Free calculator

Would a heat pump actually save you money?

Enter what your boiler burns today and what you would replace it with. Get the seasonal COP, the new running cost, the CO2 cut and the payback - for a full swap or for a hybrid that keeps the boiler.

Heatuneed

Would a heat pump actually save you money?

Prepared

The answer depends on three numbers, not on the brochure

A heat pump replaces one bought kWh with roughly a third of a kWh of electricity, but electricity costs two to four times what gas costs. Whether that trade works out depends on the seasonal COP you can actually reach, the price ratio you pay, and how much the installation costs after grants. This tool works all three out from your own figures.

Only the currency the figures are shown in changes. The prices stay exactly as you typed them, so set them to what you actually pay.

Start from a typical case

What you heat today

Take it from a full year of bills, or from two meter readings twelve months apart.
m²
Used to size the emitter upgrade, and to estimate demand if you do not know your consumption.
Hot water is counted at 750 kWh of heat per person per year, on top of space heating, unless you select No hot water.

The boiler you have now

Heat delivered per unit of energy on your bill, averaged over the year - not the nameplate figure. A condensing boiler on oversized radiators rarely beats 0.85.
$ / kWh
All in, including taxes and delivery.
$
The fixed part of the gas or fuel bill. You stop paying it if you drop the connection, so it counts as a saving on a full swap but not on a hybrid.

The heat pump

This is the single biggest lever on the seasonal COP. Every 10 degrees you take off the flow temperature is worth roughly 20 percent more heat per kWh.

Prices and investment

$ / kWh
The rate the heat pump will run on, taxes included.
$
Everything you get back: national schemes, tax credits, local top-ups.
$
Heat pump, cylinder, labour and the emitter upgrade. Suggested from the size and the emitters until you type your own.

Your inputs

Your result

Updated live as you change the inputs.

Strong case - swap it

The running cost falls far enough that the installation pays for itself well inside the equipment's life.

Saved per year —
Payback after grants —
Seasonal COP, heating —
Heat pump size needed —
Cost after grants —
CO2 avoided per year —
Net over 20 years —
Heat demand per year —
Electricity used per year —
Break-even electricity price —
Fuel you stop buying —

Yearly running cost

Boiler today —
Heat pump —
Running cost cut by —

What the flow temperature is worth

Same house, same heat pump; only the emitters change. The installed cost follows the emitter upgrade, so the payback stays comparable.

Emitters SCOP Running cost Saved / year Payback

With the boiler gone the standing charge disappears too, and it is counted in the saving. Below the design temperature an electric backup heater tops the system up.

Estimates from a bin model of your climate, a Carnot-fraction COP that follows the weather-compensated flow temperature, and seasonal efficiencies on the same energy basis as your bill. Real results move with installation quality, control settings, tariff structure and how the house is actually run.

Calculated with the free tool at heatuneed.com/heat-pump-savings-calculator/

How the calculation works

The tool rebuilds your heat demand, walks a whole year of outdoor temperatures one degree at a time, and prices both systems against the same demand.

1

Your heat demand

Fuel bought times its energy content times the seasonal efficiency gives the heat the boiler actually delivered. Hot water is separated out at 750 kWh per person per year; what remains is space heating. Describing the home instead uses floor area times a demand per square metre.

2

A COP for every outdoor temperature

Space heating is spread across a normal distribution of outdoor temperature in one-degree bins. In each bin the weather compensation curve sets the flow temperature, and the COP is a fixed fraction of the Carnot limit for that lift. Air source units also carry a defrost penalty between -7 and 5 C, where frost forms fastest.

3

Splitting the load with the boiler

A hybrid runs the heat pump at full output down to the changeover temperature and lets the boiler cover the shortfall below it. Because demand below that point is rare, a unit sized for 0 C typically still covers most of the year's heat.

4

Money, carbon and payback

Each system is priced on its own fuel and its own standing charge, then compared. Payback is the cost after grants divided by the yearly saving, and the break-even electricity price tells you how much headroom the answer has.

Common questions

Usually yes, but at a flow temperature around 55 C, which costs you roughly a third of the seasonal COP compared with underfloor heating. Radiators sized for a 70 C boiler give out about half their rated output at 55 C, so it works in houses whose radiators were generously sized to begin with. Enlarging the two or three worst rooms is normally far cheaper than replacing the whole system, and the calculator lets you price that as the low-temperature option.

It depends on what you are optimising. A hybrid sized for 0 C still covers most of the year's heat, costs much less to install, and needs no radiator work, so its payback is often the shortest of any option here. What it does not do is get rid of the fuel connection, so you keep paying the standing charge and you keep a boiler to service. Switch between the two in the calculator and compare the payback line.

Because the price ratio beat the COP. If electricity costs four times what gas costs and the seasonal COP is 3, every kWh of heat gets more expensive, not cheaper. The break-even electricity price tile tells you exactly where the crossover sits. Lowering the flow temperature is the lever with the most room in it, and a cheaper off-peak tariff is the other.

Field studies of real installations mostly land between 2.5 and 3.2 for air source on radiators and between 3.4 and 4.2 on underfloor heating, with ground source around a point higher. The figures here sit in that range because the COP is derived from the Carnot limit and then cut to a realistic fraction of it, rather than taken from a datasheet tested at 7 C.

Insulation lowers the demand and lets you run the same radiators at a lower flow temperature, which raises the COP - so it improves both terms at once. It also shrinks the heat pump you need to buy. Run the calculator at your current insulation level and then one level better to see how much of the case it moves.

Hot water needs around 50 C all year, so its COP is lower than heating and it does not benefit from a low-temperature emitter circuit. The calculator treats it separately and lets you leave it on the boiler in a hybrid, which is often the pragmatic answer for a large family in a cold region.

Want the room-by-room version of this?

Heatuneed scans each room with LiDAR and works out its heat loss through walls, windows, doors and roofs - which is what tells you whether your radiators can run at 45 C.

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