Frequently asked questions

What are Sunamp’s heat batteries?

Sunamp’s Thermino® heat batteries are compact, energy‑efficient thermal storage systems that use high‑performance phase change material to deliver reliable, mains‑pressure hot water. They’re safer, more efficient and up to four times smaller than a traditional hot water cylinder.

How does a heat battery work? 

The Plentigrade phase change material in Sunamp’s heat batteries absorb and release thermal energy during a melting and freezing process in a similar way to the gel in a pocket handwarmer.  

Our patented Plentigrade phase change material stores and releases heat as it melts and solidifies, similar to the gel in a pocket handwarmer, but engineered for long-term, high-performance hot water delivery. Learn more about how heat batteries work, or watch Sunamp co-founder Andrew Bissell explain the technology.  

How did Sunamp develop its heat battery?

The idea of storing heat in a phase change material has been around since the 1940s but existing materials didn’t perform well enough to provide reliable, high flow rate hot water over the longer term. We solved this problem, working with the University of Edinburgh, and created a stable phase change material which shows no signs of degradation over the equivalent of 50 years of use. Watch our co-founder Andrew Bissell explain how we developed our heat battery. 

What is a phase change material? 

A phase change material (PCM) absorbs and releases energy when it changes phase, for example, from solid to liquid. Applying energy in the form of heat to a solid will eventually melt it. If you then cool the liquid, it will freeze, releasing the energy used to melt it. Read more on our guide to phase change material by Dr Kate Fisher. 

What makes Plentigrade different from other PCMs?  

Our highly patented PCM formulations form the backbone of our Plentigrade platform. Our PCMs have an enviable high energy density, avoid costly or scarce components and there is no question over their sustainability as the salts are either mined, are by-products of the existing chemical industry or are simple commodity chemicals with diverse supply chains. Read more about the science behind Plentigrade by our head of R&D Dr. David Oliver 

What makes Sunamp’s PCM heat battery better than its competition?  

As Dr Kate Fisher explains, “It is not just about the chemistry, it’s about making products that work well with the PCM. Our unique selling point lies in the integration of chemistry and engineering. Sunamp is the only thermal battery manufacturer in the world to be awarded RAL certification for phase change material.” Read more on our guide to phase change material. 

What makes Sunamp heat battery an ideal replacement of a hot water cylinder?

Firstly, their small size means installation is possible where there isn’t enough space for a hot water cylinder. Sunamp Thermino heat batteries contain a phase change material which is much more energy-dense than water, meaning the systems are up to four times smaller than the equivalent hot water cylinder. Thermino heat batteries also have much lower heat losses than a cylinder and work with a range of energy sources, including heat pumps, solar PV, boilers and grid electricity. Find out more about why heat batteries are the ideal alternative to a hot water cylinder.  

How to decide which hot water system is right for you: hot water cylinder vs heat battery? 

Choosing between a traditional hot water cylinder and a modern heat battery depends on a number of factors including space, efficiency and energy source.  

How you heat your home will have an effect on which hot water system you need – 80% of homes in the UK have a gas combi boiler which provides both space heating and hot water, meaning you don’t usually need a hot water cylinder. However, gas boilers are on the way out, to be replaced with heat pumps in most situations. If you switch to a heat pump, you’ll need a heat battery or hot water cylinder to provide your hot water.  

Thermino heat batteries have many advantages over a cylinder, including their compact size, ultra-low heat losses and high efficiency. Read more about hot water cylinders vs Thermino heat batteries.  

How can heat batteries help with energy efficiency and aesthetics in your home? 

Thermino heat batteries work with heat pumps and solar PV, which can improve your home’s Energy Performance Certificate (EPC) rating. A bulky hot water cylinder can spoil the aesthetics of your home, whereas a Thermino is the ideal space-saving, sleek and stylish solution. The system’s high energy density means it’s only a quarter of the size of a conventional hot water cylinder. Read more about energy efficient hot water for home movers and improvers.

How can you save money on hot water costs with a Thermino heat battery compared to a hot water tank? 

