Short answer
The U-number on a gas meter is its badged maximum flow in cubic metres per hour of natural gas — a U16 passes up to about 16 m³/h, roughly 170 kW. If the connected load exceeds the meter's capacity, appliances will be starved of gas at full load.
Rough capacities
U6 ≈ 6 m³/h (about 60 kW), U16 ≈ 16 m³/h (about 170 kW), U25 ≈ 25 m³/h, U40 ≈ 40 m³/h, U65 ≈ 65 m³/h, U100 ≈ 100 m³/h, U160 ≈ 160 m³/h. Larger loads use rotary or turbine meters (G-rated).
Upgrading
A meter upgrade is arranged with the gas supplier and transporter. A commercial engineer calculates the new load, and alters or tests the outlet pipework once the new meter is fitted.
Meter volume in testing
Meter internal volume is added into installation volume for tightness testing and purging — see our calculators.
Figures are typical for UK natural gas. The current edition of the relevant IGEM standard and the manufacturer's instructions always take precedence on site.
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