Using MVHR with Air Conditioning: The Benefits of Combining Both Systems
- Simon Chalkley
- 3 days ago
- 5 min read
Modern homes are increasingly airtight and well insulated. This helps reduce heat loss during winter, but it also makes effective ventilation essential and can increase the risk of overheating in summer.
Mechanical Ventilation with Heat Recovery (MVHR) and air conditioning can work particularly well together because they perform two different jobs. MVHR provides continuous fresh, filtered air and removes stale, humid air. Air conditioning actively cools the home and controls the indoor temperature.
When both systems are correctly designed, they can create a home that feels fresh as well as comfortably cool.
What does MVHR do?
An MVHR system extracts stale, humid air from kitchens, bathrooms, utility rooms and other wet areas. At the same time, it supplies fresh, filtered outdoor air to bedrooms, living rooms and other habitable spaces.
Inside the MVHR unit, energy is transferred between the outgoing and incoming air without the two air streams mixing. During winter, heat from the extracted air warms the incoming fresh air, reducing ventilation heat loss.
In summer, when the home is cooler than the air outside, the heat exchanger can also help limit the amount of outdoor heat entering through the ventilation system. When it becomes cooler outside than inside, often overnight, the summer bypass can allow the cooler outdoor air to enter without recovering unwanted heat.
MVHR can support summer comfort, but it does not actively chill the air.
What does air conditioning do?
Air conditioning actively removes heat from the indoor air. A typical domestic system takes air from a room, cools and filters it, then returns it to the same space. Many modern systems can also operate in reverse to provide heating.
Most domestic air-conditioning systems recirculate the existing air within the room. They do not normally bring in enough outdoor air to ventilate the home or remove stale air from bathrooms and kitchens.
This is why air conditioning and MVHR are not competing alternatives:
MVHR controls ventilation and indoor air quality. Air conditioning controls temperature.
The problem with trickle vents and extract fans
Without MVHR, a modern home will commonly rely on window trickle vents to bring in replacement air and bathroom or kitchen extract fans to remove stale, humid air.
This provides ventilation, but it does not recover energy from the air leaving the building. During hot weather, open trickle vents can continually allow warm outdoor air to enter. At the same time, extract fans whether continuously running or activated when a room is used, remove indoor air that the air-conditioning system has already cooled.
The air conditioning then has to cool the warm replacement air entering through the trickle vents. This can increase the cooling demand and make it harder to maintain a consistent indoor temperature.
An MVHR system provides a more controlled alternative. Fresh air enters through the MVHR unit rather than numerous uncontrolled window openings, and energy from the outgoing air can be transferred to the incoming air when conditions are suitable.
MVHR will still introduce the fresh outdoor air required for a healthy home, so some cooling demand is unavoidable. The benefit is that the airflow is controlled, filtered and able to pass through the heat exchanger rather than entering directly through trickle vents.
Benefits of using MVHR with air conditioning
Fresh air while the windows remain closed
Opening windows or trickle vents during hot weather can allow warm outdoor air into the home. MVHR provides controlled fresh air while the windows remain closed, allowing the air conditioning to operate more effectively.
This can also reduce disruption from outdoor noise, insects, dust and pollen.
Better indoor air quality
Air conditioning usually filters and recirculates the air already in a room. MVHR continually introduces fresh, filtered air while removing carbon dioxide, odours, moisture and other indoor pollutants.
Together, the systems provide temperature control without allowing the home to become stale or stuffy.
Improved bedroom comfort
Bedrooms can become uncomfortable during summer, particularly in highly insulated homes or rooms within the roof space. Opening windows may introduce noise, pollen or security concerns.
MVHR supplies fresh air to the bedroom while air conditioning controls the temperature, creating a cooler and fresher sleeping environment without relying on open windows.
Reduced cooling losses through ventilation
When it is hotter outside than inside, an MVHR heat exchanger may transfer some heat from the warmer incoming air to the cooler outgoing air before it is exhausted.
MVHR does not create cooling, but this energy recovery can reduce the temperature difference the air-conditioning system must overcome. This is more efficient than simply drawing warm air directly through trickle vents while cooled indoor air is extracted outside.
Can the systems share the same ductwork?
In most homes, MVHR and air conditioning should remain separate.
MVHR ductwork is designed for relatively low, continuous ventilation airflow. Air conditioning requires much higher airflow to heat or cool a room effectively. Trying to distribute all the cooling through standard MVHR ductwork can lead to poor performance, excessive resistance and unwanted noise.
The usual approach is for the MVHR system to ventilate the whole home while separately positioned air-conditioning units provide cooling to selected rooms or zones.
Why early planning matters
The best time to consider both systems is during the design stage of a self-build or major renovation. Early planning makes it easier to coordinate:
MVHR ductwork and ceiling valves
Air-conditioning unit positions
Pipework, condensate drains and electrical supplies
Ceiling voids and service routes
Access for filter changes and maintenance
Noise-sensitive areas such as bedrooms
It also prevents clashes between services and helps ensure that both systems work efficiently without compromising the finished appearance of the home.
Do all homes need both systems?
Not every property needs air conditioning. External shading, appropriate glazing, insulation and night-time ventilation may be enough to maintain comfortable temperatures in a well-designed home.
Air conditioning may be worth considering where there are large south- or west-facing windows, extensive rooflights, bedrooms within the roof space or a known risk of overheating. It can also be installed only in priority rooms, such as bedrooms and heavily glazed living areas.
Whatever cooling strategy is chosen, the home still requires effective ventilation. MVHR provides this without relying on trickle vents and separate extract fans.
The key takeaway
MVHR and air conditioning are most effective when each system performs its own role. Air conditioning actively cools the home, while MVHR provides fresh, filtered air and removes stale, humid air.
Compared with a conventional arrangement of trickle vents and extract fans, MVHR provides more controlled ventilation and can recover energy from the air being exhausted. This helps the air conditioning maintain comfortable indoor temperatures without continually losing as much cooled air and drawing warm outdoor air directly into the home.
Together, the two systems can provide a fresher, cooler and more comfortable home
throughout the year.
Planning an MVHR system for your home?
Rega Ventilation has over 40 years of experience designing domestic ventilation systems. Whether you are planning a self-build, renovation or new development, our team can design an MVHR system around your property and wider building services.
Contact Rega Ventilation to discuss your project or request an MVHR quotation.
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