A conventional unvented cylinder is a sensible heat store: every kilowatt-hour it holds corresponds to a measurable rise in water temperature. Water's specific heat capacity of roughly 4.18 kJ/kg·K is high for a liquid, but it is still the hard limit. Storing more energy means either a larger tank or a higher setpoint, and both increase the temperature differential driving standing heat loss into the surrounding fabric.
The Sunamp Thermino replaces the water mass with Plentigrade P58, an inorganic salt-hydrate Phase Change Material. As it is charged, the PCM absorbs a large quantity of latent heat while melting at a near-constant 58°C, storing energy without a corresponding temperature climb. When a hot tap opens, cold mains water flows through a high-flow internal copper heat exchanger embedded in the PCM. The material re-solidifies, releasing its latent energy at a steady temperature and heating water on demand at mains pressure, with no stored water volume to stratify, stagnate or reheat.
The density advantage translates directly into geometry. A Thermino's compact rectangular form factor can be tucked into a kitchen cabinet, a loft void or the space under a staircase. For renovators working in apartments and terraced homes where a 200L cylinder and its airing cupboard simply cannot be accommodated, it removes the main spatial barrier to replacing a combi boiler with a heat pump or an off-peak electric system.
Metric | Standard Unvented Cylinder | Sunamp Thermino |
|---|---|---|
Energy Storage Medium | Water (sensible heat; energy stored only as a temperature rise) | Inorganic Plentigrade P58 PCM (latent heat at a constant 58°C phase transition) |
Physical Volumetric Footprint | Large cylindrical tank; a 200L unit typically needs a dedicated airing cupboard | Compact rectangular cell, up to 4x smaller; fits voids, kitchen units and under-stair spaces |
Standing Heat Loss (24h) | Higher; the full hot water mass radiates heat continuously | Significantly lower; dense storage and a smaller surface area reduce leakage |
Operational Lifespan | Governed by corrosion, scale and anode condition of the pressure vessel | PCM rated for many thousands of melt-freeze cycles with no water storage to stagnate |
Mains Pressure Hot Water Delivery | Yes, via a pressurised vessel with expansion and safety controls | Yes, water passes straight through an internal copper heat exchanger at mains pressure |
For HVAC engineers, the outcome is a store that decouples energy capacity from physical volume. For space-conscious homeowners, it means mains-pressure hot water and tariff-shifted storage without surrendering a room to a tank.
For pricing, sizing options and installation detail, see our full Sunamp Thermino review.