Introduction
Heating a swimming pool with a heat pump is an efficient and sustainable method that can significantly reduce energy costs compared to traditional gas or electric heaters. Mitsubishi Electric, known for its advanced air-source heat pump technology, offers several systems that can be adapted to heat swimming pool water effectively and efficiently.
This document explains how a Mitsubishi heat pump can be integrated into a pool heating system, the key components required, and the operational principles behind it.
How Heat Pumps Work
A heat pump extracts heat energy from the surrounding air (even in cold conditions) and transfers it to water. The process involves four main stages:
Evaporation: The refrigerant absorbs heat from the air as it passes through the evaporator coil, turning the refrigerant into a gas.
Compression: The compressor increases the pressure and temperature of the refrigerant gas.
Condensation: The hot refrigerant gas passes through a condenser (heat exchanger), transferring its heat to the pool water.
Expansion: The refrigerant cools and returns to its liquid state, ready to repeat the cycle.
Mitsubishi’s inverter-driven compressors modulate output according to demand, maximizing efficiency and maintaining steady water temperature.
Suitable Mitsubishi Heat Pump Models
While Mitsubishi does not manufacture pool-specific heat pumps, its Ecodan range of air-to-water heat pumps is highly suitable for pool heating when paired with the correct controls and heat exchangers.
Typical models include:
Mitsubishi Ecodan PUHZ-(HW/WW/YW) Series (4–14 kW range)
Ecodan CAHV or QAHV Series (large-scale commercial systems up to 45 kW or more)
The correct model depends on:
Pool size and volume
Desired water temperature
Seasonal air temperatures
Desired heating time and usage pattern
System Configuration – Key Components
Mitsubishi Heat Pump Unit (Ecodan series)Provides thermal energy by extracting heat from the air.
Heat Exchanger (Titanium or Stainless Steel)
Transfers heat from the heat pump’s water circuit to the pool water without mixing the two fluids. Titanium is recommended for saltwater or chlorinated pools.
Hydraulic Components
Circulation pumps
Expansion vessel
Non-return valves and safety devices
Pool Filtration System
Ensures clean water flow through the heat exchanger.
Control Interface
The Mitsubishi FTC5/FTC6 controller or a dedicated pool temperature controller manages water temperature and prioritizes heating between domestic hot water, space heating, and pool heating.
Installation Overview
Connection to the Pool Heating Circuit:
The heat pump connects to the pool water loop via a secondary circuit (using the heat exchanger). This avoids contamination and ensures proper flow rates.
Plumbing:
The pool water is drawn from the pool filtration system, passed through the heat exchanger, and returned to the pool.
Electrical & Control Setup:
The Ecodan’s controller can be configured to recognize the pool as an additional heating zone. Alternatively, an external pool thermostat can activate the system when pool water temperature drops below the setpoint.
Commissioning:
Verify refrigerant charge and system pressure
Balance flow rates for both circuits
Set temperature parameters and control priorities
Efficiency and Benefits
High Coefficient of Performance (COP): Mitsubishi heat pumps typically achieve COPs between 3 and 5, meaning 3–5 units of heat are produced for every 1 unit of electricity consumed.
Renewable Heat Source: Utilizes ambient air energy, reducing carbon footprint.
Quiet Operation: Inverter-driven compressors and fan design minimize noise.
Flexible Integration: Can provide heating for both the pool and the main property (domestic hot water and space heating).
Low Maintenance: Few moving parts and no combustion process reduce servicing needs.
Design Considerations
Pool Location & Size: Larger or outdoor pools require higher capacity.
Seasonal Use: In cooler climates, consider a cover or partial indoor installation for year-round swimming.
Water Chemistry: Always use a corrosion-resistant titanium heat exchanger.
Flow Rates: Maintain recommended flow rates through the heat exchanger (typically 1–2 m³/h per 10 kW).
Defrost Cycles: In colder weather, ensure proper defrosting to maintain performance.
