Heating and cooling during the ECO window
A heat pump can run when electricity is at its cheapest, provided the building can hold on to what it makes.
Updated on 14 September 2026
The fabric decides, not the machine
Shifting a heat pump amounts to asking it to make at 14:00 the heat you will want at 20:00. In between, it is the building that stores it: the slab, the walls, the water in the circuit.
An insulated house with underfloor heating does this very well. The slab is a store of several tonnes and it carries the five PEAK hours without anyone noticing. A poorly insulated house on low-water-content radiators will not hold an hour.
The machine itself is almost never the problem: every recent heat pump accepts a time schedule. What is missing is the certainty that the heat will still be there at 20:00, and that is judged on the fabric.
The settings come down to three points
The first is the set point. You do not switch the machine off at 17:00: you let it run slightly above the comfort set point during the ECO window, then fall back. The useful offset is one to one and a half degrees. Beyond that you are heating the outdoors.
The second is domestic hot water. On a heat pump that produces it as well, this is the easiest item to move onto 11:00 to 17:00, for the same reason as the electric cylinder: it stores.
The third is cooling in summer, and it is the most favourable case of all. The ECO window from 11:00 to 17:00 covers exactly the hottest hours, so cooling at the right moment costs less than cooling late, and the house benefits for longer.
The situations where we advise against shifting
- Low-inertia radiators in a poorly insulated house: the temperature falls back before 19:00.
- A heat pump already tight on output, with no headroom to run ahead of demand.
- A direct electric booster that fires on every restart, and charges in PEAK what you thought you saved in ECO.
- A home occupied all day, where the 11:00 to 17:00 window is already heating in real time.
Tell us what is in your consumer unit
Describe what sits on your board and we will say what can be shifted and what cannot. By phone on +32 495 88 75 92 or through the questionnaire.
Sources for this page
- Public Service of Wallonia, the two-rate schedule changes on 1 January 2026Checked on 2026-09-14