Paul: A Highgate Heat Pump Retrofit That Kept The Radiators

North London, Highgate. Tile Kiln Lane, named for the kiln that fired the roof tiles when this thousand-year-old village was being absorbed into Victorian London.

Paul Domjan's house sits on the footprint of a nineteenth century waterboard cottage built for the keeper of the reservoir that grew Highgate. When the cottage was rebuilt, the original brick was disassembled, stored, and laid again in the new walls. A modern building inside, a Victorian artefact on the outside.

“Although this looks like a modern house built on a blank slate, it actually is designed to sit exactly in the footprint of a nineteenth century waterboard cottage. The brick is the exact same brick that was used to build the waterboard cottage. We disassembled the nineteenth century building, stored all of the brick, redesigned in exactly the same footprint, and then rebuilt this modern building with the nineteenth century brick that was here previously.”

That's the setting for a heat pump retrofit story that mattered more than most.

The Inherited Stack

When the Domjans moved in, they walked into two different legacies. On one hand, a heavily insulated modern fabric with the appearance of a Victorian cottage. On the other, a 2008/09-vintage set of environmental technologies that were state of the art at the time, paired, somehow, with a forty-year-old Potterton Gold gas boiler salvaged from the original house.

The legacy environmental stack was a museum of late-noughties optimism. A heat recovery system pulling fresh air through an intake in the car park, distributing it underground around the house. Solar thermal panels, very efficient at heating water but very hard to maintain. Rainwater recovery that, in honest terms, didn't really work. And underneath all of it, the Potterton Gold, probably one of the oldest gas boilers still working in a recently sold house in the UK.

“You had this tremendous contrast between on the one hand a really antiquated heating system and on the other hand this really well insulated fabric of the building. And you had these beautiful but not necessarily terribly efficient columnar radiators. And that was it. We're in a huge space. It's heated by two small columnar radiators.”

This is the house most retrofit conversations begin with. Good bones, good insulation, an honest aesthetic the owners care about, and a heating system that's two decades past its retirement date.

The Brief

Paul has spent his career in energy. Oil and gas first, then the energy transition. When you've spent thirty years thinking about energy security, affordability, and climate as one connected problem, the heating system in your own house becomes a statement of values, not just a piece of plant.

The brief he set himself was difficult, because it was honest.

“In simple terms, in this house, we wanted a heat pump. We needed more radiators. We didn't want to lose space. We didn't want to change the fundamental appearance of the building. And we also wanted to do it in a way that let us continue to live here while the works were being done and do it cost effectively.”

That's a brief most heat pump installers would walk away from. The conventional answer to the radiator output question is either bigger radiators, uglier and eating more wall space, or underfloor heating, lifting floors and adding weeks of disruption. Neither was on the table here.

Why The Heat Pump Conversation Usually Stalls

There's a moment in every heat pump conversation that's worth pausing on. It usually arrives when the surveyor walks into the room and looks at the existing radiators.

“Lots of heat pump conversations run aground when the surveyor comes along and sees something like that. If they see a radiator like that, what that essentially says to the surveyor is the homeowner has some design preferences. They've not gone for bog standard, off the shelf B and Q radiators. They've got some design preferences. They're now going to have to negotiate with that customer to remove that radiator and put something in that's bigger and probably uglier. So the conversations around the whole heat pump then get pulled into question.”

That sentence captures, more honestly than most heat pump marketing, why UK heat pump retrofits stall as often as they do. The problem isn't technology, cost, or policy. The problem is the moment a homeowner is asked to accept an uglier room in exchange for a better heating system. Almost every homeowner says no, and the conversation ends there.

For Paul, the conversation didn't have to end there, because the kitchen-and-living-room space upstairs had a specific compositional problem. Half the room was a kitchen with no skirting boards, which meant a full ThermaSkirt retrofit wasn't viable. The other half had two beautiful column radiators that were nowhere near enough output for a heat pump at low flow temperature.

What he needed was a way to keep the radiators, leave the kitchen alone, lift no floors, and still get the surface area a heat pump demands.

Add2Rad

Add2Rad is exactly that. A composite system that adds heated skirting to an existing radiator's flow and return, increasing output along the perimeter of the room without replacing or relocating the radiator itself.

The principle is straightforward. The existing radiator stays where it is, doing what it always did. The skirting taps into the same flow and return circuit and runs the heat the rest of the way along the wall. At 40°C flow, a metre of skirting delivers around 80W. Four metres of skirting added in series with an existing radiator adds roughly 320W of low-temperature output to a radiator that was already there. A 3.8m run on the next wall adds another section in series. Across the room, that's around 650W of extra output.

