What are the best cast iron radiators for air source heat pumps?

Cast iron radiators are a good option for an air source heat pump, as long as you pick the right model and size it properly. Radiators with more columns per section, like our Neo Georgian 6 Column or Victoriana 4 Column, give you the most surface area to work with, so you can reach the output a heat pump needs without running out of wall space.

Browse our cast iron radiators range to compare heights and column counts before you choose.

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More columns are generally better when you’re sizing a cast iron radiator for a heat pump. Each extra column adds surface area, and surface area is what lets a radiator give off enough heat at the lower flow temperatures a heat pump produces. A 6 column radiator puts out more heat per section than a 2 column radiator of the same height. So you can often hit the number you need without the radiator running the length of a wall. That’s especially useful in bigger rooms, where a 2 or 3 column model might need an impractical length to compensate for.  

Cast iron radiators are slower to warm up than aluminium or low water content radiators, and that’s worth knowing upfront. Their thermal mass takes longer to heat through than aluminium’s. So if you’re used to a boiler firing up and a radiator going hot within minutes, cast iron feels different.

But heat pumps don’t work that way either. They run continuously at a low, steady output, rather than switching on and off. However, that means a radiator that warms up gradually and holds onto the heat for longer actually suits the job rather well. It’s a trade off that works in cast iron’s favour once the system settles into its rhythm.

Here’s how the three most common radiator materials compare on a heat pump:

Some Paladin models are better suited to heat pump systems than others. It mostly comes down to column count and the range of heights on offer:  

Sizing is where most heat pump installations go wrong, cast iron or otherwise. You need to know your room’s heat loss, not just its floor area. Because insulation, glazing and wall type all change how much heat a room actually needs. Each of our model pages has its own heat calculator, built around that specific radiator’s output, so you’re working with real numbers rather than a guess. Placement matters too, so check the clearance guidance for whichever model you choose, since it varies from one radiator to the next.

If you’re weighing up cast iron against other radiator types for your heat pump, our radiator configurator gives you a straight answer for your own room. And if you’d rather talk it through first, our team’s happy to help you land on the right model.