[Outdoor Air]
↓
┌──────────────────────────┐
│ Mitsubishi Ecodan Unit │
│ (Air-to-Water Heat Pump) │
└──────────────────────────┘
│ (Primary Circuit)
↓
┌──────────────────────────┐
│ Titanium Heat Exchanger │
└──────────────────────────┘
↑ (Secondary Circuit)
│
┌──────────────────────────┐
│ Pool Filtration System │
│ (Pump + Filter) │
└──────────────────────────┘
↓
[Swimming Pool]
Conclusion
By integrating a Mitsubishi Ecodan heat pump with an appropriately designed heat exchanger and control system, a swimming pool can be heated efficiently, sustainably, and cost-effectively. This approach not only provides comfortable water temperatures throughout the swimming season but also supports broader energy savings when combined with home heating and hot water systems.
Comparison: Heat Pump vs. Oil-Fired Pool Heating
Feature | Mitsubishi Ecodan Heat Pump | Oil-Fired Heating System |
Energy Source | Electricity + ambient air | Heating oil (fossil fuel) |
Typical Efficiency (Seasonal COP) | 350–450% (3.5–4.5 units of heat per unit of electricity) | 70–85% (0.7–0.85 units of heat per unit of fuel) |
Carbon Emissions | Very low, especially with renewable electricity | High CO₂ emissions from combustion |
Fuel Price (as of 2025) | ~£0.25–0.30/kWh electricity, but delivers 3–4× heat output → ~£0.08/kWh effective | ~£0.10–0.12/kWh oil (net heat) |
Maintenance | Minimal—no flue, filters, or combustion | Regular servicing, flue cleaning, and safety checks |
Noise and Smell | Quiet, clean operation | Odour and exhaust gases |
Lifespan | 15–20 years | 10–15 years |
Example Cost Comparison
For a medium outdoor pool requiring 30,000 kWh of heat per season:
Oil System (80% efficiency):
30,000 ÷ 0.8 × £0.10 = £3,750/year
Ecodan Heat Pump (COP 4.0):
30,000 ÷ 4 × £0.27 = £2,025/year
That’s a saving of roughly 45–50% per year on operating costs, with zero on-site emissions and reduced maintenance.
Assumptions
We’ll base this on the earlier example we used:
Your pool needs about 30,000 kWh of heat energy per season.
Your heat pump has a COP (Coefficient of Performance) of about 4.0 (so you need 30,000 ÷ 4 = 7,500 kWh of electricity).
On a “normal” electricity tariff (day time, non-off-peak) you might pay, say, ~£0.27 / kWh (this is a rough UK estimate)
On the Octopus Go tariff, the off-peak unit rate is around £0.085 / kWh (8.5 p/kWh) for the hours 00:30–05:30. Solar Advice UK+3agilebuddy.uk+3octopusreferral.link+3
We will assume you can shift all the electricity for the heat pump into that cheap off-peak window (this is optimistic but shows the maximum possible benefit).
Cost Comparison – Standard tariff cost
Electricity used: 7,500 kWh
Unit cost (normal day rate): £0.27/kWh
Cost = 7,500 × £0.27 = £2,025
This matches our earlier heat pump cost estimate of ~£2,025/year.
Octopus Go tariff cost
Assume you manage to use all 7,500 kWh in the cheap slot (8.5p/kWh)
Cost = 7,500 × £0.085 = £637.50
Plus you’ll have the standing charge component (which we’ll ignore for simplicity here, since we’re focusing on the use-cost difference).
Potential Saving
£2,025 (standard) minus £637.50 (Go off-peak) = £1,387.50 saved per season
That’s a ~68% reduction in usage cost for the electricity portion of heating.
Realistic Considerations & Caveats
It is unlikely you will shift all the heat-pump electricity into the 00:30-05:30 window (night). Pool heating often needs longer hours, maybe during day when air temperature is higher etc. So the real saving will be somewhat less.
If some of the electricity has to be used in “peak” hours (daytime) you’ll pay the higher day rate (for Go tariff that might be ~30p/kWh or more depending region). Reddit+1
You’ll also have the standing charge (daily fixed cost) which affects total cost – if you shift more usage, the proportion of standing charge becomes smaller.
The heat pump COP might vary with ambient air temperature – in cold conditions the COP may drop, meaning more electricity for the same heat output.
