Heat Pump Water Heater Payback & CO₂ Calculator
Would one actually save you money and carbon? Against an immersion heater the answer is always yes. Against gas it depends entirely on how clean your grid is — and this tool uses your country’s real figure rather than assuming.
What heats your water now?
This choice changes the answer more than anything else
A modern condensing boiler on hot water duty rarely beats 85%
%
Advanced / Custom Input — the old system
Essentially 100% at the element, minus tank standing losses.
%
Per kWh of gas burned, before boiler losses.
kgCO₂/kWh
How much hot water do you use?
Sets a typical daily volume
L/day
Advanced / Custom Input — the water
Colder mains means more energy for the same litres.
°C
Usually 55 to 60 °C, high enough for legionella control.
°C
Heat the tank loses just sitting there. Added to the load.
%
days
The heat pump, and where it would go
A heat pump takes heat from the air around it — so this matters
Filled in from the location — use the manufacturer’s seasonal figure
Advanced / Custom Input — the equipment
Not the full price — the difference against the system you would otherwise fit.
Taken straight off the extra cost.
years
Legionella cycles and cold snaps run on resistance, not the heat pump.
%
Your prices and your grid
Filled in from your country
/kWh
/kWh
Filled in from your country — this is what decides the carbon answer
kgCO₂/kWh
Advanced / Custom Input — the sums
Applied over the lifetime CO₂ figure. Most grids are getting cleaner.
%/yr
Used to express the CO₂ saving as kilometres not driven.
kgCO₂/km
Result
Tell it what you have now and how much hot water you use, then press “Work out the savings”.
Estimate only — verify with a qualified installer and your own tariff before relying on this for an investment decision. Grid carbon intensity is a national annual average and changes every year.