For refrigerant leakage, is a nameplate and leak-rate estimate or top-up records more accurate?
The Intergovernmental Panel on Climate Change (IPCC) says emission-factor methods, which multiply a charge by a leak rate, carry more uncertainty than mass-balance methods built on gas sales. Its reasons are the small unit size of most equipment and the multiplication of a small unit error.
What the IPCC says
The Guidelines say Tier 2 methods that rely on emission factors "have more uncertainty than mass balance methods that use chemical sales data". The reason given is "the small unit size of most equipment and the potential for the multiplication of a small unit error". The same passage says the ranges highlight the uncertainty in this sector. It calls the table "Table 7.8", but the ranges of charge, lifetime and emission factors are in Table 7.9. This compares national estimates with national sales data. Treating a site's service tickets as the same thing is our reading.
Where each method goes wrong
- Nameplate and rate: the ranges are wide. Air conditioning runs 1% to 10%, a tenfold spread, and chillers 2% to 15%.
- Top-up records: they lag behind leaks on units not yet serviced, and miss gas that was reused or bought on an invoice you did not file.
Which to use
- If every service ticket shows kilograms charged, use records. They avoid the leak-rate range altogether.
- If records are partial, use the estimate and say so.
- Check one against the other, as in the bought-against-need check.
- Keep the method the same each year; the Guidelines ask for the same method and data sources across the time series.
100 kilograms of R-410A in split air conditioners
- Estimate at 1% to 10%: 1 to 10 kilograms, a tenfold spread
- R-410A value from Sixth Assessment Report (AR6) component values: 0.5 x 771 + 0.5 x 3,740 = 2,255.5
- Range in carbon dioxide equivalent (CO2e): 1 x 2,255.5 = 2,255.5 kilograms to 10 x 2,255.5 = 22,555 kilograms
- Service tickets add to 6.5 kilograms: 6.5 x 2,255.5 = 14,660.75 kilograms, one figure inside that range
The bank and the 6.5 kilograms are examples. R-410A is 50% R-32 and 50% R-125 by mass.
What Senseible does here
Senseible reads fuel invoices and electricity bills into dated records. It does not read recovery notes, service tickets or equipment nameplates, so keep those papers yourself and add the kilograms to your Scope 1 figure.
Sources: IPCC 2006 Guidelines, Volume 3, Chapter 7: Emissions of Fluorinated Substitutes for Ozone Depleting Substances, IPCC Sixth Assessment Report, Working Group I, Chapter 7 Supplementary Material, Table 7.SM.7
Last reviewed 2026-11-05. Uncertainty ranking is the IPCC's national view. Applying it to one site is our reading.