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Air Source Heat Pumps and Underfloor Heating in Scotland: How They Work Together: what it means for a Scottish home, from the engineers who fit them.
Sean Hogan · Heat Geek engineer · Updated June 2026 · 7 min read
Underfloor heating and an air source heat pump are a natural pair. Underfloor heating is, in fact, close to the perfect way to deliver heat from a heat pump. If you are planning a heat pump for a Scottish home, or you are building or renovating and weighing up your heating, this is one of the most useful pairings to understand, because it has a direct effect on your running costs.
A quick definition before we go further. The underfloor heating discussed here is wet underfloor heating, where warm water runs through pipes laid in the floor. That is different from electric underfloor heating, which uses a heated mat and is not run by a heat pump at all. In Scottish homes, wet underfloor heating most often appears in extensions, ground-floor renovations and new builds, rather than across an entire existing stone property. This guide is about air source heat pumps, the type Aventus installs in homes across Scotland .
Yes. A heat pump heats water and circulates it around your home, and underfloor heating is simply one way to release that heat into a room. Radiators are another. So underfloor heating is not a requirement. Plenty of Scottish homes run very well on correctly sized radiators alone, and a heat pump does not care whether the heat leaves through a floor or a radiator.
Where it does matter is efficiency. When underfloor heating is already in place, or you are installing it as part of a renovation or new build, it is usually the most efficient option you can give a heat pump. Ground source heat pumps work on the same low-temperature principle, but everything below is written for air source, which is what most Scottish homeowners are fitting.
It comes down to one number: flow temperature. That is how hot the water is when it leaves the heat pump and heads for your floor or radiators. A gas boiler is happy pushing water out at 60 to 70 degrees. A heat pump is the opposite. It works hardest, and least efficiently, the hotter you ask it to run, and it is at its best when the water leaves much cooler, often around 35 degrees.
Underfloor heating is what makes that low temperature work in practice. Instead of a single hot panel on a wall, the entire floor becomes a gentle, warm surface. That huge area means the water does not need to be hot to keep the room comfortable. Lower flow temperature, more heat per unit of electricity, lower bills. A well-designed underfloor system on a heat pump can reach around 450% efficiency, which means roughly four and a half units of heat for every unit of electricity it draws.
That efficiency holds up through a Scottish winter, which is the question most people really want answered. A heat pump sized and designed properly keeps performing when the temperature drops, and the low flow temperature underfloor heating allows is a big part of why. There is more detail on cold-weather performance in our guide to how well heat pumps perform in Scottish winters.
“We initially had Sean over to provide a quote, and as we didn’t know much about heat pumps, he explained everything clearly and in a way we could easily understand. He emphasized the importance of proper heat loss calculations for our property, which helped us determine which existing radiators we could keep.”
Marie Penrice, ★★★★★ Google Review
The plumbing is simpler than the diagrams make it look. The heat pump sits outside and heats water to a low temperature. That warm water travels indoors to a manifold, which is the control hub of the system. The manifold splits the flow into separate loops of pipe, and each loop snakes back and forth through the floor of a room or zone before returning, now cooler, to the heat pump to be warmed again.
Alongside the heating, the same heat pump heats a hot water cylinder for your taps and showers, so one unit handles both jobs. Many systems also include a small buffer or volumiser, a tank that gives the heat pump enough water to run smoothly without short, stop-start cycles. Controls finish the picture. Each room or zone can be set to its own temperature, and weather compensation nudges the system warmer or cooler automatically as the outdoor temperature changes, so you are not constantly adjusting it by hand.
The same low-temperature water that warms your floor also feeds your hot water cylinder.
When Gavin built his home in Bathgate, he wanted one fully renewable system for both floors, with low running costs and no fossil fuels. After a room-by-room heat loss calculation, the design used a 7kW Vaillant aroTHERM plus air source heat pump running at a 35 degree flow temperature, full underfloor heating across both floors, and a 250 litre Vaillant cylinder, all tucked into a compact plant cupboard under the eaves. The system was designed for around 450% efficiency and went on to be Highly Commended at the 2025 Scottish Energy Efficiency Awards.
You do not have to choose one or the other. One of the most common setups in Scottish homes is underfloor heating on the ground floor, where new floors are often going in anyway, and radiators upstairs, where lifting existing floors would be far more disruptive. A single heat pump runs both.
It manages this by handling two flow temperatures at once. A blending valve or mixing manifold drops the temperature for the underfloor circuits, while the radiators upstairs run a little warmer. The catch worth knowing is that those radiators still need to be sized to perform at a low flow temperature. Drop a heat pump onto small, old radiators meant for a 70 degree boiler and the whole system has to run hotter, which pulls efficiency down across the entire house, underfloor included. Getting that right is its own piece of design work, covered in our guide to sizing radiators for a heat pump.
Putting new underfloor heating into a home that does not already have it is a bigger job than most people expect, and it is worth being clear-eyed about that. There are two broad routes. Low-profile overlay systems sit on top of your existing floor and add roughly 15 to 25mm of height. Full systems are set into a new screed or dug into a solid concrete floor, which is more disruptive and more expensive.
