FAQ
TL;DR: Installing a 125 mm spring-loaded check valve cut reverse-draft events by 90 % [Elektroda, zlotaraczka., post #17515708] "It just works" [Elektroda, misiekpb, post #17576358] Why it matters: stable gravity ventilation prevents damp, mould and CO₂ spikes.
Quick Facts
• Fresh-air requirement: 20–25 m³ h⁻¹ person⁻¹ at 10 Pa pressure drop [Elektroda, Wlodek22, post #16189148]
• Healthy indoor RH: 45–55 % (hygrometer control) [Elektroda, Wlodek22, post #16855905]
• 125 mm plastic check valve price: 12–15 PLN [Elektroda, misiekpb, post #16851767]
• Window trickle-vent flow: approx. 5–30 m³ h⁻¹ depending on opening [*Renson Datasheet*]
• Polish PN-83/B-03430 standard: bathroom exhaust ≥ 50 m³ h⁻¹ [PN-83/B-03430]
Why is cold air blowing into my bathroom vent?
Gravity systems need incoming air. Airtight doors and windows create negative pressure outside the bathroom, so the shaft reverses and pulls cold air inward [Elektroda, zlotaraczka., post #16187560]
How can I check if air supply is the culprit?
Open a window 1 cm; if the vent instantly switches to exhaust, the flat lacks supply air [Elektroda, zlotaraczka., post #16843318]
Do rotating chimney cowls stop reverse draft?
They help only when fitted to every connected riser; one cowl shifted the problem from bathroom to kitchen [Elektroda, daro31ie, #16187935; zlotaraczka., #16843318].
Will unsealing a window raise heating bills a lot?
Moderate trickle-vent opening raises heat loss by about 3 % yet prevents moisture-related energy waste of 5–10 % [IEA Ventilation Report].
What are window diffusers/trickle vents?
Small adjustable slots in the frame that admit 5–30 m³ h⁻¹ fresh air without full opening, easing cross-flow [Elektroda, brofran, post #16189084]
How do I fit a check valve in a gravity vent?
- Remove grille; press-fit 125 mm valve into duct. 2. Confirm flap swings freely toward shaft. 3. Re-install grille [Elektroda, misiekpb, post #16851767]
Can a check valve fail?
Edge-case: heavy soot or kitchen grease can stick the flap, blocking exhaust and spiking humidity above 65 % [Elektroda, Jan_Werbinski, post #16851758] Inspect quarterly.
What humidity and CO₂ readings signal poor ventilation?
45 % RH good; >65 % needs more flow [Elektroda, Wlodek22, post #16855905] CO₂ above 1 000 ppm means open vents [Jan_Werbinski, #16851758].
Is a single-room recuperator worth buying?
Devices like HRV100 recover up to 80 % heat but cost >550 PLN; check valves solved the forum case for <30 PLN [Elektroda, darek795, #17515638; zlotaraczka., #17515708].
Why do two adjacent kitchen grilles act oppositely?
Air follows the path with lower resistance. Covering one grille forces the other to exhaust consistently [Elektroda, brofran, post #16850744]
How do I balance multiple vents?
Fit adjustable grilles; throttle strong shafts and open weak ones until tissue tests show equal pull [Elektroda, Wlodek22, post #16189148]
What airflow does Polish code require?
PN-83/B-03430 demands 50 m³ h⁻¹ exhaust for a bathroom and 70 m³ h⁻¹ for a kitchen with gas hob [PN-83/B-03430].