That figure is small enough to sound trivial and large enough to change everything. It's the difference between a room that struggles at heat pump flow temperatures and a room that quietly hits its target without anyone noticing. The same approach was applied to one of the rooms on the floor above. Two rooms, two simple skirting additions, no radiators changed, no floors lifted.

“We've obviously been anti-radiator for a long time, twenty years. What we did earlier this year was step back from the problem and think, what actually is preventing the customer from installing the heat pump? And that is the disruption and the mess. Completely ripping out your radiators and putting ThermaSkirt in does involve some disruption mess, not as much as underfloor heating. But if you think that adding that onto that radiator is actually all that is required to make the difference, then all of a sudden the whole thing becomes quite practical and straightforward.”

That's a meaningful pivot. ThermaSkirt has spent twenty years arguing that radiators are the wrong emitter for low-temperature heat. Add2Rad doesn't contradict that argument. It accepts that for most homeowners, the existing radiators are not a problem to be solved but a constraint to be worked around.

The Pipework Reality

The detail that makes Add2Rad work in retrofit is that the skirting taps off the existing radiator pipework rather than requiring new primary distribution. The flow and return that feed the radiator at the valve continue under the skirting, then back round to the radiator. The room gets two emitters working together, fed by one circuit, with no new lifted floors, no new chasing into walls, and no new pipe drops.

For the upstairs living room and the matching room on the floor above, that single design move made the whole retrofit possible. The radiators stayed. The kitchen stayed. The artwork on the walls stayed. The heat pump got the surface area it needed to run at a sensible flow temperature, which is the single number that determines whether the system pays back its capital cost.

The Install Week

DiscreteHeat referred Paul to Gasworks, a registered installer experienced with Add2Rad. The survey, design, and install ran on a programme most homeowners would recognise as how things ought to work but rarely do.

“The process of installation was fabulous. The Gasworks team put the whole thing together, tight project plan, arrived on Monday and by Friday afternoon we had a new heating system up and running. We chose the positioning of the Add2Rad to match the existing pipework. We didn't need to cross thresholds. We didn't need to lift any flooring. Everything could be done incredibly quickly.”

Monday to Friday. One week of works. No decant. No disruption to the family routine. No structural impact on a building designed to look exactly like the nineteenth century cottage it replaced.

Living With It

The post-install experience is the bit Paul keeps coming back to, and it's the bit most heat pump owners will recognise once they've lived with the right system for a winter.

“Number one, it's much more comfortable. Even if it wasn't good for the environment it would still be much more comfortable. But I think the other thing, and maybe this resonates with other people who come from an environmental background, is there's always an element of being torn between do I want to spend more money and burn more gas to be warmer? And do I want to do what's right for both my budget and the climate and run the house at a slightly lower temperature? With this type of installation, that's not a question. We can have a really comfortable, really healthy, really pleasant home and know that that's also the optimal outcome for us, both financially and from a climate perspective.”

That's the quiet psychological dividend of getting the heat pump retrofit right. The trade-off between comfort and conscience disappears, because the system is genuinely cheaper to run at the temperature you actually want the house to be.

The Wider Pattern

The UK has a heat pump problem that isn't really about heat pumps. It's about emitters. The fabric of most British houses is good enough, with reasonable insulation, to run at heat pump flow temperatures. The legacy radiators are not. And the conventional answer to that, either supersize the radiators or rip the floor up for underfloor heating, fails almost every homeowner's brief.

“Most people are not building a house from scratch. They're not building a heating system from the ground up to support electrified heat. They're taking an existing home with an existing legacy gas boiler like we had and wanting to move it to something much more comfortable, much more environmentally friendly, and do so really cost effectively. And that just isn't an option with the existing suite of technologies. I think this fills an incredibly important niche and is going to be the backbone of a lot of retrofits if we're going to be able to roll out heat pumps at the rate we need to.”

That's the case for Add2Rad in one paragraph. Not a replacement for ThermaSkirt. Not a replacement for radiators. A composite emitter strategy that meets people where they actually are, in houses they already love, and gives them a heat pump retrofit that doesn't ask them to fall out of love with the room.

Paul's house was rebuilt to look exactly like the cottage it replaced. The heat pump retrofit was specified to keep it that way. The bricks are nineteenth century. The fabric is twenty-first. And the heating is now ready for the next hundred years.