Heat Battery UK: What It Is and How to Claim the £2,500 BUS Grant (2026)

The phrase “heat battery” sounds like it should mean the same thing as a home battery — but it does not. A home battery stores electricity. A heat battery stores heat energy. They are fundamentally different products, and confusing the two is the first thing to avoid before you spend any money or apply for a grant.

Heat batteries have quietly become one of the more interesting options in the UK's low-carbon heating landscape. In 2025, the government confirmed they would receive a £2,500 Boiler Upgrade Scheme (BUS) grant — a new category, alongside air-to-air heat pumps, as part of the expanded scheme running to 2029/30. Applications for heat battery installations are expected to open during the 2026/27 financial year, once the Microgeneration Certification Scheme (MCS) finalises the Thermal Energy Storage Systems (TESS) installation standards. This guide explains what a heat battery is, which brands make them, what the grant covers, and how to position yourself to claim it.

What is a heat battery?

A heat battery is an insulated thermal storage unit that stores heat energy rather than electrical energy. It is charged by an electric heating element, a heat pump, or a solar diverter, typically during off-peak tariff periods — for example, overnight on a time-of-use tariff such as Octopus Go or Economy 7. The stored heat is then released on demand for space heating, hot water, or both, without drawing from the grid in real time.

Think of it as a very well-insulated hot-water cylinder that can store far more energy per litre than a conventional cylinder, and release it over many hours. The best units use phase change materials (PCMs) — substances that absorb and release large amounts of latent heat as they change between solid and liquid state. This allows them to store roughly four to ten times more energy per litre than water alone, making them substantially smaller than an equivalent hot-water cylinder.

Heat battery vs home battery: the key distinction

This comparison comes up constantly, and the distinction matters for grant eligibility:

• Home battery (electrical): Stores electricity as DC power. Can power any appliance in your home. Works with solar panels to shift surplus generation to evenings. Covered under different grant routes (no dedicated BUS grant). Examples: Tesla Powerwall, GivEnergy AIO, Fox ESS. See our full guide to home battery costs UK for more detail.
• Heat battery (thermal): Stores heat energy only. Can only provide heat — for radiators, underfloor heating, and/or hot water. Cannot power a TV or a kettle. Examples: Sunamp Thermino, Tepeo ZEB. Eligible for the £2,500 BUS grant (pending MCS TESS standards).

If you are looking at integrating storage with solar panels and want flexibility across all your energy use, an electrical home battery is the relevant product. If you specifically want to cut the cost of heating your home by charging from cheap overnight tariffs, a heat battery is worth considering.

How does a heat battery work?

The charging cycle. An electric heating element inside the unit heats the phase change material until it melts and stores latent heat. This typically happens overnight when electricity prices are low. On a tariff like Octopus Go (currently around 7–9p/kWh overnight vs 24–27p during peak hours), the cost difference for the same unit of thermal energy can be substantial.

The discharge cycle. When the thermostat calls for heat, warm water from the heat battery circulates through the heating system — radiators, underfloor heating loops, or a hot-water cylinder coil — at the required temperature. The phase change material solidifies as it gives up its stored latent heat. The unit then recharges on the next off-peak window.

Heat pump pairing. A heat battery can also be charged by a heat pump, smoothing the mismatch between when the heat pump runs most efficiently (mild weather, low demand) and when heat is actually needed. Some installers pair an air source heat pump with a Sunamp Thermino to create a system that pre-loads heat during mild afternoons, then provides fast hot water on demand without the heat pump cycling on each time a tap is opened.

UK brands and products

Sunamp Thermino

Sunamp is a Scottish company and the longest-established heat battery brand in the UK. Their Thermino range uses a sodium acetate trihydrate PCM (branded “Plentigrade”) with vacuum insulation. The Thermino is primarily a hot-water replacement — it provides domestic hot water at high temperature (around 55–60°C) without a separate cylinder. A 12 kWh unit is roughly equivalent to a 300-litre cylinder in storage terms, but occupies significantly less space.

Installed prices for a Sunamp Thermino typically range from around £3,000 to £5,000 depending on model size and installation complexity. With a £2,500 BUS grant applied, the net cost could fall to the £500–£2,500 range for eligible homeowners once the grant scheme is open.

Tepeo ZEB (Zero Emission Boiler)

Tepeo is a London-based company. Their ZEB is designed as a direct replacement for a gas boiler — it charges overnight with around 40 kWh of thermal energy and provides both space heating via existing radiators and hot water during the day. Unlike the Sunamp, which is primarily a hot-water device, the ZEB is engineered specifically to deliver the flow temperatures (60–70°C) that conventional radiator systems require, making it a retrofit option without replacing radiators.

The ZEB has a purchase price of around £6,000, plus installation. Tepeo has offered an early grant match of £2,500 to eligible homeowners in advance of the formal BUS scheme opening. As with Sunamp, the BUS grant — when it opens — would be deducted at point of invoice by an MCS-certified installer.

