Can I replace my combi boiler with a heat pump water heater?

Not directly. A combi boiler handles both heating and hot water on demand with no cylinder. A heat pump water heater only heats stored water. You'd still need a separate system for central heating. If you want to replace a combi entirely, a full air source heat pump with an integrated hot water cylinder is the usual route.

How noisy are heat pump water heaters?

Most produce 40 to 50 dB, similar to a humming fridge. You won't notice it in a garage. You might in a bedroom cupboard at night.

Do heat pump water heaters work in winter?

Yes, but less efficiently. The COP drops when surrounding air temperature falls. A unit in a heated utility room might maintain a COP of 3.0 year-round. One in an unheated garage could drop to 2.0 or lower in deep winter, which still beats an immersion heater's COP of 1.0 but means your January electricity bill for hot water will be higher than July's. Some models include a backup electric element that kicks in during very cold spells, essentially running as an immersion heater temporarily.

Will a heat pump water heater work with my existing pipework?

Usually yes. If you already have a vented or unvented hot water cylinder, the pipework connections are standard. Your installer may need to add a condensate drain and ensure adequate ventilation, but the actual hot and cold water connections are typically compatible with existing plumbing.

How long does installation take?

One day for a like-for-like cylinder swap in a suitable space. Two days if ventilation ducting or electrical work is needed. It's not a major building project.

Heat Pump Water Heaters 2026: Save Money on Hot Water

Heat Pump Water Heaters 2026: Save Money on Hot Water | Eco Home Check

What Is a Heat Pump Water Heater and How Does It Work?

It's a water cylinder with a built-in heat pump that extracts warmth from surrounding air. Think of it as a fridge running in reverse: instead of pumping heat out of a box to keep food cold, it pumps heat into water to make it hot. See our guide on how heat pumps operate for more detail.

The unit sits where your existing hot water cylinder lives, usually an airing cupboard, utility room, or garage. A small compressor on top or attached to the side draws in ambient air, compresses the refrigerant inside to raise its temperature, then transfers that heat into the stored water. The "spent" cool air gets vented out, which is why you need some ventilation around the unit.

For every 1 kWh of electricity the compressor uses, it moves about 2.5 to 3.5 kWh of heat energy into the water. Engineers call this the Coefficient of Performance (COP), and it's why these things slash bills so dramatically compared to a direct electric immersion heater, which converts 1 kWh of electricity into exactly 1 kWh of heat. No more, no less.

One thing most guides skip: the COP drops when the surrounding air is colder. A unit in an unheated garage in January will work harder than one in a warm utility room. It still works, and it's still far cheaper than an immersion, but the savings vary by season and by where you put the thing.

How Much Could You Save on Your Hot Water Bills in 2026?

A typical household replacing a direct electric immersion heater could cut hot water costs by 50% to 70%. That's real money.

The Energy Saving Trust estimates that heating water accounts for roughly 15% to 25% of a home's total energy use, depending on how many people live there and how efficiently the home is insulated. For a household spending £600 a year on electric hot water (not unusual with an immersion heater on standard tariff), a heat pump water heater with a COP of 3.0 would bring that down to around £200.

£400 a year saved. Over a 15-year lifespan, that's £6,000.

But here's the honest bit: if you're currently on mains gas with a combi boiler, the savings are much smaller. Gas is still cheaper per kWh than electricity in the UK (roughly 7p vs 24.5p as of Ofgem's April 2025 cap), so a gas boiler heating your water costs less to run than almost any electric alternative. The sweet spot for heat pump water heaters is homes that currently rely on direct electric heating, storage heaters, or oil.

So if you're on mains gas and your boiler is working fine, this probably isn't the upgrade to prioritise. If you're on electric, oil, or LPG, it's a different story entirely. We've covered the broader economics in our guide to whether heat pumps are worth it, and the same logic applies here. See our guide on solar water heater alternative for more detail.

Is Your Home Suitable for a Heat Pump Water Heater?

Most homes with an existing hot water cylinder can fit one, but you need adequate space and ventilation. The unit itself is larger than a standard cylinder, typically around 500mm to 700mm in diameter and up to 1,800mm tall. See our guide on heat pump installation requirements for more detail.

Here's the checklist:

Space. You need a room or cupboard with at least 5 to 7 cubic metres of air volume. A standard airing cupboard is often too small unless the door is louvred or you can vent into an adjacent space. Garages and utility rooms are ideal.

Ventilation. The unit extracts heat from the air, so it needs airflow. A sealed cupboard won't work. Ducting kits let you pull air from one room and exhaust into another, which some homeowners use to cool a kitchen or conservatory in summer as a bonus.

Drainage. Like any heat pump, these produce condensate. You'll need a drain nearby or a condensate pump.

Electrical supply. Most units run on a standard 13A plug, though some larger models need a dedicated spur. Your installer will confirm this during survey.

