Last Updated on July 29, 2025
Air source heat pumps (ASHPs) are increasingly popular across the UK as a clean, efficient alternative to traditional boilers. Many homeowners and landlords want to know whether an ASHP can effectively provide hot water for their property and how well it performs throughout the year.
In this guide, we’ll explain how ASHPs heat your domestic hot water, what equipment is needed, typical costs, and important considerations like space requirements and winter performance.
Plus, we’ll highlight UK government grants that make switching easier and more affordable.
If you’re considering upgrading your home heating system or replacing an old boiler, read on to discover why an air source heat pump could be the perfect solution for your hot water needs.
Contents
Do Air Source Heat Pumps Provide Hot Water?
Yes, air source heat pumps (ASHPs) do provide hot water, and in most cases, they can do so without needing a boiler. But whether an ASHP alone is enough to meet your hot water needs depends on a few key factors including your home’s insulation, cylinder size, and the time of year.
Can an ASHP Fully Replace a Boiler for Hot Water?
In most modern or well-insulated UK homes, an air source heat pump can replace a traditional boiler entirely, both for space heating and domestic hot water. It uses outside air to generate heat, which is then transferred to a hot water cylinder.
You will need:
- A suitably sized cylinder (typically 150L–300L for UK households) to store the hot water.
- Proper plumbing configuration to integrate the ASHP with your hot water system.
You won’t necessarily need:
- A gas or oil boiler unless you’re installing a hybrid system, which combines both for maximum performance during peak demand.
Is an ASHP Enough to Meet Daily Hot Water Needs?
Yes, for the vast majority of UK homes. According to the Energy Saving Trust, ASHPs are fully capable of providing hot water for daily household use, including:
- Showers and baths
- Sinks and washing
- Dishwashers and laundry (if connected to hot fill)
The key is proper system design. Undersized heat pumps or cylinders will struggle, especially in busy households. That’s why working with an installer like Eco Happy ensures a tailored assessment of your needs before installation.
Will It Still Work in Winter?
This is a very common concern and the short answer is: Yes, air source heat pumps still work in winter.
Modern ASHPs are specifically engineered for colder climates:
- They can extract heat from air temperatures as low as -15 °C.
- Even in freezing weather, they maintain enough output to heat both your home and your water.
That said, COP (efficiency) does drop slightly in winter, meaning the system works harder and uses more electricity to maintain flow temperatures. A larger cylinder or increased insulation can help counterbalance this.
Even in colder UK regions like Scotland and the North East, well-installed ASHPs have shown consistent year-round performance.
When Might You Still Need a Backup?
There are a few scenarios where a backup heat source could be useful:
- Very large households with high hot water demand.
- Properties with poor insulation or restricted space for a large hot water cylinder.
- Commercial use (like B&Bs or salons), where peak usage exceeds storage.
In these cases, some people opt for:
- A hybrid heat pump system (combined with a boiler).
- An immersion heater as a backup, often powered by solar PV to reduce cost.
What Size Heat Pump and Cylinder Do You Need for Your Property’s Hot Water?
Choosing the right size air source heat pump (ASHP) is critical, not only to efficiently heat your home but also to reliably meet your domestic hot water demand.
Undersized systems struggle to keep up, especially during peak usage, while oversized units can increase costs unnecessarily.
How Does Property Size Affect Hot Water Heating?
- Smaller properties (e.g., one-bedroom flats) generally have lower hot water demand due to fewer occupants, so a smaller heat pump with a smaller cylinder can suffice.
- Medium-sized homes (2–4 bedrooms) typically require moderate hot water storage and a mid-range heat pump to cover showers, baths, and daily appliance use.
- Larger homes and multi-occupancy properties need more robust heat pump capacity and larger cylinders to ensure continuous hot water availability, especially if multiple bathrooms or commercial use are involved.
Sizing Considerations for Hot Water
- Heat pump capacity is measured in kilowatts (kW) and must match both space heating load and hot water demand.
- The hot water cylinder size should correspond to the number of occupants and their typical hot water usage.
- Larger cylinders provide a buffer for peak hot water times but require more space.
- For best efficiency, sizing your heat pump and cylinder in tandem ensures you have enough hot water without wasting energy.
Recommended Heat Pump and Hot Water Cylinder Sizes by Property
| Property Size | Typical Occupants | Recommended ASHP Size (kW) | Hot Water Cylinder Size (Litres) | Typical Hot Water Use |
|---|---|---|---|---|
| Small Flat / Studio | 1–2 | 6–8 kW | 100–125 L | Minimal hot water, low peak demand |
| Small House (1–2 bedrooms) | 2–3 | 8–10 kW | 150–180 L | Moderate hot water, 1 bathroom |
| Medium House (3 bedrooms) | 3–4 | 10–12 kW | 180–210 L | Average family hot water use |
| Large House (4+ bedrooms) | 4–6+ | 12–16 kW | 210–300 L | Multiple bathrooms, higher usage |
| Small Commercial / B&B | Varies | 16+ kW | 300+ L | High demand, continuous supply needed |
How Much Space Do You Need for the Hot Water Cylinder?
The average UK home (3–4 people) usually requires a 200L unvented cylinder, and the typical dimensions are:
- Height: 1.2 to 1.6 metres
- Diameter: 0.5 to 0.65 metres
- Minimum footprint (with clearance): around 700mm x 700mm
- Height clearance needed: at least 1.8 to 2.0 metres
Don’t forget to allow space for:
- Pipework at the top and sides
- Servicing access
- Insulation and ventilation
Where Can You Install the Cylinder?
