Calculator
How much CO₂ does each option actually emit?
A boiling water tap is often marketed as the greener choice. The honest answer depends on your kettle habits and the carbon intensity of your electricity. We model both, with current UK grid data.
Your habits
UK average household: 8-12 cups per day, 250 ml each.
Real-world UK average: 1.5x. Most kettle households boil 50% more than they drink.
Most taps 10 W. Zip HydroTap with sparkling 35 W.
UK 2026 average ~180 g/kWh. Was 250 g/kWh in 2020. Falls as wind and solar grow.
Your carbon footprint comparison
Kettle is greener by
6.8kg CO₂/yr
At your usage and idle draw, the kettle is the lower-carbon choice. The tap's 24/7 idle electricity outweighs the kettle's overfill waste.
Kettle (with overfill)
22.4 kg
CO₂ per year
Boiling tap
29.2 kg
CO₂ per year
CO₂ falls each year as the UK grid decarbonises. By 2030 the grid is projected at 80-120 g/kWh, which makes both options greener but does not change the relative winner.
How we calculate it
Grid carbon intensity defaults to 180 g CO₂/kWh, the UK 2026 average from National Grid ESO. It was 250 g in 2020 and is projected at 80-120 g by 2030. Set your own value if your supplier publishes a different figure.
Kettle CO₂ = exact litres × overfill factor × 0.102 kWh/L ÷ 0.9 efficiency × grid intensity. The overfill factor is the dominant variable.
Boiling tap CO₂ = exact litres × 0.102 kWh/L × grid intensity + 24/7 idle wattage × 8760 hours ÷ 1000 × grid intensity. The idle draw is the dominant variable.
Petrol-car equivalent uses 120 g CO₂/km, the UK new petrol car average 2026 per DfT data.
Embodied carbon (manufacturing emissions for the tap or kettle) is not included. A boiling tap has higher embodied carbon (~200 kg CO₂) than a kettle (~10 kg), which adds 8-10 years of break-even.