It also depends on whether your system (pool pump, filtration, heat exchanger) is sized and controlled so the vast majority of electricity consumption can indeed occur in the off-peak period.
Using a Home Battery (Anker SOLIX X1) to Save More – How it works
The Anker SOLIX X1 supports a Time-of-Use or Time-Slot mode: it can be configured to charge when your electricity tariff is lowest (e.g., overnight) and discharge/use that stored energy when tariffs are high. ankersolix.com+2service.anker.com+2
For example: At night (e.g., 00:30–05:30) you might pay ~8.5 p/kWh (on a tariff like Octopus Energy Go). You charge the battery then. During the day or early evening when electricity is more expensive, you discharge from the battery to power your pool heat pump (or house loads) instead of drawing from the grid at the high rate.
The result: You effectively shift your high-energy device usage (like the pool heat pump) into the low-cost window – even though the device may operate when grid rates are higher, you’re using stored energy instead of high-cost grid import.
Why this adds to the savings in your pool-heating scenario
In your earlier calculation, the pool heat pump needed ~7,500 kWh electricity per season (based on 30,000 kWh heat requirement and COP4). You assumed the heat pump draws directly from the grid at whichever rate is active.
With a battery, you can buy cheap power during off-peak, store it, and then use it for your heat pump when you’d otherwise pay a higher rate.
Suppose you pay 8.5p/kWh at night, charge battery, then use that for the heat pump instead of paying 27p/kWh. That can bring your effective cost per kWh down further.
For example: If you manage to shift 100% of the 7,500 kWh through the battery (ideal scenario):
Cost = 7,500 × £0.085 = £637.50 (plus battery losses)
Compare to direct grid cost (£2,025) and you add a further savings beyond what you got with the tariff alone.
Even if you only shift, say, 50% of usage to battery, you could still move 3,750 kWh from high-rate to low-rate: 3,750 × (0.27-0.085) = approx £683 additional savings.
Key considerations & caveats
Battery efficiency / losses: The battery is not 100% efficient. Round‐trip efficiencies for systems like SOLIX are up to ~90%. 3637446.app.netsuite.com+2portal.segen.co.uk+2 You need to factor this in: if you charge 1 kWh at 8.5p you might only get ~0.9 kWh usable output, so the effective cost/kWh rises slightly.
Battery cost & payback: The capital cost of the battery system must be weighed against additional savings. The document should note that payback will depend on battery size, number of cycles, lifespan, and how much usage you shift.
Tariff compatibility: The SOLIX X1 supports Time-of-Use scheduling, but real-world users report limitations with certain tariffs. For example:
“The Solix X1 currently only allows battery discharge if you configure the battery to use dynamic electricity pricing … I’m on Octopus Intelligent Go … the tariff selection in the app only shows the agile tariffs.” Reddit
So check that your tariff and battery control system are fully compatible.
Heat pump operational hours: Even if the battery powers the heat pump, you still need the heat pump to run when the ambient conditions and pool use require it. If those hours fall during higher-rate grid periods or when battery is depleted, you may still draw from the grid at higher cost.Battery sizing: Depending on your heat pump load, you’ll want a battery system sized to store enough energy for the peak usage periods or to overlap with high-rate windows. The SOLIX X1 is modular (5-180 kWh capacity scale) which helps. ankersolix.com+1
Lifecycle & maintenance: Battery systems degrade over time, so longer-term savings must account for eventual capacity fade, maintenance, and replacement cost.
Revised cost-saving example (including battery)
Let’s assume:
Heat pump again uses ~7,500 kWh electricity/year.
You install a battery, charge it entirely during off-peak at 8.5p/kWh. Assume 90% round-trip efficiency, so you must buy ~7,500 ÷ 0.90 ≈ 8,333 kWh at 8.5p = £708.
You then use that stored energy to power the heat pump, avoiding paying 27p/kWh on grid draw. If you did it without battery you would pay ~£2,025.
With battery scenario: ~£708 vs £2,025 → saving ~£1,317.
