Recommend inline filter box with drop in easily replicable HEPA / charcoal filters?

Forums › Home Workshop DIY › Recommend inline filter box with drop in easily replicable HEPA / charcoal filters?

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timmmay

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#3381516 7-Jun-2025 08:38

Thanks @Kickinbac . Yes it does looks like a similar filter box, but with three filters instead of one. I was just going to chuck the filter box inline and see how much air comes through. I currently have the fan set on half speed and it's working fine with the simple filter, but I imagine it might need to go up to full power. It doesn't really matter what the throughput is, so long as some air comes through, I can just run it for longer than the current few hours per day. I'd rather have less filtered air than more unfiltered or poorly filtered air.

I've asked the fan manufacturer and filter manufacturer for specs, but I doubt I'm going to get them from either. Looking at specs for similar fans it looks like it'll probably do around 200L/sec, though I have it turned down to half, so it may be 100L/sec.

I'm very likely to order this filter when I get around to it.

timmmay

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#3388444 30-Jun-2025 20:50

The KCVents filter box turned up today, it less than two weeks from China to here. Overall it's very good, very solid, but one thing may need a modification. The part where you tape the duct to the box bit screws onto the main filter body, but there are gaps between the filter attachment and the filter box body. It's mostly ok, but there's too large a gap between the screws - four more screws and it'd be fine. There's a couple of mm gap there.

Given the filter is meant to go before the fan that means ceiling cavity air will be drawn into the input and filtered output of the filter box, which is a bit of a problem given how dirty and how much rat poison is up in my ceiling space. It also smells quite off in summer when it's hot. I could instead put the filter box after the fan so it's fresh filtered air being blown out of the box rather than sucked in, but that means wasting some of the filtered air, I'd have to make significant changes to my duct layout, and the fan won't have the protection of the filter.

I guess the best option is to unscrew the duct attachment, drill extra holes, potentially put in a bit of silicone rather than the neoprene or whatever they have there or use thicker neoprene, and put it back together. I'm not that confident in my ability to drill two perfectly places holes in metal, and I don't much like modifying brand new gear that should work properly. I might even see if I can find someone to do it for me. Any thoughts / other options?

Filter Box

Cover has a seal

Slots for the three filters

Filter Box

The prefilter on the right is a bit small, by a few mm. I can put in some rubber to fix that up easily enough

Filter attachment gap #1

Filter attachment gap #2 - light shining through gap - this shows the gap size

Handle9

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#3388462 1-Jul-2025 00:51

If you want to put in extra screws use self tappers and don't disassemble it. It'll just tighten the fit up without needing to removed the existing screws.

Put duct tape over the edges and you are done.

timmmay

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#3388470 1-Jul-2025 07:09

Handle9:

If you want to put in extra screws use self tappers and don't disassemble it. It'll just tighten the fit up without needing to removed the existing screws.

Put duct tape over the edges and you are done.

Thanks @Handle9. I don't have drill bits long enough to reach that part of the filter, just because of the geometry of how it all fits together, the drill would need to be about 10cm from the metal.

Duct tape is probably a practical idea. It'll last a decent number of years before falling off. I was thinking of a permanent solution but that's probably good enough and much lower effort.

Kickinbac

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#3388554 1-Jul-2025 10:04

You could unscrew the spigot and run a bead of silicon around and screw spigot back on.

Or even easier, just run a bead around the outside and smooth it off.

Edit: you could scrape the foam tape off and seal with silicon for the best finish.

For what its worth, Mitsubishi Electric Lossnay unit spigots attach in exactly the same way. I didn't do anything extra to seal it.

timmmay

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#3388560 1-Jul-2025 10:41

The foam tape would come off cleanly if I remove the spigot. Silicone seems like it could be a good option, it would fill the 3mm gap ok, but may be a bit messy - clear silicone might be best. Tape would be easiest but is also a temporary solution, but it would last a number of years. Silicone is seeming like the best option right now. Thanks for the thoughts, any others are welcome :)

timmmay

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#3395379 18-Jul-2025 16:05

I unscrewed the spigot and used clear silicone to seal the filter box. It seems to work quite well.

It's up in the ceiling now.

The air speed at the duct with the old filter was 1.7m/s, the air speed with the new filter is 2.2m/s. That's not a good volume measurement, but it shows the new filter hasn't reduced airflow. I guess it's because it has more surface area than the old filter, and the old filter hasn't been replaced in a while and may be a bit clogged. The new one is probably higher quality generally too.

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