Glen Housing Association completed a whole-home retrofit across 30 occupied homes in Glenrothes, replacing gas combi boilers with a low-carbon system combining air source heat pumps, Sunamp Thermino heat batteries, solar PV, electrical battery storage and fabric upgrades.
The project improved the homes’ average EPC rating from around 68/D to 84/B, while giving residents more reliable hot water, stronger shower performance and additional usable space in utility cupboards.
At the heart of the domestic hot water system is the Thermino 210 xPlus heat battery, which stores heat from the air source heat pump in Sunamp’s phase change material and releases it on demand as mains-pressure hot water.
For Glen Housing Association, the retrofit was not simply a product replacement exercise. It was an engineering and delivery challenge: decarbonising heat and hot water in occupied homes, integrating multiple technologies into one working energy system, limiting disruption for residents and meeting a fixed funding deadline.
The engineering challenge
Glen Housing Association needed to move 30 occupied properties away from gas while improving energy performance, maintaining resident comfort and completing the works within the programme timetable.
Supported by the Scottish Government’s Social Housing Net Zero Heat Fund, which contributed 51% of the project costs, the association had until May 2026 to complete the improvements following funding approval in November 2025.
Each home required a coordinated set of upgrades, including external wall insulation, triple-glazed windows, solar PV, electrical battery storage, new radiators, air source heat pumps and domestic hot water storage. The existing gas combi boilers had to be removed without leaving residents exposed to extended periods without heating or hot water, particularly during colder months.
The hot water solution therefore had to meet four practical requirements:
- work efficiently with air source heat pumps
- provide reliable, high-pressure domestic hot water
- fit within constrained utility cupboard space
- support a staged installation sequence that reduced disruption for residents
The solution – compact thermal storage working with renewables
Glen Housing Association developed a whole-home approach to the retrofit, working with project manager Changeworks & installation partner Sureserve.
The improvements included external wall insulation and triple-glazed windows and each property received a 4.5 kW solar PV system, 5 kWh electrical battery storage, an Ideal HP290 air source heat pump, new radiators and a Sunamp Thermino 210 xPlus heat battery for domestic hot water. Thermino stores thermal energy in Sunamp’s Plentigrade phase change material and releases it to provide hot water when required. Unlike a traditional hot water cylinder, it does not store large volumes of water. Instead, it stores heat in a compact, high-energy-density material and transfers that heat to mains water when hot water is required.
In practical terms, this gave the project team a compact domestic hot water store that could be charged by the heat pump, with grid electricity available as back up. The Thermino units were installed first and operated using electric back up while the old gas boilers and existing space heating systems were removed. The heat pumps and radiators were then installed and connected to the Thermino units. This staged approach helped restore the full heating and hot water system quickly. The Thermino, heat pump and radiator installation could be completed within two days per property.
The benefits – better water pressure, more space and a route to lower bills
The completed retrofit has delivered measurable improvements in energy performance, resident experience and system functionality. Residents now benefit from reliable, mains pressure hot water from their Thermino heat batteries. One household, with two adults and two teenagers, spoke of an immediate improvement:
“The water is warmer. The pressure of our showers is noticeably better than before.”
In early feedback, another resident reported a total energy bill of £31 for July, including electricity used to charge an electric vehicle.
Glen Housing Association was also pleased with the simple, low-maintenance operation and ability to maintain consistent hot water temperature and pressure, even when three taps were used simultaneously.
Across the 30 homes, the complete retrofit increased the average EPC rating from approximately 68/D to 84/B, reflecting the combined impact of the fabric upgrades, new heating systems, solar PV, electrical battery storage and Thermino heat batteries.
Overall, bringing these technologies together has given residents more flexibility over how energy is generated, stored and used. The air source heat pumps and Thermino heat batteries provide a route away from gas, while the solar PV and electrical battery storage help households increase self-consumption.
The project demonstrates four important benefits:
- Performance: mains-pressure hot water with stronger shower performance and stable supply under simultaneous demand
- Reliability: a low-maintenance hot water solution that integrates with air source heat pumps and has grid back-up capability
- Cost: potential for lower household energy costs when heat pumps, solar PV, electrical storage and thermal storage are designed as one system
- Carbon: a clear route away from gas heating and hot water, supporting social housing net zero objectives
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