Can an ASHP Get You Cooling on the Dulwich Estate?
- Mick Haley
- 2 days ago
- 2 min read
ASHPs get sold on heating. Lower bills, no gas boiler, decarbonised heat. What gets missed is that most of them cool too, and with London summers only getting hotter, that's the bit worth paying attention to, especially on the Dulwich Estate.
It's just a reversal
An ASHP moves heat rather than making it. In winter it pulls heat from outside air into the house. Run it backwards and it does the opposite, pulling heat out and rejecting it outside. Most modern units are reversible by design, so cooling is often close to free once you've specified the heat pump anyway.
Radiators can't cool
Radiators are built for radiant heat and convection, not cooling. Run cold water through one and it just sweats, condensation on the floor and eventually the joists. Cooling needs a fan coil unit (FCU): a small unit that draws air across a cold coil, drains the condensate, and pushes cool air into the room. In heating mode the same unit pushes warm air instead, so it does both jobs and a radiator isn't needed alongside it.
Not a whole house job
Two ways to do it from the same ASHP:
● FCUs everywhere. No radiators at all. Consistent performance, more disruption, higher cost.
● A mixed system. Radiators stay where cooling isn't needed (bedrooms, hallways, utility spaces). FCUs go only in the rooms that overheat, south facing living rooms, glazed extensions, top floor bedrooms. Same ASHP, separate zones.
A mixed approach is often the most practical: retain radiators where they are effectively functioning, and install FCUs only in areas where cooling is essential. Additionally, it's likely that you won't need to upgrade the radiators in rooms with FCUs.
Working with the Estate, not around it
The Estate's guidelines are clear that air conditioning isn't a sustainable way to cool a building, and rightly ask that insulation and solar shading be considered first. That's good building practice on any project, Estate or not.
An ASHP fits comfortably within that thinking. It's specified as a heating system, eligible for Boiler Upgrade Scheme support, and cooling comes as a secondary benefit of the same equipment rather than the reason for installing it. Framed that way, alongside proper fabric improvements, it sits well with the Estate's sustainability aims rather than against them. It still needs the usual application if visible from the boundary, and needs to be sized and sited to minimise impact on neighbouring amenity, the same as any mechanical plant.
Worth knowing
● Chilled pipework needs proper insulation to avoid condensation on the runs themselves.
● Every FCU needs condensate drainage, gravity or a small pump.
● FCUs have a fan, so factor noise into bedroom placement.
● Radiators staying in a mixed system still need checking against the ASHP's lower flow temperature. FCU rooms don't need this check.
One more thing: move on it early
Every installer in London is booked solid the moment it gets hot, and this isn't a one-off summer. It's the pattern now. Specify cooling at the design stage rather than scrambling for an installer mid-heatwave with everyone else doing the same thing.