A Thermino heat battery can reduce hot water costs through lower heat losses and reduced maintenance requirements.  

When it comes to hot water tanks, annual inspections are a legal requirement and tank cleaning needs to be carried out every 3 years, costing you anywhere between £200-£500 for 110-500L tanks. Hot water cylinders also lose heat daily – typical standing heat losses range from 1.4kWh to 3.34kWh per day, adding significantly to annual bills.  

Thermino heat batteries don’t require mandatory maintenance on the heat battery, only on some of the external plumbing components, and heat losses are up to 75% lower than a cylinder. Read more on how to save money on domestic hot water. 

How a homeowner chose a Sunamp heat battery over a hot water cylinder 

As homeowner Michael Eve explains, “I started looking into the pros and cons of a hot water cylinder compared to a heat battery. The cylinder is obviously a more familiar technology, the only problem is that hot water cylinders still suffer from loss of energy over time, which from solar was a big problem for us. We didn’t want to put loads of energy in and by the time we got round to using it, we’d lost half of it. 

Sunamp’s Thermino heat battery became the more obvious choice. We took advice from our installer who agreed it would meet our needs. Lower heat losses and its smaller size compared to the hot water cylinder alternative were the final deciding factors.” Read Michael’s full review and find out why he chose a heat battery over a hot water cylinder.  

Which heat pumps are compatible with Thermino heat batteries?  

Thermino xPlus heat batteries are compatible with a growing list of heat pumps from manufacturers including Daikin, Samsung and Vaillant. We have tested the ability of these heat pumps to meet the flow temperatures required for the heat battery (63-65 degrees Celsius). See compatible heat pumps here.  

When switching from gas boilers to heat pumps, how can Thermino help you get to net zero emissions? 

If you’re currently on a combi-boiler heating & hot water system, the average annual gas usage for space heating & hot water is about 9600 kWh and 2400 kWh respectively. The total carbon emissions currently amount to 2190 kgs. 

When you add a Thermino xPlus and solar PV, there’s a straight 60% reduction in the amount gas used from the combi, thanks to the pre-heating provided by Thermino xPlus, and water heating demand can be met by PV-generated electricity. This cuts the emissions by about 12% over the original combi boiler system. 

Introducing off-peak electricity can eliminate gas use for hot water completely, leading to a reduction of about 20% emissions over the combi boiler system. When you later install a heat pump, hot water can be supplied entirely by the heat pump and PV, reducing onsite emissions to zero. Read more about switching from a combi boiler to a heat pump.  

What are the challenges associated with replacing gas boilers with heat pumps? How can Thermino heat batteries play a role?  

Heat pumps are an efficient and low-carbon alternative to gas combi boilers, backed by the UK government for households looking to switch. However, combi boilers take up very little space in the home, whereas heat pumps typically require a large hot water cylinder. Thermino heat batteries are up to four times smaller than the equivalent cylinder, making heat pump upgrades possible even in homes with limited space. Read more about gas boiler replacement and hot water alternatives.  

Why does Thermino need a high temperature heat pump? 

To store energy, the PCM inside a Thermino heat battery must be heated above its phase change temperature so it can fully charge. Our Plentigrade P58 PCM has a melt point of 58C, which means the heat pump needs to reach sufficiently high flow temperatures for domestic hot water delivery.  

How can a Thermino heat battery drive savings with solar PV? 

Pairing a Thermino heat battery with solar PV lets you store excess solar energy as heat for use later. One homeowner saved up to 940 kWh of electricity in a year by replacing a hot water cylinder with an electrically charged Thermino. Thermino ePlus can use PV as the primary heat source, with grid electricity automatically topping up when needed. Read more about the rise of solar PV.  

How does solar PV compare with solar thermal for hot water systems? 

Solar thermal heats water directly, while solar PV converts sunlight to electricity. With a PV diverter, surplus solar electricity can power an immersion heater or charge a heat battery. Using solar PV with a heat battery offers additional benefits such as compact size, low heat loss and flexible charging. Read more about solar thermal vs solar PV for hot water. 

