Installing filters on my ducts

October 11, 2015 10:53 PM

I have ducted, evaporative aircon in my house, with vents in the ceiling in every room. I am wondering if will help to install some sort of 'screen' or filter in the inside of the vents to prevent dust and insects being blown inside when we turn the system on? Would prefer a cheap/DIY solution (it's a rental).

I have noticed that there is literally NOTHING separating the inside of my house from the roof space (except for the lame plastic air-flow 'directors'). As in, in some cases, I can even see through to the outside. My house is a rental, with *extremely* non-responsive owners, so there is not much I can do about fixing the fact that there seems to be holes in the roof and in the ducts (I have informed them and they don't seem to care about the obvious potential for rain damage, although at the moment I don't notice any leaks or anything, so its possible its just under the eaves. It does not seem to affect anything else, except that my house is dusty). Therefore I was thinking about taping some sort 'filter-type' cloth or screen on the insides of all the vents to prevent (hopefully the majority of) dust/bugs from getting into the house. Preferably black, so it's not noticeable.

However, there seems to quite a bit on conflicting advice around the interwebs on this concept, most of it seeming to be based on the American style 'central air' heating systems, with the vents in the floor. Some say just to install cheesecloth, and other places are selling these specialised 'vent-shaped' filter pads, which is brilliant, but are obviously not built to fit on my style of vent (large and square). Others are saying that doing such will destroy your system (due to increased airflow pressure I guess, which sounds a bit urban myth-y to me...but anyways, it's not mine so I don't want to take any chances). I was not thinking of putting anything so thick it would decrease the airflow, just something to trap dust/bugs that I could either toss or wash every few months.

So could anyone who has any ducts (of any sort) in their home tell me if you have a 'filter' between the duct and your roof? What material does it most resemble? Or even better, if anyone has installed something yourself, what did you use? And did you find it decreased the airflow, or at least to such an extent that your system seems to be suffering? Anyone's system 'destroyed' by putting thin cloth-like material on the vents? Does anyone have any suggestions for what material would be best for filtering dust/bugs, without hampering the system too much?

I'm new to ducted aircon, only ever had wall-rattlers or reverse cycle, so any suggestions are most welcome :)

posted by Shibui to Home & Garden (3 answers total)

You can get spun glass filter material which is inert and won't get moldy or mildewy or linty (which adds more dust to the air). It comes in sheets or rolls, it's washable and relatively cheap. Don't have any direct A/C experience, but I've used the spun glass as furnace filter material and it works great. It's also designed so as to not add much air resistance and load down the blower.
posted by Zedcaster at 1:50 AM on October 12, 2015

If the issue is the crack between the edge of the metal duct and the drywall, which it sounds like it is, then you can just remove the vent and seal that gap up. Low-expanding spray foam works in larger gaps or you can use caulk or foam backer rod plus caulk. This will work much better than a filter for your purposes.

If the issues is something else, can you explain what it is? Why do you want to filter the air coming out of the ducts (as it is already filtered)?
posted by ssg at 12:49 PM on October 12, 2015

I'm a little confused about how your house is built. Is there actually a duct (a tube or boxy-shaped channel that the air travels through)? When you say this: "I have noticed that there is literally NOTHING separating the inside of my house from the roof space (except for the lame plastic air-flow 'directors')." I think you are saying that the air goes into the attic, rather than through a duct. Also, where I'm from, we call an evaporative system a cooler and air conditioning is a different thing, which might be confusing some people. The air is pulled from outside by a giant fan through some panels with wood shavings that water drips through, then the air is pushed into the house, right?

Did you just recently try turning the cooler on? My experience (albeit with a cooler that had metal ducts that the air traveled through) is that the cooler spits out a ton of dust the first time it's used during the season as it kicks up all the dust that had settled over the winter. We would hold damp towels over the places the air comes out to try to catch that first dust. Just for the first couple minutes. I don't think it will pull stuff from outside your roof because the cooler system has positive air pressure, but it could blow stuff that falls or crawls into the attic space into the living area.

If you've just turned it on, I'd wait to see if the problem goes away on its own before trying to filter it. I'm not sure if a filter heavier than cheese cloth would work. For the cooler to make you feel cool you have to have a lot of air moving through the room, so you need a window open near you and the air able to get through the vent. A heavier filter might not let enough air through, even if it were okay for the motor.
posted by SandiBeech at 8:43 AM on October 13, 2015