For many UK homeowners living in modern properties or space-constrained flats, the biggest hurdle to getting rid of a gas combi boiler is the hot water tank. Traditional unvented cylinders take up an entire airing cupboard. If you don't have that real estate, the Sunamp Thermino offers a revolutionary alternative: a thermal hot water battery.
⚡ FutureWatt Verdict: Sunamp Thermino at a Glance
Metric | Details |
|---|---|
Core Technology | Phase-change material (PCM) heat battery with a mains-pressure heat exchanger. |
Best For | Space-constrained homes with no airing cupboard that still need mains-pressure hot water. |
Estimated Hardware Cost | Roughly £3,400–£4,700 installed, depending on model size (indicative retailer pricing). |
Key Advantage | Up to 4x lower standing heat loss than a standard hot water cylinder. |
The Bottom Line
The Sunamp Thermino excels at reclaiming space, packing the same hot water capacity into roughly a quarter of the footprint of a standard cylinder while cutting standing heat losses dramatically. Installed hardware costs generally range from £3,400 to £4,700 depending on the model size. However, things to watch out for include its considerable dry weight — floors need to be structurally rated for it — and the fact that, unlike Mixergy, it has no native smart-tariff app, so hitting cheap off-peak rates means wiring it to a timer or home automation relay yourself.
How Does the Sunamp Thermino Work?
Sunamp does not store water. Instead, it stores heat energy using a non-toxic Phase Change Material (PCM) called PlusICE.
Think of it like a high-tech hand warmer. An internal electric immersion element or a heat pump/boiler loop charges the unit, melting the PCM core to store massive amounts of thermal energy. When you open a hot tap, cold mains water flows through a high-efficiency internal heat exchanger embedded in the core. The water instantly absorbs the heat from the core, providing high-pressure hot water straight to your shower on demand.
The Core Benefits
- Incredible Space Savings: Because PCM material stores up to four times more energy than water by volume, a Sunamp Thermino unit is up to four times smaller than the equivalent unvented cylinder. It can easily slide under a kitchen counter, fit into a small cupboard, or sit neatly next to a tepeo ZEB.
- Near-Zero Standing Heat Loss: Sunamp units are wrapped in high-grade vacuum insulation paneling. Their standing heat loss is up to four times lower than a standard hot water tank, ensuring the energy you pay for overnight stays trapped inside the battery until you need it.
- Mains Pressure Performance: Because it operates as an instantaneous heat exchanger directly connected to your mains water supply, you get excellent, unregulated shower pressure without the need for large expansion vessels or safety discharge pipes.
Sunamp Running Costs: Efficiency Through Material Science
The running cost of a Sunamp Thermino relies entirely on its exceptional vacuum insulation panels. Unlike water tanks that cool down rapidly, Sunamp’s phase-change material holds its energy with a remarkably low standing heat loss rate—just 0.48 kWh per 24 hours for a mid-sized Thermino 150 unit.
Because the unit does not natively feature its own smart-tariff cloud optimization software like Mixergy, its running costs depend on your installation setup. If you wire the Sunamp to a smart time-switch or a home automation relay configured to only activate during a 4-hour off-peak window (charging at 7p/kWh), it costs roughly £0.35 to £0.60 per day to run. However, if left completely unmanaged on a standard day rate, running costs will scale significantly higher.
Sunamp Installation: Step-by-Step Differences
Installing a Sunamp Thermino is fundamentally different from fitting a traditional water tank, making it both easier and harder depending on your property layout:
- No Discharge Pipes Required: Because the Thermino is a sealed thermal store and does not store high-pressure hot water directly, it does not require an external G3 discharge pipe or safety tundish. This means it can be installed in internal rooms, basements, or spaces where drilling through an external wall is impossible.
- Clever Space Placement: Due to its compact, cubic shape, it can be installed horizontally or vertically under kitchen counters, inside standard cupboards, or neatly alongside a floor-mounted boiler system.
- Extreme Dry Weight: While it saves space, the dense phase-change core material is incredibly heavy when empty. A Thermino 210 weighs over 180kg before any pipes are attached. Installers must ensure floors are structurally rated for concentrated loads, and getting the unit up tight domestic staircases requires multiple people or specialist lifting equipment.
Pairing this with whole-home heating: A Sunamp Thermino only handles hot water — it doesn't heat radiators or underfloor heating. Read our full Tepeo ZEB cost and grant review to see how it pairs as the space-heating half of an all-electric conversion.