Hi we have a Vortice Prometeo 400 MVHR unit. It's been in about a year now and seems ok. We had the filter warning light come on and realised is was probably time to change the filters. Big shock - 2 x F5 filters =£70! (bet they cost less than a couple of quid each to make). So that's going to add £70 pa to my running costs.

That got me thinking, why do I need filters? We are not hayfever sufferers, so not bothered about pollen (and in any case have the unit off and windows open during the summer). It's good to keep insects out but I could easily make some permanent mesh filters to achieve that? There'd be the added benefit of less air resistance in the system so less enregy running costs, i'd guess.

Anyone think why this might be a bad idea?

Thanks

I have a Vent-Axia Sentinel Kinetic BH MVHR unit. I'm pretty sure that the "check filters" warning on it is driven by a count of operating hours rather than a direct measurement of filter performance. Other MVHR units may use the same approach. I just remove them, give them a gentle shake or very careful use of a vacuum cleaner and put them back. Haven't had to have the filters replaced yet, probably on an annual maintenance visit.

The main job of the filters is to keep larger dust particles off of the fan blades and out of the ductwork. My guess is that not using approved filters might at the very least invalidate your warranty. There might be other considerations that might make it a bad idea.

Most MVHR units have fairly basic specification filters. If you want to remove allergens such as pollen and mould spores or even small particulates you would probably require a separate filter on the input. I considered an option for a separate electrostatic filter (~ £600) on my system but have decided to try without one initially.

Apart from keeping fans and ducts dust free, I assumed the main reason for the filters is to keep the heat exchanger clean. I suspect these would be quite sensitive to surface coverage, and so reduce the efficiency of heat recovery - the main point of having the MVHR unit.

Vacuum off the surface debris (some filters even recommend gentle washing with warm water and a mild detergent). I supose they can withstand wetting, as they will see condensation in normal use. I guess that without re-checking the flow rates around the house, you won't know what the increase in differential pressure across the filters will be, so you won't know what the actual "blockage" level is. I have more experience with large industrial HEPA filters, and it is quite amazing how much the air flow can be restricted.

Ignoring my comments above (as they don't actually answer the OP), you could do the vacuum cleaner thing, for a year or two, and see if you notice a deterioration in air quality around the house - ie. just begining to feel a bit stale in the morning (the air that is, not you personally).

Also, make sure you have an insect mesh on the fresh intake - and clean that out every few months.

Hope something in that helps.

GreenPaddy.

The filters in mine are quite coarse and easily cleaned by banging them on the wall as you would a rug. Now four years old.

Posted By: Simon Still

Posted By: docmartinWhen I installed the unit the installation guide advised the fitting of a pre-filter on the intake when a summer by-pass is fitted, although it has its own small filter. However the inlet filters are only trivially soiled compared with the exhaust side from the rooms.

Ha. You obviously live in the country....

My extract filter has a layer of grey dust. The 'air from outside' filter is black with London filth after 3 months or so...

No, it sounds like he lives in a pigsty inside a clean room! In the country, our 'air from outside' filter gets covered with brown stuff, presumably dust from ploughing, harvesting etc laced with fertiliser, insecticide, weedkiller. Oh and a good smattering of crane flies in season. Our 'air from inside' filter however remains fairly clean, as do the ducts.

Posted By: CerisyWith you djh - our filters need cleaning every month. Washed them many times, but had to buy new ones. Not too expensive from Titon, but I could have just bought the filter medium.

I washed out our heat exchanger yesterday (which is why i was came across this post). Instructions for the filters for my Vent-Axia said that the inlet/outlet filters could/should be vacuumed but *NOT WASHED* (in bold, explicit).

I vacuumed my Vent Axia filters and they still seemed pretty dirty so I washed them which removed a lot more dirt.

I hadn't read the manual, but it didn't appear to do them any harm. However, I don't know what I cannot see...

I bought replacement filters and filter material from http://www.fairair.eu/en/

Posted By: snyggapaWhat I don't know is which way round to install them - they appear to be "keyed" as they have a metal hook on one end and a cloth tab on the other. It goes in either way round at my whim, no idea which is correct!

The Hook is just a spacer to stop them being pushed in too far/line them up with the opening on the heat exchanger. The tab goes at the front for you to pull them out with.

I'm using FairAir filters - they don't have the hook so you just need to line them up at the front.

Pressure washing? How?

Posted By: Cerisywe don't like dull grey buildings!!

I was amazed we got away with it. Normally around here if it's part of a house then it must be painted white and if it's not part of a house then it must be painted black. It was partly as a reaction to that policy that we put untreated cedar in our application!

To be fair, I don't think our building is dull. The walls are almost all a pale cream render (actually its very pale ochre (3%) but that doesn't convey the colour very well) and the roof is silver, so the bit of cedar cladding provides a bit of relief.

If you have not got a foot to use can you use 0.3 of a metre?