Ofgem are the organisation managing the domestic RHI. Heat meters will have to be installed on the domestic RHI registered installed equipment; if a fossil fuel boiler is to be used as back up, or as an option available under the Domestic RHI where a heat meter is installed to record energy used for monitoring for the RHI; with this option an additional fee to the tariff will be paid.
Heat meter installations have to be registered with Ofgem, which is complex. Artizan offer a service to help with this stage of application, see RHI Registration Services.
Heat meters are generally placed on the return pipe with a sensor inserted in the primary flow and return. They record the liquid flow volume and the temperature differential between the flow and return pipes, calculating energy usage and displaying in KWh or MWh.
More information is available on the Itron CF PDF.