Swimming Pool Contractor: How to Choose the Right Pool Heater and Avoid Common Sizing Errors
Every swimming pool contractor has seen it occur. A homeowner buys a heating system that looks good on paper but never ever provides warm water. Or they spend too much on a system that cycles on and off too regularly. The issue normally comes down to sizing. Not the physical size of the heater however its output relative to the swimming pool\'s true heat load. Getting that incorrect can turn a backyard investment into a year-round frustration.
I have actually been on both sides of this equation. As a pool contractor, I have actually installed numerous heating systems throughout climates that range from moderate coastal to freezing mountain valleys. The errors are remarkably constant. And they are almost always avoidable if you make the effort to determine before you sign the order.
Why Heater Sizing Is Not a Guess
A pool heater's task is to change the heat that leaves the water faster than the sun can. And water loses heat constantly. Evaporation is the biggest burglar. A single square foot of open water can lose 1,000 BTUs per hour on a breezy, 60 degree day. Add wind, low humidity, and a cool night, which loss climbs up. A heating system that can not maintain will run constantly, drive up your gas or electric bill, and still leave swimmers shivering.
The opposite issue is an extra-large heating system. It heats the pool rapidly, however it short cycles. The thermostat strikes the set point, the heating unit turns off, and the water cools quickly. The heating system fires up again, runs for a couple of minutes, and shuts off. This wastes fuel and breaks components. The compressor in a heat pump dislikes this. The burners in a gas heating system develop soot. And you never ever get stable comfort.
The ideal size is the one that matches the pool's heat loss rate on the coldest day you plan to swim. A swimming pool contractor who avoids the heat loss computation is thinking with your cash.
The Three Main Heater Types and Their Real World Performance
Before we talk numbers, you require to understand what each heating system type can and can not do. Every one has a various relationship with sizing.
Natural Gas and Propane Heaters
These are the workhorses. A common property gas heating unit puts out 200,000 to 400,000 BTUs per hour. They heat up water quick, typically raising the temperature 1 to 2 degrees per hour in a basic swimming pool. They operate in any air temperature and any wind. The disadvantage is operating expense. Gas costs change. A 400,000 BTU heater running for eight hours burns around 38 therms. At $1.50 per therm, that is $57 for a single day of heating. You wish to size a gas heating unit correctly since every squandered BTU comes right out of your wallet.
A typical mistake is buying a heating system that is too small for the swimming pool volume and expected heat rise. I when saw a specialist set up a 200,000 BTU heating system on a 30,000 gallon swimming pool in a cold environment. The heating unit ran 18 hours a day and still might not reach 80 degrees on a cloudy spring afternoon. The house owner could have saved money by buying a larger unit that would run fewer hours.
Heat Pumps
Heat pumps use electricity to move heat from the air into the water. They are more effective, with a coefficient of efficiency (COP) generally between 4 and 6. That means for every single dollar of electricity, you get $4 to $6 worth of heat. However they are slower. A typical heatpump for a property pool delivers 100,000 to 150,000 BTUs per hour. That has to do with one 3rd the output of a gas heater.
Sizing a heatpump is harder because its output drops as the air temperature falls. At 50 degrees ambient, numerous heat pumps produce only half their rated output. A professional who sizes a heat pump based on summertime conditions will leave the swimming pool cold in spring and fall. I constantly run the heat loss estimation for the coolest month the owner plans to swim. If they wish to swim in March in a northern environment, a heat pump alone might not suffice. A gas heater or a hybrid technique frequently makes more sense.
Solar Heaters
Solar systems use roofing installed panels to record the sun's energy. They are the cheapest to run but the most dependent on weather. Sizing a solar system is about collector location, not BTUs. A guideline is to install a collector location equivalent to 50 to 80 percent of the pool's area. But that number modifications with your local solar insolation, roofing orientation, and shading. A swimming pool contractor should do a solar site survey that determines actual sun hours. Oversizing a planetary system can cause overheating in summer season, and undersizing will barely warm the water in shoulder seasons.
Solar is often the slowest heating option, raising water temperature by just a couple of degrees each week. It works best as a supplement to a gas or heatpump system. I have seen house owners try to rely exclusively on solar with a 1,000 square foot swimming pool in a partially shaded lawn. They ended up buying a gas heating unit after the very first cold summer. Do not let that be you.
The Heat Loss Calculation Every Contractor Should Use
An appropriate sizing calculation accounts for 4 primary factors. Here is what a pool contractor ought to measure or approximate.
- Swimming pool surface area and volume. Surface area drives evaporation loss. Volume drives the thermal mass. For a standard rectangle-shaped swimming pool, area is length times width. Volume is that times average depth, then increased by 7.5 to get gallons. An irregular shape needs a mindful measurement. Preferred temperature increase. If you desire the pool at 82 degrees and the coldest incoming water is 60, that is a 22 degree increase. The heating system needs to offer that numerous BTUs per gallon. One BTU raises one pound of water by one degree. One gallon of water weighs 8.34 pounds. So a 20,000 gallon pool needs about 167,000 BTUs per degree of increase. Heat loss rate. This is the tough part. A typical approach is to use a chart from the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). For an exposed pool at 80 degrees with air at 70 and 10 miles per hour wind, the loss can go beyond 4 BTUs per square foot per hour. That means a 500 square foot pool loses 2,000 BTUs per hour. A windbreak, a swimming pool cover, or a higher humidity will decrease that loss significantly. Security element. I include 20 percent to the computed load for unanticipated conditions like extended cloudy weather condition or an unexpected cold front. That margin also accounts for the heater's own inefficiency and the temperature level drop in the pipes.
