It does sound like you have a significant pressure buildup in the attic. If the pressure difference between the attic and the interior is high, dust will find every little hole that you can't find and get to the inside. Being able to take the attic to a negative pressure with some sort of fan would either diagnose or eliminate this as a contributing cause, with the holes in the envelope the root cause of the problem.
Originally Posted by leeannwc
If you have soffit vents, and you cover the gable vents, the pressure may not change or could go up unless you have a ridge vent or turbines for exhaust.
I think this is a very valid point and should not be overlooked. As previously pointed out, "over" filtration will cause reduced airflow, which in turn will cause reduced performance of ANY filtering method. Inducing outside air will not only provide 'new' air to the space but will also provide make up for any exhaust that you may have.
Originally Posted by mark beiser
Oh, and even a closed chimney will vent, especially in windy conditions (stack effect).
Yes, I thought that all through. My husband actually offered to go up in the attic this weekend and cover the gable vents, but I told him that would only be treating the symptoms and not the root problem. I cannot for the life of me see where we could have bypasses from the attic to finished space...I sit and just look around every day for something else to seal up. I'm to the point now, though, that I just want a break from the symptoms. We need some respite. It would also help rule-out ducts wouldn't it? I still have the heat off but I can't really tell any difference. It is hard to determine if the dust settling might have already been in the air and we have accumulated so much that one good cleaning is not enough to get it all...I'm sure it will still be around a while once we do resolve the cause.
I thought of the venting too and we do not have ridge vents or turbines?? I'm not sure what the contractor was thinking because he only had soffit vents planned...I had him add the gable vents for cosmetics having no idea at that time how it could impact anything else. It seems to me that there is really nowhere for the air to get out.
Without turbine or ridge vents I would guess the gable vents do not have enough area to relieve the pressure from the soffit vents. So if that is the case, then at least you know the pressure difference exists to be the driving force for the dust. But if there are no holes in the envelope or the ducts, it won't really matter. So there still has to be a path, which is the root cause of the problem. Your blower door test should have identified a composite hole size in the envelope. Do you know what that was? And if I remember correctly, there have been numerous corrections made since that test so was there much difference in the dust after the corrections?
Originally Posted by leeannwc
You may be onto something regarding the air movement in the attic. Soffit and gable end vents are mainly for natural convection ventilation, with cooler air entering the soffit vents and exiting the gable end vents. Wind can change this pattern, and if a gable end vent is facing the prevailing wind, it can introduce a considerable amount of air into the attic, pressurizing it to the point where the soffit vents do not have sufficient free area to relieve the pressure. Air goes wherever it can find a path, just like water.
You may have done an extraordinary amount of sealing between your living space and attic, but if you have wiring in the attic that goes down into the structure through the top plates of the walls, and those top plate penetrations are not sealed, that's yet another point of entry for air and dust.
However, it would now seem your focus should be changing the air dynamics of your attic. You might wish to go ahead and have your husband tape up some plastic over the gable end vents temporarily, just to see if that makes a difference regarding dust accumulation levels in your home. IIRC, only 10% of all airborne dust will settle out or is large enough for the average home a/c filter to catch. Since you have not been running your system and are still accumulating dust at a good clip, it strikes me you have more dust coming in, replacing what is settling out of the air. If I were at your house, knowing now what you've said about the attic conditions, I'd be looking hard at that aspect and seeking change.
I know some great professional minds have been working on this problem for awhile now but please fill me in... has a blower door test been done to identify the overall amount of house leakage? Would our pros agree or disagree on the value of this?
Best of luck -- Pstu
It appears you have done your homework and tried to do what the Pros have suggested. Time to quit until you find the source.
Now, why don't you get a couple boxes of a good quality filter. Change all the filters in your returns ( don't know how many you have). Set the system to fan on all the time. (This will keep the dust suspended)
Change the filters every 2 days until you see a significant decrease in dust. (checking the filters for dust accumulation)
I would think this will help until the source is found.....
There is no reasonable way to provide adequate whole house filtration to the degree leannwc needs to mitigate her dust problem. Most of the dust will settle out before it reaches the filter...her post history supports this...she is continually cleaning up dust from surfaces all over the house. To provide the amount of filtration and air circulation to keep these particles in suspension until they reached the filter would make the house unlivable.
Originally Posted by OlManRivah
The cause of the dust intrusion must be found, and from my vantage point I think she's closing in on it. I think she should go ahead and temporarily block the gable end vents to see if that makes a difference in dust accumulation levels. She will always have dust. But her complaint has consistently been the rate of dust gain is intolerable...I don't think she's asking for her home to be impeccably dust free, just reasonably clean.
One other thing to look at is the attic access itself. The pressurized attic can force a lot of dust into the home from this access area if it is leaky, and if the attic is breezy, you can be sure it is stirring up dust in the attic.