Pre-Filter for Log Burner Smells

[benben5555]

Hi Chaps,

 

I've been installing my Vent Axia MVHR system the last few days (designed by BPC), its got the basic filter installed which I'm planning on changing to a F7 type. I'd like to add a pre-filter and a carbon filter. I've not got the time to make my own so would really like an off the shelf product. I saw the Blauberg Clean Box which has a set of 3 filters, but is expensive and the filters are extortionate. I'm also not sure about the added air resistance.

 

Any ideas on a simple solution? I don't mind spending a few quid as long as I can get the filters subsequently for a reasonable price.

 

Thanks

[Russdl]

If your installation permits I would recommend you commission the MVHR without the extra filters and see if the wood burner smell is a problem before going to the expense and hassle of adding additional filters. 

[Duncan62]

Above advice is laudable.

However I know I'm v sensitive to this so so be installing a large carbon filter on the intake to the mvhr.

 

https://www.growell.co.uk/products/mammoth-carbon-filters?variant=44069990924532

 

Something like this, with pre filter on the outside. Nice and large to give minimal pressure drop.

[Dave Jones]

The only issue you may have is the filter getting blocked up with dust/flies etc. 

 

I was amazed just how filthy our intake filter was after just a month, it was black. Zehnder recomened 120 days but im changing them 30-60.

[G and J]

When I discussed this issue with my preferred MVHR supplier they suggested that the carbon filter be placed after the unit, so the cheap filter in the unit reduces the build up of crap on the expensive carbon filter, but also said leave room for it to be installed inline but leave it to see if it’s needed, as it isn’t actually needed that often.  That works for me.

 

And @Duncan62, I looked up that link, it says it’s a 420 filter.  Are there lots of very relaxed people around your place? 😉 

[JohnMo]

We have G3/4 filters in our MVHR and few houses around us use log burners quite a bit. No smells in house, but if you go outside in the evening you do smell the smoke. I bought a carbon filter, but have never installed it.

[Russdl]

2 hours ago, Dave Jones said:

 

I was amazed just how filthy our intake filter was after just a month, it was black.

I made a pre-filter using tights as the filter element. Catches all the big crud before the air gets to the MVHR filters. Works well. 
 

3 hours ago, Duncan62 said:

I'm v sensitive to this so so be installing a large carbon filter on the intake to the mvhr.

There is a pig farm not too far from where we live and on occasions it stinks to high heaven. To date we’ve never smelt it indoors with the standard MVHR filters (and tights!)

[Mike]

4 hours ago, benben5555 said:

Blauberg Clean Box

The Paul/Zehnder ISO-BOX DN160 is much more affordable, as are the filters. Not sure if it's still sold in the UK though - got mine here: https://www.econology.fr/zehnder-comfosystems-caisson-filtrant-isobox-dn-160-filtre-a-pollen.html

 

Edited September 25 by Mike

[benben5555]

10 minutes ago, Mike said:

The Paul/Zehnder ISO-BOX DN160 is much more affordable, as are the filters. Not sure if it's still sold in the UK though - got mine here: https://www.econology.fr/zehnder-comfosystems-caisson-filtrant-isobox-dn-160-filtre-a-pollen.html

 

I did look around for that but couldn't find it anywhere

[JohnMo]

Here is an alternative 

https://www.aliexpress.com/item/1005003455622982.html?src=google&src=google&albch=shopping&acnt=494-037-6276&isdl=y&slnk=&plac=&mtctp=&albbt=Google_7_shopping&aff_platform=google&aff_short_key=UneMJZVf&gclsrc=aw.ds&&albagn=888888&&ds_e_adid=&ds_e_matchtype=&ds_e_device=m&ds_e_network=x&ds_e_product_group_id=&ds_e_product_id=en1005003455622982&ds_e_product_merchant_id=527456140&ds_e_product_country=GB&ds_e_product_language=en&ds_e_product_channel=online&ds_e_product_store_id=&ds_url_v=2&albcp=17859500389&albag=&isSmbAutoCall=false&needSmbHouyi=false&gad_source=1&gclid=CjwKCAjw6c63BhAiEiwAF0EH1MrTImL6T5sg-4vdV9V4pJsXZrbU5HeTBo5qkiis0U3iu0Em4qvraxoC6isQAvD_BwE

[benben5555]

I did see that one on AliExpress, but initially wrote it off thinking it may be suspect quality.

 

It lists the pressure drops and airflow, but I don't understand if these would be an issue

[Iceverge]

I used car pollen filters for our MVHR as the genuine ones were a rip off. I got a good deal recently so I switched back and the crappy MDF frame I made to support them with tape was falling apart.

 

It'd be an ideal project for a 3d printer to make a frame for them. 

 

They're cheap and carbon versions are readily available. 

 

You can search by dimensions here.

 

 

https://www.mann-filter.com/uk-en/catalogue.html#newproducts

[Nick Laslett]

My MVHR is still not commissioned. But I’m always amazed that this topic doesn’t generate more discussion. Of course circumstances differ, but I’m in the countryside with 2 neighbours that have log burners going all winter. I went with the Zehnder comfowell filter box because it will be easy to get hold of the filters over the long term. You will need to size the filter box to your system requirements. 

