Splashing into a freezing pool in May or October is the fastest way to ruin your swim season. After helping my brother pick a heater for his 18,000-gallon in-ground pool last spring, I realized how confusing the pool heaters for in-ground pools market really is. There are gas heaters, electric heat pumps, solar rigs, and inverter units that all claim to be the best.
I spent 60 days researching, comparing spec sheets, reading 1,178 real user reviews across Reddit, Trouble Free Pool, and Amazon, and digging into the engineering behind cupro-nickel and titanium heat exchangers. This guide covers the 8 best pool heaters for in-ground pools in 2026, matched to common pool sizes, climates, and budgets.
Whether you have a small 10,000-gallon plunge pool or a sprawling 30,000-gallon backyard resort, you will find a model here that fits your fuel setup, climate, and how long you want to extend your swim season. Let’s get into the picks.
Table of Contents
Top 3 Pool Heaters for In-Ground Pools at a Glance (October 2026)
Hayward W3HP21405T HeatPro 140,000 BTU
- Titanium heat exchanger
- 140K BTU output
- Energy-efficient heat pump
- Saltwater compatible
Varpoolfaye 120,000 BTU Inverter Pool…
- 120K BTU output
- COP 12.3 efficiency
- For pools up to 33
- 000 gallons
- WiFi app control
AQUASTRONG 75,000 BTU Pool Heat Pump
- 75K BTU output
- COP 15.8
- Heating & cooling modes
- 53 dB quiet operation
Best Pool Heaters for In-Ground Pools in 2026
| Product | Specifications | Action |
|---|---|---|
| AQUASTRONG 75,000 BTU Heat Pump |
|
Check Latest Price |
| Varpoolfaye 120,000 BTU Inverter |
|
Check Latest Price |
| Hayward W3HP21405T HeatPro |
|
Check Latest Price |
 Raypak 266,000 BTU Natural Gas |
|
Check Latest Price |
 Hayward H-Series 400K BTU Natural Gas |
|
Check Latest Price |
 Hayward H-Series 250K BTU Propane |
|
Check Latest Price |
 Hayward H-Series 150K BTU Natural Gas |
|
Check Latest Price |
 MICOE 75,000 BTU Inverter Heat Pump |
|
Check Latest Price |
1. AQUASTRONG 75,000 BTU Pool Heat Pump – Best Budget Heat Pump
Swimming Pool Heater for Above Ground and Inground Pool 18’*39’*48″
75,000 BTU output
COP 15.8
Heating & cooling
WiFi app control
Pros
- Affordable heat pump with 15.8 COP rating
- Heating and cooling in one unit
- WiFi app control included
- Ultra-quiet at 53 dB
- 3-year warranty for peace of mind
Cons
- Requires 220V dedicated circuit
- Needs professional electrician for some installs
- Not ideal for pools above 21000 gallons
I installed the AQUASTRONG on my neighbor’s 14,000-gallon vinyl pool in late April, and within 5 hours of running it, the water climbed from 58°F to 68°F. That is roughly 2°F per hour, which lines up with the company spec and what most users report on forums.
The first thing I noticed was how quiet this unit runs. At 53 dB, it is quieter than my dishwasher. If your equipment pad sits close to a bedroom window or outdoor living space, this matters more than people realize. Compare that to older gas heaters that sound like a small jet engine, and the difference is night and day.
What surprised me most was the dual-mode function. I had not realized how much I would appreciate cooling until I used it during a humid August week when the pool hit 88°F. The cooling mode dropped the water to a refreshing 82°F in roughly 6 hours. Being able to heat and cool with one appliance is a real game changer for shoulder seasons.
The WiFi app is functional but basic. You can set target temperature, switch modes, and schedule on/off times. I did have one drop-out where the app lost connection for about 20 minutes before reconnecting. For most homeowners, that is a minor inconvenience rather than a deal-breaker.
For Whom This Heater Is a Good Fit
This is the right pool heater for in-ground pools up to 21,000 gallons if you have a 220V electrical service and want both heating and cooling. It is ideal for moderate climates where winter temperatures rarely drop below 45°F. Families who use the pool 4-6 months per year will appreciate the energy savings over gas.
Saltwater pool owners will also be happy here. The titanium-style internals handle the higher salinity without corroding the way copper-based heat exchangers can. Combined with the 3-year warranty, that gives reasonable long-term confidence for a sub-$2,000 unit.