The £2,500 Boiler Upgrade Scheme grant for heat batteries

What is confirmed

The government confirmed in the January 2026 Warm Homes Plan that heat batteries would receive BUS grants at £2,500 per installation. The full BUS grant table as of 2026 is:

• £7,500 — air-to-water heat pumps, ground-source heat pumps, water-source heat pumps
• £5,000 — biomass boilers (off-gas-grid properties only)
• £2,500 — air-to-air heat pumps (residential only)
• £2,500 — heat batteries

The BUS has a total budget of £2.687 billion running through 2029/30, with annual allocations rising from £295 million in 2025/26 to £709 million in 2029/30. The scheme is funded through to the end of this Parliament. If you are considering a heat pump alongside thermal storage, read our guide to the best air source heat pumps UK — air-to-water models attract the larger £7,500 grant and are often paired with heat batteries.

Current status: confirmed but not yet open

As of June 2026, the heat battery BUS grant has been confirmed in legislation but applications are not yet open. Grants will become available once MCS publishes its Thermal Energy Storage Systems (TESS) Installation Standard and System Performance Estimate Standard (MCS 038). MCS has launched a pilot for these standards with a selection of certification bodies and installers; full rollout is anticipated during the 2026/27 financial year.

This is different from heat pumps, for which BUS grants are fully live right now. If you need heating support urgently, an MCS-certified heat pump installer can claim a £7,500 BUS grant on your behalf today. Heat batteries require patience: the infrastructure to certify installations is being built out during 2026.

Eligibility requirements

Based on the Ofgem BUS guidance and the Warm Homes Plan, the expected eligibility rules for heat batteries mirror those for heat pumps:

• You own the property (owner-occupiers and landlords both qualify).
• The property is in England or Wales (Scotland and Northern Ireland have separate schemes).
• You are replacing a fossil-fuel or direct-electric heating system — not replacing an existing heat pump.
• The unit must provide space heating and hot water — a hot-water-only heat battery is expected to be ineligible. This is the same requirement that applies to heat pumps under BUS.
• Installation must be carried out by an MCS-certified installer — specifically one certified under the forthcoming MCS TESS standard.
• The product must appear on the MCS product eligibility list for heat batteries once that list is established.

The grant is not means-tested — any qualifying homeowner can apply regardless of income. You do not need an EPC of a particular band (the EPC requirement for BUS was removed in April 2026).

How to claim (when the grant opens)

The BUS is installer-led — you do not apply directly to Ofgem. The process is:

1. Find an MCS-certified heat battery installer (once the TESS standard is live, MCS Certified will list these at mcscertified.com).
2. The installer surveys your property, confirms eligibility, and selects a product from the MCS product eligibility list.
3. Your installer submits a BUS voucher application to Ofgem on your behalf.
4. Ofgem contacts you to confirm consent (within 14 calendar days).
5. The installer carries out the installation and deducts the £2,500 from your invoice upfront — you pay the net amount.

Is a heat battery right for your home?

Where they work well

• Time-of-use tariffs: If you are on or willing to switch to Octopus Go, Economy 7, or a similar overnight-cheap tariff, a heat battery can significantly reduce your effective heating cost per kWh.
• No outdoor space for a heat pump: Heat batteries are entirely internal — no outdoor unit, no planning permission, no noise.
• Space-constrained homes: A Sunamp Thermino takes up far less floor space than a conventional hot-water cylinder.
• Gas boiler replacement where full heat pump retrofit is impractical: The Tepeo ZEB is designed to work with existing radiators at the flow temperatures they were sized for, avoiding the need for a full radiator upgrade.
• New-build or EPC A/B homes: Low heat demand means the overnight charge can cover the full daily heating load.

Where they are less suitable

• High heat demand homes: A poorly insulated older property with high daily heat demand may exhaust the stored energy before the next charging window. A heat pump running continuously is generally better suited.
• Homes already on cheap gas: At current gas and electricity prices, electricity is still more expensive per kWh than mains gas even at off-peak rates. The economics improve as the gas/electricity price gap narrows — something the government expects to happen through the 2020s.
• Off-grid with solar only: Solar generation in winter is often insufficient to charge a heat battery fully; pairing with a time-of-use tariff and overnight grid electricity is the usual setup.

Heat batteries vs heat pumps: which should you choose?

This is genuinely situation-dependent. The headline differences:

• Grant: Heat pump (air-to-water) = £7,500 BUS, live now. Heat battery = £2,500 BUS, expected 2026/27.
• Installation disruption: A heat pump requires an outdoor unit, possibly a cylinder, possibly radiator upgrades. A heat battery is indoor-only and can often be a direct cylinder replacement.
• Running cost efficiency: A good air source heat pump has a coefficient of performance (COP) of around 2.5–4.0 — meaning it delivers 2.5–4 kWh of heat per kWh of electricity consumed. A heat battery delivers 1 kWh of heat per kWh in (allowing for standing losses). The heat pump wins on efficiency; the heat battery closes the gap by charging at lower off-peak electricity prices.
• Noise: Heat batteries are silent; heat pumps produce noise from the outdoor fan unit.

Our best air source heat pump guide covers the leading models, efficiency ratings, and cost breakdown in detail if you are weighing up the heat pump route.

Key figures at a glance

• BUS heat battery grant: £2,500 (confirmed; applications expected 2026/27)
• BUS total budget: £2.687 billion to 2029/30
• Sunamp Thermino installed cost: approximately £3,000–£5,000
• Tepeo ZEB purchase price: approximately £6,000 + installation
• PCM energy density advantage: roughly 4–10× more energy per litre than water
• BUS grant deducted upfront from installer invoice — no need to claim cash back yourself