Homeowners Professionals
Homes
Residential
Air and geothermal
Solar

Rooftop ASHP with microbore tubing more than a pipe dream!

When Richard Smith’s combi boiler began to fail at his modern three-bedroom semi-detatched home near St Albans, he knew he wanted a more efficient and environmentally friendly system to replace it. Despite limited outside space and narrow pipework throughout the property, his dream of owning a heat pump was successfully realised with a roof installation.

Rooftop ASHP with microbore tubing more than a pipe dream!

A greener solution

Built in 2018, Richard Smith’s home in Bricket Wood, Hertfordshire, is a compact (108 m2), flat-roofed, two-storey, brick building in a contemporary Dutch style. However, despite being fitted with a modern gas combi-boiler and solar panels, it wasn’t as energy efficient as it could be. 

“The boiler had been there from the start and wasn’t much good,” explains Richard.  “When it started to malfunction, I saw no point in replacing it. I’d always been thinking about a heat pump but wasn’t too sure how to go about it. So, I did my research.”

He soon discovered that the size of the pipework throughout his property might present a problem for the flow rate of the potential new system. “To get the best efficiency out of a heat pump, you want the pipes to be as big as possible. That’s why you hear about them making pipes 22 mm wide. The pipes in most UK homes are 15 mm, but the ones in my property were 10 mm or even smaller.  

Pipes under 15 mm in diameter are termed ‘microbore’. Changing them is a big job which would then require much of the house to be redecorated – an expensive disruption that Richard was keen to avoid.

He set about looking into the topic more deeply, finding lots of helpful information on the Heat Geek website, among other places. By the time he reached out to heat pump experts Tom Sullivan of Active Heating & Renewables and Andrew Millward of Home Comfort Assured, he had already carried out his own heat loss calculation using a free estimator tool from heat-engineer.com.

Existing infrastructure

Richard was delighted to discover that, with full insulation, it would be possible to install an air source heat pump and achieve an efficiency level several times that of a gas boiler, even with his home’s narrow pipes. “This is why I think my project is good for others to hear about when they’re doing their research,” he enthuses. “It proves heat pumps can work in modern houses with microbore tubing. So much so, in fact, that we only needed to change one radiator! And that was in a room that has always felt cold because it has two patio doors, and the previous radiator was too small.”

Tom and Andrew advised Richard to opt for a 4kW Viessmann Vitocal 151-A air source heat pump with weather compensation and integrated 190-litre DHW cylinder. Optimised for power consumption from photovoltaic systems, it offers both heating and cooling and is exceptionally quiet and highly efficient in operation. 

Vicare 4kW Viessmann Vitocal 151-A air source heat pump

Lack of space

The next issue to look at was where to site the heat pump itself. The compact indoor unit fitted snugly inside the property’s small boiler cupboard. But, with only a very limited external footprint to play with, the location of the outdoor unit was less clear cut. Says Richard, “As this is a modern development, there is no space at all, really. The roof is the only place to put things.”

Tom concurs: “The roof was definitely the most sensible place. We’ve done heat pump roof installations before, so we knew how straightforward the process could be, with the right crane driver. We used London Transport and Lifting Ltd. There was no need to close the road for the crane, as there was plenty of space for cars to go around it.”

Richard organised scaffolding to provide access to the roof, and the installation of the outdoor unit took around an hour in total. 

“It’s a flat, new roof, with solar panels there already,” continues Tom. “So, we knew the structure would be sound. For anyone thinking of doing similar with a heat pump installation, if they’re unsure if their roof is capable of supporting the unit, they can get a structural survey to check.”

Comfort and economy

Richard was keen to add an OpenEnergyMonitor device to the system to share data about its performance online and help to dismantle some widely held myths about where heat pumps do and don’t work. Since going live in April 2024, the Coefficient of Performance (CoP) of the new heat pump has averaged 3.5, with a flow temperature of 45-50oC. 

Richard switches the hot water on once or twice a day during off-peak periods. He uses the Octopus Cosy tariff for heat pumps. However, he is also making use of his scaffolding to add further solar panels – ten in total – as well as a battery to store generated power, to his roof. This means the heat pump will operate at virtually no cost at all. The cost of all these upgrades has been offset by a £7,500 grant from the Boiler Upgrade Scheme.

“Installations like this one showcase that heat pumps can go anywhere,” observes Tom.  “There’s so much more flexibility than most people realise. I can definitely see installations like these becoming more common.” 

Equipment

Related References

Vitosol 300-TM solar thermal system case study
Residential

Vitosol 300-TM solar thermal system case study

The designed system to provide 52% of the property’s hot water from the solar thermal, with the ASHP backing up the remaining 48%.

Read more
West Linton Home Air Source Heat pump outside
Residential

Saving on fuel costs with an air source heat pump that fits a cupboard.

Renewables expert Chris Collins of Optama proposed an air source heat pump, using the government’s renewable heat incentive (RHI) and an interest free loan from Home Energy Scotland to cover the costs.

Read more
Georgian House
Residential

Heat pump system for Georgian House

Discover how Viessmann installation partner, Heat Different, was called to provide a ground source heat pump solution within a two-month timeframe.

Read more
Thomas Telford School
Residential

Updated heating system improves efficiency at top performing school

Three 500 kW floor standing Vitocrossal 200 CM2 boilers were installed in the third storey plant room to provide heat for the large site.

Read more
Boutique Hotel Bar in Cork Ireland
Businesses
Commercial
Air and geothermal

Boutique hotel in listed Victorian factory building

The owners of a boutique hotel in a Grade 1 listed Victorian factory building in the centre of Cork, Ireland, wanted to improve its heating and cooling systems and reduce its carbon footprint.

Read more
2020 National Heat Pump Awards
Residential
Air and geothermal

2020 National Heat Pump Awards

Domestic Air Source Heat Pump Project of the year 2020, Sheffield Passivehaus

Read more