Ventilation Planning: Natural vs Mechanical Systems

Requirements:

• Open windows for 5–10 minutes twice daily (full purge) where safe to do so.
• Run existing extractor fans during and for 10–20 minutes after cooking and showering.
• Keep trickle vents or background vents unobstructed; do not block them.
• Use lids when cooking and dry clothes outdoors where possible; avoid indoor tumble drying without venting.
• Put a simple hygrometer in key rooms; act when RH > 60% (ventilate, reduce moisture sources).
• If you see mould, remove safely (clean, dry, then fix ventilation/humidity source) and investigate cause.

Requirements:

• 1) Survey: record building type, occupancy, current ventilation routes, and moisture sources.
• 2) Monitor: measure humidity and CO2 at representative times (living room, bedrooms, kitchen).
• 3) Strategy decision: choose natural, mechanical (MVHR or MEV) or hybrid based on airtightness, pollution and budget.
• 4) Rate calculation: size ventilation by room-by-room L/s or whole-house approach (see targets below).
• 5) System selection: pick equipment meeting energy, noise and filter targets; specify commissioning.
• 6) Duct & layout: short, direct ducts; acoustic attenuation; accessible service routes and maintenance access.
• 7) Commissioning: measure and balance flows, provide user settings (boost, summer bypass) and handover documentation.
• 8) Maintenance plan: filter schedule, access, servicing intervals, and user training.

Requirements:

• Balanced supply and extract for MVHR; continuous low flow with boost for cooking/showers.
• Heat recovery with bypass for summer; condensate drain and frost protection where needed.
• Accessible, replaceable filters and clear maintenance access.
• Low specific fan power and clear performance curves; thermostatic or humidity/CO2 controls as needed.
• Ductwork sized to meet target flows with anti-vibration mounts and acoustic silencers near bedrooms.
• Commissioning certificate: measured airflow report and labelled ducts/registers to each room.

Requirements:

• Provide adequate openable area and cross-ventilation paths for purge ventilation.
• Size trickle vents and window vents to give continuous background flow compatible with airtightness.
• Design for occupant use: clear controls, safety restrictors if needed, and insect/screens where required.
• Do not rely solely on natural ventilation if building is very airtight or if outdoor air is poor (traffic/pollution).

Requirements:

• Use mechanical background ventilation with natural purge capability or automatic boost based on humidity/CO2.
• Controls should be simple for occupants and include override, timer/boost and summer bypass modes.
• Ensure automatic switching logic avoids short-cycling and unnecessary energy use.
• Design to prevent unwanted drafts and ensure acoustic comfort when mechanical boosts run.

Requirements:

• Do not let ventilation systems depressurise rooms containing open-flued combustion appliances — consult a heating engineer.
• Install fire-stopping/fire dampers where ducts penetrate fire-separating elements when required by regulation.
• Avoid recirculation of polluted air (kitchens, garages, biomass wood stoves) without appropriate filtration and separation.
• Ensure electrical work is completed by a qualified electrician and systems are protected by appropriate controls.
• Provide user documentation: how to operate boost, change filters, seasonal adjustments and fault signs.
• Plan for access and safe maintenance — lack of maintenance is the most common failure mode.