The Boiler Upgrade Scheme just had its biggest shake-up since it started. From 28 April 2026, homeowners no longer need an Energy Performance Certificate (EPC) to apply for the £7,500 grant towards an air-to-water heat pump, the type that runs through existing radiators. The scheme has also been extended out to 2030. For thousands of owners of period homes, many still fitted with the cast iron radiators their houses were built with, a heat pump has gone from “worth a look” to “actually on the table” almost overnight.
There’s a catch, though. It has nothing to do with paperwork.
Heat pumps run much cooler than a gas boiler. The water sits at 35°C to 55°C, against 60°C to 75°C for most old systems. Drop the water heat and every radiator in the house has less to give out, unless something makes up for it. In a new-build with double glazing and thick walls, the sums often still work. In an old, solid-walled home with high ceilings and single-glazed sashes, they usually don’t. Not without bigger radiators.
This is normally where the conversation turns to ripping the old ones out. It’s also where it gets more interesting than most homeowners expect.
Old iron, new rules
Cast iron has a genuine trait working in its favour here and it’s down to plain physics, not nostalgia. A cast iron radiator has a large surface and a heavy metal body. It stores heat in the iron itself, not just in the water flowing through it. So, once warm, it keeps giving off heat for a long time. A modern steel panel typically cools much faster once the heat source stops.
Paladin Radiators points to this as one reason cast iron still has a place in a heat pump home. Its radiators are hand built, finished and tested at its Lincolnshire factory. The casting itself happens at a separate, dedicated foundry that casts for Paladin alone.
Fitting a heat pump to an old home still needs a proper heat loss check for each room. A qualified fitter works out how much heat each room needs, based on its walls, its windows, its size and how draughty it is. Whatever radiator ends up on the wall, whether that’s cast iron or something more modern, it has to be sized against that figure rather than guessed at.
The homes the scheme wasn’t built for
The EPC rule was the detail that used to shut a lot of homes out. Listed buildings and homes in conservation areas are often let off some EPC advice. That meant many owners of exactly the homes best suited to cast iron radiators, older homes with real character, sometimes couldn’t get the paperwork the old scheme asked for. Taking that rule away opens the scheme to a part of the market it has always struggled to reach.
The timing matters too. Interest in cast iron was already on the rise before any of this. Homeowners are moving away from hiding their radiators and starting to treat them as a feature, picked for colour and shape as much as for heat. Paladin, a Registered Supplier to the National Trust, matches colours against the Farrow and Ball and Little Greene ranges as well as its own metal finishes. The finish now matters as much as the output.
What this means if you’re weighing it up
If you’re weighing up a heat pump quote or wondering if your old radiators would survive the switch, the real questions haven’t changed. What’s the heat loss in each room? What heat will the pump actually run at? Does the radiator have enough surface to cope? A good fitter should be asking these anyway, whatever the EPC does or doesn’t say.
What has changed is who gets to ask them. More period homes can now apply for the grant without the EPC hurdle that used to stop applications before they began. Whether cast iron or a modern radiator ends up being the right call for any one house still comes down to that room-by-room sizing, not to which material sounds more traditional.
Paladin’s cast iron radiators are available directly from the manufacturer, along with a free heat calculator to help size a room correctly.
