Insect mesh size behind intake and exhaust grills

[Thorfun]

greetings. I have fitted the supplied Lindab 250mm grills to our MVHR intake and exhaust vents and it seems apparent that maybe I should put some insect mesh behind them as it sure does look very open for insects and spiders etc to find their way into the system.

 

 

the 250mm grills attach to a 250mm -> 200mm reducer and then we have 200mm ducting to the Zendher Q600 unit. I was wondering what size mesh would be best to not limit the air intake/exhaust but that would be effective in stopping insects entering and setting up home somewhere in the system. I found an eBay site that offers woven stainless steel mesh in the following mesh size. 

 

 

I'm thinking the 20 mesh count with a 52% open area would definitely stop insects but is that too restrictive? maybe the 10 mesh count would be better but at 2mm average hole size it seems large enough to let insects in? 

 

anyone got any suggestions/recommendations/comments?

 

[Conor]

There should be mesh on them. There is on mine. Speak to lindab in case it's a mistake.

[Thorfun]

11 minutes ago, Conor said:

There should be mesh on them. There is on mine. Speak to lindab in case it's a mistake.

interesting and thanks. I will speak to Linda. that looks rather large mesh openings though, not sure if that will stop any form of insect though will it?

[JohnMo]

Mine has about 4 to 6mm mesh openings.  Did read somewhere that if it has a fine mesh it should be removed.

[Thorfun]

ps. I can't take them back now as I've painted them black! so I might just have to bite the bullet and purchase my own mesh.

[Conor]

1 minute ago, Thorfun said:

interesting and thanks. I will speak to Linda. that looks rather large mesh openings though, not sure if that will stop any form of insect though will it?

Nope. My filter gets cleared out regularly.

[Thorfun]

Just now, JohnMo said:

Mine has about 4 to 6mm mesh openings.  Did read somewhere that if it has a fine mesh it should be removed.

thanks. I found this thread on here

 

 

where @Gone West was purchasing 1.67mm mesh and it was deemed that wasn't an issue. that's why it's all so confusing, there seems to be much conflicting information out there.

[Thorfun]

1 minute ago, Conor said:

Nope. My filter gets cleared out regularly.

that was my other option, forget about the mesh and just clean out the filter more regularly! but swmbo is worried about spiders getting in even though I've explained there's a filter in the unit they wouldn't get through. I think the thought of 1000s of spiders dropping down through the MVHR vents while she sleeps is weighing on her.

[Gone West]

23 minutes ago, Thorfun said:

that was my other option, forget about the mesh and just clean out the filter more regularly!

Where are your vents fitted? I fitted ours in a position where it was easy to brush them off two or three times a year. The insect screens worked well but the important thing is that the mesh open area is sufficient for the vent size and duct cross sectional area so there isn't any reduction in flow rate.

[Thorfun]

3 minutes ago, Gone West said:

Where are your vents fitted? I fitted ours in a position where it was easy to brush them off two or three times a year.

at the front of the house between the front door porch (which is the to right in the photo below) and the side door (the glazing at the left of the photo). so access is pretty easy.

 

 

6 minutes ago, Gone West said:

The insect screens worked well but the important thing is that the mesh open area is sufficient for the vent size and duct cross sectional area so there isn't any reduction in flow rate

how do you begin to calculate that? 

[Gone West]

2 minutes ago, Thorfun said:

how do you begin to calculate that? 

Now you're asking. I'll have to try to remember how I did it. IIRC  I worked out the area of the duct, which in my case was quite small, so I didn't want to restrict the flow at all. I then made a square cover, as in the original thread, which was larger than the duct, which when multiplied by the open area of the mesh gave at least as much area as the duct.

[Russdl]

@Thorfun I had similar concerns and ended up making a ‘pre filter’ box between the vent and the MVHR unit. I used a pair of tights as the filter material, works a treat. If you’ve got the space/time it may be worth a go. 
 

 

[Thorfun]

3 minutes ago, Gone West said:

Now you're asking. I'll have to try to remember how I did it. IIRC  I worked out the area of the duct, which in my case was quite small, so I didn't want to restrict the flow at all. I then made a square cover, as in the original thread, which was larger than the duct, which when multiplied by the open area of the mesh gave at least as much area as the duct.

sounds complicated. might be easier just to clean the filter in the unit more often! 

 

I presume also that as I'd have to clean the mesh behind the grill regularly that the grills can't be glued in any way and will need to be attached with screws? I guess I could vacuum the mesh through the grill slats if I did use adhesive/silicone to affix the grill and seal around it?

[Thorfun]

Just now, Russdl said:

@Thorfun I had similar concerns and ended up making a ‘pre filter’ box between the vent and the MVHR unit. I used a pair of tights as the filter material, works a treat. If you’ve got the space/time it may be worth a go. 
 

 

thanks. didn't find that thread in my search! will read with interest.

[Thorfun]

17 minutes ago, Russdl said:

@Thorfun I had similar concerns and ended up making a ‘pre filter’ box between the vent and the MVHR unit. I used a pair of tights as the filter material, works a treat. If you’ve got the space/time it may be worth a go. 

read through the thread now. very impressive indeed! but I don't have the space in the plant room for anything like that. might have room for one of those pre-made inline filters that were linked in the thread though. I'll speak to the MVHR designer and installers and see what they suggest with regards to insect mesh, pre-filters. but maybe, I am, as usual, just worrying about nothing and shall just clean out the MVHR filters more regularly.

[tuftythesquirrel]

How about a small piece of 3-4mm anti-alkaline render mesh. Cheap and lasts for ever.

[Thorfun]

3 minutes ago, tuftythesquirrel said:

How about a small piece of 3-4mm anti-alkaline render mesh. Cheap and lasts for ever.

still quite large though albeit kind of midway between the 1.67mm and 4mm - 5mm others have.

 

I can guarantee you that I will end up not bothering! it's one of a 1000 things on my list of things to do and think about and it is rather rapidly moving down that list.