Information for solar thermal installers

Solar thermal for heating domestic hot water never has to be metered. If that’s all your customer has installed, you don’t need to read this page.

Metering performance

As an installer you need to know when a system must be  and/or when a system must be ; how these types of metering work; and what metering documents you need to complete and give to your customer for their application.

Where systems need to be metered for payment

Below we’ve highlighted some common situations which require metering for payment, but for further details read our Essential Guide to Metering.

Where there’s back-up heating

This applies where:

  • The renewable heating system is installed alongside a fossil fuel space heating system. For example, where there’s a biomass boiler and a back-up oil boiler.
  • The renewable technology is a heat pump with an integrated fossil fuel system, like a gas boiler, built into it.
  • There’s more than one renewable heating technology for space heating, for example, where there are two biomass boilers. See  for more information. (Remember that it is fine to have a solar thermal plant installed alongside your other technology, as long as it’s only heating domestic hot water).

Back-up heating that doesn’t count

The system doesn’t need metering if the back-up heating is only designed and installed to heat a single room, such as an open fire or plug-in electric heater. Similarly, immersion heaters and supplementary electric heaters, that some heat pumps and biomass systems have, don’t count. Heat recovery systems that recycle air but don’t generate additional heat also don’t need to be metered.

Where there’s a biomass heating system that isn’t designed to heat the whole property

Biomass systems must meet all of the space heating requirements for the property. If this is not the case then the system will need to be metered.

Where the property is occupied for less than half the year

Homes that have been lived in for less than half the year must be metered. This includes second homes or tenanted properties, which have been empty for 183 days in the 12 months prior to applying to the scheme.

The applicant needs to declare on the application form if their home is occupied for less than 183 days a year. If your occupancy drops below 183 days in any 12 months after your accreditation, you may also require metering for payment. This rule doesn’t apply if the applicant is applying as a .

Where systems need to be metered for performance

This section only applies if your customer has a heat pump. If they don’t have a heat pump then go to the metering for payment section to see if their renewable energy plant needs to be metered for payment.

From 22 May 2018 it’s a requirement that all new applications for air source and ground source heat pumps must have electricity metering arrangements alongside their heating systems to be eligible for the Domestic Renewable Heat Incentive (RHI).

There are three metering arrangement options available for metering for performance, which can be used alone or in combination:

The meter(s) will be required to record and display:

  • electricity used by the plant to generate heat;
  • electrical input into any supplementary electric heater controlled by the same control system as the heat pump; and
  • electrical input into any immersion heater for a domestic hot water cylinder where the immersion heater is controlled by the same control system as the heat pump.

This will need to be added to the customer’s MCS Certificate. For full details and examples, please read our Essential Guide to Metering.

If there are multiple supplementary or immersion heaters controlled by the same control system as the heat pump, a single meter can be installed to record the total combined electrical input; or, each heater can be metered separately. Metering input to each heater separately could help monitor the efficiency of the heat pump and identify if there is an issue with an individual immersion heater/supplementary heaters. 

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