Heat Pump Compatible Cast Iron Radiators

Top picks for heat pump compatible cast iron radiators

For heat pump installations, deeper column models give the highest output per section at Delta T 30. Less wall length needed for the same BTU target.

Neo Georgian 6 Column: The deepest column option in the range. Highest surface area per section. The best-performing model per section at heat pump temperatures. Available in 505mm, 660mm or 960mm heights with 3 to 40 sections (even longer sizes available on request). For heat pump systems where wall space is limited but BTU demand is high, this is the most efficient cast iron option.

Neo Georgian 4 Column: Verified output of approximately 200 watts and 682 BTU per section at Delta T 50. Delta T 30 output available on request. Available in 360mm, 505mm, 660mm, 760mm or 960mm heights with 3 to 40 sections (even longer sizes available on request). The most flexible heat pump compatible column radiator in terms of height options.

Victoriana 4 Column: Four-column depth for solid output at lower temperatures. Freestanding on four cast iron feet. Available in 460mm, 660mm, 760mm or 813mm heights with 3 to 40 sections (even longer sizes available on request). The best heat pump compatible cast iron radiator for period homes where appearance is as important as output.

Saint Paul: At 800mm tall, one of the largest standard models in the range. High section surface area. Well-suited to heat pump installations in large rooms where a single substantial radiator is preferable to multiple smaller ones. Available with 3 to 40 sections (even longer sizes available on request).

Are cast iron radiators compatible with heat pumps?

Yes. Cast iron radiators are fully compatible with modern heating systems including combi boilers, system boilers and heat pumps. They use standard half-inch BSP connections and work with any modern valve. Heat pump compatibility is confirmed across every Paladin model.

The consideration isn't whether cast iron radiators work with heat pumps. It's how you size them. Heat pumps run at lower flow temperatures than traditional gas boilers (typically 35 to 55°C for standard air source heat pumps, and up to 65 to 75°C for high-temperature heat pumps using R-290 refrigerant). Lower flow temperatures mean lower BTU output per section. You compensate by specifying more sections.

Cast iron's thermal mass works in your favour here. It absorbs and holds heat effectively even at lower temperatures, and continues radiating warmth after the heat pump cycles off. A correctly sized cast iron radiator on a heat pump keeps the room warm between cycles rather than requiring the heat pump to run continuously to maintain temperature.

Delta T: why sizing cast iron radiators for heat pumps is different

Delta T is the temperature difference between the average water temperature in your radiator and the ambient room temperature. A gas boiler running at 75°C flow and 65°C return gives a Delta T of 50. A standard air source heat pump running at 50°C flow and 40°C return gives a Delta T of approximately 25 to 30.

At Delta T 30, each section of a cast iron radiator produces substantially less heat than at Delta T 50. The Neo Georgian 4 Column produces approximately 200 watts and 682 BTU per section at Delta T 50. At Delta T 30, that output is significantly reduced. To hit the same room BTU target, you need more sections.

Paladin provides BTU output figures at both Delta T 50 and Delta T 30 for every model in the range. Heat pump cast iron radiators are sized using the Delta T 30 figures. Call us with your heat loss calculation and heat pump flow temperature and we'll specify the exact section count.

High-temperature heat pumps and cast iron radiators

High-temperature heat pumps using R-290 refrigerant-grade propane can deliver flow temperatures of 65 to 75°C. At these temperatures, cast iron radiators perform at or close to their Delta T 50 rated output. High-temperature heat pump compatible cast iron radiators don't require upsizing compared to a gas boiler installation: the same section count gives comparable output.

High-temperature heat pumps are fully eligible for the Government's Boiler Upgrade Scheme grant. If you're specifying cast iron radiators for a new heat pump installation, it's worth discussing the flow temperature your heat pump will operate at with your installer before we size the radiators.

How to size cast iron radiators for a heat pump

Sizing cast iron radiators for a heat pump system follows the same principle as conventional sizing but uses different BTU figures per section.

1. Get a heat loss calculation. Room dimensions, insulation levels, glazing type and external wall construction all affect the BTU requirement. Our radiator configurator gives an estimate. A qualified MCS-accredited installer should provide a full heat loss calculation for a heat pump installation.
2. Use Delta T 30 BTU figures. Paladin provides BTU output at Delta T 30 for every model. Call us with your flow temperature and we'll give you the correct per-section output to work from.
3. Specify more sections. At Delta T 30, more sections are needed to hit the same room BTU target as at Delta T 50. This is normal for heat pump radiator sizing across all radiator types, not a cast iron-specific issue.
4. Discuss with your installer. We'd always recommend discussing your specific heat pump setup with a qualified heat pump installer before finalising radiator sizing.