FAQs

Do heat pumps work in cold temperatures?

Yes. Heat Pumps are designed to work in much colder climates than we have in the UK. Scandinavia for example has been installing heat pumps for many decades. Both air and ground source heat pumps can work down to external temperatures of -15degC and below, however the design point for properties in South Wales and the South West of England are typically -2 to -5degC, depending on location and height above sea level. It is at this design point that the heat pump for your property would be sized to ensure it can heat the property comfortably in even the most extreme cold snaps.

Do heat pumps work in older buildings?

Yes, heat pumps can and do work well in older buildings and WDS Green Energy have installed many systems in older, solid-walled properties. The importance of a thorough design process is crucial to sizing the heat pump to the property’s demand correctly, as well assessing and potentially upgrading of heat emitters (radiators and underfloor heating) to meet room demands at the lower flow temperatures of a heat pump system (typically 50-55degC in an older building). As part of the design process WDS will assess your existing radiators and advise of any required or recommended upgrades. Older buildings also benefit from typically having a large thermal mass – the solid walls act as a heat battery, absorbing heat and releasing slowly back into the house; you will often find that even on freezing nights the temperature in the house doesn’t drop that much overnight when the heating is off because the walls are releasing heat back into the house.

Can heat pumps work with radiators or only underfloor heating?

Heat pumps can work with both underfloor heating and radiators. Most ground and air source heat pumps produce flow temperatures of up to 55degC. There are a few higher temperature units on the market that will produce flow temperatures of up to 65-70degC which can be used in buildings with poor insulation levels with high heat loads where it is impractical or extremely costly to install underfloor heating or upgrade the existing radiators and/or heating distribution system.

Although heat pumps are most efficient matched with underfloor heating this is not to say that they aren’t very efficient working at flow temperatures of 45-55degC for a correctly sized radiator system, delivering efficiencies close to or sometimes in excess of 400%.

Will I need an additional source of heat?

No, so long as the system has been designed correctly you will not necessarily need an additional source of heat. We do always install a back-up immersion within the hot water cylinder as standard. Some heat pumps have a maximum flow temperature of 55degC so this immersion can be brought on automatically to bring the cylinder temperature up to 60-65dgeC as part of the thermal disinfection programme for legionella protection but also means you have a back-up should the heat pump breakdown. Some manufacturers also have in built back-up heaters for heating purposes, which can be used in the event of a breakdown to provide background heat.

Some customers choose to go for a bivalent system whereby the heat pump will provide heat to a certain point with an auxiliary gas or oil boiler providing the rest of the heat. These type of installations tend to be either on commercial properties (where the client wants to be able to have an additional back-up for emergencies) or very large older properties with high heat loads (i.e. high ceilings/single glazed/no insulation). Importantly, however, bivalent systems are not eligible for the Boiler Upgrade Scheme grant.

Do I need to leave my heating all of the time?

This depends on the property and how you live. Due to the fact that you are running at lower temperatures than a conventional boiler system the heat up time `(i.e. set periods of on/off). We would suggest that you have a programmable thermostat which you can use to set back the temperatures during the night and days (outside of the peak heating requirements). Working at lower flow temperatures means that the heat pump will not be as reactive as a 70-80degC boiler so the idea is to run the heat pump for longer at lower temperatures, ‘longer and lower’ is a mantra you might often hear us say. This type of heating is much more comfortable for the end user rather than sporadic on/off bursts of heat. With more people working from home, the idea of maintaining a warmer room temperature throughout the whole day has become a reality for many.

Are heat pumps expensive to run?

No. In general heat pump running costs are the same as a mains gas boiler, around 10-30% cheaper than an oil boiler and up to 50% cheaper than an LPG boiler, depending on how much you are paying for the equivalent fossil fuel. As part of our quotations WDS Green Energy provide you with a document with estimated running cost comparisons against your existing or alternative heating system.

Once you have decided to install a heat pump system you should endeavour to get yourself onto the best electricity tariff available. Whereas in the past you may have had a dual fuel bill such as gas and electric or paid separately for oil or LPG it is important to remember that your heating system will now run on electricity and so electric will be your main bill.

How do I choose which type/manufacturer of heat pump to install?

WDS Green Energy have built up very strong working relationships with a number of different manufacturers over the years. When selecting which products to install we value the following:

A strong aftersales support team based in the UK. If something does go wrong we want to be able to rectify it as quickly as possible.
A strong name and years of experience in the heating industry, companies who have a long history in heating and ventilation and are not likely to disappear overnight.
A long warranty period (all manufacturers that we use offer between 5-7 years) We appreciate that the systems that we install are not cheap and our customers should expect the systems to last for a long time after installation (a lot longer than the warranty period, even)
Quality products which are built to last
High efficiency systems

How long will a heat pump system last?