How can heat batteries maximise the benefits of off-peak tariffs?  

Heat batteries make it easy to shift hot water production to cheaper, off-peak periods. Hot water accounts for 17% of total household energy consumption, so storing heat when electricity is cheapest can deliver meaningful savings. With very low standing heat losses, a Thermino heat battery can hold that stored energy efficiently and release it throughout the day. 

When paired with time-of-use tariffs, Thermino can charge during low cost periods and meet hot water demand later, effectively aligning usage with the most cost effective electricity rates. Find more about cutting hot water costs with off-peak electricity. 

How is the heat output regulated?

Thermino heat batteries use Plentigrade, a high-performance phase change material which is similar to the material in a handwarmer. Plentigrade releases heat only when there is a demand for hot water, unlike a handwarmer which releases all of its heat at once. Thermino then only recharges the portion of PCM that has discharged to heat up the water. 

In terms of the temperature of the water coming from the taps, a tempering valve mixes cold water from the mains and hot water from the heat battery to achieve the desired water temperature. 

Does Thermino require any accessories?  

Yes. The following mandatory plumbing components must be installed to protect and maintain good working order and performance of Sunamp heat batteries: 

• Heat battery isolation valve  

• Mains cold water pressure reducing valve (PRV)  

• Mains expansion relief valve (ERV) 

• Expansion vessel/shock arrestor  

• Hot water thermostatic mixing valve  

• Water conditioner, in areas with hard water 

• Auto-bypass valve, for indirect models only 

• Expansion vessel (primary circuit), for indirect models only  

All mandatory components must be maintained in line with the manufacturer’s instructions. Find out more about the mandatory plumbing components here.  

Is any annual maintenance required for Thermino heat batteries?  

Thermino doesn’t need any maintenance on the heat battery itself. Routine checks are standard for the external plumbing and safety components such as the expansion vessel, in line with the component manufacturer’s instructions.

Why should you become a Sunamp certified installer? 

Becoming a Sunamp certified installer allows you to benefit from a free listing on our installer map. This can increase your visibility, making it easier for customers in your area to find and contact you when looking for a Thermino installer. The first step is to complete our free online training, then your first installation will be assessed by Sunamp’s technical team to make sure there are no issues. You can then be added to the map and will also benefit from access to promotional materials and technical support. Find out more about the benefits of becoming a Sunamp certified installer.  

What training do you need to install Thermino heat batteries? 

We expect installers to have the required qualifications, knowledge and experience to understand the plumbing and electrical requirements necessary to install something like an unvented hot water cylinder. We offer free online training for installers to upskill and learn to install Thermino heat batteries, which is a requirement for installers who are looking to be listed on our certified installer map. Find out more about installer training (anchor link to section of installer hub).  

What are the advantages of installing a Sunamp heat battery?  

Thermino heat batteries are quicker to install than a traditional hot water cylinder and can be easily fitted to pretty much any pre-existing type of plumbing system. They are also flexible to fit – at about 4 times smaller than the equivalent hot water cylinder, a Thermino can be fitted in a corner of a garage, airing cupboard, under the sink or under the stairs. There’s no stored water in a heat battery so there’s no requirement for advising customers about procedures for Legionella checks or annual servicing – and the product comes with 10 year warranty on the heating element and storage core. Read more about the business opportunity for installers. 

How can Thermino heat batteries help maximise the benefits of heat pump and solar installs? 

A key benefit of the Thermino system is the ability to store the energy captured by a heat pump or generated by solar panels so it can be used for hot water at a time when it’s needed. This helps maximise the use of low carbon heat or electricity which may have been lost otherwise, and can reduce a household’s energy bills as less energy needs to be purchased from the grid. On a wider scale, energy storage can help balance the grid as the proportion of energy generated by renewables continues to grow. Read more about maximising the benefits of heat pumps and solar installs with Thermino.  

How can Thermino help your customers improve their EPC ratings? 

