Mechanical Ventilation Heat Recovery Unit: filter replacement
A very high level of airtightness is a key component of an energy efficient building. Such buildings therefore also require a good quality mechanical ventilation heat recovery (MVHR) system to (i) provide an extremely high indoor air quality, and (ii) avoid surface and interstitial condensation.
Like a number of items in many homes, an MVHR unit requires servicing, and, mostly, this is extremely simple and can be done by the owner. Here, we describe the main servicing needed: the five-minute six-monthly job of cleaning/replacing the air filters with the MVHR unit we have — a Zehnder Comfoair Q350.
Our MVHR controller [1] tells us when its filters should be cleaned (after 6 months) or changed (after 12), based on the time since the last filter service.
Flapping down the plastic cover on the front of the MVHR unit (see photo above) reveals a menu panel and the two filter covers [2].
Touching the ∟character under the ‘change’ [2] and then ‘next’ [3] headings will take you through the step-by-step filter change program.
The first step is to remove the pull-out filter covers to reveal the filters [4]. The filter on the left is the finer-grade F7 intake filter cleaning the air coming in to the house, and the standard G4 extract one, on the right, stops the dust picked up in the house from entering the MVHR mechanism. They have different labels — just be sure to get them round the right way when you replace them.
Touching the ∟character on the menu screen as you work through each stage [5] and [10] tells you what to do.
Next slide out the left-hand (intake) filter [6] and [7] - which will be the dirtiest, and then the right-hand indoor (extract) filter [8] and [9].
Originally, we replaced both filters every six months, but have been since advised that tapping the dirt off and then gently vacuum-cleaning them at six months and replacing them yearly is sufficient.
The amount of dirt and insects trapped by the intake filter [6] and [7] over six months seems incredible and shows what the MVHR system is helping to keep out of the house — and is one of the reasons why a passive house indoor environment always feels so fresh and clean.
Following the menu instructions [10], slide in the clean left filter, ensuring it’s the correct one [11], touch the ∟character and insert the other filter [12] and [13] and then, following the menu instructions each time you touch the ∟character, replace the filter covers [14].
Confirm that you want to exit the filter change wizard [15] and close the front cover [16]. Simples!
We get replacement filters from our original MVHR system designer/supplier (Green Building Store). Buying in bulk saves money and transport costs.
We recommend that you don’t skimp on filter cleaning/changing (and remember to wash the grease filter on the kitchen extract duct every three months or so) — it’s really simple and quick and will help to ensure that you continue to have a clean, fresh indoor environment and that your MVHR unit is protected from the sort of debris you can see in the photographs above.
Experience the passive house difference yourself by staying at Woodlands Malvern B&B; we’ll be pleased to talk with you about our experience of self-building and living in a certified passive house.