Yes. MVHR can be retrofitted, but it is usually easiest and most cost-effective during a major renovation, extension or deep energy upgrade when ceilings and walls are already being opened.

A survey is needed to confirm space for the unit, supply and extract duct routes, external intake and exhaust terminals, a condensate drain, electrical supply, room air-transfer paths and future maintenance access. The building’s airtightness should also be assessed, because the benefit of heat recovery reduces as uncontrolled air leakage increases.

Where a full ducted system is impractical, another compliant solution – such as continuous mechanical extract ventilation (MEV), demand-controlled ventilation or suitable room-based units – may be more appropriate. Zehnder offers upright ComfoAir Q units and compact ceiling-mounted ComfoAir Flex units, giving designers options for different layouts.

Ventilation can help remove excess heat when the outdoor air is cooler than the indoor air, particularly in the evening and overnight. An MVHR summer bypass allows cooler outdoor air to bypass the heat exchanger so that unwanted heat is not recovered. MEV can also increase air change by extracting warm indoor air and drawing replacement air through the building’s air inlets.

However, MEV and MVHR are ventilation systems, not air-conditioning. Their normal airflow is limited and they cannot always offset strong solar gains. Shading, glazing design, insulation, thermal mass and purge ventilation should be considered first. Zehnder ComfoAir Q includes a modulating summer bypass; where active tempering is required, a compatible ComfoClime unit can supplement cooling, subject to a proper overheating assessment and system design.

Yes, a correctly designed and continuously operated MVHR system can greatly reduce the risk of surface condensation and mould by removing humid air from kitchens, bathrooms and utility rooms and supplying fresh air to living rooms and bedrooms.

It is not a cure for every damp problem. Water leaks, rising or penetrating damp, cold bridges, inadequate heating, blocked terminals or poor commissioning must be addressed separately. Filters also need to be maintained and occupants should use boost mode when cooking, showering or drying clothes indoors.

MVHR will operate in any building, but it gives its best comfort and energy performance in a well-sealed home. If a building is leaky, cold air can bypass the ventilation system and heat exchanger, making airflow less controlled and reducing the value of heat recovery.

In Ireland, TGD F provides guidance for purpose-provided ventilation in dwellings with air permeability of 5 m3/(h.m2) at 50 Pa or less. For homes below 3 m3/(h.m2) at 50 Pa, a designed continuous mechanical system is needed rather than relying on background ventilators and intermittent fans. An MVHR target of about 3 m3/(h.m2) at 50 Pa or better is therefore a sensible starting point, with lower leakage normally improving performance further. The selected approach must be designed and commissioned to the current Irish Building Regulations.

Mechanical Ventilation with Heat Recovery is a balanced whole-house ventilation system. It extracts warm, moist or stale air from wet rooms and supplies filtered outdoor air to living rooms and bedrooms.

Inside the unit, the two air streams pass through a heat exchanger without normally mixing. Much of the heat in the outgoing air is transferred to the incoming fresh air, reducing ventilation heat loss and cold draughts. MVHR provides ventilation and heat recovery; it is not, by itself, the home’s main heating system. Zehnder publishes heat recovery of up to 96% for the ComfoAir Q range, although actual installed performance depends on airflow, duct resistance, commissioning and operating conditions.

MVHR is most appropriate in a new or comprehensively renovated home that is well insulated and airtight, where duct routes and maintenance access can be planned from the outset. It is especially useful where good indoor air quality, filtered supply air, low draughts, acoustic comfort and reduced ventilation heat loss are priorities.

It may be less suitable as a small stand-alone retrofit in a leaky dwelling or where there is no practical route for ducts. In those cases, MEV, demand-controlled ventilation or local room ventilation may provide a better result. The choice should follow an assessment of the full dwelling, not simply the purchase of a fan or heat-recovery unit.

Building and airtightness. Is it a new build, deep retrofit or light renovation, and what airtightness will be achieved?

Compliance and airflow. The system must meet the dwelling’s calculated whole-house and room extract rates under current Irish guidance.

Space and access. Allow for the unit, ducts, external terminals, condensate drainage, filters and eventual servicing or replacement.

Comfort. Consider noise, draught risk, filtration, humidity, controls, summer bypass and any overheating risk.

Performance. Compare heat recovery, fan energy, performance at the design pressure and availability of test or certification data – not just maximum airflow.

Delivery. Use a specialist who will design, install, balance and commission the complete system and provide drawings, results and user instructions.

For Versatile projects, the available range includes ComfoAir Q for larger upright applications, ceiling-mounted ComfoAir Flex for tighter spaces, and coordinated ComfoTube, ComfoWell and ComfoPipe air-distribution components.

There is no single allowance because it depends on airflow, house layout, structure and the duct system selected. Space is required not only for the room ducts, but also for the larger intake and exhaust ducts at the MVHR unit, manifolds or attenuators, bends, insulation, fire stopping and access.

A radial system commonly routes one or more small semi-rigid ducts from a central manifold to each room terminal. These can often be coordinated within floor zones, service voids, dropped ceilings, wardrobes or purpose-made bulkheads. The main external ducts are larger and should be kept short, well insulated where necessary and free from tight bends. Duct routes should therefore be agreed early with the architect and structural designer rather than fitted into leftover space. Zehnder’s coordinated air-distribution range provides several duct and manifold arrangements, but each project still requires a scaled design.

The best option depends on the room and the problem being solved. A bathroom or WC may only need a correctly sized intermittent or continuous extract fan. A habitable room may need a decentralised supply-and-extract heat-recovery unit. A damp issue affecting several rooms is usually better addressed through a whole-house ventilation assessment rather than fitting an isolated product.

Check airflow, noise, filtration, external-wall position, controls and how replacement air will move. A single-room unit should not be presented as a substitute for a compliant whole-dwelling strategy unless the complete design demonstrates that it meets the required ventilation rates.

People, cooking, showering, cleaning products, furniture and the building itself all add moisture, odours and pollutants to indoor air. As homes become more airtight, these contaminants can no longer be assumed to escape through gaps in the structure.

Effective ventilation supplies fresh air and removes moisture and pollutants. This supports occupant health and comfort and helps protect the building from condensation and mould. It should be controlled and continuous where required – opening windows remains useful for short-term purge ventilation, but it is not a dependable year-round ventilation strategy on its own.

The homeowner should follow the manufacturer’s instructions and keep the system running. Typical tasks include checking or replacing unit filters every 3 to 6 months, keeping internal valves and external grilles clear, and checking that the condensate drain is unobstructed. Dirty filters should be replaced rather than repeatedly run beyond their useful life.

A specialist should periodically inspect the unit, fans, heat exchanger, controls, airflow and accessible ductwork. The exact service interval depends on the product, location and indoor and outdoor air quality. The ComfoAir Q components are designed to be accessible for checking, cleaning and replacement, and its controls provide filter and status information.

It means customers can obtain Zehnder domestic ventilation products through an authorised Irish distribution partner, supported by local ventilation specialists. Versatile can assist from initial product selection and system design through supply, installation support, commissioning and aftercare.

The benefit is a coordinated, manufacturer-backed route rather than treating the MVHR unit and ductwork as unrelated products. It also gives the project a clear Irish point of contact for technical guidance, product support, warranties and ongoing service. The exact scope should always be confirmed in the project quotation or service agreement.