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Reaching new heights: aerial heat pump installations are on the rise


With demand for air source heat pumps (ASHPs) growing in built-up areas, many customers are looking for space-saving solutions. Viessmann partner and low-carbon energy expert Tom Sullivan of Active Heating & Renewables explains how to make high-level installations work safely and efficiently


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ir source heat pumps are gaining traction in the UK as a key technology for decarbonising homes. But in cities and densely populated


areas, finding suitable places for outdoor units (ODUs) can be a major hurdle. Many properties simply lack the space at ground-level, forcing installers to think vertically. Today, roughly a fifth of the ASHPs we fit are mounted off the ground, usually on single-storey garage roofs, though we’ve also fitted them on top of townhouses and several meters up external walls. With careful design and proper safety precautions, aerial installations can work perfectly.


Wall or roof – choosing the right spot


There are a number of factors to consider when deciding where to site an ODU and every property is different. However, fixing it directly to a solid wall can avoid several potential issues that can arise with roof fittings. These include the risk of snow build-up, leaks due to penetrating roofing membranes or vibration-noise issues (although flat roofs fitted with rubber membranes do tend to absorb sound well). Check the area you plan to fix the appliance to


can support its weight, remembering that twin-fan ODUs are substantially heavier than single-fan models. If you’re not trained to assess this yourself, a structural survey - typically around £100 - is a good investment. Manufacturer-approved brackets and wall supports are essential, too, for both safety and warranty compliance. Viessmann, for example, provides purpose-made brackets for its larger units - one reason its ASHPs are often our first choice,


Left: Viessmann partner and renewables specialist Tom Sullivan of Active Heating & Renewables lifts the lid on what’s involved in aerial ASHP installations


alongside their high build quality and superior weather compensation features. Some heat pump brands actually prohibit roof mounting altogether under their warranty terms or allow it only on concrete structures. Customers can choose to proceed at their own risk, but that should be confirmed in writing before work starts.


System design


When it comes to heat pumps, shorter pipe runs generally lead to better system efficiency. This will therefore affect decisions about the best place to site the ODU. Additionally, it shouldn’t be positioned too close to windows or skylights, especially if it uses R290 refrigerant. Minimum clearance rules also apply. These typically specify at least one metre from the roof edge, though some models require more. Likewise, avoid siting units in narrow gaps where wind-tunnel effects could disrupt airflow. Where possible, fitting an ODU on a wall


overhanging a flat roof is ideal. As well as satisfying warranty requirements, it reduces the fall distance if brackets were ever to fail and can make for easier servicing access. Engineers will need to reach the unit safely and conveniently on an ongoing basis without the need for scaffolding.


Budget and admin Aerial installations usually carry additional costs for labour and lifting of equipment. If a crane is required, that will add around £500 (including the driver) and may necessitate a road closure. If so, a Temporary Traffic Order (TTO) will be needed, potentially adding further time and expense to the project. Safety is, of course, paramount during high-


level installations. Typically, at least two people are needed to manoeuvre an appliance into position, or three for heavier models. Most insurance policies cover work up to 10 metres above ground, but it’s vital to verify this. Ensure all staff are trained and certified for working at height and that crane or lift operators hold the correct qualifications. Once the unit is properly secured, the


installation process is essentially the same as at ground level and everything should function normally. Planning permission is seldom needed unless the property is listed or located within a conservation area. Standard limits for boundary distances and noise levels still apply, though these restrictions are being relaxed nationally.


Urban opportunity


With initiatives such as the London Plan driving low-carbon heating in urban developments, installers that can help customers fit ASHPs in properties with little or no outdoor space are at an advantage. Aerial installations aren’t right for every customer, but when space at ground level is tight, they’re always worth considering.


Above: Ensure the structure you plan to fix the unit to is strong enough to sup- port its weight.


32 December 2025


Above: Once the appliance is properly secured, the installation process is es- sentially the same as at ground level and everything should function normally.


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