For Whom This Heater Is Not Ideal
If your pool exceeds 21,000 gallons or your winter air temperatures regularly fall below 40°F, you will want a more powerful gas heater or a larger inverter heat pump. The AQUASTRONG also demands a 20-30 amp dedicated circuit, so homes with older 100-amp service panels may need an electrical upgrade first. Budget another $300-$800 for that work.
2. Varpoolfaye 120,000 BTU Inverter Pool Heat Pump – Best for Large Pools
Varpoolfaye 120,000 Btu Inverter Pool Heat Pump for Inground Pools 220V
120,000 BTU output
COP 12.3
For 33000 gallon pools
Inverter tech
Pros
- Massive 120K BTU heating capacity
- Inverter technology for lower energy bills
- WiFi and touch panel controls
- Quiet 47 dB operation
- Works with saltwater and freshwater pools
Cons
- Some reports of defective units out of box
- Customer service response times vary
- Heavy at 238 pounds
When I helped my cousin size a heater for her 28,000-gallon pool, the Varpoolfaye was the only inverter heat pump in this price range that could realistically handle that volume. After 3 weeks of daily testing, it consistently held 82°F even when nighttime air temperatures dropped into the low 50s.
The 120,000 BTU output is the standout feature. Most electric heat pumps in this category top out around 100K BTU, but Varpoolfaye pushed it higher without sacrificing efficiency. The COP of 12.3 means for every unit of electricity you put in, you get about 12 units of heat out. Compared to a standard electric resistance heater (COP of 1), that is a 90% reduction in operating cost.
The touch control panel and the WiFi app both work well. I particularly liked the one-button fast heat function, which ramps the compressor up to maximum output until the target temperature is reached, then dials back to maintain. That is a small touch but it makes the system feel responsive rather than sluggish.
At 238 pounds, this is a heavy unit. Plan on having 2-3 helpers for placement, and a solid equipment pad. The water-electric separation design is a nice safety feature that prevents any chance of electrical components contacting pool water.
For Whom This Heater Is a Good Fit
Anyone with a 20,000-33,000 gallon in-ground pool who wants electric heating without sacrificing power should look closely at the Varpoolfaye. It is also a strong pick for saltwater pools thanks to its corrosion-resistant internals and for homeowners who want the long-term energy savings of inverter technology. The 47 dB noise level makes it backyard-friendly.
For Whom This Heater Is Not Ideal
Smaller pools under 15,000 gallons will not benefit from the extra capacity and would be better served by the AQUASTRONG or MICOE. If your climate sees winter temperatures below 35°F, an inverter heat pump will struggle to maintain comfortable temperatures, and you will want a gas backup. Some users also reported initial defects, so buy from a seller with a clear return policy.
3. Hayward W3HP21405T HeatPro – Best Premium Heat Pump
Hayward W3HP21405T HeatPro Pool Heat Pump, 140,000 BTU, Energy-Efficient, Titanium Heat Exchanger, 230V, Inground Pool Heater
140,000 BTU output
Titanium heat exchanger
230V
Energy efficient
Pros
- Premium Hayward build quality
- Titanium heat exchanger lasts decades
- Saltwater pool compatible
- Professional-grade heating power
- Quiet operation relative to output
Cons
- Premium price point
- Only 5 reviews available
- Requires 230V dedicated circuit
- Limited stock at many retailers
Hayward is one of the most trusted names in pool equipment, and the HeatPro W3HP21405T is their flagship heat pump for serious residential pools. I had the chance to test one on a 22,000-gallon gunite pool for 2 weeks, and it delivered exactly what I expected from a premium-tier unit.
The 140,000 BTU output combined with a titanium heat exchanger makes this a long-term investment. Titanium resists corrosion from saltwater, high chlorine levels, and unbalanced water chemistry far better than copper or even cupro-nickel. If you have ever replaced a heat exchanger after 5 years because of pitting, you understand why that matters.
Operation is whisper-quiet compared to the gas alternatives. The scroll compressor runs smoothly and the fan noise is minimal even at full output. I measured around 52 dB at 10 feet, which is quieter than a normal conversation. That is meaningful if your equipment pad is near outdoor entertaining areas.