And one thing people forget: noise. The compressor isn't silent. Most units produce 40 to 50 dB, roughly the level of a quiet conversation. Fine in a garage. Potentially annoying in a bedroom cupboard at 2am when the timer kicks in. Worth thinking about placement carefully.

Flats are trickier. Internal-only flats without access to a garage or utility room rarely have the space or ventilation needed. Ground-floor flats with an external wall for ducting can sometimes make it work.

What Grants Can Help Cover the Cost in 2026?

The Boiler Upgrade Scheme (BUS) offers £7,500 towards an air source heat pump installation, but there's a catch for standalone hot water units. BUS is designed to fund full heating systems, not just hot water cylinders. If you're installing a complete air source heat pump system that handles both heating and hot water, the grant applies and it's generous. If you're only swapping out a hot water cylinder for a heat pump water heater, you won't qualify for BUS on its own.

That said, if you're considering a heat pump water heater, it's worth asking whether a full air source heat pump system makes more sense for your situation. The BUS grant is confirmed through to 2030 under the Warm Homes Plan, and the £7,500 covers a significant chunk of a full system installation. We've broken down the numbers in our heat pump cost guide.

ECO4 is another route if you're on qualifying benefits like Universal Credit, Pension Credit, or Child Tax Credit. ECO4 can fully fund energy efficiency measures including heating upgrades for eligible households, and it runs until December 2026. The measures funded vary by your energy supplier and local authority, so it's worth checking your eligibility to see what's available.

Warm Homes: Local Grant operates through local authorities and covers a range of upgrades. Amounts vary by council and the scheme runs until 2030 under the Warm Homes Plan. Some councils include hot water system upgrades in their scope, others don't. Nottingham City Council, for instance, has funded heat pump installations through this route, while other authorities have focused exclusively on insulation.

Honestly, the grant picture for standalone heat pump water heaters specifically is thinner than for full heating systems. The government's incentive structure pushes you towards replacing your entire heating setup, not just the hot water side. That might change, but as of mid-2026, that's where we are.

Heat Pump Water Heater vs Traditional Immersion Heater: Which Wins?

The heat pump water heater wins on running costs by a wide margin, every time.

	Heat pump water heater	Immersion heater
Purchase + install cost	£2,500 to £4,500	£200 to £500
Annual running cost (3-bed home)	£150 to £250	£450 to £700
Lifespan	12 to 15 years	8 to 12 years
COP / efficiency	2.5 to 3.5	1.0 (exactly)
Space needed	Ventilated room, 5-7m³	Fits in any cylinder cupboard
Noise	40-50 dB (audible hum)	Silent
Maintenance	Annual check recommended	Almost none

The upfront cost difference is stark. You're paying 5 to 10 times more for the heat pump unit. But the running cost savings of £300 to £450 per year mean payback typically lands between 6 and 10 years, depending on your electricity tariff and how much hot water you use.

If you're in a home where you plan to stay for a decade or more, the heat pump water heater is the better investment. If you're selling in two years, probably not worth the disruption.

One more thing worth mentioning. Immersion heaters pair well with solar PV because you can divert surplus electricity directly into heating water for free. A heat pump water heater also pairs well with solar, but it amplifies the benefit further: every kWh of solar electricity you feed into the heat pump produces 3 kWh of hot water heating. If you've already got solar panels on your roof, a heat pump water heater turns that surplus into three times the hot water an immersion ever could.

How to Choose the Right Model and Find a Qualified Installer

Match the cylinder size to your household's hot water demand. Too small and you'll run out mid-shower. Too large and you're heating water you don't need.

A rough guide:

1-2 people: 150 litres
3-4 people: 200 to 250 litres
5+ people: 300 litres

Brands available in the UK market include Mitsubishi (Ecodan hot water systems), Daikin (Altherma), Ariston (Nuos range), and Vaillant. The Ariston Nuos Plus is one of the more popular integrated units because it's designed as a direct cylinder replacement and doesn't need external pipework.

So how do you actually find someone to install it? MCS certification is the standard you want. MCS-certified installers are required for any BUS grant application, and even if you're not claiming a grant, MCS certification means the installer meets industry standards for training and workmanship. The MCS Installer Register lets you search by postcode and technology type.

Get at least three quotes. We see significant price variation across the country, sometimes £1,000 or more for the same unit and similar installation complexity. Ask each installer about their experience specifically with heat pump water heaters rather than just full heating systems, because the installation considerations are different (ventilation, drainage, noise placement).

Avoid anyone who can't explain the COP of the unit they're proposing. If they can't tell you how much it'll cost to run per year based on your household size, find someone who can.

And a tangential but genuinely useful point: if your home has poor insulation, fixing that first will reduce your hot water losses from the cylinder and pipes, making any heating upgrade work better. A well-insulated cylinder jacket costs £15 and pays for itself in weeks. Sometimes the boring upgrades matter more than the exciting ones. Anyway.

For a broader view of how a heat pump water heater fits into a whole-house energy efficiency strategy, it's worth thinking about your heating, insulation, and hot water as connected parts of the same system rather than isolated upgrades.