Do Heat Pumps Need A Water Tank?

Last Updated on June 20, 2025

If you’re considering making the switch to a low-carbon heating solution, there’s a good chance you’ve asked yourself: do heat pumps need a water tank? This is a common question for UK homeowners and landlords thinking about upgrading from a gas boiler to an air source heat pump. 

With so much information floating around about different system setups, it’s vital to understand whether a hot water tank is necessary, when it’s required, and how it fits into your heating system overall.

In this guide, we’ll walk you through everything you need to know, from when a water tank is required to the types of tanks that work best with air source heat pumps. 

We’ll also cover efficiency, system design, cost implications, and more. If you’re looking to install a heat pump and want a clear understanding of what’s involved, you’re in the right place.

Do Air Source Heat Pumps Always Need a Water Tank?

Not always, but in most UK homes, air source heat pumps do need a hot water cylinder. That’s because the vast majority of installations are air-to-water systems, which distribute heat through wet central heating systems (like radiators or underfloor heating). 

These systems also provide domestic hot water, usually stored in a cylinder because heat pumps operate most efficiently when heating water gradually over time.

If you opt for a hybrid system, where a heat pump works alongside your existing boiler, a water tank may still be required depending on your hot water demand and system design.

Can You Use a Heat Pump Without a Hot Water Cylinder?

Yes, but it’s not common. Some compact systems, like air-to-air heat pumps, don’t provide hot water at all and therefore don’t need a tank, but these aren’t popular in the UK due to our central heating culture. 

Alternatively, thermodynamic water heaters or instantaneous water heaters can be used in very small properties or flats.

For most UK homes, though, particularly those looking to completely replace their boiler, installing a hot water tank is essential. If you’re wondering about how this might work alongside your current heating system, you might want to read our guide on how heat pumps work with existing radiators to see how compatible your setup is.

What Kind of Hot Water Cylinder Do You Need for a Heat Pump?

You’ll typically need an unvented hot water cylinder that’s compatible with lower flow temperatures. These are specifically designed for renewable heating systems, including heat pumps.

When discussing your installation with an engineer, they’ll calculate the ideal tank size based on:

• Your household’s hot water demand
  
• Number of bathrooms
  
• Usage patterns
  
• Cylinder heat-up time

Check out our air source heat pump installation guide to see what this process looks like step-by-step.

Do You Need a Buffer Tank as Well?

Sometimes, yes. A buffer tank isn’t the same as a hot water cylinder. It stores heated water for your central heating system and helps to reduce short cycling, which can improve system efficiency and lifespan.

Whether you need one depends on your property’s layout, insulation levels, and how often your heating system turns on and off. High-demand homes or those with older heating systems may benefit more from a buffer tank. 

If your home is older, take a look at our article on how air source heat pumps work in old houses to understand performance expectations.

Why Do Most Air Source Heat Pump Systems Use a Hot Water Tank?

Heat pumps operate at lower flow temperatures than traditional boilers. This means they take longer to heat water and work best when paired with a well-insulated cylinder that stores the hot water until it’s needed.

Here’s why a hot water tank is beneficial:

• Energy efficiency: The system doesn’t have to work hard to meet sudden demand.
  
• Off-peak savings: You can heat water during cheaper tariff hours.
  
• Thermal storage: Useful for homes with higher hot water usage.

If you’re weighing up your heating options, it’s also helpful to compare the cost to replace a gas boiler with a heat pump and consider how the tank fits into that investment.

Does Having a Tank Affect Air Source Heat Pump Efficiency?

Not negatively, a hot water tank can improve efficiency when used correctly. By heating water slowly and storing it for use when needed, the system can run at lower flow temperatures, which increases the coefficient of performance (COP).

You’ll also likely benefit from reduced running costs and longer compressor life. To explore these savings in more depth, read our guide on heat pump running costs and see how this compares to your current energy bills.

Can a Heat Pump Be Installed in Homes With Limited Space?

If you live in a smaller home or flat, space-saving options like slimline or wall-mounted cylinders can be used. In some cases, thermal stores or combi-style heat pump units (where the cylinder is built-in) may be viable.

For properties with limited internal room, locating the tank in a utility room, airing cupboard or loft can work well. Just be aware that your home must still meet suitability criteria. Check out our guide on determining if your house is suitable for a heat pump for a breakdown of property types and system requirements.

How Do Tanks Influence the Overall Installation Cost?

Installing a hot water tank will add to the overall cost of an air source heat pump system. This includes:

• The tank unit itself
  
• Pipework and fittings
  
• Labour for installation
  
• Additional space preparation

However, the cost can be offset by available government grants like the Boiler Upgrade Scheme (BUS), which provides £7,500 towards air source heat pump installations.

Can Heat Pumps Still Work Without a Tank in the Future?

Technically, yes. Ongoing innovation in the UK renewables market means tankless heat pump solutions could become more common. That said, current technology still favours cylinders for performance and comfort, especially in larger or family homes.

If your main concern is futureproofing, check out our on the best heat pump brands to find systems with adaptable features and warranty coverage for long-term reliability.

Is It Worth Getting a Heat Pump and Tank Setup in the UK?

Yes, for most UK homes, an air source heat pump paired with a hot water cylinder is an efficient and futureproof solution. With rising gas prices, increasing demand for sustainable heating, and generous government incentives, this combination offers strong long-term value.

Ready for an Efficient Heating Upgrade? Request a Free Air Source Heat Pump Quote Today

Now that you know the answer to whether heat pumps need a water tank, it’s time to take the next step. Whether you’re planning a full boiler replacement or just exploring your options, Eco Happy can help.

Our certified engineers provide expert assessments to determine the right setup for your home, including whether a tank is required and what size system you’ll need. We’ll also guide you through grants, savings, and installation options with no obligation.

Request your free air source heat pump quote today and discover how easy it is to upgrade your home with low-carbon, high-efficiency heating.