Manufacturers advise that heat pumps will last a similar length of time as an equivalent gas or oil boiler, between 15 and 20 years for a GSHP and 10 and 15 years for an ASHP. Our oldest installs are approaching 18 years old (at time of writing in 2024), the vast majority of which are still running without a hitch

How much space do I need for the kit internally?

The internal equipment for a heat pump system consists primarily of a hot water cylinder (sized to your property’s number of bedrooms and bathrooms), a smaller buffer tank, expansion vessels and ancillary pipework and accessories. A ground source heat pump system will also have the GSHP unit inside, and hence does require more space.

For an air source heat pump system a space approximately 1.5m x 1m is required, with access along the 1.5m side (think of a double door cupboard 5 feet wide, 3 feet deep, full ceiling height).

For a ground source heat pump system, which has the GSHP unit itself inside, a space approximately 3m x 2m is required, again with access along the longer 3m side.

In retrofit properties the location of the plant equipment will need to be considered in relation to the existing boiler and distribution pipework as connections will need to be made into the existing system.

How loud is an air source heat pump?

The Sound Power rating of the ASHP units are typically around 50-54dB for a 4-8kW unit and 54-60dB for 10-14kW units. This does drop significantly to 40dB or less at 3m distance which is roughly comparable to the noise levels of a fridge/freezer. Vaillant have a ‘Soundbox’ in which you can listen to a heat pump unit in operation: https://www.vaillant.co.uk/homeowners/advice-and-knowledge/how-different-technologies-work/heat-pumps/ (bottom of the page).

We are happy to provide you with site references to visit one of our existing customers to see a unit in operation.

Where could or should I site my air source heat pump?

The air source heat pump is best sited on an external wall of the property, with pipework connected through the wall behind to the internal equipment. They can be located away from the property and would then just require a buried run of pre-insulated pipe to limit any heat loss. In order to adhere with permitted development regulations this will need to be 1m (England)/3m (Wales) from the site boundary and not visible from the highway (Wales only). See the permitted development regulation link below for more detail. If this is not possible the installation of an air source heat pump will need planning permission. Most units are approximately a 1.1 x 0.45m footprint and require a clearance of 300mm behind, 300-600mm each side and 1m in front of the fan.

Wales PD: https://gov.wales/planning-permission-heat-pumps

England PD: https://www.planningportal.co.uk/info/200130/common_projects/27/heat_pumps/2

Do heat pump systems require servicing?

As with any heating system an annual service is recommend to ensure efficient and clean running of the system. It is usually a condition of the manufacturer warranty that the system is serviced annually by an accredited installer of that manufacturer’s products, and it is also a condition of the Renewable Heat Incentive that the system is maintained properly. Please ask one of the WDS design team for a guidance on WDS’ costs for annual servicing.

Are boreholes more efficient than horizontal ground collectors?

Marginally, yes, in the sense that a borehole system will need less total pipework than an equivalent horizontal system as it is able to draw more watts per metre of pipework. However overall performance of the system will be almost identical, and as borehole drilling costs are much higher than digging trenches we would generally recommend horizontal ground collectors if you have the space available.

How much space do I need for a ground collector?

This will depend entirely on your property’s heat demand and the size and power of heat pump required, as well as your property’s location and height above sea level. However, as a broad rule of thumb a 6kW system will require 150-200m of total trench and 12kW system 300m of total trench. This total length is then typically split into 50m, 75m or 100m lengths, with minimum 3-5m space between each trench. So a 12kW system with 6no. 50m trenches (300m total) would need a space roughly 50m long x 25m wide, or 1,250m2/0.31 acres. Note that any plants with deeper root stock (trees) would need to be avoided and cannot then be planted on top of the trenches as they can interfere with the buried pipework.

How deep are horizontal ground collector trenches?

Collector trenches are generally 1.2m deep and 0.6m wide. They also need to be 3-5m apart from the nearest trench or building.

Is a ground source or air source pump better for me?

We are always happy to provide our customers with a price for both ground and air source heat pumps and whilst we are happy to provide you with advice the decision will ultimately be yours, but we suggest you consider the following:

Capital investment is much higher with a ground source heat pump as you have the associated ground works package including trenching/borehole costs.
Boiler Upgrade Scheme grant amount is the same for GSHPs & ASHPs, £7.5k either way.
Internal space available – As the GSHP will be sited internally you will require more internal plant space for a ground source heat pump as opposed to an air source heat pump.
No external air source heat pump unit with a ground source heat pump system. We have had customers opt for GSHP simply because they do not like the appearance of an ASHP outside of their property

Frequently Asked Questions

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