" I'm not going back there until the problem is fixed, whatever it is."

Holy smokes Ed,say you are not serious. It would take more than a dirty house to estrange us from our family,esp grand kids. At any rate I can tell you are wanting a solution so I'm commited to helping you find one. Right out of the blocks I can tell you the filter rack size is inadiquate for 2000 sq feet of air conditioning. Compounding matters is the fact only about half of the under size filter is being utilized. First order of business is to increase filter size to at least 20x25 or add a secound 20x20. Whichever is chosen,there must be at least 2" free air space behind intire filter ( notice the bull's eye in center of filter). Next is finding air leaks between living area,attic and outdoors. The most common way of going about it is called "blower door test"but there are other less dependable ways. Are you planning a diy project or hireing a pro? Are you still with me Ed?

Thanks Klem. You make some good points. Their existing filter set-up is in a hallway ceiling, and the filter presses right up against a piece of duct work that I assume leads to the indoor coil in the attic. Haven't really taken a good look at the system yet, but there doesn't seem to be a plenum, which is why I think the filter is pushed right up against the piece of round duct work. So your first two points are good. Somehow we need to get some space behind the filter so the whole filter is utilized, and increasing the rack size is also a good idea. I might have over estimated the size of their house a bit. Also I might have been a bit rash about not going back there, but have just never seen that kind of dirt in such a short time frame.....literally 7 days. Bigger filter or not, even if the whole surface area of a 20 x 25 was used, I'm sure it would be black in a month, but not really sure, just guessing. Finding the air leaks will be the next phase, but first we need to address the filter situation. I'll keep you posted. Thanks again, Ed

If a filter is getting dirty that quick it's doing it's job... filters are there to collect dirt. The more dirt there is the quicker the filter will get dirty. I agree the filter is undersized, just as much as I bet there is a reason for that too.

Where is the dirt coming from?

Crystal Ball: from you most likely you filthy human. Skin dander, hair, dirt tracked in from out doors, pets, smoking cigarettes, normal dust in the air.

If a filter isn't getting dirty, there is a much better chance there are air leaks than one that gets dirty. WHY? The return air isn't going thru the filter > yeah as simple as that.

Common sales tactics: You need a new system that eliminates dust. When in fact, nothing eliminates dust. Remember the Intel bunny suits? Why do you suppose they put people in bunny suits to make computer processors?

The more air infiltration from the outdoors not to mention a house under negative pressure can make the home more dusty than a tighter sealed home. However, there are ramifications for a tighter home that can lead to an unhealthy environment indoors... which leads to a controversial syndrome called: Sick Building Syndrome.

Pros and Cons to everything folks....

That amount of accumulation after one week is not normal in my opinion. That looks like brown dirt. Dust usually has a dark grey color.

Does the duct work run in a dirt covered crawl space or through a unsealed attic. If the return duct work has leakage, it could be sucking in dirt and debris from unfinished parts of the house. I suggest doing a visual inspection for leaks of all visible duct work and seal them. Otherwise the filter will have to be changed weekly and the return duct work is going to accumulated dirt.

pics and more info would allow us to make educated guesses.

Filter dirt color resembles brick construction mentioned by OP. Or GA clay a la Zac Brown Band?

Well the fact you decided to go back before it is fixed tell's me there's still hope. Just rattling your chain Ed,keep us posted and we shall overcome. BTW, bad as i hate throwing fuel on the fire,there's worse news to come. With that much dirt on filter,99 to 1 odds say the coil will require expensive cleaning to prevent compressor going belly up prematurly. Good news is the coil cleaning should cut energy cost by 50%.

Yeah, I'll check the coil. We had a funky smell on ours, and all it took was a careful spray of some coil cleaning stuff we got at Lowes, and the smell was gone. This might be worse. Will post results of next inspection. Might be a couple of weeks though.

First thought was return is leaky in an attic and is sucking up cellulose insulation and the dust that is involved with cellulose. Or worse, a supply is disconnected and blowing attic dust into the house which in turn gets pulled back by the return.

