Whilst in England and Wales installers of MVHR systems need to have some basic training (BPEC course on domestic ventilation), in Scotland there is no training mandatory. As you can imagine this leaves the door wide open for a variety of quality levels and approaches.
If you want to know what are the top 10 mistakes what we often find on various sites, see below. You can forward the slides by clicking on the right h/s of the image.
- MVHR ducting needs space within the service zones. Other services can easier be installed around the ventilation ductwork. We therefore recommend to co-ordinate the services and give the ventilation ductwork priority at first fix.
- Keeping ductwork clean is important. Ductwork should be capped off with end caps and kept in clean storage spaces.
- This image sadly shows a typical MVHR installation in the UK: PVC ducting with sharp bends, no silencers, flexi-insulated ducting. We do recommend to avoid PVC ducting and keep flexi ducting to minimal lengths if at all. Machine and cross-talk silencers and appropriate insulation should not be overlooked.
- Rectangular PVC ducting has the advantage of using little service spaces, but it has got major disadvantages, too. Whatever the ductwork, appropriate sealing of all components is important. System-specific sealant rings are to be preferred over tapes or mastic. Rigid metal ducting e.g. can be purchased with double seals at all connectors. Please do not use duct tape as it is not a permanent solution.
- If short lengths of flexible ducting is to be used, it should be of good quality, e.g. canvas ducting, rather than foil-based types, which can be easily damaged. Connections with flexible ducting should be robust, e.g. with jubilee clips. If possible avoid flexible ducting, especially in inaccessible spaces (ceiling zones).
- Supply and extract ductwork in cold roof spaces need special attention. Ideally it should be kept 100% within the thermal envelope, e.g. fully underneath the loft insulation. Any ducting outwith the thermal envelope should be heavily insulated, e.g. with 100mm of ductwrap.
- Cold bridges and thermal bypasses can greatly affect the performance of a system and the building in general. Please be aware of the all-round integrity of the insulation.
- Forming the external penetrations for the intake and exhaust early in the building progress will avoid complications in the later stage. The type of insulation of the ductwork outwith and within the wall needs to be specified, as well as the connection to the air tight envelope, e.g. with air tightness grommmets.
- We often find extract valves next to bathroom doors, which short-circuits the air flow. Also wall supply valves often need to be of special design. The typical plastic vales are to be avoided as they often cannot be properly locked in position. If deviations from the ducting layout and specification are necessary, please contact the designer.
- All whole house MVHR systems need specialist commissioning at the end, in order to check and adjust the unit and each room outlet. At the same time the end-customer can be given a short introduction into the system. Without a handover the customer is more likely not understanding the purpose of the system, using and maintaining it in-correctly.