At Heat Pump Gang, we've seen a growing interest in air source heat pumps (ASHPs). However, many people still find this renewable heating system a bit of a mystery, so we decided to create a series of blogs to provide consumers with all the information they need.
While it's generally well known that having a heat pump installed is a great way to reduce your carbon footprint, as well as enjoy lower energy bills, few people are aware that you need to choose the right size heat pump for your heating demands.
To remedy this, we're looking into air source heat pump sizing to see what we can discover!
These innovative systems offer a sustainable alternative to traditional gas boilers, but choosing the right size is crucial for optimal performance.
In this blog, we'll explain everything you need to know about picking the correct air source heat pump size for your home. We'll explore factors like property size, insulation levels, and climate to help you determine the perfect fit for your needs. By the end, you'll be well-equipped to make an informed decision and enjoy the benefits of lower heating bills and reduced carbon emissions.
A correctly sized heat pump for your home will operate much more efficiently. Heat pumps are famous for their energy efficiency, but only when they're the right size!
If the heat pump is too small, it will constantly struggle to keep up with the heating demand, leading to short bursts of intense operation (known as short cycling). This is inefficient and reduces the lifespan of the unit, so your investment will be wasted!
Conversely, an oversized heat pump system will reach the desired temperature quickly but then cycle on and off frequently, leading to uncomfortable temperature fluctuations in your home.
Either way, an inefficient heat pump will work harder to maintain the right temperature, resulting in higher running costs.
Choosing the wrong size heat pump will put so much strain on the unit that it will eventually break down, requiring expensive repairs, or even replacement.
In short, choosing the right size ASHP ensures you get the best performance in terms of efficiency, comfort, cost, and lifespan.
It's worth noting that this isn't as much of an issue with ground source heat pumps, as they rely on ground temperature, which is more stable and constant all year round.
Basically, the bigger your home, the greater the heat pump's output should be. This means that very large properties require a more powerful heat pump to compensate for the escaping warmth. The rule of thumb suggesting 5kW per 100 square metres offers a basic guideline, but it doesn't account for other important aspects.
Homes with high ceilings create a larger air volume to heat, again requiring a more capable heat pump.
Bedrooms are typically used for sleeping and require a comfortable temperature. The number of bedrooms directly impacts the overall heating demand on the ASHP.
Also, we all have varying comfort preferences. With more occupants, the heating system needs to cater to everyone's needs, potentially requiring a higher overall temperature to ensure everyone feels comfortable.
Finally, unless everyone in the house is constantly active, the heat generated by people might not be enough to keep up with the natural heat loss, especially during colder periods.
Take a look: Heat Pumps For Flats
Detached houses stand apart from other structures, meaning they have more external walls compared to other property types. These exposed walls come into direct contact with the outside environment, leading to a greater rate of heat loss. During colder months, heat naturally flows from warmer areas (inside the house) to cooler areas (outside). With more exposed walls, detached homes lose heat at a faster pace.
Semi-detached and terraced properties share one or more walls with neighbouring houses. These shared walls act as a buffer, reducing the overall exposed surface area. This translates to less heat loss compared to detached houses, potentially allowing for a slightly smaller heat pump capacity.
Warm air naturally rises, and a poorly insulated house will lose a lot of heat; uninsulated lofts act like chimneys, allowing precious heat to escape through the roof.
Proper loft insulation creates a barrier, trapping heat within the living space. This significantly reduces the amount of heat lost, making it easier for a smaller heat pump to maintain a comfortable temperature throughout your home.
By minimising the amount of heat escaping through the loft, you can potentially opt for a smaller heat pump capacity, leading to lower upfront costs and potentially improved efficiency.
If you're installing an air source heat pump in an older property, it must meet the minimum insulation levels set by the UK Building Regulations.
Insulating against heat loss is vital, as heat pumps don't heat water to the same high temperature as a boiler would do. This means that the water in your hot water cylinder is a little cooler, but is pumped consistently rather than in short bursts. A poorly insulated property will lose this heat as rapidly as it is being produced.
Cavity walls, the space between the inner and outer walls of your property, can allow a significant amount of heat to escape if not insulated.
Cavity wall insulation fills the gap between the walls, creating a thermal barrier that reduces heat transfer to the outside environment. Similar to loft insulation, this reduces the loss of heat and potentially allows for a smaller heat pump size to meet your heating needs.
Windows are another area where heat is lost. Single-glazed windows offer minimal insulation, allowing heat to escape more easily compared to double-glazed windows.
Double-glazing consists of two panes of glass with a sealed air gap in between. This air gap acts as an insulator, significantly reducing heat transfer through the windows. By minimising the heat lost through windows, you can potentially opt for a slightly smaller heat pump capacity.
The local climate of your location in the UK plays a crucial role in determining the ideal size for your air source heat pump.
Take a look at these two key climate factors that will influence heat pump selection...
Location
The UK experiences a wide range of temperatures across different regions. Colder areas in the north tend to have lower average winter temperatures compared to milder southern regions.
Air heat pumps work harder in winter. Extracting heat from the outside air and warming it through the heat exchanger coils becomes more challenging! To compensate for this and ensure sufficient heating in colder regions, a more powerful heat pump with a higher capacity is generally required.
Minimum Outdoor Air Temperature
Understanding the lowest expected winter temperatures in your area is crucial for choosing the right heat pump size. These minimum temperatures (known as the outdoor design temperature) determine how efficiently your heat pump can operate, and a large disparity between outdoor and indoor temperatures makes the pump work much harder.
While a heat pump might function adequately during most of the winter, it's essential to ensure it can handle the coldest days. An appropriately sized heat pump will maintain your desired room temperature even during extreme cold snaps.
Essentially, the higher the coldest temperature outside, the smaller your heat pump should be!
Explore: Do Air Source Heat Pumps Work In Winter?
The type of heating system you have plays a significant role in determining the ideal power output for your air source heat pump, as you’d imagine:
Larger radiators have a greater surface area, allowing them to transfer more heat to the surrounding air. Consequently, a larger radiator requires a more powerful heat pump to deliver enough heat to maintain the desired temperature in your home.
The material of your radiators can also impact heat pump size. Aluminium radiators generally require a higher flow temperature compared to cast iron radiators, which retain heat more effectively. A higher flow temperature might necessitate a slightly larger heat pump capacity.
Underfloor heating systems typically operate at lower flow temperatures compared to radiators. This is because the heat is distributed more evenly throughout the floor, radiating upwards and warming the room from the ground.
The lower flow temperature requirement of underfloor heating allows you to potentially consider a slightly smaller heat pump capacity compared to a radiator system. However, the overall heat output rating still needs to be sufficient for your property size and insulation levels.
Some air source heat pumps also feed the hot water cylinder for your taps and showers while heating your home.
If your ASHP is responsible for both heating and hot water, you need to factor in your hot water needs when determining the required capacity. A higher hot water demand requires a more powerful heat pump to ensure sufficient capacity for both functions.
Heat Pump Gang takes all of the above into account while making heat pump sizing calculations. While we do all the work for you, it's always best to gain an understanding of what's involved, which is why we've made this blog.
Sadly, there's no magic heat pump size calculator! It takes knowledge, experience, and a bit of common sense to calculate heat pump sizes accurately, and this is what we do best.
Ultimately, it all comes down to calculating heat loss to determine heat demand (Which can be taken from the building's current energy performance certificate).
It's also worth considering installing a ground source heat pump, although issues such as poor insulation still need to be addressed.
When you decide to invest in a new heat pump, Heat Pump Gang will support you with professional advice and service to help you maximise the benefits.
