Insulate first or install a heat pump first? The right order for your home in Belgium
Short answer: Have heat loss calculated room by room, insulate the biggest losses, then size the heat pump. That avoids an oversized unit. According to an installer summarising the Flemish Warmtepompklaar tool, below 70 W/m² a full heat pump almost always works, and above 105 W/m² you should insulate first. An air-to-water heat pump costs roughly €8,000–18,000 installed on the Belgian market.
Prices in this article are indicative Belgian market ranges, not Alpha Services Benelux's price list. Your fixed price is in the quote.
The right order: measure, insulate, then size
The logical order is: calculate heat loss, tackle the biggest losses, size the unit on the new heat loss, then balance the system. The reverse order, choosing a heat pump based on the old boiler, often produces an oversized unit.
- Have an installer calculate heat loss room by room.
- Have the biggest losses assessed: roof, walls, glazing and floor.
- Check whether existing radiators still work at a lower temperature, or whether low-temperature emitters are needed.
- Size the heat pump on the new, lower heat loss.
- Have the hydraulics balanced room by room and the heating curve set as low as comfort allows.
Insulating everything is not always necessary. If the home is already reasonably insulated, the heat pump can go in straight away. In a poorly insulated home, a hybrid system (heat pump plus the existing gas boiler as back-up) is a stepping stone. Have the insulation work assessed by a professional.
How heat loss sets the size of the unit
The more heat your home loses, the bigger and more expensive the unit must be. A detailed heat-loss calculation gives the exact capacity in kW; the old boiler's output or floor area alone is not enough.
One price guide gives this example: a 150 m² home with average insulation needs 8 to 12 kW, while a well-insulated 120 m² home needs only 4 to 6 kW. The difference comes from the insulation, not the house itself.
| Heat demand | Direction |
|---|---|
| Below 70 W/m² | Almost always a full heat pump |
| 70 to 105 W/m² | A hybrid set-up is the safer choice |
| Above 105 W/m² | Insulate first |
Oversizing is a real trap: in a poorly insulated home an oversized unit keeps switching on and off, which speeds up wear and lowers efficiency. If you insulate only after installation, the unit was chosen for a home that no longer exists.
Which emitters suit low temperature?
Underfloor heating works best at 30 to 35 °C, low-temperature radiators at about 45 to 55 °C; old cast-iron or high-temperature radiators are the weak point. The lower the flow temperature, the better the efficiency.
- Underfloor heating: ideal, but not mandatory.
- Low-temperature radiators or fan coil units: a good option in renovation without floor works, with a large emitting surface.
- Existing radiators: sometimes usable once the home is better insulated. A heat pump typically delivers water at 35 to 55 °C; with radiators that need 65 to 70 °C, efficiency drops sharply.
Insulation and emitters are therefore linked: less heat loss lets existing radiators work with a lower flow temperature. An installer can give a first indication with a simple test (temporarily setting the existing boiler's flow temperature to about 50 °C in the heating season and checking that every room stays warm enough), but the room-by-room calculation remains decisive.
What ventilation and commissioning add
Ventilation and commissioning cost extra, but they decide whether insulation and heat pump reach their efficiency. Airtightness and ventilation usually come last in the insulation order and are often underestimated.
A more airtight home needs deliberately controlled air exchange. The heat-loss calculation should state its assumptions for airtightness and ventilation rate. A system D (balanced ventilation with heat recovery) makes most sense in a well-insulated, airtight home.
| System | Price range |
|---|---|
| C (mechanical extraction) | €2,000 – €3,500 |
| C+ (demand-controlled) | €2,500 – €4,000 |
| D standard (with heat recovery) | €4,500 – €6,500 |
| D premium | €6,000 – €8,500 |
Other price guides give different amounts, for example €3,000–€3,500 for system C and €4,000–€7,000 for system D, without saying whether VAT is included. So the price depends on the home, the brand and the VAT basis.
Commissioning means balancing the hydraulics room by room (flow, pipe diameter). That is not a luxury: an unbalanced system overheats some rooms and under-heats others.
What does a heat pump cost and what drives the price?
An air-to-water heat pump costs roughly €8,000 to €18,000 installed on the Belgian market. Sources differ: one quotes €10,000–€18,000, another €8,000–€20,000 depending on capacity.
| Situation | Price range |
|---|---|
| Heating only, small insulated home | €8,000 – €11,000 |
| Heating plus domestic hot water | €11,000 – €15,000 |
| High capacity or complex works | €15,000 – €18,000 |
| Hybrid (with gas boiler) | €8,000 – €13,000 |
| Monobloc 5–8 kW (other source) | €8,000 – €12,000 |
What drives the price:
- the capacity needed, so the home's heat loss;
- insulation level: poorly insulated homes (EPC D–F) need a more powerful unit;
- the existing system: with high-temperature radiators, low-temperature emitters or fan coil units come on top;
- a possible electrical upgrade, which one price guide puts at €1,000 to €2,500 extra;
- domestic hot water, brand and model.
