Gone West Posted August 16, 2018 Share Posted August 16, 2018 I have aluminium outlet and intake vents for the MVHR with aluminium insect screens behind. They have been fitted for a couple of years or so and today while I was cleaning the crud off the intake vent insect screen I noticed the the aluminium had started to corrode. I could replace the aluminium insect screen or try brass or stainless steel. I originally used aluminium because I thought it would negate any possible galvanic action between the vent cover and the insect screen but if it's corroding anyway would brass or stainless steel be better? Link to comment Share on other sites More sharing options...
MikeSharp01 Posted August 16, 2018 Share Posted August 16, 2018 You are a long way from the sea so it's probably not salt corrosion, lets hope @JSHarris has some chemical theory as pretty much everything corrodes given the right atmosphere, might it be something the local farmer puts in the air as you are a bit exposed there - sadly the best solution might be, I hesitate to say it, plastic sorry. Link to comment Share on other sites More sharing options...
Onoff Posted August 16, 2018 Share Posted August 16, 2018 You could get the aluminium vents powdercoated as one option. If you replace them with "whatever" and have concerns over reaction between the two then tape the rear of the vent so it doesn't come into contact with the screen. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted August 17, 2018 Share Posted August 17, 2018 No to brass, but stainless should be fine. Stainless and aluminium aren't that bad together, copper or brass with aluminium are. You want stainless woven mesh, coarse enough to keep out larger flies but not so coarse as to cause any significant flow restriction. You can buy small pieces on ebay easing enough, just search for "stainless mesh" and make sure it'e the woven stuff. 1 Link to comment Share on other sites More sharing options...
Ian Posted August 17, 2018 Share Posted August 17, 2018 @PeterStarck all new bare (mill finish) aluminium will form a very thin and hard layer of aluminium oxide on the surface. That’s what gives it resistance to any further corrosion and it makes it highly durable Link to comment Share on other sites More sharing options...
Jeremy Harris Posted August 17, 2018 Share Posted August 17, 2018 The problem with aluminium is when it's in contact with itself. Stack two sheets together outside and it will corrode quite badly in the anaerobic zone where there in close contact, particularly if it's also damp, This will be exacerbated if one bit of aluminium is anodised and has breaks in the anodising, for example where there are screw holes or areas that were punched out after anodising. Stainless mesh will be fine, and almost certainly won't harm the aluminium sheet. It you are worried about it, then space the aluminium cover sheet off the mesh around the edge with some reasonably thick (say 2mm) double sided foam tape. If it were me I'd not bother with this, as I've banged enough stainless rivets into aircraft aluminium over the years and never yet seen a corrosion problem. If possible, don't choose "marine stainless", 316, but use 304, the standard grade. This isn't that far away from 6063 aluminium architectural alloy, which is what the plate will be made of, and won't cause a problem. 1 Link to comment Share on other sites More sharing options...
Gone West Posted August 17, 2018 Author Share Posted August 17, 2018 Thanks for all the replies. Looks like I'll be ordering something like this https://www.themeshcompany.com/products/-12-Mesh---1.67mm-Aperture---0.45mm-Wire-Diameter---SS304-Grade---Woven-Wire-Mesh--68.html#SID=60 Link to comment Share on other sites More sharing options...
Jeremy Harris Posted August 17, 2018 Share Posted August 17, 2018 Looks like it will do the job. You could possibly increase the mesh size a bit to get less airflow restriction if you wished, and still keep out most flies. Work out the area of the holes in your grille, than use the openness factor of the mesh to reduce the area caused by the mesh restriction and compare it with the cross sectional area of your ducting. Ideal the total effective area of the grille and mesh always needs to be greater than that of the ducting. Link to comment Share on other sites More sharing options...
Gone West Posted August 17, 2018 Author Share Posted August 17, 2018 It's got 62% open area which is fine for my grille and ducting size. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted August 17, 2018 Share Posted August 17, 2018 Sounds good to me. My concern was that with the first grilles I bought, the total grill area barely matched the duct area, and when restricted further by the plastic mesh insect screen it was around 30% or so smaller in area than the duct, even though it was designed to fit a 150mm diameter duct. Link to comment Share on other sites More sharing options...
Gone West Posted August 17, 2018 Author Share Posted August 17, 2018 Yes I understand, I bought very nice looking stainless steel bullnose vents with built in insect screens but when considering the loss of flow through the 90 degree bend and the insect screen I decided not to fit them. Shame really they did look good. Link to comment Share on other sites More sharing options...
Mr Punter Posted August 17, 2018 Share Posted August 17, 2018 21 minutes ago, PeterStarck said: Yes I understand, I bought very nice looking stainless steel bullnose vents with built in insect screens but when considering the loss of flow through the 90 degree bend and the insect screen I decided not to fit them. Shame really they did look good. I have bought some nice looking stainless steel vents with non-return type flaps and some have gone a bit rusty. Link to comment Share on other sites More sharing options...
Onoff Posted August 17, 2018 Share Posted August 17, 2018 You could design your own fancy vent cover and give a .dxf to a laser or water jet cutting place. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted August 17, 2018 Share Posted August 17, 2018 1 minute ago, Mr Punter said: I have bought some nice looking stainless steel vents with non-return type flaps and some have gone a bit rusty. I had this problem with some "stainless steel" bolts I bought for the shed. They also went rusty, not massively so, but enough to look unsightly. I believe there is a lot of really rubbish Chinese "semi-stainless" steel around, particularly with things like this. A friend has just had a similar problem with some "stainless steel" hinges he bought and fitted to lockers on his boat; they've actually rusted up so they barely move now, and that's mainly on fresh, or at the most brackish, water. Link to comment Share on other sites More sharing options...
D Walter Posted March 18, 2021 Share Posted March 18, 2021 Slightly off topic, but is there any guidance on use of insect mesh on the air intake for an MVHR system. We are in a rural area and the air intake filter gets a significant covering of insects in the summer so I have fitted a mesh cover to the external air inlet. As this could could inhibit the air intake flow rate is there any guidance/recommendations other than keeping the insect mesh clear? Link to comment Share on other sites More sharing options...
PeterW Posted March 18, 2021 Share Posted March 18, 2021 An internal filter box is a good idea as it’s a larger area and easier to clean out. 1 Link to comment Share on other sites More sharing options...
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