Chimney & ventilation

• How much heat is lost

  Natural exhaust moves 60–100 m³/h per channel: ~1–3 kWh of heat per day per channel. A flue without a damper works as an exhaust fan when the burner is off.

• Damper

  A flue damper closes when the burner is off. Residual draft is needed for CO escape — don't seal fully; use a damper with an unregulated minimum gap.

• Ventilation flaps

  Gravity flaps (KIV/back-draft) in kitchen and bathrooms: open with airflow, close in stillness. A cheap way to remove constant draft.

• Recuperator

  A plate/enthalpy recuperator returns 70–90% of exhaust heat to the supply air. For a 100 m² house it pays back in 2–4 winters.

• Supply/extract balance

  Extract without supply creates negative pressure → backdraft through the flue (CO danger). Minimum — supply valve or micro-ventilation in rooms.

• When the flue pulls blindly

  An idle fireplace/stove with an open flue: warm air rises up the pipe by itself. Close the damper/firebox door after burnout — standard practice.

• Maintenance

  Flue cleaning 1–2 times per season: soot weakens draft and is a fire risk. Check draft with a smoke pellet or anemometer, not a candle.

An open flue and natural exhaust can 'pull' 15–25% of a home's heat. But draft is needed for safety (CO!) — don't plug ventilation, control it: dampers, gravity-closing flaps, a recuperator.