Insulation work itself is not included; ask for a separate quote after a site visit.
VAT and premiums: in brief
For dwellings older than 10 years, renovation work generally qualifies for 6% VAT instead of 21%, under conditions. It must be private use and work invoiced to the end consumer by a registered (VAT-liable) contractor; materials you buy yourself stay at 21%. This is relevant, for example, for insulation and ventilation work. For the supply and installation of an all-electric heat pump, 6% VAT also applies from 1 January 2026 to 31 December 2030 in new builds and dwellings younger than 10 years, under conditions (the same installer supplies and installs, private use, not for cooling only; hybrid systems are excluded). Check with the federal tax authority (FOD Financiën, circular 2026/C/19) or your contractor.
For premiums we point to the official portals, because conditions and amounts change regularly and differ by region. In Brussels, Homegrade offers free advice and your municipality may have local premiums. In Wallonia, see energie.wallonie.be for the current scheme. In Flanders, applications go through vlaanderen.be/mijn-verbouwpremie.
Comparing quotes without surprises
Only compare quotes that rest on the same calculation. The prices here are market ranges, not fixed rates.
- Ask whether the quote is based on a room-by-room heat-loss calculation, with stated assumptions for airtightness and ventilation.
- Check whether emitters (radiators, floor), commissioning, ventilation and electrical upgrade are included or listed separately.
- Check whether the price includes VAT and which rate was applied.
- Ask which capacity in kW is proposed and why, and compare it with your insulation plan.
- A quote without a site visit cannot give a reliable capacity.
Alpha Services Benelux, active since 2014, carries out heating and boiler work with its own team across Belgium and provides a fixed written quote after a site visit. Work is by appointment. See our boiler and heating page, our renovation services or the renovation calculator, or call 0485 44 55 12.
Fixed quote after a site visit
Alpha Services Benelux does the work with its own team, active since 2014. VAT BE 0541.320.178.
Request a quoteFrequently asked questions
Do I have to insulate before installing a heat pump?
Not always. If the home is already reasonably insulated, the heat pump can go in directly. With a very high heat demand, above roughly 105 W/m² according to Warmtepompklaar, insulating first is wiser. A hybrid system is a stepping stone. Have a heat-loss calculation assess this first.
Can a heat pump work with my existing radiators?
Sometimes, especially after better insulation, since a lower flow temperature then suffices. Old radiators that need 65 to 70 °C reduce efficiency sharply. Low-temperature radiators work at about 45 to 55 °C, underfloor heating at 30 to 35 °C.
How many kW do I need?
Only a room-by-room heat-loss calculation can tell. One price guide cites 8 to 12 kW for 150 m² with average insulation and 4 to 6 kW for a well-insulated 120 m². The old boiler's output is not a reliable yardstick.
What does an air-to-water heat pump cost in Belgium?
On the market, roughly €8,000 to €18,000 installed, depending on capacity, hot water and complexity. A hybrid system costs €8,000 to €13,000 according to one source. An electrical upgrade can add €1,000 to €2,500.
Do I need ventilation if I insulate and fit a heat pump?
Better airtightness calls for deliberately controlled ventilation. A system D with heat recovery costs about €4,500 to €6,500 for a 120 m² terraced house incl. 21% VAT; system C about €2,000 to €3,500. Have a professional assess the choice.
What happens if I install the heat pump first and insulate later?
The unit was chosen for a home that lost more heat than it will afterwards. It is oversized, cycles on and off more often and runs less efficiently. That is why you size it on the heat loss after insulation.
Sources
- Lucht/water-warmtepomp: werking, prijzen en premies in België in 2026 — Facq
- Pompe à chaleur air-eau : fonctionnement, prix et primes en Belgique 2026 — Facq
- Circulaire 2026/C/19 betreffende de herinvoering van een verlaagd btw-tarief voor de levering met plaatsing van warmtepompen — FOD Financiën (circulaire van 20.01.2026, via OECCBB)
- Warmtepomp prijs 2026: compleet overzicht per type — Solarnation
- Hoeveel kost een warmtepomp voor je bestaande woning? Realistische prijzen + besparing 2026 — Luminus (Lumiworld)
- Warmtepomp en isolatiegraad: welke keuze past bij uw woning? — Sun4Power (installer, summarising the Flemish Warmtepompklaar tool)
- Prijs ventilatiesysteem in België (2026) — Prijs-Ventilatie.be
- Wat is de prijs van mechanische ventilatie in 2026? — Verbouw-prijzen.be (Bobex)
- Prijs warmtepomp 2026: kosten, premies, terugverdientijd — Energiebewust ontwerpen
- Mijn VerbouwPremie — Vlaanderen.be