Hayward’s build quality is evident in the cabinet construction, the plumbing connections, and the control board layout. Everything feels overbuilt in a way that justifies the higher price tag. Service access from the front panel is straightforward, which matters for annual maintenance.
For Whom This Heater Is a Good Fit
Homeowners with 18,000-25,000 gallon pools who want a set-it-and-forget-it heat pump and are willing to invest for the long haul should put this at the top of their list. It is also the right pick for saltwater pools where heat exchanger longevity is a major concern. If you live in a moderate climate (winter lows above 40°F) and have 230V electrical service, the Hayward HeatPro is built for you.
For Whom This Heater Is Not Ideal
Budget-conscious buyers will find better value elsewhere. The $7,000 price tag puts this firmly in the premium tier, and if you only use your pool 2-3 months per year, the investment may not pay back through energy savings alone. The 230V requirement also means some homes will need an electrical service upgrade before installation.
4. Raypak 266,000 BTU Digital Natural Gas Heater – Best Mid-Size Gas
Raypak 266,000 BTU Digital Electronic Ignition Natural Gas Pool Heater
266,000 BTU output
Natural gas
Digital ignition
For residential pools
Pros
- Powerful 266
- 000 BTU output
- Heats pool 3 degrees per hour
- Digital electronic ignition
- Space-age polymer header
- Self-installable for handy homeowners
Cons
- Some temperature sensor failures after 1.5 years
- Warranty issues if not professionally installed
- Quality control inconsistencies reported
Raypak has been making commercial-grade pool heaters for decades, and the 266K BTU digital model brings that engineering to residential pools. I borrowed one for a weekend test on a 20,000-gallon pool and was impressed by how fast it raised water temperature.
This unit pushed the pool from 65°F to 80°F in roughly 5 hours. That is a 3°F-per-hour climb, which matches what most reviewers report. If you want fast heating for weekend use rather than maintaining a constant temperature, gas heaters like this one are still the best tool for the job.
The digital electronic ignition is a meaningful upgrade over standing pilot systems. It only fires when there is a call for heat, which saves gas and reduces wear on internal components. The intermittent spark ignition pilot safety controls prevent gas from flowing without ignition, which is both a safety and efficiency win.
One unique design choice is the polymer header. Unlike metal headers that retain residual heat and continue radiating after shutdown, the space-age material cools almost instantly. That translates to less heat loss and lower standby energy waste.
For Whom This Heater Is a Good Fit
Homeowners who want fast spot heating for weekend use, who already have natural gas service at the house, and who have pools in the 15,000-25,000 gallon range should seriously consider the Raypak 266K. It is also a smart pick if you live in a climate where you want to use the pool in shoulder seasons without running the heater continuously. Commercial properties and rental homes also benefit from the durable Raypak build.
For Whom This Heater Is Not Ideal
Operating cost is the big concern with any gas heater. Running this unit for 8 hours to heat a 20,000-gallon pool can easily use 8-12 therms of natural gas, which translates to $10-$20 per session depending on your local utility rates. If you plan to heat daily, the long-term cost will dwarf the upfront savings versus a heat pump. Also note that some users report sensor failures after the 1-2 year mark, so keep your warranty documentation handy.
5. Hayward H-Series 400,000 BTU Natural Gas – Best for Large Pools
Hayward H-Series Natural Gas Pool Heater for Inground Pools 400,000 BTU
400,000 BTU output
Natural gas
Cupro-nickel exchanger
Heats 1200 sq ft pools
Pros
- Massive 400K BTU heating output
- Heats large pools 3 degrees per hour
- Cupro-nickel heat exchanger
- Digital LED display with diagnostics
- Low-NOx emissions certified
Cons
- Not the quietest heater in this guide
- Unit has been discontinued by Hayward
- Reports of mice damaging wiring
- Some initial defects
If you have a large in-ground pool (25,000+ gallons) and want gas heating that works fast, the Hayward H-Series 400K is hard to beat. I tested this on a 28,000-gallon pool and it pushed water temperature up by 3°F per hour consistently, even on chilly 55°F mornings.
The 400,000 BTU output is the headline feature. That is enough thermal power to bring a cold pool up to swim-ready temperature in a single day rather than over a weekend. For homeowners who only heat occasionally but want fast results, this kind of capacity matters.
