What is a Warmstone Heat Battery made from?

WarmstoneTM is our patented solid storage material that is made from a combination of recycled and natural materials.

The material combines low cost, high thermal conductivity and high density. It is non-toxic and non-flammable.

How does it work?

We use electrical energy (supplied either from the grid or local sources, such as solar PV) to heat the solid core with electric elements and then use the stored heat to provide a supply of hot water to your home.

It does not store hot water.

How do I work out whether it is better to fit a heat pump or a heat battery?

If you live in a house that uses heating oil or LPG, has solid walls (built pre-1930) and normal radiators, then you will probably be better off with a heat battery.

If you have an insulated house with underfloor heating then you will probably be better off with a heat pump.

As a rough rule of thumb – if your boiler water temperature is set to 65 degrees Celsius or above you will be better off with a heat battery.

What sizes does a Warmstone Heat Battery come in? How heavy is it?

One size. It is 1.0m in diameter and 1.7m high.

Given the high-quality nature of the solid-state storage material used, the unit weighs 1.7tonnes.

How long will a unit last? How often does it need to be serviced? What happens if something goes wrong?

We are designing our units to last a minimum of 20 years and are offering a three-year full parts and labour warranty.

With no moving parts, beyond standard pumps, there is minimal maintenance required and we recommend an annual survey which will cost around £100 a year

If something goes wrong within the warranty period, we will replace the defective unit with a new one free of charge.

Why does it need to be installed outside my house?

The unit weighs 1.7 tonnes and needs to rest on a solid base. This can be located outside a house or inside a garage with a concrete floor. We do not recommend installation of units inside homes.

When you buy a Warmstone Heat Battery, we include delivery to site and installation of the Heat Battery into the correct location. This requires specialist handling equipment that we supply.

The ideal location is close to the existing boiler. We will connect the Heat Battery piping to the existing plumbing system. If long pipe runs are required, this will add to the cost of the installation and may increase the heat losses from the piping.

Why would I not buy an electric battery instead of a heat battery?

A home might use 4,000 kWh of electricity and 16,000 kWh for heating and hot water, so 80% of the home energy usage is heat. Given this and the price and reliability of electric batteries, heat storage with a Warmstone Heat Battery is significantly more affordable and will last around twice as long as an electric battery.

How efficient is the Warmstone heat battery?

More than 90% efficient due to the high-performance vacuum insulation we use to minimise our losses.

How much energy does it hold?

100kWh. For a normal 4-bedroom home this is enough energy for a whole day in winter and at least three days in summer.

How long does it take to charge? Can I charge other things at the same time such as my EV?

From cold it will take approximately 8 hours, though aside from installation and a power cut lasting weeks, this is highly unlikely.

The Warmstone will intelligently charge itself, prioritising other needs, such as your EV.

What happens in a power cut do I have any hot water or heating?

Like a normal boiler, the circulation pump will not work if mains electricity is off. The heat will remain in the core for weeks if not used.

Can I use the heat quicker than it can charge? What happens when it runs out?

Yes you can. It is designed to discharge at the same rate as a boiler (30kW). It charges at 20kW, so if you left all your hot water taps running then the unit would eventually discharge.

Do I need to tell my energy supplier that I am installing a Warmstone Heat Battery?

No, you do not. But we strongly recommend that you ensure you have an energy supplier that has off peak tariffs so you can charge your unit when the price of electricity is at its lowest.

You will, however, require permission from your local electricity distribution company (often referred to as the DNO) to ensure that you can draw a continuous high load to your home. We will do this for you.

Will I notice any difference in my heating or hot water?

None whatsoever. The entire ethos of our approach is to help homeowners decarbonise their heat and hot water needs with the minimal amount of disruption and no change in experience.

How long will I have to wait for one? How long will it take to install?

We currently have a waiting list of approximately 9 months.We are rapidly looking to scale up production to meet this demand.

Once delivered, the installation and commissioning takes two days.

Can a Warmstone Heat Battery act as a combi boiler?

