Keep Above
Electric heater or heat pump
A plug-in heater and a heat pump can both warm a room, drawing very different power to do it. Enter each unit's rated input watts — the electricity it draws from the wall — how long a session runs, and your own price per kWh, and the page lands both on a cost per use, per week and per year. The purchase prices are not counted here, and no winner is declared.
On the rating plate or label
On the rating plate or label
Put in your price per kWh from your power bill, then each side's rated power and how long one use runs. Nothing here is read from your budgets, and nothing is saved.
| Option A | Option B | |
|---|---|---|
| Rated power | — | — |
| Energy one use takes | — | — |
| Cost of one use | — | — |
| Cost a week | — | — |
| Energy a year | — | — |
| Cost a month | — | — |
| Cost a year | — | — |
Why isn't comparing watts the same as comparing warmth?
A plug-in electric heater turns the electricity it draws into heat in the room, so its input and its output are the same quantity described twice. A heat pump works the other way about: it spends electricity moving heat that is already in the outside air into the room, so the warmth it delivers and the electricity it draws are not the same quantity at all. That is why this page compares electricity only — the one thing both units take from the same wall and the same bill.
How much heat a pump moves for a given amount of electricity is not fixed either, because it depends on how much heat there is in the outside air to move. The same unit, in the same room, doing the same job would draw differently on a mild evening and a freezing one, and one figure for the year cannot hold both. Both sides also stop drawing their full rating once the room is at temperature — one by cutting in and out, the other by easing off — so the hours entered above are hours of the unit being on, not hours of it drawing everything it can.
This is one of the tools built into Keep Above
Keep Above is a budgeting app where you enter your bills and income and it works out the balance you need to keep — so you can see what's safe to spend. No bank connection, no ads on your data.
Running costs never arrive as a bill with a date on it; they show up inside the balance — budgeting apps with no bank connection sets out what each one asks you to keep entering.
About this calculator
Which wattage counts for a heat pump?
The rated input power — the electricity the unit draws — not the heating output on the brochure, which is a different and larger number. This page compares electricity only: what each unit would take from the wall for the hours you run it. Whether the two would deliver the same warmth in your room is a question about the units and the room, not one this arithmetic can settle.
Does the outdoor temperature change these figures?
For a heat pump it changes what an hour of warmth costs, because how much heat it can move depends on how much is in the outside air to begin with. For a resistive heater the draw is the same whatever the weather; what the cold changes there is how many hours it runs. Either way it shows up on this page in the minutes and the uses a week, not in the rated-power field, which stays as the plate states it.
Does either unit draw its rated watts for the whole session?
Not for a whole session with a thermostat in it. A heater at its setting cuts the element in and out once the room is there; a heat pump more often eases its compressor down and holds a lower draw. The plate figure is what each would take flat out, so the columns here are the upper end of both rather than a meter reading.
Where is the input wattage written on a heat pump?
On the plate of the unit that does the drawing. On a split system that is the outdoor unit rather than the head on the wall, and its plate gives an input in watts or kilowatts beside a heating output, which is a different and larger figure. A plug-in heater carries its plate on the back or the base, near the cable, and its rating is the only figure it has. The price per kWh is taken from your own bill and nowhere else.
Why do both sides share one figure for uses a week?
Because a use here is an evening of heating a room, and the room wants heating the same number of evenings whichever unit does it. The count is about the weather and the household, not about the appliance, so it belongs to both sides at once. How long one of those evenings runs can differ, and that has its own field on each side.