My Zehnder Q350 MVHR was installed as part of a (partial) deep retrofit in 2017 so it’s about 5 years old. Firstly, the MVHR system has been amazing. Trickle vents don’t work, and opening windows just wastes heat and leads to poor comfort, but the MVHR means year round excellent indoor air quality and comfort, energy savings, and added benefits such as beiog able to keep windows shut when the neighbour has a party (or the seagulls are on your roof!) and also clothes dry quickly, sometimes overnight.
That said, maintenance of the MVHR system has been more involved than expected and in my case living in a city, the INTAKE filters need changing every 6 months, but the EXTRACT (which can be vacuumed) can last up to 12 – 18 months, so a total cost of about £50/year. The kitchen grease filter needs flipping over every month or so and changing every couple of months, but these are cheap. I had fitted the black fleece filters to the extract terminals in the bathroom and ensuite to reduce the dust making it to the EXTRACT filter in the unit, but these clog up fast and need vacuuming (at the very least monthly), so maybe best left off and keep a closer eye on the filter in the unit itself. The Q350 controller indicates when the filters in the unit need attention but no such alarm for the kitchen grease filter, whcih gets clogged quick and I suspect there are many systems out there, even in Passivhaus buildings, with blocked kitchen extracts.
You’re supposed to maintain the unit itself every couple of years, but I didn’t do this as everything looked good, i.e. the unit was using a similar amount of energy as when installed (just ~21W) and noise was normal, but then the EXTRACT fan failed. A new fan was £460 plus fitting (so not cheap) but when removed it was clear that even with a well maintained grease filter in the kitchen it had got pretty grimy, (although this may or may not have been the cause of it’s failure), but I’ll be maintaining the unit every 2 years from now on (perhaps a further £100 per year if undertaken by a third party).
The heat exchanger wasn’t too bad, just need a vacuum and a degrease to remove the fat from the kitchen
Two of the sensors on the unit had failed and were swapped out FOC by Zehnder.
So overall the cost of running an MVHR could be seen as similar to a gas bolier?
The kitchen has a recirculating cooker hood with the MVHR terminal nearby (as per Passivhaus doctrine) but in future (retrofit) projects I’ll consider ducting the cooker hood directly to the outside as it’s much more effective for removing smells and should go a long way to reducing the build-up on the (expensive) MVHR unit.
The kicker is that when rechecking the flow rates to the terminals, we noticed that one or two of the extract terminals couldn’t reach the desired flow rates and on inspection found that at least one duct had come away. This is a shame as the system was very carefully designed and installed. More on the resolution to this issue next time.
Maintenance by Carl Fivash of Eco Ventilation info@cfecoventilation.co.uk