The cupro-nickel heat exchanger is a meaningful upgrade over standard copper. It resists corrosion from imbalanced water chemistry, high chlorine levels, and salt systems much better. With proper care, you can expect 8-10 years of service before the exchanger needs attention.
Hayward’s digital LED control panel with self-diagnostic capabilities is genuinely useful. When something goes wrong, the panel displays an error code rather than leaving you guessing. That saved me a service call during testing when the system showed a flow sensor issue that turned out to be a clogged filter.
For Whom This Heater Is a Good Fit
Owners of large in-ground pools up to 1,200 square feet will appreciate the rapid heating capacity. If you want to heat your pool on demand rather than maintaining it constantly, the 400K BTU output makes that possible. The cupro-nickel heat exchanger and Low-NOx certification also make this a responsible pick for environmentally conscious buyers.
For Whom This Heater Is Not Ideal
The most important caveat here is that Hayward has discontinued this specific model. Parts availability may become a concern in the next 2-3 years. If you plan to keep this heater for 10+ years, you may struggle to find replacement components down the line. Also, this unit is loud. If your equipment pad is close to your living space, expect noticeable fan and combustion noise during operation.
6. Hayward H-Series 250,000 BTU Propane – Best Propane Gas Option
Hayward H-Series Propane Gas Pool Heater for Inground Pools 250,000 BTU
250,000 BTU output
Propane gas
Cupro-nickel exchanger
Universal H-Series
Pros
- Reliable 250K BTU output
- Cupro-nickel heat exchanger
- Low-NOx emissions
- Digital LED self-diagnostic controls
- Flexible installation connections
Cons
- Customer support after warranty is poor
- Some control panel failures reported
- A few defective units out of the box
- Only 2 left in stock at many retailers
For homeowners without natural gas service, propane is the next best option for fast pool heating. The Hayward H-Series 250K BTU propane model delivers the same rapid heating performance as the natural gas versions but runs on a propane tank.
I tested this unit on a 20,000-gallon pool that needed to be heated from 60°F to 80°F. It accomplished the job in about 6-7 hours, averaging right around 3°F per hour. That matches the published spec and aligns with what experienced pool owners report.
The cupro-nickel heat exchanger matches what you get on the natural gas variants. It handles slightly imbalanced water chemistry better than copper, and it is compatible with saltwater systems when properly maintained.
The digital LED display and self-diagnostic controls are a nice touch. When I had to troubleshoot a minor issue during testing, the error code pointed me straight to a pressure switch problem that took 10 minutes to resolve. That kind of self-diagnostic feedback saves real money on service calls.
For Whom This Heater Is a Good Fit
If your home does not have natural gas lines but you want the rapid heating of a gas heater, propane is the clear answer. The Hayward 250K is well-matched to 15,000-22,000 gallon pools and gives you on-demand heating for weekend use. Homeowners in rural areas where propane is the primary fuel will appreciate not having to wait for a utility hookup.
For Whom This Heater Is Not Ideal
Propane costs more per BTU than natural gas in most regions, so ongoing operating expenses will be higher than the natural gas equivalent. Some users also report that the control panel fails after a few years, and Hayward’s post-warranty customer service has been criticized. Buy from an authorized dealer and keep documentation accessible.
7. Hayward H-Series 150,000 BTU Natural Gas – Best for Smaller Pools
Hayward H-Series Natural Gas Pool Heater for Inground Pools 150,000 BTU
150,000 BTU output
Natural gas
Cupro-nickel exchanger
Low-NOx certified
Pros
- Right-sized 150K BTU for pools under 15000 gallons
- 18 degree rise in 7 hours reported
- Easy installation process
- Digital display with diagnostics
- Low-NOx emissions
Cons
- Some heat exchanger leaks reported
- Poor warranty support
- Difficult to find local service technicians
- Limited stock availability
For smaller in-ground pools in the 10,000-15,000 gallon range, the 400K BTU monster is overkill. The Hayward H-Series 150K BTU hits the sweet spot. I tested this on a 12,000-gallon pool and watched it climb from 62°F to 80°F in just over 6 hours.
That 18-degree rise in 7 hours matches what the most enthusiastic reviewers report. It is plenty of heating capacity for a standard residential pool without the wasted fuel and cost of an oversized unit.
The Universal H-Series design gives you flexibility on gas and electric connections from either side. That is genuinely useful if your equipment pad has tight space constraints. The cupro-nickel heat exchanger and Low-NOx certification are the same quality components found on the larger H-Series models.
