Leaky windows and doors are underestimated heat consumers. Warm air escapes through microscopic gaps, cold air flows in. With new or adjusted seals you stop these leaks, they cost almost nothing and work immediately.
Step by step
Every door and window has rubber or silicone seal lips at the edges. Over years these harden or deform. Air escapes through gaps without you noticing (convection through small openings). Your heating system must deliver more energy to replace lost heat. With new seals you close these leaks, even a 1 mm gap across 4 window sides adds up to significant winter energy loss.
Source: Bundesstelle für Energieeffizienz (BfEE), Leaky windows/doors account for 5–10% of heating loss in old buildings
Step by step
- Do a draft testHold a burning candle or damp cloth next to your window and door edges. If the flame flickers or the cloth moves, there's a leak. Mark these spots with sticky notes.
- Identify seal typeLook at your existing seals: are they rubber profiles (usually U or D-shaped) or foam strips? Buy replacement seals in the same profile (hardware store, €5–15 per window).
- Remove old sealsPull the old seals out of the grooves or channels, it takes some force. Clean the channels with a brush or old cloth until no dirt or rubber remains.
- Press in new sealsPush the new seals firmly into the channels. Start at one corner and work around the window. Press firmly so there's no gap and the seal stays under load.
- Seal window thresholds (optional)For patio doors the threshold area is critical. With silicone sealant (about €8) you can fill gaps below the door. This blocks floor drafts effectively.
Worked example
Before: Old building with 10 windows + 2 doors. Seals 15–20 years old, partly hardened. Draft measurable at least 6 spots. Heating costs €2,000/year.
After: New seals in all 10 windows + 2 doors (costs: €60–80 material, 2 hours work). No more measurable draft. Heating system runs evenly, no over-heating to compensate. Savings 3–5% (about €60–100/year). Pays for itself in 1 year.