You are correct that is not normal, even living in a dusty environment and having leaky windows that's too much accumulation too quickly. Looks like a standard pleated filter so I don't think too high of a MERV is causing it either

Just to make matters worse, the house is only 1571 sq ft.

The filter is flush with the hallway ceiling, so all the dirt on the filter came from the living area of the house. We thought about dirty air being blown into the area from the supply ducts, but they a white and clean as can be. You'd think that if the air supply was dirty, the registers and the surrounding white ceiling should at least show some dirt. Yeah, they have 2 dogs and a cat and 2 kids, but there just shouldn't be that much dirt. First order of business is a better examination, and figuring out some way to use the whole 20 x 20 filter area.

"all the dirt on the filter came from the living area of the house..."

"they have 2 dogs and a cat and 2 kids..."

The color of the dirt on the filter looks pretty similar to the color of the dirt/lawn at the base of the brick wall in the picture

"all it took was a careful spray of some coil cleaning stuff we got at Lowes,"

According to the little pamplet included with my tool belt it might require lots of elbow grease and far more than some spray to clean up that mess. Much depend's on wherthar unit was ever run without filter and/or useing cheap fiberglass filter. Coils,return plenum,ducts and grills must be squeaky clean,even if that mean's replacement. Yea,yea yea I know Tha Said and Eye Herd told us duct cleaning is wasted time and expense but like Austin's ball,the little pamplet has never steered me wrong.

No I'm not saying theirs is an easy cleanup job by any means....just plugging the coil cleaner stuff for minor issues. The a/c folks wanted to sell us a new coil, lovely folks :-( A pro might be required here, but it'll take a lot more investigation.

"You'd think that if the air supply was dirty, the registers and the surrounding white ceiling should at least show some dirt."

What I think is your stepson need's to stop messing round and hire rater. Not only is the health of the system at risk,so is that of everyone living there. And his bank account due to high energy bills.

Don't they have new tech now that can seal all the ducts without replacement using an aerosol and a pressurized system. Cleaning of the air handler would be needed as well, shouldn't need new coil the coil cleaner will most likely be sufficient.

Looked up that new tech it is called aeroseal.

https://aeroseal.com/

This old house video aeroseal

http://www.jetsongreen.com/2011/11/aeroseal-indoor-air-duct-leak-seal-airtight.html

Perhaps find someone that will do it locally or pay someone that knows how to do it travel there and do it. Probably vacuum out all of the returns first before you do this (aka duct cleaning with a shop vac)

There's more than one system advertised to repair failing ducts. Useing one of those on a system like this might qulify as putting a silver saddle on a jackass. The process is expensive but sometimes worth it where ducts are inaccessiable. Chances are good the system in question has flex duct anyhow.

Is there anything in the ceiling nearby that could be leaking air right into the return from the attic, can lights or something like that? Along those lines, is the living space near the return severely depressurized when the blower is running? (Maybe the whole house is depressurized?) Ie. does air rush in when doors are open?

Are the kids capable of throwing soil to the ceiling and sweeping up the excess when no one is looking ;-)

You could conduct an experiment by taking the kids, the dogs and the cat with you to your house for a couple of weeks and then check your own filter.

Crystal Ball says: 'I would like to know how much dirt 2 kids, 2 dogs & a cat make in a couple of weeks.'

hahaha lol. Or they could all come and stay with you, with their parents. :-)

"At my stepson's house in GA, this is only after one week."

So a family of 4 with pets has to change their filter every week? I would agree if the dirt was grey and it looked like that after 3 months. But the fact the color is brown and it is happening so quickly indicates to me there is more to this than people and pets.

Do you know if the blower is set to run continuously? That would just aggravate the problem.

We have a natural scientist with an hypothesis-testing mind in Austin Air. I am with Mike for the null hypothesis despite my suspicion of the kids, and it is a good question about continuous blower.

I asked them. Blower is not continuous. Fan is set to auto.

"fact the color is brown and it is happening so quickly"

Cooking grease?

"hahaha lol. Or they could all come and stay with you, with their parents. :-)"

The reason I put it to you this way is that it's an easy excuse to spoil the kids, the pets and at least eliminate a possible cause. Just make sure you prep and change the filters in your house and house in question.

