Technical Bulletin 162: Reduction in gas rate (heat input) test duration for metric gas meters

Technical Bulletin 162 is intended to give guidance on reducing the recognised test duration of gas rating an appliance on a metric gas meter from two minutes to one minute.

Developed with Large Business Forum (LBF)
Date issued: 26 September 2023

This Technical Bulletin advises on the rationale behind a change to the two-minute gas rate (heat input) check for domestic installations with metric (ultrasonic and diaphragm) gas meters. It should be noted that a large number of imperial gas meters are still in service and that the gas rate method for this type of meter will remain unchanged, and that one complete revolution of the dial is required.

The two-minute gas rate was introduced in 1995 and has become the industry-recognised procedure for carrying out a gas rate. However, it can be difficult to accurately carry out a two-minute test with larger appliances installed with a smaller heat load requirement. As such, a trial was set up to test a one-minute test duration.

Several trials by British Gas and Gas Safe Register were carried out using a one-minute test-time duration. The trials proved that the reduction in time did not negatively affect the accuracy of the test and, in many cases, gave a heat input to nearer that given by the manufacturer.

Although the initial aim of the trial was to make gas rating less frustrating for installers, it highlighted that considerable savings of gas and water consumption per annum could also be achieved.

For gas, there would be savings in usage and wasted energy, with a reduction in CO2 emissions also achieved. For water (eg, combi boiler hot taps running during check), there would be savings in water usage and a reduction in water/drainage charges for the gas user.

Adopting the one-minute check
Because the check is shorter, the calculation must be altered. Only the changes made to the previous calculation are highlighted below:

  1. Ensure all other appliances are turned off
  2. Set the appliance up for a gas rate (heat input) check as detailed in the manufacturer’s instructions
  3. Note the initial meter reading
  4. Operate the appliance for one minute1
  5. After one minute take the final meter reading
  6. Subtract the initial meter reading from the final meter reading. This is the amount of gas used, and will be half of what you are currently used to recording.

1 Add any additional seconds that it takes for the display to change after one minute and include these in your calculation.

While a one-minute test duration is shown to have many benefits, this is not a requirement. If you wish to continue using the two-minute test duration (such as using an application on a mobile device), then this is your prerogative. The intention of this Technical Bulletin is to show that a reduction in test duration to one minute is both beneficial and accurate, and so would now be an acceptable test procedure.