[JohnMo]

1 hour ago, benben5555 said:

pressure drops and airflow, but I don't understand if these would be an issue

Really depends on your system design and where you sit with regard pressure drops. More pressure drops require higher fan speed and more potential noise. You can always go big and use reducer to you duct - bigger the filter the lower the pressure drop.

[benben5555]

3 hours ago, Nick Laslett said:

My MVHR is still not commissioned. But I’m always amazed that this topic doesn’t generate more discussion. Of course circumstances differ, but I’m in the countryside with 2 neighbours that have log burners going all winter. I went with the Zehnder comfowell filter box because it will be easy to get hold of the filters over the long term. You will need to size the filter box to your system requirements. 

Thank you! This I think is what I've been searching for! Which size did you use and where is it mounted? Between intake and MVHR unit? Or before the manifold?

[Nick Laslett]

3 minutes ago, benben5555 said:

Thank you! This I think is what I've been searching for! Which size did you use and where is it mounted? Between intake and MVHR unit? Or before the manifold?

I have a Zehnder ComfoAir Q600. Looking at the design spec for my install the supply air (240m­³/hr =67l/s). I went with the Zehnder ComfoWell filter housing, CW-F 625. 
 

https://www.zehnder.co.uk/en/productsceletons/zehnder-comfowell-filter-box/zehnder-comfowell-filter-housing-cw-f-625

 

Due to space constraints in my install, I have the filter on the intake before the MVHR unit. The filter is designed to be fitted on the supply pipe after the attenuator and before the manifold. 

 

[MJNewton]

When our neighbour installed a wood burner I went in to full-on damage limitation mode, admittedly prior to even knowing whether there was any damage to limit! Instead of additional filters though what I did was install an air quality sensor in the intake duct and if/when it detects smoke particles (actually, it is not that discriminatory but smoke is within scope of what it can pick up) it triggers the MVHR to stop pumping in air for a while. There's some info of the approach here:

 

 

Incidentally, it turns out that in practice my wife's cooking appears to be arguably more of a threat than the neighbour's wood burner! So, I now have *two* sensors - one that turns the MVHR down if the neighbour's wood burner goes wild and another that boosts it when dinner's nearly ready. 😂

Edited September 26 by MJNewton

[MikeGrahamT21]

I’ve got a blauberg Cleanbox, it’s still on its first carbon filter 3 years in, and has done a cracking job, not had any smoke smells since it went in.

 

the other filters have been replaced once, a new G4 and then replaced the F7 with a H15, but agreed they are expensive.

 

I too found the Comfowell, but not til after I’d got this one. It’s available in the UK from Paul HR direct - https://www.paulheatrecovery.co.uk/product-category/mvhr-ducting/comfowell-modular-air-manifold-silencer-system/

 

id probably have gone for that just based on cost if I’d found it sooner!

[Duncan62]

10 hours ago, MikeGrahamT21 said:

I’ve got a blauberg Cleanbox, it’s still on its first carbon filter 3 years in, and has done a cracking job, not had any smoke smells since it went in.

 

the other filters have been replaced once, a new G4 and then replaced the F7 with a H15, but agreed they are expensive.

 

I too found the Comfowell, but not til after I’d got this one. It’s available in the UK from Paul HR direct - https://www.paulheatrecovery.co.uk/product-category/mvhr-ducting/comfowell-modular-air-manifold-silencer-system/

 

id probably have gone for that just based on cost if I’d found it sooner!

The comfowell looks like a good solution, can't believe I've not come across it sooner! Thanks

[benben5555]

On 26/09/2024 at 21:19, MikeGrahamT21 said:

I’ve got a blauberg Cleanbox, it’s still on its first carbon filter 3 years in, and has done a cracking job, not had any smoke smells since it went in.

 

the other filters have been replaced once, a new G4 and then replaced the F7 with a H15, but agreed they are expensive.

 

I too found the Comfowell, but not til after I’d got this one. It’s available in the UK from Paul HR direct - https://www.paulheatrecovery.co.uk/product-category/mvhr-ducting/comfowell-modular-air-manifold-silencer-system/

 

id probably have gone for that just based on cost if I’d found it sooner!

How have you found it? I've gone full circle and come back to thinking that the Blauberg is the best solution. Did you notice any extra noise due to the increased resistance from the filter?

[MikeGrahamT21]

5 hours ago, benben5555 said:

How have you found it? I've gone full circle and come back to thinking that the Blauberg is the best solution. Did you notice any extra noise due to the increased resistance from the filter?

It’s been flawless since the day it went in, still amazes me when I go outside and they’ve been burning stuff on the farms nearby, inside you would never know.

 

No noticeable noise increase, my unit is fairly small though since it’s only serving around 72m2 and the cleanbox is rated for a much higher throughput.

 

it did take 3 attempts at getting a unit which was completely intact with all the rivets where they should be, hopefully that will have just been bad luck