Home Ventilation Systems

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 reduces the heat normally lost when warm indoor air is replaced with cold outdoor air. It does not create free heat; it transfers much of the heat in the outgoing air to the incoming fresh air.

There is no single percentage saving that applies to every home. The benefit is greatest in a well-insulated, airtight dwelling with a correctly designed and commissioned system. Savings depend on the climate, indoor temperature, ventilation rate, airtightness, heat-recovery efficiency, fan electricity and how the occupants use the system.

Normally, no. A standard MVHR unit is a ventilation appliance, not the home’s main heating system. It recovers existing heat and supplies tempered fresh air, but the airflow required for good ventilation is usually too low to carry the full heating load of a normal house.

In some exceptionally low-load Passive House projects, a suitable post-heater may provide all the space heating, but this must be confirmed through PHPP and room-by-room heat-loss calculations

The preferred location is inside the insulated and airtight envelope, in a dry, frost-free utility room, plant room or suitable service cupboard. This limits heat loss and condensation risk and makes filter changes and servicing easier.

The unit needs a firm load-bearing wall or suitable floor support, a nearby electrical supply, a correctly trapped condensate drain and clear access to the front and filters. The four main ducts must also be routed without tight bends or unnecessary length.

Avoid locating the unit in or immediately beside a bedroom where possible.

Use a purpose-designed, airtight ventilation duct system with smooth internal surfaces. A radial semi-rigid system from supply and extract manifolds is usually the best domestic solution because it reduces joints, makes balancing easier and limits room-to-room sound transfer. Properly sealed rigid ductwork can also be used.

The main ducts between the unit and the manifolds or outside terminals must be sized for low velocity and low pressure loss. The outdoor-air and exhaust-air ducts passing through warm parts of the building must be vapour-sealed and thermally insulated to prevent condensation and unnecessary heat loss.

A well-designed MVHR system should be very quiet in normal operation. Noise problems are usually caused by an undersized unit, excessive duct pressure, high air velocity, poor terminal selection, missing attenuation, vibration transfer or incorrect commissioning.

Noise must be considered as a complete system: sound from the unit casing, fan noise travelling through ducts, air noise at valves and grilles, and cross-talk between rooms. The unit should be selected to operate comfortably below its maximum airflow at normal duty.

Good practice includes low-resistance duct routes, correctly sized valves, attenuators between the unit and room ductwork and vibration-isolated mounting.

Supply fresh air to habitable rooms such as bedrooms, living rooms, studies and dining areas. Extract stale, humid air from kitchens, bathrooms, shower rooms, utility rooms and WCs. Air then transfers through the dwelling, normally through door undercuts.

Place supply terminals so the air can mix across the room without blowing directly onto beds, sofas or regularly occupied seating. Locating a supply terminal away from the doorway generally encourages air to sweep through the room before leaving.

Place extract terminals close enough to the moisture or odour source to be effective, while keeping them accessible for cleaning.

Yes. The system should be designed so the valves, manifolds and ducts remain accessible. Smooth-bore radial ducts can be cleaned from the room terminal or manifold using specialist brushes and vacuum equipment.

The first priority is prevention: keep the unit running with the correct filters fitted, change filters when indicated or at the recommended interval, and clean room valves without altering their commissioned setting. Extract ducts normally collect more dust than supply ducts.

There is no need to clean all ductwork to a fixed short timetable if inspection shows it is clean. Inspect periodically and arrange professional cleaning where there is visible contamination, reduced airflow, persistent odour, building dust or evidence that the system was operated without filters.

Summer bypass allows some or all of the incoming fresh air to physically bypass the heat exchanger when heat recovery would make the home less comfortable. Ventilation continues and the incoming air remains filtered.

It is most useful when the house is warm and the outdoor air is cooler, for example during a summer evening or night. It does not provide air-conditioning and cannot cool the home below the outdoor-air temperature. Shading, limiting solar gains and purge ventilation remain important.

During a very hot day, recovering the relative ‘coolth’ from cooler indoor extract air can be better than bypassing. For this reason, an intelligent system considers both indoor and outdoor conditions rather than simply opening the bypass whenever it is summer.

Heat-recovery efficiency describes how effectively the heat exchanger raises the outdoor air temperature using heat from the extract air. In simplified form: efficiency = (supply temperature after the exchanger – outdoor temperature) ÷ (extract temperature – outdoor temperature) × 100.

For example, with 20°C extract air and 0°C outdoor air, 90% temperature efficiency would give a theoretical supply temperature of about 18°C before allowing for fan heat and duct losses.

A quoted 90% or 96% does not mean the total heating bill falls by that percentage. It refers to heat transfer under stated test conditions.

Electricity use varies continuously with airflow and duct resistance. Because fan power rises sharply as airflow and pressure increase, an oversized pressure drop caused by small ducts, dirty filters or restrictive terminals can materially increase consumption.

The best estimate comes from the selected unit’s duty-point data, including both fans and the actual external pressure. Annual use can then be estimated as electrical input in kW × operating hours. For example, 40 W continuously is about 350 kWh/year; 70 W is about 613 kWh/year.

MVHR and a heat pump are complementary but normally separate systems. The heat pump normally provides space heating and, where designed to do so, domestic hot water; the MVHR provides continuous fresh air and reduces the ventilation heat loss that the heating system must replace.

The room heating system – for example underfloor heating, radiators or fan coils – should still be sized from a room-by-room heat-loss calculation. That calculation should include the residual ventilation loss after heat recovery. MVHR should not be switched off to save electricity, as this can lead to poor indoor air quality and moisture problems.

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.

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.

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.

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.

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.