Hot water cylinders are most commonly installed in:
- Airing cupboards (often replacing an old boiler or vented tank)
- Utility rooms
- Lofts (must be structurally strong and well-insulated)
- Under-stairs cupboards (only suitable for slimline models)
Ideally, the cylinder should be located close to your bathrooms and kitchen, to minimise heat loss and reduce the time it takes for hot water to reach taps.
What If Your Home Has Limited Space?
If your home is compact or lacks a suitable cupboard, you still have viable options:
- Slimline cylinders: Taller, narrower tanks designed to fit tight spaces
- Smaller capacity cylinders: Ideal for flats or 1–2 person households
- High-recovery cylinders: Heat up quickly, meaning you can use a smaller tank
- Hybrid systems: Use a combi boiler for hot water, ASHP for heating only
- Thermal stores: Combine space and water heating in one unit, often more compact
A professional installer like Eco Happy will assess your space and recommend the best-fit solution ensuring your system is efficient, compliant, and tailored to your lifestyle.
How Much Does It Cost to Heat Hot Water with an Air Source Heat Pump?
When it comes to heating hot water, air source heat pumps (ASHPs) are significantly more efficient than traditional boilers, meaning lower running costs over time. But how much can you expect to actually spend?
Electricity Usage vs. Efficiency
Air source heat pumps typically use electricity to extract heat from the air, but thanks to their Coefficient of Performance (COP) of 3 to 4, they generate 3 to 4 units of heat for every 1 unit of electricity consumed.
According to the Energy Saving Trust, this high efficiency means ASHPs can deliver over 300% efficiency, compared to around 90% for a modern gas boiler.
This means that even though electricity is more expensive per kWh than gas, you’ll use far less energy overall to heat your water.
For example:
- A typical UK household uses around 3,000–4,000 kWh per year for hot water.
- With an ASHP and a COP of 3, you’d only use about 1,000–1,300 kWh of electricity.
- At an average electricity price of 24p per kWh (as of 2025), that’s roughly £240–£312 per year to heat your water.
In contrast, a gas boiler may cost upwards of £400+ per year for hot water alone, due to lower efficiency and higher consumption.
| System | Annual Hot Water Usage | Efficiency (COP) | Energy Used | Estimated Annual Cost |
|---|---|---|---|---|
| Air Source Heat Pump | 3,000–4,000 kWh | 3.0 | 1,000–1,300 kWh (electricity) | £240–£312/year |
| Gas Boiler | 3,000–4,000 kWh | 0.9 (typical) | 3,300–4,400 kWh (gas) | £400–£500+/year |
Installation Costs for Hot Water Setup
When it comes to the hot water element of an ASHP system, installation costs usually include a hot water cylinder, which can add around £800–£2,000 to the project depending on the size and insulation.
However, these costs are typically bundled into the full ASHP system quote.
Government Support Reduces Upfront Costs
With the Boiler Upgrade Scheme (BUS), UK homeowners can receive up to £7,500 towards a new air source heat pump system substantially reducing the financial barrier (gov.uk).
Long-Term Savings
Switching to an air source heat pump (ASHP) can result in significant long-term savings, especially when replacing an older, inefficient heating system.
According to the UK Government, households switching from a gas boiler to a heat pump could save around £234 per year, particularly when using a smart electricity tariff. This estimate is based on current Ofgem energy price cap data and assumes a well-installed, efficient ASHP system.
Additionally, the Energy Saving Trust states that households replacing an older G-rated gas or oil boiler could save between £295 and £425 per year, depending on:
- The type and efficiency of the existing heating system
- Occupancy levels and usage patterns
- The heating controls and insulation levels in the property
If you combine your ASHP with solar PV panels, your savings could increase further by generating free electricity to power your heat pump reducing your reliance on grid electricity.
Ready for a Quote?
Request Your Free Air Source Heat Pump Quote from Eco Happy Today
Take the next step, request your bespoke ASHP assessment from Eco Happy now. We’ll evaluate your property, help with grant applications, and deliver a comprehensive report showing your energy savings and hot water system design.
Don’t wait, secure your clean, low-cost hot water system with Eco Happy today!
FAQs
What size cylinder do ASHPs need for a family home?
Typical UK homes require 150–210 L cylinders. We assess your usage patterns to specify the right size when quoting.
How long does it take to heat a cylinder?
With an ASHP, a full cylinder heats in 2–3 hours, depending on cylinder size and ambient conditions.
Can ASHP supply hot water during power outages?
No, since ASHPs run on electricity, you’d need a backup like a hybrid boiler or immersion heater connected to a generator or PV system.
How often should hot water cylinders be serviced?
Annual checks are recommended, Eco Happy offers full servicing to ensure optimal cylinder insulation and heating efficiency.
Can ASHPs meet commercial demand for hot water, e.g. in B&Bs?
Yes, commercial-grade cylinders and buffer tanks, sized for peak demand, ensure steady hot water delivery in businesses and rentals. We design these specifications in our commercial quotes.
Conclusion
An air source heat pump can absolutely provide hot water efficiently, sustainably, and cost-effectively. You’ll need a cylinder, adequate space, and proper system design for flow temperatures and insulation.
With rising UK sales, generous grants, and efficiency benefits, ASHPs are the smart choice for homeowners and landlords aiming to decarbonise their water heating.
James Elston
Boiler Expert
James Elston is the top boiler replacement and heating expert at Eco Happy. He has over 20 years of experience in the industry, focusing on Gas Safe boiler installations and offering home-heating and energy-saving solutions to homeowners across the UK. From sourcing the most energy-efficient combi boiler to providing specialist heating advice, James ensures that Eco Happy maintains the highest standards and best customer service.