Let me walk through a real example. A 16 by 32 foot pool has 512 square feet of surface area. Average depth is 5 feet, so volume is 16 times 32 times 5 times 7.5 equates to about 19,200 gallons. Desired temperature is 82 degrees, incoming water is 60 degrees in the spring, a 22 degree rise. That needs 19,200 gallons times 8.34 pounds per gallon times 22 degrees equates to approximately 3.5 million BTUs just to initially warm the water. Once as much as temperature level, heat loss at 3 BTUs per square foot per hour (with a cover utilized in the evening) has to do with 1,536 BTUs per hour. Include a 20 percent safety element brings it to 1,843 BTUs per hour.
Now compare heating system sizes. A 200,000 BTU gas heater can supply that level of heat while likewise having lots of reserve to reheat after a swim. However a 100,000 BTU heatpump would be borderline due to the fact that its output at 60 degrees ambient might be just 50,000 BTUs. You would require a much bigger heat pump or accept that it will take many hours to recuperate.
I always advise that the pool contractor run this computation in writing and share it with the homeowner. It constructs trust and avoids disagreements later.
Typical Sizing Errors and How to Spot Them
Numerous installers still size heating units by old general rules. Here are the most frequent mistakes I see, and the fixes.
Using Pool Volume Alone
Some specialists look only at gallons and choose a heating unit from a chart. A 20,000 gallon swimming pool gets a 250,000 BTU gas heating unit. But that disregards surface area, wind direct exposure, and cover usage. 2 swimming pools with the same volume but various shapes or areas can have considerably various heat loss. A long, narrow swimming pool loses more heat than a compact square. A swimming pool in an open field loses more than one sheltered by a house. Volume alone is inadequate.
Ignoring Wind and Shade
Wind accelerates evaporation. Even a light breeze can double heat loss. I have actually determined a pool on a windy hillside that lost heat twice as fast as a protected swimming pool in the same area. A swimming pool contractor ought to keep in mind the prevailing wind instructions and consider a windbreak or a swimming pool cover. Numerous homeowners do not recognize that a basic solar cover in the evening cuts heat loss by 70 percent. That can enable a smaller, cheaper heating system to work just great.
Oversizing a Heat Pump for Summer Use Only
A common situation: a house owner wants a heatpump to extend the swim season, and the professional sizes it for 80 degree days. Come October, the heatpump can not maintain. The professional states, "It's working as created." However the house owner feels cheated. The fact is the heat pump was never ever sized for the shoulder season. A responsible contractor will ask, "When do you in fact wish to swim?" Then run the calculation for that month.
Forgetting the Pool Cover
I can not count the number of times I have sized a heater for an exposed pool, only to have the house owner later ask why it costs a lot to run. A swimming pool cover decreases heat loss so considerably that the heater runs half as typically. If you plan to utilize a cover, the specialist needs to consist of that in the heat loss formula. If you do not prepare to utilize one, the heating system needs to be sized for the maximum loss. Be honest about your practices.
Setup Considerations That Affect Performance
Sizing is just half the battle. The installation itself can cripple a completely sized heating system. A couple of things a pool contractor need to check.
Plumbing diameter and length. A heater requires appropriate flow. If the pipe is too small or the run is too long, the water velocity drops, the heater's internal pressure switch might journey, or the heat exchanger may overheat. I always validate that the https://precisionpoolsandoutdoors.com/ pump can deliver the needed circulation rate at the head loss of the system. For a common gas heater, that is 30 to 50 gallons per minute for a 250,000 BTU unit.
Venting for gas heating units. Right venting is nonnegotiable. A high performance gas heating unit uses a sealed combustion system with PVC venting. A basic performance heating system utilizes metal flue pipeline. The vent length and termination must match the producer's requirements. A swimming pool contractor who shortcuts venting dangers carbon monoxide poisoning or devices failure.
Electrical supply for heat pumps. Heat pumps draw significant amperage. A 100,000 BTU unit may require a 50 amp devoted circuit. If the existing panel is complete, the upgrade cost can shock the property owner. Always inspect the available capability early in the process.
When a Single Heater Is Not Enough
For big pools, spas with water features, or properties with severe wind direct exposure, a single heating system may not be practical. In those cases, I have actually used numerous heating units in parallel or a combination of a gas heating system for fast recovery and a heatpump for upkeep. That method gives the property owner the flexibility to heat quickly when needed and save energy the remainder of the time.
Another alternative is a variable speed pump integrated with a pool cover and a correctly sized heatpump. The pump performs at low speed throughout maintenance heating, which lowers electrical power use and extends the heating system's life. But this just works if the heat pump's minimum flow rate is satisfied at low pump speed. Some heatpump need a minimum water circulation of 30 GPM. If the pump at low speed provides only 15 GPM, the heatpump will short cycle or toss an error. An educated pool contractor will check that compatibility.
The Bottom Line from Experience
Picking a swimming pool heater is not a one size fits all decision. The best system depends upon your environment, your pool geometry, your cover usage, and your convenience expectations. The very best way to prevent mistakes is to deal with a pool contractor who does a full heat loss computation before pricing quote. That calculation must be documented and gone over. If the contractor gives you a rate without ever inquiring about wind direct exposure or how frequently you prepare to use a cover, ask to return and do it appropriately.
A well sized heating system will pay for itself in lower utility expenses and trusted performance. An inadequately sized one will cost you more in the long run, both in cash and disappointment. Take the time to get it right. Your swimming pool contractor ought to be your partner because process, not just a vendor pushing a heating unit off a shelf.