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Pool Heaters for 20,000 Gallon Pools

Inverter and Standard Pool Heat Pumps for 10,000 to 20,000 Gallon Inground Pools

This collection covers heat pumps and gas heaters sized for pools from 10,000 to 20,000 gallons - the most common range for residential inground pools in the US. It includes inverter heat pumps from Madimack and AquaCal, standard heat pumps from FibroPool and Hayward, GulfStream electric heat pumps, and the Hayward H135 gas heater in natural gas and propane versions. The H135 is the only above ground compatible model here; all others are designed for inground pools.

Pool Heater Sizing Guide: 50,000 to 135,000 BTU Options by Pool Volume

Select your pool size or use case below to see which models fit, estimated monthly running costs, and what sets each option apart.

My pool holds approximately...
Select your pool size above to see recommendations.
10,000-12,000 gal - recommended: 50,000-66,000 BTU

The Madimack InverECO 50K and Hayward HeatPro 50K are both rated to 12,000 gallons. The AquaCal T70 at 63,000 BTUs is rated to 15,000 gallons - sizing up slightly is a sound choice, especially in cooler climates or if your pool is uncovered.

12,000-15,000 gal - recommended: 63,000-70,000 BTU

The FibroPool FH270 is the most affordable at 70,000 BTUs. The Madimack and AquaCal inverter models cost more upfront but use noticeably less electricity for day-to-day maintenance heating. The GulfStream HE110 RA at 115,000 BTUs heats faster than its pool size rating suggests - a good choice if fast heat-up matters more than energy efficiency.

15,000-17,500 gal - recommended: 84,000-85,000 BTU

Both are inverter models rated to 17,500 gallons. The FibroPool FH285-i is a strong value. The Madimack InverELITE 84K is a premium unit with a more robust build, WiFi, and spa mode - the price premium reflects a significant step up in quality and features.

17,500-20,000 gal - recommended: 90,000-118,000 BTU

The Madimack InverTitan 90K is the most efficient option at this size. The Hayward HeatPro 100K is a proven standard-speed unit with broad installer support. The GulfStream HE125 TA adds heat and cool capability and spa mode at a competitive price point.

Gas heaters in this collection - Hayward H135

The Hayward H135 is a gas heater - it burns natural gas or propane to generate heat directly rather than moving heat from the air. Gas heaters heat pools significantly faster than heat pumps and work at any air temperature, making them a practical choice for cold climates, shoulder seasons, or pools used occasionally. The H135 is also above ground pool compatible. It requires a gas line or propane tank plus a 120V electrical connection. For larger pools needing gas heat, see the 30,000 gallon collection for H150, H200, H250, and H400 models.

Spa-capable heaters in this collection

All models above can maintain spa temperatures to 104 F. Heat pumps heat gradually at 1 to 2 degrees F per hour - ideal for maintaining a spa/pool combination kept warm together, but slow for heating a cold spa from scratch on demand. The Hayward H135 gas models heat much faster and are the better choice if you need quick on-demand spa heat. For spa-capable heaters for larger pools, see the 30,000 gallon collection.

Monthly cost estimates assume a moderate climate swim season and average US electricity rate of $0.17/kWh. Pool cover use reduces running costs by up to 40%. Models tagged Spa support spa mode heating to 104 F. Call us at 800-809-3741 for personalised sizing advice.

FibroPool, Madimack, AquaCal, GulfStream, and Hayward Pool Heaters Compared

This collection mixes heat pump and gas heater types across a wide BTU range. The Hayward H135 is the only gas model and the only above ground compatible unit. All heat pump models require a 220/240V dedicated circuit.

Pool Size Unit BTUs Type / Mode Price
Up to 12,000 gal Madimack InverECO 50K 50,000 Heat/Cool Inverter Spa $2,680
Hayward HeatPro 50K 50,000 Heat/Cool Spa $2,999
Up to 15,000 gal AquaCal T70 TropiCal 63,000 Heat/Cool Inverter Spa $3,311
Madimack InverECO 66K 66,000 Heat/Cool Inverter Spa $3,115
FibroPool FH270 70,000 Heat/Cool from $1,935
GulfStream HE110 RA 115,000 Heat Only Spa $3,895
Up to 17,500 gal FibroPool FH285-i 85,000 Heat/Cool Inverter from $2,386
Up to 20,000 gal Madimack InverELITE 84K 84,000 Heat/Cool Inverter Spa $6,230
Madimack InverTitan 90K 90,000 Heat/Cool Inverter Spa $5,000
Up to 20,000 gal Hayward HeatPro 100K 100,000 Heat/Cool $5,499
GulfStream HE125 TA 118,000 Heat/Cool Spa $4,695
Up to 25,000 gal Hayward H135 Natural Gas 135,000 Gas Heat Only Spa $2,399
Hayward H135 Propane 135,000 Gas Heat Only Spa $2,399

