How to work out the F-Gas leak check interval

Published 9 September 2026, last reviewed 4 October 2026. Written by the Maintivo team at Boroto Ltd, who build the F-Gas forms with a working HVAC firm. This guide reflects the F-gas rules in Great Britain (the retained EU Regulation 517/2014) as generally applied. Always confirm against the current regulation text and GOV.UK F-gas guidance; the registered engineer remains responsible for the check and the record.

Why is the interval based on CO₂e and not kilograms?

A charge in kilograms tells you nothing on its own, because different refrigerants warm the atmosphere by very different amounts. The regulation therefore measures a system by its carbon dioxide equivalent: the charge weight multiplied by the gas's Global Warming Potential. Ten kilograms of R32 and ten kilograms of R410A are the same weight but land in different bands, which is exactly why doing the sum by hand is where mistakes creep in.

How do I calculate tonnes of CO₂e?

The formula is simple: charge in kg, multiplied by the refrigerant's GWP, divided by 1,000. The GWP figures used by the regulation for the common gases are R32 at 675, R134a at 1,430, R407C at 1,774, R410A at 2,088 and R404A at 3,922. So a 10 kg charge of R410A is 10 x 2,088 = 20,880 kg CO₂e, which is 20.88 tonnes CO₂e.

What are the leak check intervals?

Once you have the tonnes of CO₂e, the interval follows from the band the system falls into. Below 5 tonnes there is no mandatory leak check. From 5 tonnes the system must be checked at least every 12 months. From 50 tonnes it is at least every 6 months. From 500 tonnes it is at least every 3 months, and a fixed leak detection system is also required. Where a leak detection system is fitted, each interval doubles: 24, 12 and 6 months respectively. Hermetically sealed equipment that is labelled as such has a higher exemption threshold of 10 tonnes rather than 5.

Three worked examples

A small split system holding 3 kg of R32: 3 x 675 = 2,025 kg, or 2.03 tonnes CO₂e. That is under 5 tonnes, so no mandatory leak check applies.

A VRF system holding 10 kg of R410A: 10 x 2,088 = 20,880 kg, or 20.88 tonnes CO₂e. That is in the 5 to 50 tonne band, so a leak check is due at least every 12 months, or every 24 months with a fixed leak detection system.

A chiller holding 40 kg of R134a: 40 x 1,430 = 57,200 kg, or 57.2 tonnes CO₂e. That is in the 50 to 500 tonne band, so a leak check is due at least every 6 months, or every 12 months with a fixed leak detection system.

What goes wrong when it is done by hand?

The dangerous mistake is not a wrong answer on the day. It is a system quietly put in the wrong band, checked at the wrong interval for a whole year, with nobody noticing until an audit. That usually comes from grabbing the wrong GWP, mixing up kilograms and tonnes, or forgetting that the interval halves when the charge crosses a threshold.

Can an app do the sum on the form?

Yes, and that is what Maintivo's F-Gas app is built for. On the Split AC / VRF leak check and Chiller service forms you pick the refrigerant and type in the charge. The app applies that gas's GWP, converts the charge to tonnes of CO₂e, tells you which leak check band the system is in and writes the next check due date against the unit in your asset register. The owner then gets an iPhone notification 90 days out, 30 days out and again if it goes overdue (optional, switched on in Settings); on the web, what is due shows on the dashboard. The refrigerant designation and charge weight print on the record exactly as entered. The app uses the Great Britain F-gas bands; Northern Ireland and EU rules are not built in. You sign the record and remain the competent person; Maintivo produces and keeps it.

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