Underfloor heating vs radiators: when each one actually wins

Underfloor heating vs radiators isn’t really a fair fight once you bring a heat pump into it. Underfloor wins, and it isn’t close. That’s the honest answer to whether underfloor heating is worth it: yes, if you’re already taking the floors up. But that answer only holds for a new build or a full renovation. Retrofit into a house you’re living in, and radiators win far more often than anyone selling underfloor heating will tell you.

The reason underfloor heating and a heat pump get on so well comes down to one number: flow temperature. A heat pump wants to push water round the system at 35-45°C, not the 70°C a gas boiler is happy with. Underfloor heating, because it’s spreading warmth across an entire floor rather than through a handful of hot metal panels, can heat a room comfortably at those low temperatures. Ask a radiator to do the same job at 40°C and you need one roughly three times the size of the one already on the wall to shift the same heat. That’s the whole case for underfloor, and it’s a good one.

Where it falls apart is retrofit. I did a heat pump install in a 1930s semi in Sittingbourne last spring, downstairs was solid concrete, and the customer had seen underfloor on a renovation programme and wanted it throughout. Once I’d costed lifting the floors, insulating properly underneath, screeding, then relaying whatever was going back on top, it came to more than the heat pump itself, before I’d heated a single room. I’ve seen quotes for underfloor retrofit into an existing slab run £4,000 to £6,000 for a modest ground floor. New radiators, sized correctly for a lower flow temperature, is a day’s work and a few hundred pounds a room.

The bit nobody selling underfloor mentions is that most existing radiators don’t need replacing at all. A heat-loss survey usually finds them oversized for the room already, because whoever installed the boiler-era system erred generous. Run those same radiators at a lower flow temperature, with the pump speed turned down, and they’ll heat the room just as well, more gently, over a longer stretch, which is exactly how a heat pump wants to run anyway. I’ve fitted heat pumps in Tunbridge Wells cottages where not one radiator changed size, just the settings.

So the honest version of underfloor heating vs radiators is this. Taking the floors up regardless, building an extension, building new: put underfloor heating in and don’t think twice, it’s the better system and it runs cheaper for the life of the house. Retrofitting a heat pump into a house you already love the floors of: radiators sized properly for a low flow temperature get you nearly all the efficiency for a fraction of the disruption. The showrooms sell the dream because underfloor is the bigger job with the bigger bill. My job is telling you when that bill buys you something, and when it just buys the fitter a better year.