Community Heating System Metering

Hello. In Germany, we had a central boiler for the individual flats, and each radiator had a calorific meter attached so they could charge appropriately for the heating energy used. A quick google search "calorific meters uk" brings up a fair amount, but I'm not an expert!

Thanks Guy, I understand all the principles of it but would like to speak to someone who understands how the billing is converted from the gas supply bill to the heat interface units that measure in the individual apartments - it should be simple but it doesn't appear to be.