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Commercial RHI Heat Metering

Keeping a close eye on the amount of hot water that’s running through your biomass heating system is a great way to predict your quarterly payments. OFGEM itself uses heat metering to calculate how much you’re owed.

Our customers in the Wye Valley receive RHI approved heat meters as standard with any biomass boiler installation.

Biomass Boiler Heat Meter

Heat meters must not be tampered with to affect the readings and must comprise:

  • A flow sensor which determines the volume of fluid which has passed through a pipe within a certain amount of time. 
  • A matched pair of temperature sensors (such as two thermocouples) which have been calibrated together to make sure the temperature difference between the input and output of the system is measured to the stated accuracy level
  • A calculator/digital integrator (although in some systems a Building Management System may replace the integrator) which uses information provided by the flow meter and the matched pair of temperature sensors to calculate the heat energy that is being transferred.

As part of the accreditation process OFGEM will also ask for (for each heat meter):

  • Manufacturer, model and serial number or, if the components of the meter have been purchased separately, the serial number of the flow meter component
  • A brief product description
  • Meter reading and the date taken
  • Applicant's confirmation that all meters were installed in line with the manufacturer's instructions and calibrated prior to use.

Complex Metering

Please read the guidance documents in full for more information on important updates to complex metering e.g. for district heating schemes:

  • Additional information for systems with more than three RHI-relevant meters
  • Meter placement for both simple and complex installations
  • Meter placement for complex installations where the heat transfer medium is a liquid (i.e. not steam)
  • Metering heat where there are multiple buildings (district heating schemes). An important change relates to heat lost in transportation between buildings which is not an eligible purpose, so will not be included in any claim for payment. The simplest way to achieve this is to meter each building individually.
  • Location of meters on boilers with heat recirculation
  • Shared meters, installations in series, metering by difference, installation of meters

Independent Report on Metering Arrangements

Where an installation is classed as complex for RHI metering purposes, OFGEM will require an independent report by a competent person. A competent person may be someone who:

  • is an experienced and suitably qualified engineer
  • has experience and expertise in flow measurement and heat/steam measurement systems demonstrated by training and development records
  • has a relevant background in energy, utilities, building services, heating system design, heating system operation & maintenance
  • is covered by Professional Indemnity Insurance of at least £1m
  • is unbiased and impartial

They must visit the installation and sign a declaration to confirm that they meet the competency criteria and that the information provided in the report is accurate to the best of his or her knowledge. A competent person is unlikely to be regarded as unbiased and impartial if:

  • they are an employee of the owner or heat user
  • they are related to the owner or heat user
  • they are contractually obliged to author reports exclusively for a given owner
  • the submission of the report could have a material impact on a significant portion of his or her income.

Heat meters, or individual components used for RHI purposes, must comply with Class 2 accuracy requirements as set out in Annex I to the 2004 Measuring Instruments Directive (MID) (2004/22/EC), Annex MI-004 of the MID, and within accuracy Class 2 as defined in Annex MI-00470.

OFGEM will also accept other methods of demonstrating compliance with Class 2 requirements, please see the full guidance for more information.