mesh size for external MVHR intake

[Tom]

The C02 levels seemed to be creeping up in the bedroom for the last week, so I checked the filters on the MVHR and the inlet one was absolutely caked in crap, including lots of quite large insects. This prompted me to take a closer look at the external inlet and it seems it has a 10mm mesh covering it. Is this a bit coarse? I don't want to have to be clearing the mesh every two minutes, but then again it seems like at 10mm it lets pretty much everything through...

[Russdl]

If you make the external mesh size much smaller it’ll be that which is bunged up in no time. 
You have to decide which filter you want to give the most regular attention to.
 

Personally I knocked up a pre filter to sit between the two, and now, on the Mk2, it’s all going very well - but it does need frequent cleaning, pretty much every 3 months. 

[JohnMo]

10 hours ago, Tom said:

inlet one was absolutely caked in crap, including lots of quite large insects

How often do you inspect - if it's that bad, maybe up the inspection and replace frequency?

 

Small mesh can equal frozen inlet in winter or an issue you need a ladder or scaffolding to fix

[mike2016]

My intake is metal but has big enough holes

My supplier recommended against any insect screen to prioritize air flow. Stops the fan demanding more power and providing less air to the house due to the blockage that can build up. Will need to clean the intake duct every few years. The insect screen will not filter dust, just insects. Depends where you live I guess, risk of bee hives? Not heard of any.....

[Mike]

My Zehnder intake is around 10mm too - enough to stop leaves, bats & birds.

 

 

I then have a filter box before the MVHR unit, with a large filter that can easily be changed, before the MVHR filter takes out anything that remains.

 

[Jolo]

43 minutes ago, Mike said:

I then have a filter box before the MVHR unit, with a large filter that can easily be changed, before the MVHR filter takes out anything that remains.

 

 

Can I ask where you bought that, Mike? I wanted something already insulated, but couldn't find where to buy one! Ended up using a metal one and covering it in Armaflex, which does work but it was a faff

Edited yesterday at 12:27 by Jolo

[Tom]

Thanks all. Seems like 10mm pretty standard for the external intake. I'll just have to change the MVHR filter more often, to that end have bought a 5m roll of filter wool 

[Nick Laslett]

Earlier thread on same topic, which didn’t really reach any conclusions. 
 

 

5mm mesh seems like a better size, but if Zehnder and Lindab both use 10mm, there must be a good reason. 
 

Some expensive options from this company. 
 

https://www.expandedmetalcompany.com/applications/filtration/air-filtration

[Mike]

1 hour ago, Jolo said:

Can I ask where you bought that, Mike? I wanted something already insulated, but couldn't find where to buy one!

Yes, on the intake it'd definately easier to have one that doesn't need extra insulation.

 

Mine was from Econology in France (site temporarily down). InovaTech in Germany sell a smaller one. So too does HomEvap, sold here in the Netherlands.

 

 

[Jolo]

Thank you @Mike that's useful info!

 

I discovered last night that despite my best attempts to cover the metal box, some condensation is forming in awkward to cover places, so I might take the plunge and get a proper one.

 

I do like DIYing stuff, but with the time and money I've spent on trying to insulate a metal box, I could have gotten the proper one!