The overlay route is the usual choice for retrofits, but raising the floor has knock-on effects. Doors may need trimming, skirtings and thresholds may need adjusting, and the transition to other rooms has to be managed. None of this is a dealbreaker, and on a ground floor that is being renovated anyway it often makes complete sense. Upstairs, or in an occupied period property where you do not want to lift every floor, correctly sized radiators are frequently the more practical and cost-effective call. Older Scottish stock has its own quirks, and our guide to heat pumps in older Scottish homes goes into them in more depth.
“Sean/Aventus Eco were outstanding in helping me explore and decide that this was right solution. Additionally it involved full house re-plumb because of problems with the old system, This was handled sensitively and professionally by all the members of the team with Sean setting very high expectations for everyone.”
Robert Henderson, ★★★★★ Google Review
Because an underfloor system on a heat pump runs at a low temperature, the surface you put on top of it matters more than it would over a hot gas-fed system. The floor finish either lets that gentle heat through or holds it back.
Hard finishes are the best performers. Tile, stone and polished concrete conduct heat readily and let the room warm as designed. Engineered wood and LVT work well too, within sensible limits. The one to watch is carpet. A thick carpet over a high-tog underlay behaves like a blanket laid over your heating, trapping warmth before it reaches the room and forcing the system to run hotter to compensate. A useful rule of thumb is to keep the combined tog rating of carpet and underlay around 2.5 or below. The practical takeaway is simple: tell your installer exactly what flooring you are using in each room, so the heat loss calculation and the system design account for it from the start.
What a heat pump with underfloor heating costs depends heavily on how much underfloor heating is new. Using floors that are already being laid in a renovation is one thing. Retrofitting an overlay system across a whole ground floor, or digging into solid floors, adds materially to the bill. The heat pump itself is a separate piece, and its price tracks the size and complexity of the system rather than the flooring.
On sizing, the single most important point is that the heat pump is specified from a room-by-room heat loss calculation for your actual property, not from floor area or a rule of thumb. In a very well-insulated home the size can even be driven more by hot water demand than by space heating, which is exactly why the calculation matters. A unit that is too big short-cycles and wastes money; one that is too small struggles on the coldest days.
On grants, the Home Energy Scotland scheme currently offers up to £7,500 towards an air source heat pump, rising to around £9,000 with the rural uplift for eligible properties, with an optional interest-free loan on top. That support applies to the heat pump, not to underfloor heating itself. For the full breakdown of pricing, see our guide to what an air source heat pump costs in Scotland.
“What really stood out was the additional guidance Sean provided about how we could improve our home’s insulation and reduce drafts. He explained how making these simple DIY improvements would help lower the heat loss in our home, ultimately reducing our energy bills in the long run.”
Tony McCole, ★★★★★ Google Review
If there is one thing to take away, it is that this pairing rewards good design. Underfloor heating gives a heat pump the low flow temperature it wants, the result is a warm, even home on lower running costs, and the Bathgate project shows what that looks like when it is done to an award standard. The figures that decide whether underfloor heating, radiators or a mix is right for you all come from your own property, not from an article.
That is what an engineer-led survey is for. Aventus is an MCS-certified, Heat Geek Mastery trained installer working across central Scotland, and a survey gives you a heat loss figure, a system design and a clear answer on grants.
Yes, and it is one of the best combinations there is. Underfloor heating runs at the low flow temperature a heat pump prefers. A heat pump can power underfloor heating on its own or alongside radiators.
No. A heat pump works perfectly well with correctly sized radiators, and many Scottish homes run on radiators alone. Underfloor heating is optional, and where it is present it usually improves efficiency.
Usually around 35 degrees, occasionally a little higher depending on the floor build-up and the property’s heat loss. That low temperature is what keeps the heat pump efficient.
Yes. A single heat pump can serve both, using zoning and a blending valve to give each the right temperature. The radiators do need to be sized for a low flow temperature, or the system loses efficiency.
The size comes from a room-by-room heat loss calculation for your home, not from floor area. In a very efficient property, hot water demand can influence the size as much as the heating does.
It can, but a thick carpet with a high-tog underlay reduces the heat that reaches the room. Keep the combined tog low, around 2.5 or under, and tell your installer the finish so the design allows for it. Tile, stone and engineered wood perform best.
Yes. The same heat pump heats a hot water cylinder for your taps and showers as well as running the heating. The cylinder stores that hot water ready for use.
Some reversible heat pumps can circulate cooler water through the floor loops in summer. In Scotland this is rarely specified, since the priority for almost every home is heating rather than cooling.
It depends on how much underfloor heating is new versus existing, and on your specific property. The Home Energy Scotland grant currently offers up to £7,500 towards the heat pump, which brings the net cost down. Our Scotland cost guide breaks the numbers down in full.
We’ll assess your home, explain your options, and leave you to decide.
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