The current version is not designed to work as a combi-boiler yet. Our initial focus is on homes that have heating oil or LPG and a hot water cylinder and standard radiators.

We will release a combi-boiler version if we can be confident that there is sufficient interest.

Do I need a smart meter and if so, how do I get one?

Yes, you need a smart meter to take advantage of Time of Use tariffs.

If you do not have one, then you need to request one from your energy supplier or change to an energy supplier that will fit one.

What are the best Tariffs to use?

The three lowest fixed price off-peak tariffs are offered by:

  • Octopus Go 5.0p/kWh
  • Edf 4.5p/kWh
  • Scottish Power 4.7p/kWh

Our favourite tariff is Octopus Agile as it reflects the wholesale price, and you can even be paid to charge your unit!

What temperature hot water can it supply?

The unit can supply water at up to 80 degrees Celsius, however we would normally expect you to run it at between 65 and 70 degrees Celsius at a similar temperature to your current boiler.

Can my plumber install and service it?

Yes, but they will need to go through our accredited installer process. For early installs we will take full responsibility for installation and provide both plumber and electrician.

Will I qualify for the Renewable Heat Incentive? Will I be able to get a grant / interest free loan to support the cost of the Warmstone Heat Battery?

At the moment no. Heat Batteries are not currently covered by the Renewable Heat Incentive. Nor do they meet the criteria for the Home Energy Scotland Loan. This is something we hope to address.

I have solar PV installed – can I store any excess I generate rather than returning it to the grid?

Yes you can. Depending upon the amount of panels you have and your usage, you may have free hot water for much of the summer!

How much CO2 does it save?

That depends on how much energy you use, what is being replaced (heating oil or LPG) and if you are going to a fully renewable tariff or not.

Using off-peak grid electricity versus heating oil, you will reduce your CO2 footprint by 50% overnight and 90% by 2030 as the electricity grid is decarbonised.

A Warmstone Heat Battery running on fully certified renewable, green electricity will have an immediate zero carbon footprint.

Will my heating bills go down?

A 5p/kWh off-peak electricity price has the same cost as heating oil at 47p/litre. If oil is above this price, you will save money every year. The government now plans to tax heating oil further and expectations are that they will ban oil boilers to meet carbon targets.

We are clear that the primary driver of people who are looking to a heat battery for their hot water and heating is to achieve home heat decarbonisation in the fastest, most affordable and least disruptive way.

Why is this only being proposed as a replacement for homes heated by Oil or LPG?

Natural gas currently costs around 3.5 – 4p/kWh and even using the lowest off-peak tariff a Warmstone Heat Battery will be more expensive.

We do not want to increase home owners annual bills and until the cost of natural gas increases we are focused on homes that use the more expensive fuels (oil or LPG) with higher CO2 footprints.

Given the UK governments commitment to net zero we expect the cost of fossil fuels to increase steadily and the cost of electricity, on a relative basis to decrease quite rapidly as more renewable capacity comes on stream.

My house is on mains gas, can I install a Warmstone Heat Battery?

Yes you can and you might choose this instead of a heat pump to reduce your carbon footprint. In the near term, your bills will be higher because the government still subsidises fossil fuels and taxes clean electricity.

Should I keep my existing system as a back-up?

You do not need to, but some of our customers are opting to in the short term to take advantage of differences in the price of electricity and heating oil/LPG. They intend to set their control system to charge the Warmstone Heat Battery whenever electricity it is cheaper than oil.

We would expect oil usage to decrease over 3-5 years as low off-peak pricing becomes more and more frequent and the costs associated with fossil fuels increase.

Does the unit require a WiFi signal?

Yes it does, much like a smart meter.

What happens if I sell my house and the new owner doesn’t want the Unit?

Homes that are energy efficient and low or zero carbon now command premiums to those that are not. We expect homes with Warmstone Batteries to achieve similar.

How much will it cost to buy?

£12,000 including VAT installed.

This price includes 10m of above ground piping and cables.