Thermino has an A+ energy rating and is the only PCM-based thermal battery with RAL certification. Our PCM has been tested to 40,000 cycles, or around 50 years of use, with minimal degradation. With heat losses 2–3 times lower than a cylinder (0.5–0.77 kWh), Thermino delivers highly efficient hot water and supports improved EPC ratings. Read more about how Thermino can help improve EPC ratings.

How can efficient energy storage help tackle fuel poverty in social housing?  

Improving energy efficiency and optimising energy use can significantly reduce running costs for fuel poor households. Thermal storage allows residents to store energy during periods of low demand from renewables and release it during peak hours, enabling residents to benefit from cheaper electricity tariffs. 

The EastHeat report shows the significant impact heat batteries have had in tackling fuel poverty. heat batteries enabled many 1–2 bed homes to access ‘free’ hot water from excess PV generation that would otherwise have been exported back to the grid, increasing self-consumption and reducing bills. Find out more about how heat batteries can contribute to tackling fuel poverty.  

What are the challenges of using electric storage heaters in social housing, and what are the available solutions?  

Traditional electric storage heaters can be costly to run due to high unit electricity prices and can be particularly inefficient in older, poorly insulated homes. Modern high heat-retention models introduced after 2018 are more efficient and meet stricter standards, and grants such as ECO4 and the Affordable Warmth Scheme are available to support upgrades. Sunamp’s Thermino heat batteries offer a smart alternative to Economy 7 water heaters, providing efficient hot water storage with lower heat losses. Find out more about pairing Thermino heat batteries with electric storage heaters. 

Can heat batteries help realise energy and cost savings in social housing?  

PCM heat batteries can significantly improve building efficiency by storing heat during off-peak periods and releasing it during peak demand. They can reduce environmental impact, optimise energy use in home, and even save residents up to £485 a year on hot water costs. In one retrofit project at Thurrock, replacing old storage heaters with heat pumps and heat batteries reduced residents’ energy bills by 67% and cut CO₂ emissions by 70%. Read more about how energy storage can contribute towards a sustainable future in social housing.

What are some decarbonisation grants available to housing associations to retrofit low carbon technology: heat pumps, solar and thermal storage?  

Social landlords in Scotland can apply for the Social Housing Net Zero Heat Fund, a £200m funding pot which is available over the next 5 years to help social landlords reach net zero by 2045. In Wales, the Optimised Retrofit Programme is open to registered social landlords and local authorities to help install decarbonisation measures in existing housing stock. 

In England, the Social Housing Decarbonisation Fund is open to social housing providers, local authorities and charities to help upgrade homes with energy efficiency improvements. The Wave 3 application window is opening soon. Overall, the UK Government has committed £3.8bn to the fund over a 10-year period to help reach net zero by 2050. Find out more about how Thermino works with heat pumps in social housing.  

Can heat batteries help in energy and cost savings in social housing?

PCM heat batteries can significantly improve the energy efficiency of housing associations’ buildings. By storing excess thermal energy during off-peak periods and releasing it during peak demand, the heat batteries reduce environmental impact and optimise energy use in homes, not to mention they can deliver savings of up to £485 on the cost of hot water energy bills. One of our green retrofit projects at Thurrock estimates a 67% reduction in residents’ energy bills and a 70% reduction in CO2 emissions after replacing old storage heaters. Read more about how energy storage can contribute towards a sustainable future in social housing.

How can Sunamp heat batteries help architects design low-carbon green buildings?  

Thermino heat batteries offer: 

High energy efficiency: Thermino batteries are packed with high-performance vacuum insulation which achieves up to 19 times the insulation performance of polystyrene foam. This translates to ultra-low heat losses (up to 2-4x lower than a cylinder: 0.5-077 kWh vs 1.3-3.4kWh), meaning high efficiency and more energy savings for residents.  

Achieving SAP compliance: Thermino ePlus & xPlus heat batteries can be manually entered and modelled in SAP 10.2 software to help you monitor dwelling energy performance. See the technical guidance here.  

Load flexibility: According to Ofgem, the expected electricity generation capacity from renewables and other zero-carbon sources will reach 300GW by 2035. PCM heat batteries can help manage peak demand more effectively.

