Steve Mongan, Head of Marketing at Xpelair Ventilation Solutions, discusses whole house ventilation.

Ensuring adequate ventilation for dwellings is more important than ever before with further changes to the Building Regulations having come into force in October 2010. With Part L dictating that carbon emission levels will have to be cut by another 25% compared to 2006 levels, and Part F ensuring that homes have to become more airtight, it is not surprising that interest in whole house ventilation systems has increased.

The two main types of whole house ventilation systems are Mechanical Extract Ventilation (MEV) and Mechanical Ventilation with Heat Recovery (MVHR). MEV systems can comprise either a whole building central extract system or low energy extract fans in individual rooms. Designed for simultaneous ventilation in separate areas of a building, the unit is located in a loft or airing cupboard, with ducts running to quietly remove pollutants at source from areas such as bathrooms, kitchens and utility rooms. Alternatively, individual continuous running extract fans can be installed to form a MEV system in new or refurbished properties.

MVHR continuously extracts polluted air from a building. This stale air is passed through a heat exchanger, which is then used to pre-warm incoming fresh air. This ensures a fresher, warmer and more comfortable environment. No window trickle ventilation is required avoiding noise ingress issues.

Technological advancements

Whilst whole house ventilation has been around for decades, major technological advancements have been made in recent years. More energy efficient heat recovery cells have been incorporated that can recover up to 95% of a property’s heat that would otherwise be wasted. A move from AC to DC motors has also resulted in at least 50% less power required to run the system. More recently, EC (Electrically Commutated) motors, which have all the electronics built-in to them, have also been developed to save even more energy. There has also been a growing emphasis on aesthetic appeal, meaning the whole design, look and feel of a solution has been completely transformed.


The fact that these systems need a certain amount of ducting means they are ideally suited to the new build marketplace or the refurbishment sector where ducting can be installed without restrictions. To help, Xpelair has put together a step-by-step installation guide for its Xcell 150QVW – a new generation of MVHR units. With a highly insulated structural foam body and four 125mm top entry spigot connections, the range features a 90% energy efficient heat exchanger, EC ultra low energy multi-speed single inlet external rotor motors and long life G4 filters.

Step 1

Measuring before mounting wall brackets
Make sure the wall brackets are level using a spirit level

The unit, which weighs only 17kg, can be mounted direct onto a block or brick wall using the 3 mounting brackets supplied. If the wall is low density, a 15mm plywood board should be fixed to the internal frame of the wall and the unit mounted to that. Mark the positions for the holes using the diagram included in the installation booklet and use a spirit level to ensure that the installation will be level when completed in order to ensure effective drainage of condense. The condense drain will require connection to the waste water system via a trap, therefore consideration should be given to this when selecting where the unit will be sited along with future access for routine maintenance. The unit can be mounted R/H or L/H to assist in the later routing of ducting.

Step 2

Installing an MVHR system

Having checked that there are no buried pipes or cables, the wall can be drilled and wall plugs fitted. The brackets are then securely fixed in place ready for mounting the MVHR unit. Slotted fixing points allow for minor adjustment to heights at the next stage.

Step 3

Use the fastening screws to secure the unit to the wall

Determine whether the unit is to be mounted R/H or L/H then remove two fastening screws from the top of the unit and four from the bottom, the unit can be supported in place whilst the 6 fastening screws are re-fitted securing the unit to the wall.

Step 4

Connecting the condense drain

The condense drain can now be connected, this must be installed to the wastewater system in accordance with Building Regulation H1. If this is to run through a frost prone area, this will need heat tracing. To access the inner casing, rotate the access cover to the left, this will reveal the heat exchanger and filters, these can be carefully pulled out noting which side of the filters faces the heat exchanger. Fit the drain tube supplied through the hole on the underside of the machine ensuring the end with non slip tape is used. Once the condensate drain assembly is complete, the heat exchanger and filters can be replaced. The heat exchanger retaining bracket must then be fitted and the access cover replaced.

Step 5

Removing the electrical cover on the top of the machine gives access to the PCB where both the mains supply and connections to the controller are made. This must be carried out in accordance with the wiring diagrams provided in the installation booklet and current IEE Wiring Regulations.

Step 6

The ducting system can now be installed in accordance with the prepared design. It is very important to follow the design closely with regard to duct type and size, noting where bends and reductions in size are shown, they have a major influence on the final performance.

Step 7

Use rigid ducting before sealing all joints with flexible ducting

Rigid ducting should be used with flexible duct only for final connections, rigid duct creates considerably less resistance as the air passes through and is not as prone to damage or inadvertent restrictions. It is very important to properly seal all joints within the ductwork system using a flexible silicone sealant and tape. This ensures against leaks. All joints should be properly supported to avoid strain and the risk of failure at a later date.

Step 8

Insulate ducting passing through unheated spaces

All ducting passing through unheated spaces must be insulated to prevent condensation and to preserve heat. Whether in an unheated space or not, the two ducts running from the machine to atmosphere must be fully insulated. Care should be taken to ensure that there are no areas of the duct missed.

Step 9

MVHR duct passing to the atmosphere

The two ducts passing to atmosphere should be sited apart, we recommend by two metres, and must not be located where there are flue outlets, foul vents or opening windows. Where wall terminals are used, the cored holes should fall slightly to the outside to prevent water ingress.

Step 10

Using an anemometer with a venturi cone fitted to check and set the flow rate at each extract and supply valve

Having installed the system it must now be set up to meet the design flow rates, this is carried out using an anemometer with a venturi cone fitted to check and set the flow rate at each extract and supply valve.

Step 11

Adjustment can be made to the Xcell 150 QVW low normal and boost rates by adjusting the potentiometers on the PCB located underneath the electrical cover.

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