Lidstein
The short answer: A heat pump works in an older building if the house stays warm on cold days at around 55 °C flow temperature. Existing buildings reach that through envelope insulation and sufficiently large heat emitters — precisely the measures a full renovation involves anyway. Cost for a detached house: a benchmark of €27,000 to €40,000 before subsidy; the KfW grant covers up to 70 % of eligible costs.
Why is the flow temperature so decisive?
A heat pump lifts ambient heat to heating level. The smaller the temperature lift, the less electricity it needs: at a 35 °C flow (underfloor heating) a good unit reaches a seasonal performance factor of 4 or more — one kilowatt-hour of electricity becomes four kilowatt-hours of heat. At a 65 °C flow (an uninsulated old building with small radiators) efficiency collapses and running costs rise. Hence the rule: reduce the heat load first, then replace the heating.
What does an older building need to meet?
- An insulated envelope: Roof, façade and new windows often halve the heat load — a core part of the “building envelope” package in every full renovation.
- Large heat emitters: Underfloor heating is ideal; generously sized or low-temperature radiators will also do.
- Hydraulic balancing and proper sizing: A room-by-room heat load calculation is mandatory, not optional.
- Siting and noise: Distance and noise limits towards neighbours apply to the outdoor unit — in dense built-up areas a planning matter, not a deal-breaker.
What does switching cost — and what comes back?
| Item | Amount |
|---|---|
| Unit including installation, cylinder, reworked distribution | 27.000–40.000 € |
| KfW grant (programme 458): 30 % base subsidy | –9.000 €* |
| + 20 % speed bonus (replacing oil or gas) | –6.000 €* |
| + 30 % income bonus (taxable income up to €40,000) | –6.000 €* |
| Maximum grant (70 % of €30,000 eligible) | –21.000 € |
*Based on maximum eligible costs of €30,000 for the first dwelling unit; bonuses can be combined, capped at 70 %. As at early 2026 — current terms at kfw.de.
Why is a full renovation the best moment?
- One design case instead of patchwork: Insulation, windows, emitters and heat pump are calculated together — the system runs at its optimum operating point from day one.
- Open installation routes: During first fix, walls and floors are open. Underfloor heating, new distribution and a buffer cylinder then cost a fraction of what retrofitting would.
- One interface fewer: At Lidstein the heating, electrical and plumbing teams plan in one chain of dates — the heat pump is part of the building services package, not an alien object in the programme (what that means for the overall budget).
The best heat pump is the one whose house does not let it down: envelope first, then the plant.
Frequently asked questions
Does a heat pump work without underfloor heating?
Yes — with sufficiently large or dedicated low-temperature radiators, provided the flow temperature stays low.
What is a good seasonal performance factor?
In a renovated building, 3.5 to 4.5 is realistic. Below 3 the sizing should be reviewed — usually the flow temperature is too high.
Is combining it with solar panels worthwhile?
Often yes: self-generated electricity lowers the running costs further, especially with battery storage and smart control. If the roof is being renewed, solar can be planned in at the same time.
Does Lidstein install heat pumps outside a full renovation?
Yes — replacing the heating is possible as a standalone measure. We check honestly beforehand whether your house already meets the requirements or whether the envelope comes first. Get in touch.
Is your house ready for a heat pump?
Year of construction, heating, insulation — three details are enough for an honest first assessment.