Space-saving design: Thermino heat batteries can fit into tight spaces, where a hot water tank cannot, thanks to their compact cuboid design. This means more design freedom for architects and designers, and more precious floor space available for residents. Find out more about how these heat batteries work for modern contemporary designs.

Why pair renewable technologies in newbuilds with energy efficient thermal storage?  

As developers move away from gas boilers to meet SAP, Future Homes Standard and futureproofing requirements, heat pumps and solar PV become essential. Both require efficient thermal storage to deliver hot water reliably. Thermino provides a compact alternative to bulky cylinders with much lower heat losses, helping maintain EPC ratings and reduce residents’ energy bills. Find out more about reducing carbon emissions in new buildings. 

Does Sunamp offer CPD sessions on thermal storage for architects and specifiers?  

Yes, we offer free CIBSE-approved CPD sessions covering phase change materials and their application in thermal storage. This is a great way to find out more about our heat batteries and how they can help solve a key challenge facing specifiers when designing sustainable homes – finding space for thermal storage. Request a free CPD session here.  

Who can install a Sunamp Thermino heat battery?  

Sunamp Thermino heat batteries can be fitted by a qualified plumber or electrician in accordance with the relevant installation manual. Search our map to find approved stockists and installers near you, or view Thermino installation manuals here.  

The Sunamp product warranty states that you must be a competent person to install a heat battery. This means we don’t demand any specific training courses, however it is expected that you have the required qualifications, knowledge and experience to understand the plumbing and electrical requirements to install something like an unvented hot water cylinder. We also offer free training for installers.  

What can a Thermino heat battery be used with?  

Thermino heat batteries connect with mains electricity and many other heat sources, including heat pumps, solar PV and boilers. They are ideal space-saving replacements for traditional hot water cylinders. 

As we are often asked this, Sunamp Thermino batteries do not connect to solar thermal units, pellet, oil or wood burning stoves, swimming pools or hot tubs. 

How much does a Sunamp Thermino heat battery cost? 

The Thermino range comes in different sizes and configurations depending on your desired application. Our approved stockists and installers will be happy to help with pricing – search the map to find one near you.  

How much does it cost to run a Thermino heat battery? 

Running costs depend on many different factors unique to your home including electricity tariff, energy usage, energy source, frequency of usage, ambient temperature versus indoor temperature and heat battery size. There is potential for long term cost benefits as Thermino heat batteries have much lower heat losses than a traditional hot water cylinder and don’t require weekly energy-intensive anti-legionella cycles. 

Where can I buy a Sunamp Thermino heat battery?  

Sunamp does not sell directly to homeowners. Our hot water products are available through our approved stockists who will be happy to help you.  

Any direct sales enquiries received from individuals are forwarded to our installer and distributor network. Search here to find an installer or stockist near you. 

What grants and funding schemes are available to switch to renewables and heat batteries in the UK?  

Depending on where you are in the UK, homeowners can apply for: Boiler upgrade scheme (Also supports Sunamp heat battery as thermal storage), Energy company obligation (ECO4, help from your energy supplier), Home Upgrade Grant, the Great British Insulation Scheme, Energy saving funding options in Scotland, Green Deal scheme, The Welsh Government Warm Homes Nest scheme, Northern Ireland Sustainable Energy Programme, and Affordable Warmth Scheme.

I live in an area with hard water. Can I use a Sunamp thermal battery? 

Yes. We recommend you use a water conditioner, such as a HS38, to keep limescale in the water to under 150 ppm. This can be used with any size of heat battery. 

I’m looking for technical specifications and product dimensions. Where is this information? 

Please refer to our product data sheets and installation manuals (link to knowledge base).  

How do I register my Sunamp product warranty? 

You can register any of our domestic hot water products – Thermino and UniQ – by visiting the warranty registration page. 

Who do I contact for after sales service? 

To get in touch with us, please email [email protected]  

Please include all details of your enquiry, including the model, serial number (found on the silver sticker near the bottom of the unit) and relevant product warranty information. We will respond to all enquiries in a clear and friendly manner within one working day.