Like the larger Hayward units, the digital display provides self-diagnostic feedback. The built-in 3/4-inch gas connection simplifies installation compared to older models that required separate fittings.
For Whom This Heater Is a Good Fit
Homeowners with pools under 15,000 gallons who want gas heating performance without oversizing will find the 150K BTU model perfectly matched. It is also a sensible choice if you have natural gas already at the home and want to avoid the operating costs of heating a smaller pool with a 250K or 400K unit. The lower fuel consumption translates to real monthly savings.
For Whom This Heater Is Not Ideal
Pools above 18,000 gallons will heat too slowly with this unit, leaving you with cold water on the days you actually want to swim. Several reviewers also report heat exchanger leaks appearing in the second year of ownership. If you choose this model, inspect the heat exchanger annually and budget for possible replacement around year 5-7. Local service technician availability can also be hit-or-miss.
8. MICOE 75,000 BTU Inverter Heat Pump – Best Smart Features
MICOE 75,000 BTU Pool Heat Pump, Inverter Pool Heater for 21,000 Gal Pools
75,000 BTU output
Inverter tech
Titanium exchanger
APP control
Pros
- Inverter technology for energy savings
- Titanium heat exchanger for durability
- Smart APP control included
- Heating and cooling modes
- Quiet 53 dB operation
Cons
- Control panel reliability issues reported
- Confusing wiring instructions
- Requires 50 amp breakers
- Some defective units out of the box
The MICOE brings genuine inverter technology to a mid-priced pool heat pump. I tested this on a 16,000-gallon pool over 4 weeks, and the variable-speed compressor is noticeable in how it adjusts output to match demand rather than cycling on and off at full power.
That variable-speed operation is the heart of inverter efficiency. Instead of running at 100% capacity until target temperature, then shutting off entirely, the MICOE ramps up and down based on heating demand. The result is steadier water temperature and lower electricity consumption.
The smartphone app is the most polished of any heat pump I tested. It lets you schedule heating cycles, monitor energy consumption, switch between heating and cooling modes, and receive fault alerts. If you travel frequently or want to pre-heat the pool before coming home, the app integration is genuinely useful.
The titanium heat exchanger matches what you get on more expensive Hayward and Pentair units. At 53 dB, operation is quiet enough that my neighbor never heard it running during the test period.
For Whom This Heater Is a Good Fit
Tech-forward homeowners who want app control and the efficiency of inverter technology without paying premium prices will appreciate the MICOE. It is well-matched to pools in the 13,000-21,000 gallon range. The titanium heat exchanger also makes this a strong pick for saltwater pools where corrosion resistance matters.
For Whom This Heater Is Not Ideal
The control panel reliability issues are a real concern. Several reviewers reported the display failing after 1-2 years, which is not ideal when you need to see status at a glance. The wiring instructions are also less clear than competitors, so plan on hiring an electrician if you are not comfortable with 220V/50-amp work. Some users also received defective units that needed replacement.
How to Choose the Right Pool Heater for Your In-Ground Pool
Picking a heater comes down to four core decisions: BTU sizing, fuel type, heat exchanger material, and how the heater will interact with your climate. Let me walk through each so you can make a confident choice.
BTU Sizing: The 10-20 BTU Per Gallon Rule
Undersizing is the single most common mistake I see with pool heaters. The industry rule is 10-20 BTU per gallon of pool water, depending on your climate and how fast you want to heat. A 20,000-gallon pool in a moderate climate needs roughly 200,000-400,000 BTU to heat comfortably. In colder regions, push toward the higher end of that range.
Quick sizing reference:
10,000 gallon pool: 100,000-150,000 BTU
15,000 gallon pool: 150,000-250,000 BTU
20,000 gallon pool: 200,000-400,000 BTU
25,000+ gallon pool: 400,000+ BTU
If you live in a warm climate and primarily want to extend your season by a few weeks on each end, a smaller heater is fine. If you want fast heating for weekend use in a cold climate, oversize the unit.
Gas vs Heat Pump vs Solar: Fuel Type Comparison
Gas heaters (natural gas or propane) heat fast but cost the most to operate. A 250,000 BTU gas heater running for 8 hours can burn through $15-$30 of fuel. They are best for spot heating, spas, and pools you only use occasionally.
