Heat pump or gas/oil boiler: which to choose?

The day the boiler gives out, the question always arises: should you replace it like for like or switch to a heat pump? Burning gas or oil remains a reassuring reflex, but the maths have changed. Between the cost of energy, the tightening of Belgian regulation and grants now reserved for renewables, the heat pump increasingly stands out as the long-term choice. This guide helps you decide with full knowledge of the facts.

Two opposing heating logics

A boiler produces heat by burning a fuel — gas or oil — for which you pay every kilowatt-hour at the market price. A heat pump, on the other hand, burns nothing: it moves heat already present in the air, the water or the ground, and only uses electricity to drive that transfer. That is the whole difference.

In concrete terms, for 1 kWh of electricity consumed, a heat pump returns 3 to 4 kWh of heat into your home. That ratio is the COP (coefficient of performance). A boiler, even a condensing one, will never exceed 1: it cannot return more energy than it burns.

Running cost: the decisive argument

It is on the annual bill that the gap widens. An oil or gas boiler depends on a fuel whose price is volatile and trending upwards, carbon taxes included. The heat pump consumes electricity, but in a quantity three to four times smaller than the heat produced.

The result: even allowing for an electricity price higher than gas per kilowatt-hour, the heating cost of a properly insulated house drops sharply with a heat pump. And the gap widens further if you pair the heat pump with photovoltaic panels, which feed part of its consumption at almost no cost.

Install cost: the heat pump is more expensive to buy

Let’s be honest: at installation, a heat pump costs more than a boiler. The equipment is more sophisticated, and the works may involve adapting the emitters (radiators, underfloor heating). It is the main psychological barrier to switching to a heat pump.

But two factors quickly rebalance the scales. First the grants: in Wallonia, Brussels and Flanders, replacing a boiler with a heat pump is strongly supported, whereas fossil boilers no longer receive anything. Then the annual running saving, which pays back the extra cost in a few years. Over the life of the installation, the heat pump is almost always the winner.

Environmental impact and the Belgian framework

Beyond the wallet, the choice is also regulatory. Belgium is gradually tightening the screws on fossil heating energies. In renovation as in new build, installing a new oil boiler is increasingly ruled out, and financial support is now steered towards renewable solutions.

The logic is clear: you no longer subsidise an energy you are trying to phase out. A heat pump emits no combustion gas on site and becomes all the more virtuous as the electricity mix decarbonises. Replacing an old oil boiler with a heat pump therefore means anticipating the regulation while reducing your footprint.

Comfort and conditions: what to check

A heat pump does not heat quite like a boiler. It spreads a softer, continuous heat, at a low supply temperature, which is very comfortable — but assumes a home suited to it. Three points are worth a look before deciding.

The home’s insulation

This is criterion number one. A heat pump is all the more efficient when the heating needs are low: a well-insulated house makes full use of its COP. In an energy-sieve home, it is better to insulate first, or turn to a high-temperature heat pump, even a hybrid solution.

The heat emitters

Underfloor heating is the heat pump’s ideal ally, because it works at a low temperature. Large radiators also suit it very well. Small old radiators, designed for very hot water, may on the other hand need to be replaced or supplemented.

The type of heat pump

Air-to-air, air-to-water, ground-to-water: not all are equal depending on your existing installation and your needs. Correct sizing is essential to guarantee comfort without over-consuming.

The hybrid: the smart compromise

Hesitating because your home is not yet perfectly insulated? The hybrid heat pump is made for this case. It pairs a heat pump, which covers most of the year’s needs, with a small backup boiler that only kicks in during the deep cold, when the output of the heat pump alone would drop.

It is an excellent gateway to renewables: you immediately enjoy the heat pump’s savings without major works on the emitters, and you keep a safety margin for the winter peaks. Ideal for a renovation carried out in stages.

Three scenarios to decide

When to replace your boiler with a heat pump

There is no point scrapping a recent, high-performance boiler. But as soon as it nears the end of its life (15 to 20 years) or suffers a major breakdown, the question must be asked seriously. Reinvesting in a fossil energy means committing for fifteen years to a fuel that is getting dearer, getting taxed and losing its grants.

The most obvious case remains oil: replacing an old oil boiler with a heat pump combines the biggest running saving, the most generous grant and compliance with a framework that is tightening. If you are in this situation, the maths almost always lean towards the heat pump. A heat pump advisor takes stock with you, quote in hand, before any commitment.

Our recommendation

In the long run, the heat pump wins in the vast majority of cases: its unbeatable running cost, grants reserved for renewables and regulation that pushes to abandon fossil energy draw a clear trajectory. The fossil boiler only makes sense in the very short term, the time of a quick repair. And if your insulation is not yet up to scratch, the hybrid offers a gentle transition without giving up the savings.

The 30-second recap

Guide checked in May 2026 · updated every year