Castrads have published a comparison between the carbon footprint of new cast iron radiators and new steel radiators.
 
'We calculated the carbon footprint per watt of heat output for all of the Castrads cast iron radiators. We did the same using data from a popular brand of steel panel radiators. The average results for each range of products are:
Castrads radiators: 0.15kg of carbon per watt of heat output
Steel panel radiators: 0.06kg of carbon per watt of heat output
So, on average, cast iron radiators have a carbon footprint that is a bit more than double that of a steel panel radiator.'
 
Taking the long term view, says Castrads, many cast iron radiators last 100 years and can be repaired by replacing just the damaged section while a typical steel panel radiator lasts 25 years and often needs to be completely replaced when it breaks. So cast iron radiators are the winner over modern steel panel radiators due to their long life spans.
 
It should come as no surprise that investing in good quality products, that last, makes environmental sense states Castrads.