TL;DR:

  • Heat batteries charge on electricity during cheap-rate periods and discharge as hot water and heating on demand — no gas required
  • Unlike heat pumps, they fit into existing radiator and hot water systems without modification, making them easier retrofits for older homes
  • Tepeo’s ZEB and Sunamp’s UniQ range are the two main UK products; neither is cheap upfront, but cheap overnight tariffs can make running costs competitive with gas

If you’ve been told heat pumps won’t work in your home — because your radiators are too small, your house is poorly insulated, or your property doesn’t suit the disruption of a full retrofit — heat batteries are worth understanding. They’re a less-discussed alternative that sidesteps several of the most common heat pump objections, at the cost of different trade-offs.

What Is a Heat Battery?

A heat battery is a device that converts electrical energy into stored heat, then releases that heat into your home’s hot water and central heating system on demand. The core concept: charge it on cheap overnight electricity (using a time-of-use tariff like Octopus Go or EDF GoElectric), store that energy as heat in a phase-change material or water-based thermal store, and use it throughout the day exactly as you’d use a boiler.

From your home’s perspective, the experience is similar to a conventional boiler — you get hot water and heated radiators, controlled by your existing thermostat and programmer. The difference is that there’s no combustion, no flue, no gas connection required.

Two products currently dominate the UK market:

Tepeo Zero Emission Boiler (ZEB): charges overnight and can store enough heat for around 24 hours of typical domestic use. It uses a high-temperature phase-change material to store more energy in a compact unit than a simple water tank could manage. Fits in a standard cupboard space. Tepeo markets it specifically as a like-for-like boiler replacement, compatible with existing wet radiator systems.

Sunamp UniQ range: uses a similar phase-change material approach and comes in several sizes. The UniQ 9e and 12e are the most common domestic installations. Sunamp also makes units designed to work alongside solar panels, charging from both grid and solar generation.

The Core Advantage Over Heat Pumps: Compatibility

Heat pumps work best in well-insulated homes with large heat emitters (underfloor heating or oversized radiators). In a leaky Victorian terrace with standard-sized radiators, a heat pump may struggle to maintain comfortable temperatures efficiently, or may require expensive radiator upgrades to work at all.

Heat batteries don’t have this constraint. Because they output heat at boiler-like temperatures rather than heat pump temperatures (which are typically 35-55°C at the flow), they can drive existing radiators just as a gas boiler does. No radiator upgrades, no underfloor heating retrofits.

This makes them a credible option for:

  • Houses with older or undersized radiators
  • Homes where planning or budget rules out major heating system work
  • Rental properties where landlords want electrification without disruption
  • Properties with no external space for a heat pump outdoor unit

How the Costs Stack Up

The honest answer is that heat batteries are expensive upfront and the economics depend heavily on how cheaply you can charge them.

Tepeo ZEB: roughly £5,000-£7,000 installed, depending on size and complexity. Sunamp units: £3,500-£5,500 installed for the common domestic sizes. Neither qualifies for the Boiler Upgrade Scheme grant in 2026, which covers heat pumps and biomass boilers but not electric thermal storage products. Check the BUS eligibility list before assuming — this may change.

Running costs are the key variable. Heat batteries are effectively electric heating, so if you paid standard rate electricity for all the energy they use, they’d be more expensive to run than gas. The products are designed to be charged on cheap overnight tariffs.

On Octopus Go (around 7-8p/kWh overnight in 2026), the running economics become competitive with gas for many households — particularly as gas prices remain elevated. The calculation depends on your usage, the size of your battery, and your overnight tariff rate. A home spending £1,200/year on gas might spend £900-£1,100 on a heat battery with overnight charging, though this varies significantly.

The break-even point against a new gas boiler (which costs £2,000-£4,000 installed) is long — potentially 10-15 years at current prices. Heat batteries make more financial sense when compared against the alternative of a heat pump that would require significant radiator or insulation upgrades.

Practical Considerations Before Installing

Electrical supply: heat batteries charge at 3-6kW and need a dedicated circuit. Most UK homes can accommodate this without an electrical upgrade, but check with an electrician first, particularly if you also have an EV charger.

Tariff essential: without a cheap overnight tariff, a heat battery loses most of its economic case. You need to be able to switch to or maintain a time-of-use tariff — not always possible if you rent.

Hot water demand: phase-change storage systems have a fixed capacity. If your household uses a lot of hot water (several showers back to back, large baths), check the product sizing carefully. Some households find they need a larger unit than the standard recommendation.

No BUS grant in 2026: unlike heat pumps, heat batteries don’t currently attract the Boiler Upgrade Scheme subsidy. This is a significant financial difference — a heat pump with a £7,500 grant is often cheaper net than a heat battery at list price.

Who Heat Batteries Actually Make Sense For

Heat batteries aren’t the right choice for everyone, and they’re not trying to be. They make the most sense for households where:

  • A heat pump retrofit would require significant additional expense (radiator upgrades, insulation) that changes the heat pump’s cost-benefit calculus
  • The property has no suitable outdoor space for a heat pump unit
  • Getting off gas is a priority but the budget or disruption tolerance for a full heating system overhaul isn’t there
  • You’re already on or can switch to a cheap overnight tariff

For a well-insulated modern home with a south-facing garden and suitable radiators, a heat pump with the BUS grant will almost certainly be the better long-term financial decision. But not every home is that home.

The UK’s heat pump installation numbers continue to lag targets significantly. Heat batteries won’t single-handedly close that gap, but for the subset of homes where pump retrofits are genuinely difficult, they represent a legitimate route off gas that’s been underappreciated.