Inverter models vary output based on demand - quieter and more efficient than standard units. Heat/Cool units both heat and chill. Heat Only costs less upfront. Gas heaters require a gas line or propane tank and heat faster than heat pumps at any air temperature. Spa units are rated for spa use to 104 F. All heat pump models require a 220/240V dedicated circuit. Cold-climate buyers should consider sizing up one tier.

Frequently asked questions

How do I know if my pool is around 20,000 gallons?

A standard rectangular 16x32 foot inground pool with an average depth of 5 feet holds approximately 19,200 gallons. An 18x36 foot pool at the same depth is around 24,300 gallons. For a rough estimate: length x width x average depth x 7.5 = gallons. If you have an irregular shape or are unsure, call us at 800-809-3741 and we can help you size correctly.

Why does the GulfStream HE110 RA have 115,000 BTUs but only cover 15,000 gallons?

BTU output and pool size rating are related but not directly proportional for heat pumps. The GulfStream HE110 RA is a standard single-speed compressor unit - it produces 115,000 BTUs when running at full capacity, but the manufacturer rates it conservatively for pools up to 15,000 gallons based on real-world heating conditions including overnight heat loss and cold weather performance. An inverter unit like the Madimack InverELITE 84K at 84,000 BTUs is rated to 20,000 gallons because it runs continuously at variable speeds, maintaining temperature more efficiently over time. For a detailed explanation, see the FAQ on the main pool heaters page.

Should I choose a heat pump or gas heater for a 20,000 gallon pool?

For a pool used regularly from spring through fall in a warm or moderate climate, a heat pump will cost significantly less to run - typically $50 to $90 per month vs. $200 or more for a gas heater at current energy prices. Heat pumps work best for keeping a pool at temperature day to day. Gas heaters are the better choice if you want to heat your pool quickly from cold, if you swim year-round in a cold climate, or if your pool sits unused for weeks at a time and you need rapid on-demand heat-up. Many pool owners in colder climates use a heat pump as their primary heater and a gas heater for early and late season use.

What does inverter mean on a pool heat pump?

An inverter heat pump uses a variable-speed compressor that adjusts its output to match what the pool needs at any given moment - running quietly at low power when the pool is close to temperature, ramping up when it needs to catch up. Standard (non-inverter) units run at full speed and cycle on and off. Inverter models use 20 to 40% less electricity over a full season, run noticeably quieter, and typically have longer compressor lifespans. In this collection, the Madimack InverECO, InverELITE, and InverTitan models and the AquaCal T70 TropiCal and FibroPool FH285-i are all inverter units.

Can these heaters heat a pool and a spa at the same time?

The heat pump models tagged with Spa in the table above - Madimack InverECO 50K and 66K, InverELITE 84K, InverTitan 90K, AquaCal T70 TropiCal, GulfStream HE110 RA, and HE125 TA - are all rated for pool and spa use to 104 F. They work well for pool/spa combinations kept at temperature together. For heating a cold spa quickly on demand, the Hayward H135 gas heater is the faster choice - gas heats water significantly faster than a heat pump.

Do heat pumps work in cold weather?

Heat pumps extract heat from the surrounding air, so efficiency drops as air temperature falls. Most standard models in this collection operate down to around 45 to 50 degrees Fahrenheit. The Madimack InverTitan and InverELITE series are cold-weather rated and can operate down to 14 degrees Fahrenheit, making them a practical year-round option in most US climates. The Hayward H135 gas heater works at any air temperature with no efficiency loss.

Do you offer installation?

Yes. Visit our installation support page for details on connecting with a licensed installer in your area. Gas heater installation requires a licensed contractor in most jurisdictions. Heat pump installation involves plumbing into your return line and a dedicated 220/240V electrical circuit.

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