Mechanical Ventilation Heat Recovery (MVHR) systems have in recent years become ever more popular, especially in new build homes. They ventilate the home at the right rate, recover heat from the stale extracted air and filter the incoming air to keep the home fresh and healthy.
However, while most MVHR systems are described as almost fit-and-forget systems, with claims that you only need to check the filter ‘every now and then’, this is only partially true.
As with any mechanical technology there is always the chance of mechanical wear and tear, or even failure, and therefore periodic inspection and preventative maintenance is advised. But exactly how often is ‘every now and then’?
Does MVHR maintenance involve a lot of work?
As the manufacturers state, the main component of an MVHR system requiring regular maintenance are the filters. That said, it’s not a difficult task or one that will take you hours.
Most of the rest of the MVHR system does not need constant maintenance, but there are some items of the MVHR system that may need periodic inspection just to check that they have not suffered with substantial wear or unusual dirt build up.
MVHR costs can be high, so you’ll want to take care of your system properly to avoid any problems. It is also important to ensure ensure it’s serviced regularly by a qualified professional as well as the MVHR maintenance tasks you can perform yourself.
MVHR maintenance: Filters
Most MVHR fan units will have a minimum of one set of filters. They are dust filters and could be either G3 or G4 filters. These are coarse particle filters with the G4 being slightly finer than a G3.
Other filters that are used for the supply air are F7 or F8 filters, which are very fine filters that can potentially filter fine airborne particulate such as pollen. Another filter that is often found in MVHR units is a charcoal (carbon) Nox filter. This filter potentially filters out exhaust fumes or smoke, which is particularly useful near busy roads.
The frequency of filter changes depends a lot on how much work the filter has to do, although every 3-6 months is often recommended.
It is common to change the dust filters around once or twice a year and sometimes cleaning them with a vacuum cleaner can be helpful, albeit not all dirt is dry, or loose enough to vacuum out.
The charcoal and pollen filters on the other hand are more expensive and as such, to save on costs, the pollen filters for example, can be used at certain times of the year rather than throughout the whole year.
As an example, I have G4 filters in the fan unit and then on the supply air I have a filter box with a further G4 filter as well as an F7 and Nox filter to filter the air going to the home.
Less popular, but also an option for a busy kitchen is to have grease filters in the room extract vents to prevent any dirt clogging up the heat exchanger in the fan unit. These filters are sometimes part of the ceiling vent, but for bigger filtration volumes you may need to install a plenum box, which is effectively a grill on the ceiling that has a box behind it that is hidden in the ceiling void and holds the filter.
Maintaining the filters is a fairly simple user-friendly operation. However, the fan unit should be installed in an area that is easy to reach or it simply won’t be done and your MVHR unit could then clog up with dirt and the air flow will be restricted, resulting in a humid home as well as the potential to burn out the fan motors.
Filters can be purchased from the fan unit manufacturer, but there are also many other online vendors of the filters that offer competitive pricing. Filters can be bought from 3rd party vendors but spare parts for the fan unit should always be purchased from the manufacturer.
Shop for replacement MVHR filters
Vent-Axia Heat Save Pm10 Iso G4 Coarse 60% Filter
These coarse filters are available from Screwfix
Vent Axia Kinetic Advance F7 Particulate Filter
An F7 filter for trapping finer particles
Airflow Dv90sck Dv90se Filter Pack
A pack comprising two G4 filters and one F7
Other elements requiring MVHR maintenance
Other parts of your MVHR system requiring occasional maintenance are as follows.
Condensate drains
Any condensate drains should be periodically checked to ensure they still work and have not got blocked due to dirt buildup.
The condensate drain should have a dry trap fitted to it which is a short piece of pipe that has a rubber non-return valve in it. This lets the condensate water run to the waste pipe, but prevents smells from the waste pipe entering the MVHR system and filtering into the home.
Ceiling valves
The ceiling valves in each room can get quite dirty, especially the extract valves in the bathroom and kitchen because the air is moist and laden with airborne contaminants. Subsequently, the valves will need cleaning.
The white metal valves on your system are fairly easy to clean. They twist out of the ceiling, but be careful to only twist them by the outer rim as the inner plate can move, potentially changing the airflow and balance of the system.
Wipe them with warm water and household cleaner, but be careful to make sure you dry them to avoid rust.
Another important tip is to make sure you do not get the valves mixed up. Even though they will fit in the ceiling fittings in other rooms, they will have been adjusted and set for that particular valve. If the valves do get mixed up or readjusted, then you will need to get them rebalanced by an experienced MVHR installer with a calibrated anemometer.
Be sure not to mix up your ceiling vents when undertaking MVHR maintenance(Image credit: Rega Ventilation)
Digital display
Many MVHR units have a digital display. Always check that the display is working as some have small batteries in them to run the memory. Any boost switches may also have batteries in them if they are wireless, or fitted in wet rooms.
FAQs
Does a noisy MVHR system mean it needs maintenance?
Although some claim noise is one of the MVHR disadvantages, the MVHR unit should not be a source of noise. If you notice new sounds then you may need to check with the installer as sometimes the bearings can get worn in the fan motor, which creates a breakout sound.
A fan motor replacement is a job that should be done by an experienced installer. The fan unit itself will usually have a five year warranty with the first year or two including parts and labour and the remainder parts only. Always check what is covered and for how long to avoid any nasty surprises.
As with all mechanical technologies the quality can vary between products and so does the price. The MVHR fan unit is running all day, every day, and therefore it is worth getting a good one and then making sure it is maintained to optimise its life expectancy.
Under normal design working conditions and with the basic maintenance regime followed, the MVHR system should keep you and your home fresh and healthy for many years, without you really knowing it is there.
Considering one for your self build? Find out what’s involved when adding one to your design, in our guide to MVHR installation.
View the original article and our Inspiration here
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