If battery shift is only 75% of the usage: 7,500 × 0.75 = 5,625 kWh from battery, need to charge ~6,250 kWh (at 8.5p) = £531. Then the remaining 1,875 kWh drawn from grid at 27p = £506. Total = £531 + £506 = £1,037. That’s still ≈£988 savings versus direct grid cost.
Summary for the section
In summary, adding a home battery system like the Anker SOLIX X1 to your pool-heating setup allows you to charge electricity during very low off-peak prices, then use (or discharge) that power when your heat pump would otherwise draw at much higher rates. This shifts your energy usage profile in your favour and can generate significant additional savings beyond just switching to a low-rate tariff. However, it requires careful sizing, good tariff compatibility, and realistic usage assumptions to realise those savings.
Understanding Battery Shift and Its Role in Pool Heating
What “Battery Shift” Means
“Battery shift” refers to the proportion of your total electricity use that you can move (or shift) from expensive, high-rate times of day to cheaper, off-peak periods — by storing energy in a battery when electricity prices are low, and using that stored energy later when prices rise.
In this setup:
You charge the Anker SOLIX X1 battery overnight on a low-cost tariff such as Octopus Go (e.g. 00:30–05:30 @ 8.5 p/kWh).
During the day, when electricity can cost around 27 p/kWh, your heat pump and other loads draw electricity from the battery instead of the grid.
This effectively shifts your energy use from high-price hours to low-price hours.
The higher your “battery shift percentage,” the greater your savings.
Example: Battery Shift in Practice
Let’s assume your Mitsubishi heat pump uses 7,500 kWh of electricity each pool-heating season.
You might not be able to run the heat pump entirely at night (when rates are cheapest) because:
The air temperature is lower, slightly reducing efficiency (COP).
You may want the pool heated during the day for swimming.
However, a battery allows you to store cheap electricity overnight and use it in the day — so the pump still “runs on cheap power.”
Battery Shift Scenarios
Scenario | Shift % | Electricity Sourced from Battery | Approximate Cost (with Octopus Go) | Saving vs Standard Tariff (£0.27/kWh) |
Full shift (ideal) | 100% | 7,500 kWh | £708 (includes 90% round-trip efficiency) | £2,025 − £708 = £1,317 saved |
Moderate shift | 75% | 5,625 kWh | £531 (from battery) + £506 (grid) = £1,037 | ≈ £988 saved |
Partial shift | 50% | 3,750 kWh | £354 (from battery) + £1,012 (grid) = £1,366 | ≈ £659 saved |
No shift | 0% | 0 kWh | £2,025 (all grid) | £0 saved |
(Assumes off-peak rate 8.5 p/kWh, on-peak 27 p/kWh, 90% battery efficiency.)
Why Battery Shift Works So Well for Heat Pumps
Predictable, steady loads: Pool heat pumps run for long, consistent periods — ideal for timed battery discharge.
Smart scheduling: Many modern heat pump controllers (including Mitsubishi’s FTC5/FTC6) can coordinate with smart battery systems to optimize when heating occurs.
Thermal storage: The pool water itself acts as a thermal battery — you can heat it slightly more during off-peak hours, then let it gradually cool during the day.
Grid independence: Drawing less electricity during daytime peaks also reduces grid strain and can help avoid demand-related surcharges or outages.
Practical Implementation Tips
Battery size: To meaningfully power a pool heat pump (often 3–10 kW running load), you’ll need a battery capacity of at least 10–15 kWh, or modular expansion. The Anker SOLIX X1 can scale up to over 180 kWh.
Automation: Use the battery’s time-of-use settings to charge only during cheap hours and discharge automatically when prices rise.
Heat pump scheduling: Program your pool heating control to run primarily during the day, using the stored off-peak energy from the battery.
Weather compensation: On cooler days, extend operation slightly into the cheap charging window to maintain consistent water temperature efficiently.
Summary
Battery shift allows you to use low-cost electricity whenever you need it — not just when it’s cheap.
By combining:
Octopus Go off-peak charging,
a Mitsubishi Ecodan heat pump, and
an Anker SOLIX X1 battery,
you can achieve substantial running-cost savings, typically £650–£1,300 per year for a medium-sized pool, while also reducing reliance on fossil fuels and grid-peak electricity.