Efficiency House 40 for a 90 m² prefab bungalow: 2026 planning

Quick answer: building first, equipment second

For a 90 m² prefab bungalow, Efficiency House 40 should not be sized in isolation. Design heat load, envelope performance, hot-water demand, occupancy, roof area, shading and grid connection belong in one energy concept. A generic equipment size or PV capacity based only on floor area can lead to oversizing or comfort problems.

Data needed before requesting quotations

Good installers need more than living area. The energy standard, design temperature, heat emitters, hot-water profile, desired indoor temperatures, roof orientation and electrical connection all matter. For new builds, coordinate services design with the final building design and an energy-efficiency expert, particularly where KfW programmes are being considered.

Assess the economics of Efficiency House 40

Compare capital cost, imported electricity, maintenance, service life, self-consumption and technical dependencies. Solar PV can reduce grid electricity used by a heat pump, but winter heat demand and solar generation do not fully coincide. A battery shifts electricity within the day; it does not replace a realistic annual energy balance. Use credible load profiles rather than maximum self-consumption promises.

Funding and technical requirements

Funding programmes and technical requirements change. New-build KfW programmes such as 296, 297/298 or 300 may be relevant where their conditions are met. PFlower therefore does not hard-code current interest rates into evergreen guidance. Check the current KfW product page before application and project commencement, and have eligibility confirmed professionally.

Technical checklist

• Establish heat load and envelope performance before equipment selection.
• Document roof area, shading and grid connection.
• Check heat-pump noise, location and service access.
• Model PV, battery and heat pump as one system.
• Coordinate funding application and contract timing.
• Obtain at least two technically comparable quotations.

How to use this guide for your own project

Do not copy the checks into your project without context. Connect them to your plot, contract stage and technical documents. First mark which assumptions have already been confirmed by plans, quotations or authorities and which come only from brochures or early conversations. Obtain written answers for open points and compare alternatives using an equivalent scope. In Energy & technology, a seemingly small difference in use, location, finish level or contract scope can change the conclusion. Treat this page as a working tool: it is designed to expose unanswered questions, structure decisions and help you request more comparable quotations or authoritative answers. Practical tip: keep a simple comparison sheet for your project and record the current evidence beside every cost, technical or legal item: quotation, drawing, permit, insurance wording or funding document. Add the date, contact person and unresolved questions. This makes it easier to spot not only price differences but also missing services and assumptions that can become expensive later. Re-check the information whenever the plot, floor area, finish level, financing or timetable changes.

What to document before deciding

Record assumptions, quotations, design versions and unresolved questions. This makes later changes traceable and makes it easier to see whether a new offer is truly comparable. For dynamic topics such as funding, rates, insurance terms or permission procedures, the current information from the responsible body takes precedence.