How to Size a Madimack Heat Pump: The Complete BTU Guide

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Pool volume, climate zone, and heating time all factor into picking the right Madimack model. Here's how to calculate it — with model recommendations for every pool size.

Picking the wrong size heat pump is the most common mistake pool owners make. Undersizing means your pool takes days to heat or never reaches target temperature. Oversizing wastes money upfront. Madimack's inverter technology handles a range of pool sizes better than conventional units — but you still need to start with the right model.

How to Calculate Your Pool Volume

Example: A 16 × 32 foot pool with an average depth of 5 feet = 16 × 32 × 5 × 7.5 = 19,200 gallons. If you're not sure of your volume, your pool builder's paperwork or local pool service company can usually provide it.

Calculate Your Minimum BTU Requirement

A rough rule of thumb: 3,000–5,000 BTUs per 1,000 gallons of pool volume, adjusted for climate zone.

Climate Zone BTU Factors

Example using our 19,200 gallon pool in Georgia (moderate zone, 4,000 BTU factor): 19.2 × 4,000 = 76,800 BTU minimum. The Madimack InverELITE 84K would be the starting model; the InverELITE 116K provides comfortable headroom.

Key Variables That Affect Heat Pump Sizing

The BTU calculation above is a baseline. Adjust upward if:

• No pool cover: add 15–25% more BTU. Uncovered pools lose heat overnight at a significant rate.
• Windy location: add 10–20% (wind accelerates evaporation and heat loss).
• Spa attached: add the spa volume to the total and increase BTUs accordingly.
• Fast heating required: heating from 60°F to 84°F in 24 hours vs. 48 hours requires more BTUs.
• Shaded pool: shaded pools don't gain passive solar heat, requiring more from the pump.

Madimack Model Selector by Pool Size

Madimack Model Family: InverECO vs InverELITE vs InverTitan

Heating Time Expectations

How long will it take to heat your pool from cold? A correctly sized Madimack heat pump will raise pool temperature approximately 1–2°F per hour in ideal conditions (70°F+ ambient air). Below are realistic estimates:

Estimates based on 75°F ambient air temperature, no pool cover. Colder air, wind, or no cover increases heating time. A pool cover reduces it significantly.

Sizing for Cooling in Hot Climates

If you're in Florida, Texas, Arizona, or similar climates, your heat pump will also run in cooling mode during summer. All Madimack models heat and cool by default — no separate sizing calculation is required. In extreme heat (ambient air above 100°F), cooling output is reduced; sizing slightly larger helps in those conditions.

Common Madimack Sizing Mistakes

• Using surface area instead of volume: volume is what matters for heat energy, not surface area
• Ignoring wind exposure: wind-exposed pools in hot climates can lose as much heat as pools in cooler sheltered climates
• Not accounting for a spa: if the heat pump will also serve a connected spa, add those gallons to your total
• Undersizing based on minimum BTU: always give yourself buffer above the calculated minimum
• Comparing BTUs without COP: a 150K BTU conventional pump at COP 6 provides the same net heat as a 60K BTU inverter at COP 15

Frequently Asked Questions

For a 22,000 gallon pool in a warm climate (Florida, Texas), the 84K may be sufficient — but the 116K gives you meaningful headroom and faster heating times. In moderate climates, we'd lean toward the 116K. The price difference is relatively small compared to the performance benefit.

Yes — dual units are sometimes used for very large pools (40,000+ gallons) or for redundancy. Two InverELITE 116K units running in tandem provide 232K BTU with full inverter efficiency and better warranty coverage than a single InverTitan 140K. Requires proper plumbing configuration.

The inverter advantage is efficiency and quiet operation at any load — not a reason to dramatically undersize. The BTU math still applies. However, because inverter compressors handle extended low-speed run time well, sizing to the upper edge of a model's range is less problematic than with conventional units.

See also: Madimack heat pump review | Madimack warranty guide | All pool heat pumps