1st January seemed like a good date to pick to swap the MVHR filters. They’re expected to need changing three times a year (the reminder on the unit is set to 120 days) but it’s generally recommended to do the first swap a bit early since there tends to be a fair bit of dust from all the construction.

Before and After on the first set of MVHR filters

The F7 filter (left pair) is on the Intake (from outside into the heat exchanger) and the G4 (right pair) is on the Extract (from the house into the heat exchanger – to protect the heat exchanger from dust). You can probably tell which are the old and new filters within each pair 😉 . The “new” G4 isn’t quite as white as the new F7 because it was in the MVHR unit as supplied from the factory but swapped for an F7 at commissioning time (2016-08-25). For information about the different grades of filter see this Wikipedia article.

I must say I’m surprised the intake filter is so dirty after just over 4 months of use in a relatively rural location. Houses in London need filters changing quite often (see e.g. http://www.bere.co.uk/tags/mvhr) but I was expecting South Derbyshire to be cleaner. Maybe pollution from the traffic on the nearby A50 is to blame. Whatever the source, it’s better to have the dirt trapped by the filter than carried into the house.