The heat pump is the heating system of the moment – and for three weeks a year its own worst enemy: when it is minus ten degrees outside, its efficiency drops, the electric heating element kicks in and the electricity meter spins. That is exactly when a wood stove is not a nostalgic extra but the second pillar of the heating system. Why the combination works so well and what matters.
The problem of the cold days
At +7 °C outside temperature, an air-to-water heat pump turns one kilowatt hour of electricity into three to four kilowatt hours of heat. At −10 °C it is often only two – at the same time as the house's heat demand peaks. Many systems then switch on the electric heating element, which works at a factor of 1. These few days account for a surprisingly large share of annual electricity costs.
What the wood stove takes over
A wood stove in the living area brings 4 to 6 kW directly into the room where the family sits in the evening. The heat pump then only has to keep the remaining rooms at temperature and runs in its efficient range instead of heating-element mode. Anyone who covers 3,000 to 5,000 kWh a year via the stove saves €250 to €500 in electricity depending on the tariff – for about a tonne of wood briquettes or two and a half stacked cubic metres of beech.
Water-bearing: the stove feeds the heating
A water-bearing wood stove is even more effective: it delivers 60 to 70 percent of its output to a buffer tank that the heat pump also uses. On cold days the stove then supplies heating and hot water for the whole house while the heat pump pauses. The investment is higher (buffer tank, hydraulic integration), but the combination is eligible for subsidies and makes the house independent of electricity price peaks.
The right fuel for supplementary heating
Anyone who runs the stove specifically on cold days and in the evenings needs fuel that is predictable, storable and clean:
- Hardwood briquettes (RUF, Nestro): long-lasting embers, little ash, one pallet lasts the winter. Ideal if the stove is to last through the night.
- Kiln-dried beech: the beautiful flame for the evening; ready to use, no two years of drying.
- Softwood briquettes or kindling: for quick lighting before the hardwood briquettes take over.
Which combination is more efficient is shown in the article Firewood or wood briquettes.
What to look for in the stove
In a well-insulated heat pump house, a small stove (3–5 kW) is the right choice; more overheats the room. With a ventilation system the stove must be room-air independent. A model with storage mass extends heat output after the fire burns down. The complete buying checklist can be found in the article Buying a wood stove.
And the emissions?
A modern stove to BImSchV level 2, operated correctly (dry fuel, top-down lighting, full air supply when lighting), burns cleanly. Wood from certified forestry is CO₂-neutral within the cycle – and on the critical days it replaces electricity that in winter comes predominantly from gas and coal. More on this under Clean heating.
Conclusion
Heat pump and wood stove are not an either-or. The heat pump delivers the base load efficiently, the stove the peaks and the cosiness. With hardwood briquettes and dry beech wood, the combination becomes a heating system that lowers electricity costs and gets through winter with ease.
HEIZFUXX® · SIMPLE. CLEVER. HEATING.
Wood pellets, wood briquettes, firewood, kindling, peat briquettes and hard coal – by the bag at DIY stores, by the pallet online. Where to get HEIZFUXX®.