temps were not high enough to get much useful heating.
It's not possible for that to be correct. For every ton of capacity, 12,000 BTUs must be absorbed at the evaporator which means about 15,000 BTUs (including superheat etc.) must be rejected at the condenser. This has not changed, and cannot change, regardless of new vs. old, compressor or refrigerant type, SEER, or whatever. The FPH is condensing the refrigerant in the pool water, and 100% of the rejected heat will go into the pool. Cold is not “created”. Heat is moved. The heat has to go somewhere. This is basic refrigeration theory and applies to all systems that use a compressor.

Why is a titanium heat exchanger needed?
Other lesser materials like stainless steel, copper, or cupronickel will corrode and eventually fail when exposed to the chlorine levels found in swimming pools.

What other materials are used to make the FPH heat exchanger?
The FPH titanium heat exchangers are encased in PVC (Polyvinyl Chloride) which is naturally resistant to chlorine. Actually PVC is 58% chlorine. All water contact surfaces are either PVC or titanium. Copper stubs are added to the ends of the titanium coil (outside of the PVC shell) at the factory because it is very difficult to braze copper to titanium in the field.

What is the FPH expected life span and warranty?
The titanium heat exchanger can last 25-30 years or longer and carries a 10 year limited warranty. The valves and control components are made by leading manufacturers who supply HVAC industry system manufacturers and typically have a life span equal to that of a new air conditioner, 12-20 years or so, these parts have either a one or two year limited warranty depending on their respective OEM warranty. There is no warranty on cosmetic issues that do not affect performance.

Will my AC manufacturers warranty automatically be voided if I install heat recovery?
A manufacturer cannot automatically void a warranty solely because of adding a 3rd party aftermarket component designed to improve it's performance unless it is specifically disclaimed in their warranty, it’s not even legal to do so. We are aware of no major manufacturers warranties with such disclaimers. We have seen cases where the local HVAC dealer or distributor may say something different but this cannot be relied upon. If you have any question about this, read your warranty or consult the manufacturer of your system directly and do not rely on 3rd party "local" information. The manufacturer generally has to prove that any problem was caused by the aftermarket component or modification, and the burden of proof is on them. (Magnuson-Moss Warranty Act, 15 U.S.C. § 2301 et seq.). We have never had a voided warranty situation with any of our heat recovery products.

How do you size a heat recovery pool heat system?
The information needed includes the approximate dimensions (not gallons) of the pool, the capacity (tons or BTUs) of the cooling system, the size of your pool pump, and the distance between the pool pump and your AC unit. We also need to know if it's a heat pump or normal AC unit. Providing the complete model number allows us to know the exact size of unit you have. With this information we can help you determine if your situation is right for a heat recovery pool heater, and what size and configuration is needed.

Why do the number of gallons in the pool not matter?
A normal paid-energy pool heater is very expensive to operate and most people only turn it on when they plan to use the pool so the heater must have a high hourly BTU capacity to be able to heat a cold pool quickly. In the case of a paid energy pool heater, the gallons matter because it affects how long it will take to heat a cold pool. Heating a cold pool requires 8.33 BTUs per degree of temperature rise, per gallon. But the gallons do not affect the rate of heat loss, which is determined by surface area. Since the FPH system uses free energy for pool heating it can run every day for free and keep the pool warm all season. It only has to heat a cold pool when you first turn it on at the beginning of the AC season. During the season the requirement is only to maintain temperature, i.e., replace the lost BTUs, so the gallons do not matter. When you first turn the FPH on in the beginning of the season it may take a couple days or so, depending on the gallons, to get the pool to the right temperature, but once the pool is warm the gallons don’t matter as far as replacing lost heat to keep it warm.

What is the temperature rise of the water through the FPH?
This is variable with the actual flow rate of the pool pump and is not the right question to ask. For example, with a high power pump and faster water flow, the temperature rise would be lower but the BTUs per hour and average pool temperature would be the same. Likewise, a slower speed pump will give more temperature rise, but the BTUs per hour and pool temperature still remain the same.

How does a heat recovery pool heater compare to a solar pool heater?
Either system will extend your swimming season and heat your pool for free. However, some people can't use solar because of roof orientation, shade problems, or homeowners association rules. And, some people don't prefer the "look" of large black plastic panels on their roof. Beyond that, solar panels can cause roof problems and have to be removed and reinstalled when the roof is repaired or replaced. And, solar pool panels have a tendency to be damaged or lost in severe wind. The FPH pool heater works in the rain, and at night. The final installed cost is usually lower for our AC recovery pool heaters than it is for solar. Of course, solar doesn't slash your air conditioning bill by up to 40% like a heat recovery pool heater can.

Do you provide installation?
No, we are system developers and manufacturers of equipment. We do not perform or schedule installations. We will be happy to introduce you to installers that we know of who have installed our products in the past whenever possible. Any experienced and licensed air conditioning service technician should be able to install the FPH. It is the customer’s responsibility to hire a local AC contractor to perform the installation. HotSpot supports installations with a detailed installation guide and expert phone support if needed.

How much does a FPH cost?
The systems vary in cost based on system size, type, model, and installation requirements, but for nearly all pools it will be less costly than installing a paid-energy (gas or electric) pool heater. And owning the FPH instead of a paid energy heater will ultimately end up costing nothing, as it quickly pays for itself in energy cost savings. See pool heater energy cost comparison. Standard system kits are usually in the $1600-$1800 range with heat pump models ~$200 extra. Installation costs vary depending on prevailing rates in your area and system complexity.

How quickly will it pay for itself?
The payback rate will depend on specifics and what energy source you are comparing it to. Here are some projected payback comparisons:
VS. a heat pump pool heater: 2-3 years payback.
Vs. propane gas pool heater: 1-2 years payback.

See the details here: HotSpot Pool Heater.

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HotSpot Energy Inc. | 4021 Holland Blvd. | Chesapeake VA 23323 | 757-410-8640
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