How we rate impact

Each item shows how much energy it saves in a year in an average Flemish house. It is a rough size, meant to show which steps matter most, not a forecast for your home.

The average house

An average Flemish house uses about 15,000 kWh of gas a year for heating and about 2,000 kWh for hot water, plus about 1,000 kWh of electricity per resident (Vlaamse overheid, section "Huishoudelijk energiegebruik"). Heating is by far the largest part, so heating items tend to rate highest. We use this Flemish reference house for all of Belgium, because we have not found a comparable official figure for Brussels or Wallonia yet; homes there differ, so read the bands as a rough guide.

Where a source gives a saving in cubic metres of gas, we count 1 m³ as at least about 8.8 kWh, based on the Dutch government's reference of 31.65 MJ per m³ (IPLO).

The bands

Each rated item says which figure from its sources gives its band. A Big win has a large impact and costs nothing or less than €100.

CO₂ and trees

For savings on gas and electricity, we also show the CO₂ you avoid. Burning natural gas releases about 0.202 kg of CO₂ per kWh, the standard factor of the Flemish Energy and Climate Agency and the Flanders Environment Agency (VEKA and VMM). The average house heats with gas, so we use this factor for heating and hot-water items.

For electricity we use 0.381 kg of CO₂ per kWh. This is the fixed factor the Flemish Energy and Climate Agency gives for a kWh that is saved and so not produced in a gas-fired power plant (a STEG plant), assuming that every saved kWh is one kWh less from such a plant (VEKA, section "Elektriciteit", step 3). It is a simplification. The average of Flemish power plants, which also counts nuclear, wind and solar plants, was 0.244 kg per kWh in 2024 and has ranged from 0.178 to 0.332 kg since 2017 (same page, step 2). We use the gas plant factor because it is meant for savings and doesn't change from year to year. As electricity gets cleaner, it may overstate the CO₂ you avoid.

To make the number easier to picture, we compare it with trees. On the item cards, a number followed by a tree icon is that number of trees. An average tree in a Dutch forest takes up about 11 kg of CO₂ a year, based on the Dutch national forest inventory (Klimaathelpdesk, Wageningen University & Research). We use this as the nearest published average for Flanders. A free-standing tree can take up between 10 and 40 kg a year depending on its age and size (Staatsbosbeheer), so treat the tree count as a rough picture, not a measurement. Avoiding CO₂ is also not the same as planting trees: a tree stores carbon only for as long as it and its wood last (Klimaathelpdesk).

Making your own power

Solar panels, home batteries and heat pumps get no energy band and no CO₂ figure. They change where your energy comes from rather than how much you use, and their effect on the climate depends too much on your home and on the time of day to fit in one number.

Solar panels lower your CO₂ a lot over their lifetime, but not to zero. Most of their emissions come from making the panels: over its life, a rooftop system emits about 36 g of CO₂ for each kWh it produces, assuming European sunshine and a life of 30 years (IEA PVPS, slides 7 to 10). That is about a tenth of the 0.381 kg per kWh of a gas-fired power plant given above. The panels pay this back in their first years and save CO₂ after that.

You also keep using the grid. With solar panels alone, a household uses on average about 28% of the power it generates itself (Vlaamse overheid). At night, in the evening and in winter your power comes from the grid, and in Belgium the grid emits the most CO₂ per kWh in the evening, most of all in winter (Electricity Maps). On sunny days the grid already has plenty of solar power: in 2025 the wholesale price of electricity in Belgium was negative for 519 hours (same page). A kWh you send to the grid in such an hour avoids little CO₂.

The time of day also matters if you have no panels. On a summer day in Belgium in 2025, power at noon caused about 104 g of CO₂ per kWh, against about 216 g at 8 pm (Electricity Maps). So running the washing machine or dishwasher around midday is better for the climate too.

In most homes, heating weighs more. The average house above uses about 17,000 kWh of gas a year for heating and hot water, which is about 3.4 tonnes of CO₂ with the factor above, against about 0.4 tonnes for 1,000 kWh of electricity per resident. That is why items that cut heating, such as insulation, tend to rate highest.

Why energy and not euros

Prices change too fast for euro amounts to stay correct. The Flemish energy regulator's estimate of a yearly bill for a new contract went from about €2,240 in September 2021 to about €9,210 a year later (VRT NWS). A kWh of electricity usually costs more than a kWh of gas, so an electricity item can weigh more on your bill than its band suggests.

Payback time

We only show a payback time when an official source states one, and we link to that source. Payback depends on energy prices, so these items are marked "Subject to change".

Read the bands with care

Real savings are often smaller than calculated. Households in poorly insulated homes already use much less energy than models predict, by about 30% on average in a large German study, with similar patterns in Belgium (University of Cambridge). In a large US home insulation programme, households saved only about 40% of the projected amount (NBER).

In Flanders, the EPC for your home lists recommended measures in order of priority, and for houses gives a cost estimate for the priority ones (Vlaamse overheid). Your Energiehuis can advise you on what to do first.

In Brussels, a PEB certificate issued since March 2023 sets out a recommended renovation scenario, step by step (Brussels Environment, in French), and Homegrade can help you read it (Homegrade, in French). In Wallonia, certificates issued since 1 September 2026 show an indicative renovation path towards label A (SPW Énergie, in French), and a Guichet Énergie gives free advice (Wallonie.be, in French).

How this site is made

This site is made with AI. Claude, an AI model by Anthropic, searched for and read the sources, wrote the texts in Dutch, French and English, rated the impact of each item, and built the website. A person, the maintainer of the project, decides what goes on the site and approves every change before it is published.

AI can get things wrong. That is why every item links to the sources it is based on, so you can check what it says. If you find a mistake, please report it on GitHub.