Why replace your gas boiler with a heat pump?

Following the extraordinary rise in gas prices over the year 2021, tariffs for this fossil fuel are beating their highs of around 10 years ago. Without the government's decision to "freeze" gas prices in November 2021, rates would have continued to rise. If prices don't come down in 2022, the government has promised to lower taxes to regulate them, so 2022 should remain "normally" stable, but what does the future hold?

As if Bitcoin were crashing, the rising price of gas is inducing panic among consumers and sparking interest in alternative solutions, including heat pumps. In this article we'll look at why you might want to replace a gas boiler with a heat pump, and whether it's feasible or cost-effective.

Reasons to change a gas boiler for a heat pump (electric)

As mentioned above, gas rates can be scary We're also looking at the impact of current price hikes, and the need to switch energy sources in anticipation of future price rises. The world's major emerging powers, with their billions of inhabitants, are increasingly using fossil fuels for heating. As demand rises, so do prices.

On the other hand, the price of gas depends in part on the price of oil, which, for similar reasons, is also subject to substantial increases, as you can see every day as you drive past your local gas station.

There's every reason to believe that the price of gas will continue to rise, as demand increases, extraction becomes ever more difficult, and energy is by nature fossil and finite.

A long-term vision of your finances, as well as a clear enthusiasm for renewable energy, are all reasons to turn to a heat pump for heating. The heat pump runs on electricity, which can be generated by wind, solar or nuclear power.

A willingness to consume nationally or regionally is also an argument in its favor. Today, whether in France, Belgium or Switzerland, most of the gas is imported from Norwaythe Russia, Algeria or the Netherlands.

Main sources of imported gasNorwayRussiaAlgeriaNetherlands (EU)Other

As can be seen, there is a strong dependence on foreign countries, European or not. With the precipitous closure of gas production in the Netherlands (shutdown of the Groningen power plant in 2022) this dependence will only increase.

But there's more to it than that, and several other reasons may lead you down the path of gas shut-off. You may have heard of a gas ban in France?

Indeed, the 2020 environmental regulations indicates that on January 1, 2022 the end of gas heating in new homes. In other words, it will no longer be possible for architects and other project managers to plan gas boilers in new homes! Of course, you can keep your gas boiler in your home as long as you like, and no one will come and dismantle it! However, this determines the willingness to shut off gas and sketches a future in renewable energy in which you may or may not want to enroll.

Which heat pump to choose to replace a gas boiler?

Let's briefly review the heat pump principle. It's a device that extracts calories from an external energy source (air, water or ground) and releases them to your home's heating medium (mainly water, sometimes air).

There are many different types of heat pump, but when it comes to replacing a gas boiler, there are two to choose from. The air-to-water heat pump, which pumps energy from the outside air, and the geothermal heat pump, which pumps heat from the garden soil. (If you live near a lake, the water-to-water heat pump is a third option, pumping calories from the water. It's generally very efficient).

How to choose between an Air-Water heat pump and a Geo heat pump?

Advantages and disadvantages of the two PAC systems


Faster to installsmall footprint of the machine
No drilling, no geological riskExcellent coefficient of performance (COP) (4 ->5)
Less expensiveAcoustic and visual discretion


Compressor in the garden = noiseExpensive drilling
Ugly exterior groupGeological risk
Lower COP than geothermal (3)More complex authorization file

A geothermal heat pump requires you to drill a hole in your plot of land. The borehole is usually between 50 and 200 m deep. As you can imagine, this is a tricky operation. If you don't have a garden, you can forget it. If you do have a garden, you're going to have to accept that it's going to look "ugly" for a while after the drilling, or hire a landscaper. Finally, you'll have to bear the cost of drilling, which quickly exceeds 15kCHF or 10k€.

In short, if you are looking for simplicity, you will quickly turn to an Air Water heat pump. It is certainly less economical in electrical energy, but it is easier and faster to install, while offering an acceptable COP and a lower investment.

How to estimate the savings by replacing a gas boiler with a heat pump?