This sleuth work you can easily do, but you have to want to get to the bottom of it.

At the end of the 2 weeks, 1 week etc. Pull both filters and compare them. It doesn't get any easier than that.

If the filter in the suspect house is the dirtier of the two after this event, you probably have an infiltration problem, house under negative pressure drawing dusty air from outside.

You make a good point about the negative pressure, and yes, I realize you are well intentioned about the kids and pets. Just not an option. Maybe they could go on vacation for a week or so. Thumbs up. So, what causes negative pressure. Oversized unit? Undersized return. That small round supply duct? I know in our own house, when our 3 ton unit comes on, the coil/return is near our son's bedroom door, and if the door is nearly shut, the negative pressure between the return, and the supply in his room will suck the door closed.

Not to imply Ed's situation is normal but kids and pets do make a huge difference in nessary filter change intervals. For that matter what mom and dad do every day can be game changers. It is for that reason I don't subscribe to one size fit's all filter change schedules. A real life example is my experience with child care buildings. You can identify age groups if filters from different age rooms are layed side by side. During summer break,30 days is not often enough to change filters in elementary school age rooms. At the other extreme,an infant room filter wouldn't get dirty if left in place 6 months. I made an interesting discovery while working for those corporate child care companies. A degree in finance,business management,accounting or human services trump's one in engineering any day of the week. I was never able to convince them good filteration could reduce sickness dramatically in their buildings. They did get a laugh from my PowerPoint when the bacteria and viruses were shown hitching rides on floating dust particles,but still didn't believe it. I'll say this for them,like most corporate types I've dealt with,they did subscribe to ball elixirs.

YEP, business and HR politics is definitely something to vomit over.

Overall interior/exterior pressure differentials are caused by duct leaks if the duct leaks are to the exterior of the building. Leaks in supply ducts depressurize the home. Leaks in the return path suck in air from outside into the duct and pressurize the home. There are some pretty good cartoon drawings of this on the web.

Then you have local pressure differentials as you noted. They are just as much a problem if not more. The door on your son's room is as much an aerodynamic consequence as static pressure, but I'll use it to illustrate the problem anyway. Slam the door and air gets pushed into the attic through the can lights or out past poorly-sealed windows in that room. At the same time, the hallway gets depressurized and air gets sucked in through the attic via the can lights there or through some other leak. That is why it is best to have a return in each room.

I know in our own house, when our 3 ton unit comes on, the coil/return is near our son's bedroom door, and if the door is nearly shut, the negative pressure between the return, and the supply in his room will suck the door closed.

Yes, you've got the idea. To take it a step further when this room is under negative pressure like that if there is any leakage in the house shell in that room it will suck whatever air it can get from anywhere else, attic, crawl space, outdoors, other rooms of the house etc.

Power exhaust vents in the attic can put the entire home under negative pressure as another example.

And the award for coolest grandpa / uncle goes to? You have something here that could be more fun and teach the kids something not taught in school. 'Think for yourself.' -take pictures of the 'camp grounds' and include them as well as your son in the experiment--- you nor them will ever forget it. Holidays right around the corner.

Ah the 'price' of free advice. I LOVE IT!

is the return in the ceiling or in a wall chase?

still no pic? how about a verbal description of return location?

best of luck

The return is flush with the hallway ceiling. I said I would get pics and a better descrip as soon as possible. Haven't been back there yet.

a look at the insulation around the return air from in the attic

will show trails of dirt where air is sucked into the return.

with a ceiling mounted return, given the configuration of

the dirt on the filter, the return is probably flush with the

top of the ceiling joists. the top will have duct to equipment.

the framing of the return should be caulked or mastic sealed.

dirt trails will show you where, but 2x's to attic floor, corners of 2x's

sealed, and top of plenum where duct is attached should be

sealed to 2x framing. duct collar of return duct sealed air tight.

then duct to equipment sealed air tight.

just pointers if anyone wants to seal it up themselves.

I like paint on mastic or Hardcast brand 1402 rolled mastic tape.

Usually a combination of the two to get a good seal.

foil tapes & duct tapes will fail. as with any tape, surfaces

must be clean and dry for proper adhesion.

best of luck