Before instructing an installer to fit an MVHR (Mechanical Ventilation with Heat Recovery) system, there are several questions we'd recommend to help you qualify if they have the necessary skills and understanding.
Here are some important Q & As to ask to help validate your installer:
Q1 What experience and industry qualifications from industry-recognised organisations do you have?
The BPEC Domestic Ventilation training scheme or The NICEIC Domestic Ventilation Training Course are two of the more common qualifications for ventilation installation. These are good qualifications to have but the practical application of installation should be checked by the years of experience in installing MVHR and whether references from previous projects can be provided.
Q2 How do you make sure the MVHR system design for my house is right?
The first check box is to see if the installer produce will produce a full ventilation system design. To do this, they would need a set of architectural drawings. From the architectural drawings, a system design will be developed planning the duct runs and ensuring that they work with the structure of the building and that any potential structural clashes are identified.
Once this is done, the designer calculates the required air flows and the amount of pressure required to achieve them. This is known as ‘system pressure’. The longer and more convoluted the duct runs, the greater the pressure required to move the specified amount of air and the bigger the unit required. This information is used to match the size of motor/unit to the system.
Asking to see copies of previous plans can be useful. You should expect to see something like this setting out the duct runs supply/extract together with a table calculating the airflows required for each room.
Q3 How do you know what size MVHR unit to install?
From the system design, the amount of air and size of unit to move it is calculated. An essential part of this is to ensure that an undersized unit is not used.
The principle here is to select an MVHR unit to run at a maximum of 60% motor capacity on trickle speed and 66% on boost. Often, units are undersized so have to run harder to meet the air flows required. This can make quotes look financially more attractive, as smaller units cost less, but as the motor runs harder, the unit’s lifespan is reduced as components wear out more quickly and system noise increases. It’s a bit like running a 1-litre car @ 70 mph vs a 2-litre car at the same speed. The bigger motor the less stress it has so it does it with less noise and it lasts longer.
Q4 Ducting - What type of ducting system do you use?
There are two formats of ducting often known as a) radial and b) leg and branch – metal or PVC.
Leg and branch is a traditional duct format which takes its air flow from one main duct run – like branches of a tree:
The modern alternative is radial ducting. This takes individual duct runs from a central manifold directly to each room. Like spokes from the hub of a wheel:
Different installers have their own preferences depending on the system that they are used to working with. Our preference is to use radial ducting as it is more secure and easier to install and commission.
What is important is that your installer should have awareness of both systems and be able to explain the differences between them.
For more details on this please see our post on ‘Ducting Systems’ here
Q5 Installation Process
It is often a good idea to ask some general questions around the installation process. Here are three quick questions:
Q i Do you need to insulate any of the ductwork?
A: Any ducting running in a ‘cold space’ i.e. outside of the thermal envelope of the home and not in a ‘warm’ loft area should be insulated.
Q ii During installation and throughout 1st and second fix, does dirt get into the duct work and what about the MVHR Unit?
A: The open ends of the ducting should be sealed at all times during construction to prevent the ingress of dirt and dust. This is good practice. Most good semi rigid ducting has end caps available for this purpose.
The MVHR should be kept sealed or ideally off site until after 1st fix and the majority of the 2nd fix items have been installed. The unit should be one of the last items to be installed/delivered.
Q iii Where should I site the MVHR unit?
There are few issues here – not least of which is subject to available space but the principles are that the unit should ideally be sited within the warm space of the home, have room enough to provide for servicing and maintenance such as changing filters and be in a central location which minimises the duct runs. If the unit is to be situated in a cold space, i.e. loft or garage, additional attention will need to be paid to insulating the unit/ducting.
Q6 Commissioning
After installation, what is the process for commissioning the unit?
Once all ducts are in place, the valves installed and the unit connected, it is necessary to commission the system. Commissioning is part of the Building Control sign off process and seeks to ensure that the air flows specified at the design stage are matched by those achieved in practice. To explain a little further.
In the design, flow rates for individual rooms and the house as a whole are calculated to meet Part F Building Regulations. Ultimately, the design equation means air in vs. air out is equal. As you can see on the chart below, extract and supply rates are equal for both on normal and boost speeds.
It is the job of the commissioning engineer to make sure that the specified flow rates for each room are achieved in practice, set, and recorded. In summary the commissioning engineer should check details are as per the specification and provide documentation at handover for Building Control and ongoing reference.
If you'd like to find out more about how an MVHR systems operates, why not check out one of our other blogs: The Anatomy of an MVHR System
Epicair Ltd is a leading designer and installer of MVHR systems in the UK. Please give us a call on 01892 600121 or contact us on mvhr@epicair.co.uk to talk to our experts who will be happy to answer your questions on your MVHR project.