First of all, you need to find your previous annual gas consumption. This is usually shown directly on your bill, in kWh.

Let's take for example a consumption of 15'000kWh of gas per year. To obtain an estimate of your future electricity consumption with the heat pump, you can divide this value by the SCOP value indicated on the technical data sheets. If this is 4.5, then 15,000 / 4.5 = 3333kWh will be your likely electricity consumption. This equates to €533 per year, and around €45 per month.

Your heat pump will therefore always produce the 15,000kWh you need for heating. Of these 15,000 kWh, 3,333 kWh will be taken from electricity and the remaining 11,666 kWh will come either from the ground if you've opted for geothermal heating, or from the air in the case of air-water heating.

NB: of course, in order to reduce the home's initial heating energy requirements, it is possible to rethink the insulation of the envelope. In this way, the 15,000kWh could be transformed into 10,000kWh, with the heat pump pumping just 2,222 kWh of electricity in our example.

If your gas bill indicates quantities in m3, then multiply them by 11 to get a rough estimate of the kWh equivalent. 11 is a factor that corresponds roughly to the calorific value of gas. Example: 1'500 m3 of gas is equivalent to 16'500kWh. However, gas bills are usually quoted in kWh, as one m3 of gas does not always contain the same amount of energy, depending on its geological origin.

How to proceed to the replacement of the gas boiler by a heat pump ? Processes and constraints.

The heat pump is a heating system

  • Which works optimally if it produces water at a low temperature (35°C). Its COP will be excellent in this case.
  • It works on a delta T° (difference of temperature going and return) of 5°C in general.

Based on these findings, several cases can be distinguished:

Case of underfloor heating

This is the ideal case. An underfloor heating system requires low water temperatures, which is exactly what the heat pump offers, with its best coefficient of performance. In this case, all you have to do is disconnect the gas boiler from the underfloor heating network, and connect the heat pump (its internal module) instead.

The next step is to connect the heat pump's indoor and outdoor modules. If you've opted for a split heat pump, refrigerant circulates between the two modules, so you'll need a real refrigeration engineer to take care of the connection. If you've opted for the monobloc version, then remote pipes will link the two units. These pipes must be buried in the garden.

Case of radiators

If you have an older system with radiators. These require higher water temperatures, and a higher delta T° to ensure the necessary heating power.

While a heat pump works ideally with a certain flow rate, and a certain delta T° of 5°C, your radiators need a different flow rate and delta T°.

The solution involves decoupling. This involves installing a decoupling cylinder to separate the primary circuit (heat pump) from the secondary circuit (radiators). This enables each to operate under ideal conditions on its own.

In addition to separating the two networks, the decoupling bottle, also known as a pressure-breaking bottle, is used to degas and purge air, as well as to settle and flush out sludge, since flow rates are very low in the bottle, allowing impurities to fall to the bottom.

Two-zone or multi-zone systems

It's not always easy to install underfloor heating in every room in the house, especially upstairs. That's why it's common to have a first floor with underfloor heating, and an upper floor with radiators.

In this case, the secondary network consists of two zones. The floor zone and the radiator zone. Each of these zones requires different temperatures and flow rates.

In the same way, a decoupling bottle is ideal. It will decouple everything:

  • The primary network (PAC)
  • The 1st secondary network = floor
  • The 2nd secondary network = radiators

Each of these circuits will be connected to the bottle. This will allow each one to function in an optimal way.

The various heat pump manufacturers all offer a bi-zone kit option for their heat pumps. These bi-zone kits contain everything you need to manage both circuits: valves, circulators, sensors, thermostats and controllers. You can see an example with the Daikin Altherma. here.

Also read these related articles:

Detailed operation of a heat pump

Split or monobloc heat pump?

How much electricity does a heat pump consume?

About the author

Juliena mechanical engineering graduate and specialist in climate engineering since 2009, has become a writer specializing in renewable energies, with expertise in heat pumps and photovoltaic solar panels for individual housing.