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How do I choose my boiler ?

To choose a new boiler, you must take account of the following factors:
- the type of fuel
- the efficiency
- the combustion system
- the space available in your home
- your hot water requirements

With regard to the price, you must take account of the purchase price but also the running costs. A more efficient boiler (for example a condensing boiler) will require a financial effort at the time of purchase, but this will be redeemed little by little every day during the initial years and will then start saving you money.

You should also take into account the Rénolution grants available for certain types of boilers, which make them more affordable.

Choose the right power level

Are you building? Before thinking about boilers, examine other alternatives: the “passive house” (ultra-low energy requirements), without heating or with cogeneration (simultaneous production of heat and electricity).

If you have to replace an existing boiler, look for independent advice at Homegrade, from an architect, from someone you know who has done the same thing recently etc. Then consult the manufacturers’ websites, compare installation estimates and enquire about the reputations of the installers. Also ask the heating specialist to justify the choice of model that he suggests.

These are the most important points to be taken into account when making your choice.



1. The fuel

  • You can base your choice on the purchase price of the fuel. It is difficult to predict the development of the price of heating oil but everything suggests that it will be more expensive than natural gas in both the medium and long terms. The choice of supplier can also be a determining factor; there are already some who no longer base the price of gas on the price of crude oil.
  • The financial assistance you can benefit from will certainly play a role in your choice. Brussels Environment only gives Energy grants for natural-gas boilers. Similarly, the cost of connecting to the gas network is reduced.
  • The environmental impact is another important criterion. You should be aware of the fact that gas is less polluting than oil but also consider renewable sources of energy: sun, wood etc.

2. The efficiency

A highly efficient boiler will enable you to save on your energy costs and will reduce CO2 emissions. This is true of low temperature gas boilers (carrying the label HR+) and even more of condensation boilers (with the label HR Top). These models are more expensive but more economic to run. With regard to oil, the low-temperature and condensation models carry the labels Optimaz and Optimaz Elite.

3. The combustion system

There are two systems:

  • Open or “atmospheric” boilers take the oxygen necessary for combustion from the room in which they are installed; it is therefore essential that this be well ventilated. They are equipped with a chimney through which the waste gases escape.
  • Closed or air-tight (“room-sealed, balanced-flue”) boilers do not use room air. They take it from the outside through a double-walled pipe, which also allows the waste gases to escape. An access to the outside is therefore indispensable (through the wall or roof). These models are a little more expensive but offer several advantages:
    • they do not need a traditional chimney. A less expensive, steel exhaust pipe is enough;
    • they may be installed in an unventilated area, such as a cupboard;
    • they are noiseless;
    • the are safer (less risk of CO poisoning) ;
    • they consume 4% to 5 % less fuel.

4. The space available

Low-temperature and condensation boilers come in two versions.

  • If you haven’t enough room, consider wall boilers. Compact, light and silent, they can be installed unobtrusively in the kitchen or bathroom.
  • Floor boilers are generally sturdier but they are also bulkier.

5. Hot-water requirements

For your hot water, you can also choose between several solutions. Factor in your habits, the quantity of water you need (according to whether you generally take baths or showers, whether you live alone or not etc.).

  • A separate hot-water tank stores the water and keeps it constantly hot. This is the least economic solution with regard to energy.
  • A “mixed” or “combined” boiler heats both the radiators and the water used for the kitchen and bathroom. This is a more economic solution and is more practical for small dwellings.
  • An instant water heater, separated from the boiler, heats water as required. This system is still more economic.
  • A solar water heater makes it possible to heat a great part of the water one uses ecologically and “free”. It may be combined with a boiler which supplies the necessary extra heat if the production is not enough in winter.

Don’t forget …

Choose the right power level

When renovating, do not be satisfied with just replacing the old boiler with a model of equivalent power. The calculation methods of the past are no longer applicable. Have a heating specialist check the actual and present needs of your dwelling with regard to heating power. Take into account the improvements to it (insulation, double-glazing, proofing etc.) which have already been carried out or are planned.

Consider installing back-up heating (wood or pellet stove) to be used in between-season periods or as a supplement during very cold periods.

Calculations of the theoretically necessary power take account of certain weather conditions which last only a few days in the year. Do not then be too ambitious to too little effect and avoid over-powering the boiler. Otherwise, wasteful consumption is guaranteed! With regard to the cost, you also win: the prices increase faster than the power in the same range of boilers: a (very) powerful model will be proportionally more expensive than a less powerful one.

Adapt the chimney and radiators if necessary

Have a check carried out to see if the chimney can take the presence of condensates (flow of slightly acid water coming from condensation). If not, there are some solutions: intubation, sealed boiler. Also, a low-temperature boiler needs bigger radiators to increase the heat exchange.

Have your heating specialist check that your existing radiators have a sufficiently large exchange surface. If they do not, it may perhaps be necessary to add one or two or to replace one or other of them.

Have an efficient regulation system

The best of boiler will fail to give its best if it is not controlled by an efficient regulation system: a programmable thermostat, outdoor sensor and thermostatic valves add a certain value to your boiler: a form of “intelligence”…


New boiler: nothing but benefits!
A couple of weeks ago I had my boiler replaced and I haven’t yet regretted it for an instant. I am enjoying greater comfort and more safety... and I’m curious to see my first adjusted bill!

Read the testimonial

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