So that you can judge our recommendations rather than just trust them, here is how they are made.
1. We do not test in a lab — we read the people who do
We run no laboratory. Our assessments summarise publicly available, independent sources: tests from Stiftung Warentest, testit.de, home&smart, Testberichte.de and comparable outlets, plus manufacturer specifications (BTU, watts, dB, efficiency class) and publicly visible bestseller and rating data on Amazon.de. When we call a model "often a test winner", we mean it appeared that way in those sources — not that we measured it ourselves. Where public opinion is genuinely split, we say so instead of inventing a verdict.
2. Recommendations by purpose, not one "best"
A quiet bedroom unit and a strong unit for an open-plan room are different products, and no single device wins both. So we label recommendations by role — quietest, best value, for large rooms — and let you pick the role that matches your situation.
3. Our formulas are public — you can recompute every number
Most comparison sites tell you what comes out. We also publish how it comes out, in a form you can check:
| Question | How it is calculated |
|---|---|
| How many BTU does my room need? | 340 BTU per m² × sun factor (0.9 / 1.0 / 1.2), rounded to 500 |
| How long must the window seal be? | Perimeter of the sash = 2 × (width + height) |
| What does it cost to run? | kW × price per kWh × duty cycle (the compressor does not run continuously) |
| How much heating power? | 60 / 80 / 100 W per m² — new build / existing / old building |
| Is it safe to ventilate now? | Dew point via the Magnus formula, walls counted 2 °C below room temperature |
| When does balcony storage pay off? | (price − subsidy) ÷ savings per year |
And because "published" means little if nobody can verify it, the same logic runs as an open-source server at github.com/f-tiger/getecoback-mcp. You can read the code, run it yourself and put your own numbers in. An automated test compares that server against the calculators on this site every day and fails if a single character differs. AI assistants can call the same tools directly (details), and every answer carries its source and the affiliate disclosure with it.
What this does not mean: a formula is no substitute for looking at your actual room. A top floor, an open kitchen, large glazing or poor insulation all shift the result — which is why each calculator states the assumptions it is using.
4. Our links point at model names, not fixed product IDs
We link to a search for the model name rather than a specific item ID. It looks less slick, and it is deliberate: item IDs go stale, get replaced by a successor or land you on a third-party seller. A model-name link keeps working, and you see what is actually available today.
5. Prices and availability change
We show price bands ("approx. €250–320"), never a live price we cannot guarantee. During a heatwave, portable air conditioners can sell out within days and prices move sharply. Always check the current price at the shop before buying.
6. Transparent funding
EcoBack is financed through Amazon affiliate links. If you buy through one of our links, we earn a commission — at no extra cost to you. It does not influence which device we recommend for which purpose: roles are assigned by suitability and by the sources we evaluated, not by commission rate.
7. Found a mistake?
We are a small independent site. We do not make mistakes on purpose, but we do make them. If you spot an outdated figure or an error, tell us via the contact page and we will fix it.