How many kW heat pump do I need? Rules of thumb per home, the calculation from your gas consumption and why too big is also wrong

Short answer: the heat pump output you need depends on your heat loss: a hybrid heat pump for an average Dutch home needs 4 to 6 kW, an all-electric heat pump 6 to 10 kW. The quickest estimate comes from your annual gas consumption: subtract 300 m³ for hot water, multiply the rest by 8.8 and divide by 2,000. At 1,500 m³ a year that gives roughly 5.3 kW. That is the output you need on the coldest day; with all-electric the heat pump must deliver it at -10 °C, with a hybrid the boiler tops up and the heat pump can be smaller. An oversized heat pump cycles on and off and wears out, an undersized one runs on the electric element all winter. That is why you should always have a heat loss calculation made for all-electric.

Step 1: the calculation from your gas consumption

Your gas consumption is the most honest measure of your home's heat demand, because insulation, draughts, heating habits and floor area are already built into it. The calculation goes like this:

1. Take the annual consumption in m³ from your annual energy bill and subtract 300 m³ for showering and cooking (400 for a large family).
2. Multiply by 8.8: one cubic metre of gas delivers 9.77 kWh and a condensing boiler turns about 90 per cent of that into heat.
3. Divide by 2,000: the number of full-load hours a heating system runs per year in the Netherlands (in colder climates the figure is higher).

Gas consumption per year	Space heating demand	Required output (indicative)	Hybrid	All-electric
900 m³	5,300 kWh	2.6 kW	4 kW	4 to 5 kW
1,200 m³	7,900 kWh	4.0 kW	4 kW	5 to 6 kW
1,500 m³	10,600 kWh	5.3 kW	4 to 5 kW	6 to 7 kW
2,000 m³	15,000 kWh	7.5 kW	5 to 6 kW	8 to 10 kW
2,500 m³	19,400 kWh	9.7 kW	6 to 8 kW	10 to 12 kW

Why the all-electric column comes out higher than the calculation: a heat pump's rated output applies at 7 °C outside and 35 °C flow temperature (A7/W35). At -7 to -10 °C the same machine delivers 25 to 40 per cent less, and even less with radiators at 45 or 50 °C flow. So check the output at A-7/W45 or A-10/W35 in the datasheet, not the number in the product name.

Step 2: rules of thumb per type of home

If you do not have an annual bill, for example in a new home, the type of home and its energy label give a useful first estimate of the heat loss per square metre.

Home	Label	Heat loss	Example 120 m²	Suitable model
Flat or mid-terrace house built after 2000	A or B	40 to 50 W/m²	5 to 6 kW	Elga Ace 4 kW (hybrid) or Intergas Xtend Eco 5 kW (all-electric)
Tussenwoning 1975 tot 2000, dubbel glas, dakisolatie	C	55 to 70 W/m²	7 to 8 kW	Hybride 4 tot 5 kW; all-electric 6 tot 8 kW
End-of-terrace or semi-detached house, partly insulated	C or D	70 to 90 W/m²	8 to 11 kW	Hybrid 5 to 6 kW; all-electric 8 kW or more
Detached or pre-war, moderately insulated	D to G	90 to 130 W/m²	11 to 16 kW	Hybride 6 tot 8 kW; all-electric pas na isoleren

Above 12 kW of heat loss, all-electric is rarely sensible in an existing home: the heat pump becomes expensive, loud and large, and electricity consumption rises. Insulating first and then recalculating pays off more than a bigger machine.

Step 3: hybrid or all-electric determines the size

With a hybrid heat pump, the heat pump covers the base load and the boiler takes over the peaks and the hot water. You choose the output so that the heat pump keeps the house warm on its own down to an outdoor temperature of roughly 0 to 3 °C (the bivalent point). A 4 or 5 kW unit then already replaces 60 to 80 per cent of your gas. Choosing a bigger one gives little extra saving, because the remaining cold hours are only a small part of the year.

With all-electric there is no boiler to top up. The heat pump must deliver the full heat loss at the design temperature of -10 °C, plus the hot water via a cylinder. Here a room-by-room heat loss calculation (EN 12831 or your national equivalent) is not a luxury but a necessity: it also shows whether your radiators are big enough for a flow temperature of 35 to 45 °C. More on this in Does a heat pump work with ordinary radiators?.

Why too big is also wrong

A heat pump modulates, but not without limit: an 8 kW unit usually does not go below 2.5 to 3 kW. In spring and autumn, when your house only needs 1.5 kW, such a unit keeps switching on and off. This cycling costs efficiency, makes noise and shortens the life of the compressor. An undersized heat pump has the opposite problem: on cold days the electric element (the "backup heater") kicks in, and that uses three times as much electricity as the compressor. The right size is therefore close to the calculated heat loss, with a margin of 10 to 20 per cent, not 50.

A buffer tank helps against cycling: it gives the heat pump a volume of water so it can run longer. In a home with many thermostatic radiator valves or a small heat emitter system, we recommend a 50-litre buffer tank; discuss this with your installer when choosing your · .

The models in our shop by output

Power	Hybrid	All-electric
4 kW	Remeha Elga Ace 4 kW € 3.069	Intergas Xtend Eco 5 kW all-electric € 3.989 (from 5 kW)
5 kW	Intergas Xtend 5 kW split € 3,609; Xtend Eco monoblock 5 kW R290 € 3,989	Xtend Eco monoblock as all-electric in small, well-insulated homes
6 kW	Remeha Elga Ace 6 kW € 3,799; Itho Daalderop Amber 6.5 kW hybrid € 4,780	Intergas Xtend Eco 7 kW all-electric € 4,464
7 to 8 kW	Remeha Elga Ace 8 kW € 4,274; Xtend Eco 7 kW R290 € 4,464	Intergas Xtend Eco 7 kW all-electric € 4,464

Prices are shop prices including VAT, excluding installation and before any subsidy (September 2026). All models are in the · ; Instalpunt does not install, so have a qualified local installer fit and commission the unit. See also our installation service.

Frequently asked questions

What heat pump output do I need at 1,500 m³ of gas a year?

According to the calculation (1,500 − 300) × 8.8 ÷ 2,000, that is roughly 5.3 kW of heat demand on the coldest day. A hybrid heat pump of 4 to 5 kW is then enough; all-electric needs 6 to 7 kW, because the output at -7 to -10 °C is lower than the number in the product name.

Can I use the output of my boiler as a guide?

No. A 24 or 28 kW boiler is sized for hot water (the CW class), not for heat loss. Most homes need only 5 to 10 kW on the coldest day.

What is the difference between thermal and electrical output?

The thermal output is the heat the heat pump delivers; the electrical output is what it draws from the socket. With a COP of 4, 1 kW of electricity delivers 4 kW of heat. The kW in the product name is always thermal.

Do I need a 3-phase connection?

Up to 8 kW thermal, a single-phase connection with a dedicated 16 A circuit is usually enough. Above 10 kW, or combined with an EV charger and induction hob, 3-phase is often sensible; your grid operator can upgrade the connection.

What if my calculation falls between two sizes?

For a hybrid choose the smaller one, for all-electric the larger one, and have the installer confirm it with a heat loss calculation. With all-electric the hot water demand also counts: a family with a bath needs a larger cylinder and more output to heat it up in time.