AllStar – Air Conditioning – London



What is MVHR and how does it work?

A balanced heat recovery ventilation system (MVHR) works by continuously extracting air from the wet rooms within your property (e.g. kitchens and bathrooms) and simultaneously pulling in fresh air from outside which is filtered, introduced and extracted via a network of ducting Mechanical Ventilation with Heat Recovery (MVHR) is a whole house ventilation system that both supplies and extracts air throughout a property. Heat recovery is a domestic heat recovery system, which is increasingly used to reduce the heating and cooling demands of buildings.


What’s the difference between MVHR and MEV?

MVHR allows the recovery of a substantial part of the heat extracted by the ventilation thanks to a heat exchanger, while humidity sensitive MEV (or, more generally, a demand-controlled system) automatically reduces the rate of air renewal in order to limit heat loss as soon as the home is less occupied (which is usually most of the time). When the climate is temperate, the MVHR and the humidity sensitive MEV are almost equal. The MVHR becomes more beneficial in energy terms when the outdoor air is very cold, as it is the case of the Nordic countries.

Are MVHR systems worth it?

Within older buildings that have a persistent issue with dampness and mould, MVHR units are a blessing that will help eliminate these ongoing issues. If you are looking to achieve Passivhaus levels of air tightness, then a MVHR is a must.

Does MVHR prevent condensation?

An MVHR System is the best solution to preventing condensation problems in the home. Whether in new builds, or installed during renovation, an MVHR is the best system to install to ensure humidity comfort. An MVHR system will also supply fresh filtered air into the habitable rooms in your house.

Does MVHR reduce humidity?

MVHR systems will additionally reduce the indoor humidity, through the de-humidification effect of heat recovery. The more outside air temperatures are colder than inside air temperatures, the incoming air will increase in temperature and thereby decrease in relative humidity.

Can MVHR heat a house?

MVHR will re-use the heat which already exists in your home produced by occupants and electrical equipment. Some systems can be designed to have an additional in line heater, to heat supply air, but this can only provide a small amount of heating.

Do you need heating with MVHR?

MVHR systems are based on air supply, air extract and transfer zones within the building. The need to completely heat the fresh air as it enters the building is eliminated. Efficient systems typically heat cold outside air from 0ºC to 18ºC through the heat transfer, when the extract air is 20 ºC.

How does MVHR work in the summer?

Many MVHR units now come with true summer bypass which is designed to ventilate the home and supply fresh filtered air all year round. Incoming filtered fresh air bypasses the heat recovery element during the warmer summer months when heating isn’t needed.


The summer bypass is set for both comfort temperature and minimum external temperature. This allows a home to be pre-cooled for the following day by taking advantage of cooler night-time temperatures.

Is MVHR air conditioning?

MVHR systems are ventilation systems, not heating or cooling systems (although heating and cooling of the supply air can be provided).

Can MVHR cool a house?

As MVHR facilitates air movement, and the exchange of heat that is already present within the home, it will NOT cool the air or heat the air to a temperature greater than that already existing inside the house.

Where can MVHR be situated?

The unit is normally installed in the loft space or cupboard and rigid ducting supplies fresh filtered air to the habitable rooms and extracts stale polluted air from the ‘wet’ rooms. Supply and extract diffusers are fitted to the ceilings and are adjusted to balance the system.

Can you turn off MVHR?

It is important to remember that the MVHR ventilation removes VOCs and moisture. Fresh filtered air and good air movement also prevents mould growth so the MVHR should not be switched off.

How do you calculate MVHR?

On larger homes multiply the usable floor area to achieve a minimum ventilation rate of 0.5 air changes per hour. e.g. a 5-bedroom house with a floor area of 200 m2 would need 66 l/s (200x height of rooms of 2.4 m =480 m3 / 2 = 240m3 /3600(seconds/hr) = 66l/s).

Does MVHR reduce dust?

Yes, all of our MVHR systems have F7 and G4 filters which will filter out pollen, carbon dust, insects, etc from the incoming air.

CAre MVHR systems noisy?

MVHR can be most problematic, as supply air ducts run directly to noise-sensitive rooms (bedrooms and living rooms), however noise from continuously running extract systems in wet rooms (bathrooms and kitchens) also have the potential to annoy residents, particularly in open plan kitchen/dining/living rooms. Noise in mechanical ventilation systems is a common problem. Even though systems are often able to provide the required ventilation rate, the occupants lower fan speed setting because of the noise disturbance. Too little attention is paid to noise during the design and construction phases.

What is MVHR boost?

January 25, 2021. Mechanical Ventilation with Heat Recovery (MVHR) is a continuous source of ventilation that extracts stale, moisture-laden air from a building and resupplies fresh, filtered air back in, resulting in a comfortable and condensation free environment all year round.

Are trickle vents required with MVHR?

The short answer is no, you do not need trickle vents if you have a full mechanical ventilation and heat recovery system. A properly commissioned and installed MVHR system will meet the necessary building regulations relating to ventilation.

Do you need an extractor fan with MVHR?

Whole house ventilation eliminates the need of extractor fans, as MVHR extract terminals are installed in all wet rooms, sanitary accommodation and kitchen, which extract excess humidity and pollution.