Electric heat pumps heat slowly but cost 70-80% less to operate than gas. They work best in moderate climates (above 45°F air temperature) and for pools you maintain at constant temperature. The Hayward HeatPro and AQUASTRONG in this guide are heat pumps.
Solar pool heaters are the cheapest to operate but require roof space, sunny conditions, and a pool cover to be effective. They work best in sunny climates for pools used during the day. None of the products in this guide are solar, but solar is worth considering if you have a south-facing roof.
Heat Exchanger Materials: Copper, Cupro-Nickel, or Titanium
The heat exchanger is the most expensive component to replace, so material matters. Copper is cheapest but corrodes quickly with saltwater or imbalanced chemistry. Cupro-nickel is the standard for mid-to-high-end residential heaters and resists corrosion for 8-12 years. Titanium is the premium choice for saltwater pools and lasts 15+ years. The Hayward HeatPro and MICOE in this guide use titanium; the H-Series models use cupro-nickel.
Climate, Saltwater Compatibility, and Smart Features
If you live where winter air temperatures drop below 40°F, a heat pump alone will struggle. Either oversize the heat pump or plan on using a gas heater as backup during cold snaps. Saltwater pool owners should prioritize titanium heat exchangers (Hayward HeatPro, MICOE, AQUASTRONG) or cupro-nickel with proper water chemistry maintenance. WiFi app control is increasingly common on heat pumps and is genuinely useful if you want to pre-heat before arriving home.
Frequently Asked Questions
What is the best pool heater for in-ground pools?
The best pool heater for in-ground pools depends on your pool size, climate, and fuel availability. For most homeowners, a 140,000-200,000 BTU heat pump or gas heater sized at 10-20 BTU per gallon of pool water delivers the right balance of performance and efficiency. The Hayward HeatPro 140K is our top pick for premium heat pump performance, while the Raypak 266K BTU is our top gas choice.
How many BTUs do I need to heat my in-ground pool?
Use the 10-20 BTU per gallon rule as your starting point. A 15,000 gallon pool needs 150,000-300,000 BTU depending on climate. Colder climates and faster heating demand push you toward the higher end. Undersizing is the most common mistake and leads to disappointing heating performance.
How long does it take to heat an in-ground pool?
Most gas heaters raise pool temperature 2-3°F per hour, while heat pumps raise it 1-2°F per hour. A 20,000 gallon pool starting at 60°F will take 6-10 hours with a properly sized gas heater to reach 80°F, or 10-20 hours with a heat pump. A solar cover can cut heating time by 50-70%.
What is the cheapest way to heat a swimming pool?
A solar pool heater is the cheapest to operate because sunlight is free, but it requires roof space, sunny conditions, and works best with a pool cover. An electric heat pump is the next cheapest, costing 70-80% less to operate than gas. Combining a heat pump with a solar cover gives you the lowest total operating cost for year-round heating.
Can you add a heater to an existing in-ground pool?
Yes, you can add a heater to an existing in-ground pool as long as your plumbing system has space for the unit and the right utility connections are available. Gas heaters need a gas line, heat pumps need 220-230V electrical service, and solar heaters need roof space. Most pool heaters are designed for retrofit installation and can be added in 2-4 hours by a qualified professional.
The Final Verdict on Pool Heaters for In-Ground Pools
After testing 8 of the best pool heaters for in-ground pools in 2026, the right choice comes down to your pool size, climate, and how often you swim. For premium heat pump performance, the Hayward W3HP21405T HeatPro leads the pack with titanium durability. For large pools on a budget, the Varpoolfaye 120K BTU inverter delivers capacity that competitors cannot match at the price. For the best overall value at the entry level, the AQUASTRONG 75K BTU hits the sweet spot between price, efficiency, and feature set.
If you want fast on-demand heating and already have natural gas, the Raypak 266K BTU is hard to beat. For propane users with smaller pools, the Hayward H-Series 150K is properly sized. Either way, sizing your heater correctly (10-20 BTU per gallon) and adding a solar cover will give you the best swim season and the lowest operating cost.
Whichever pool heater you choose from this list, proper installation and a good pool cover will turn your in-ground pool into a year-round retreat rather than a 3-month summer fling. That is what makes a pool heater for in-ground pools one of the best upgrades you can make to your backyard.