Heat-Recovery Ventilation: Fresh Air, Less Heat Loss

A heat-recovery unit transfers the warmth of outgoing air to incoming fresh air. In an airtight home it provides fresh air without opening windows or throwing heat outside.

Modern windows and insulation make homes airtight. That keeps heat in, but it raises a question: where will fresh air come from? Opening a window throws out warmth in winter and coolness in summer, and lets in street noise and dust. Heat-recovery ventilation was designed to resolve this contradiction: the air is changed while most of the energy stays in the house.

How it works

At the heart of the system is a heat exchanger. Stale air extracted from the kitchen, bathroom and toilet and fresh air drawn from outside pass through it without mixing, along channels separated by thin walls. In winter, warm outgoing air gives part of its heat to the cold incoming air; in summer the process runs the other way, with cooled room air taking the edge off hot outdoor air.

Fresh air is supplied to bedrooms, the living room and the study, while stale, humid air is extracted from places like the kitchen, bathroom and walk-in wardrobe. This flow moves air through the whole house from clean rooms toward "dirty" ones.

Some exchangers transfer only heat, while others also transfer part of the moisture. The second type helps prevent overly dry air in winter and too much humidity coming in during a humid summer.

Central and single-room units

In a central system, one unit serves the whole house and air is distributed to rooms through ducts. This is considered the most efficient and quietest option for private houses and large apartments, as the unit is hidden in a plant room, attic or above a suspended ceiling. Ducts, however, need space: some ceiling height or dedicated shafts.

Single-room, wall-mounted units need no ducts. They are fitted into a hole in the external wall and usually work in pairs: one extracts while the other supplies, then they swap direction. They are practical where ducts cannot be run in an existing apartment or where individual rooms need a solution. Their efficiency and acoustic performance can differ from a central system, so noise levels deserve special attention in bedrooms.

Design and installation

A central system must be installed during the rough stage of a renovation, before ceilings and partitions are closed. During planning, these questions need answers:

• where the unit will sit and whether there will be easy access for changing filters;
• whether the fresh-air intake and exhaust outlet are far enough apart, and away from bins, parking or chimneys;
• whether ducts have silencers so sound does not travel between bedrooms;
• whether supply and extract grilles are placed where furniture and curtains will not block them;
• whether gaps under doors or transfer grilles in walls allow air to pass between rooms;
• whether ducts running through cold zones are insulated and condensate drainage from the exchanger is provided.

The airflow is calculated by an engineer according to floor area, number of occupants and room use. A wrongly sized unit either delivers too little air or becomes noisy at high speed.

The kitchen hood is a separate matter. Its greasy air must not pass through the heat-recovery exchanger, since grease fouls the exchanger and ducts. The hood either has its own exhaust duct or works in recirculation mode, filtering the air and returning it to the room; with powerful extract hoods in an airtight house, a route for make-up air should also be planned so the home is not starved of air.

Maintenance

The unit's filters must be replaced regularly, more often in dusty surroundings or near construction work. A dirty filter reduces airflow, strains the unit and worsens air quality. The exchanger and drain line are checked periodically, and access hatches are provided for cleaning the ducts.

In summer, when outdoor air at night is cooler than the rooms, a bypass mode that skips the heat exchanger is useful: cool fresh air is supplied straight into the house. Ask whether the unit has this feature when choosing.

Who needs it

Heat-recovery ventilation makes particular sense in well-insulated, airtight houses, in apartments on noisy or dusty streets, in households with allergy sufferers, and where bedroom air feels stuffy in the morning. Compared with window ventilation, the system delivers a constant, measured and filtered supply of air.

Zaferoğlu İnşaat sets the position of building services together with the ceiling plan and design project in apartment and house renovations. If you want to plan early how ventilation ducts can be hidden within the interior, write to us.