Specifiers Guide to Design

Ventilation is often overlooked or considered late on when a site has already installed joists, heating and plumbing pipes and sometimes even ceilings. This can result in a number of obstacles for the designer and the installer of the MVHR to overcome and the consequence is often time consuming, costly and can result in a less efficient system.

It is important to work with CVC Direct right from the start, when designing your building, as this will allow the MVHR design to be incorporated with other services such as timber joist frames, water and heating pipes, that all have to be fitted together.

To maximise the Heat Recovery System performance, especially the heat exchange efficiency, it is suitable for dwellings with an air tightness levels of 5ach or below (air changes per hour).

Basically, the more sealed the dwelling, the more effective the heat recovery system will be for the home and its occupants.  

If the building is leaky to begin with, the rewards of recovering the heat are minimised and somewhat lost! 

Provision for system from the start.

Unlike intermittent unitary fans, whole house ventilation systems cannot be specified towards the end of a project, because it is extremely important that their ductwork be considered in the structural design of a property, as well adequate space for the unit and associated components, be considered.

The larger the property, the larger the volume of air required to ventilate the property. So it is very important that the correct unit is specified from the start and that adequate space is left for the unit. 


Once MVHR has been selected, it seems in some projects it is quite forgotten until installation. In the meantime timber or eco joists are installed in a home without considering how the ductwork interacts with them.

As MVHR gains in popularity Posi and Eco joists are increasingly specified alongside, since they offer easy access for the installation services. These types of “open-web” joists combine timber with aluminium struts in the middle allowing space for the ductwork to go straight through. However, these joists are not the sole answer for MVHR installations which allow designers to ignore the detail in their ventilation strategy. Although these joists are a simple idea which can be effective, designers need to ensure the joists line up and are properly installed otherwise the ductwork will not fit through. 


As well as considering joists it is essential to select the correct type of ducting for an MVHR system, to ensure the correct ventilation rates are achieved. When designing and installing ducting it is important routes take the path of least resistance. Plus it is important to size ducting correctly to suit the system you are using. There are numerous solutions for ducting, for which CVC can help you choose  the correct solution for your project. 

Again advice on ductwork specification should be left to a ventilation expert. Unfortunately leaving the services to this late stage can cause problems such as noise issues and, at worst, a system that cannot be Commissioned for Building Regulations. Meanwhile, without detailed drawings for the MVHR systems at the design stages often developers can find SAP calculations can fail to add up at the end of the project, causing costly alterations to be made. To ensure the best outcome it is important for architects and designers to seek expert ventilation advice at the design stage.