Audits for Ventilation Systems

A ventilation audit examines how fresh air enters a home, how stale, moist air leaves, and whether that exchange is controlled, adequate, and balanced across rooms. It checks trickle vents, window opening, extract fans in kitchens and bathrooms, passive stacks, and mechanical systems with or without heat recovery, alongside humidity, condensation and indoor air clues. Ventilation is the system most often damaged by energy work, because sealing and insulation change airflow, so auditing it before retrofit is protective as well as diagnostic.

A ventilation audit does not aim to maximise airflow or minimise it, but to achieve controlled exchange: enough fresh air for health and moisture removal, without excessive heat loss through uncontrolled draughts. That balance is room-specific, since kitchens and bathrooms generate most moisture, bedrooms need overnight fresh air, and living rooms need comfort without draughts, and an audit should judge each room's ventilation against its use.

Route checks come first: where does air enter, through trickle vents, windows, or a mechanical supply, and where does it leave, through extract fans, stacks, or a mechanical extract. An auditor will check whether vents are open or painted shut, whether fans work and vent outside rather than into a loft or cavity, whether duct runs are long, kinked or blocked, and whether internal doors allow air to move from supply rooms to extract rooms via undercuts or grilles.

Measurement adds to observation: airflow rates at extract fans, humidity readings, carbon dioxide logging where used, and condensation patterns across seasons. A fan that runs but extracts little air, due to a blocked duct or failed motor, is a common finding, as is a trickle vent system defeated by occupants closing every vent to stop draughts, which then causes condensation that is blamed on insulation rather than on ventilation loss.

Check fan and vent function before the audit: run each extract fan, note noise, airflow feel, and whether it vents outside, and check trickle vents are open and clean. Note window opening habits, laundry drying locations, and cooking and bathing patterns, because ventilation needs follow moisture generation, and an auditor who does not know moisture sources cannot judge whether ventilation is adequate.

Check for combustion and safety interactions: open fires, stoves and gas appliances need air supply, and mechanical extract in a home with an open flue can affect flue operation. Tell the auditor about all combustion appliances, and ask how ventilation changes will be checked against appliance safety, because ventilation and combustion safety are linked and must be designed together.

In the UK, ventilation audit practice follows building regulation ventilation guidance, which sets different provisions for new and existing homes, and retrofit standards that require ventilation assessment alongside airtightening. A UK auditor should therefore check ventilation against current regulation and retrofit guidance for the home's type, not against a generic airflow figure imported from another system.

In EU member states, ventilation traditions vary widely: mechanical ventilation with heat recovery is standard in Nordic new homes, natural ventilation with trickle vents dominates in many Western European homes, and passive stack systems appear in older stock. A homeowner abroad should check national ventilation standards and common systems for their building type, because a ventilation audit's expectations differ sharply between those traditions.

One ventilation mistake is auditing ventilation only after sealing work. An audit carried out after draught-proofing and insulation, when condensation has already appeared, must diagnose a problem created by earlier work, while an audit before work could have prevented it by specifying ventilation alongside sealing. Ventilation audit should precede airtightening, not follow it as remediation.

Another mistake is treating a single fan or vent as the whole system. Ventilation works as a route: supply, transfer and extract together, and a powerful extract fan with no supply route, or a supply vent with no extract route, will underperform. An audit should judge the whole route, room by room, rather than rating individual components in isolation.

Keep the ventilation audit report, fan airflow results where measured, humidity and condensation notes, duct and vent photographs, and any mechanical system manuals and servicing records. That file allows future retrofit professionals to design ventilation alongside fabric work, rather than rediscovering routes and faults.

Ask an auditor what ventilation each room needs, what route supplies and extracts it, and what changes if airtightness increases. Ask how ventilation interacts with combustion appliances, and what maintenance fans, filters and vents will need. Those answers turn ventilation from an afterthought into a designed system.