Dust in home

[stardotstar]

Would it be a correct assumption that dust in a home coming from an ac system, made of metal ducting, would stand a greater chance of entering the sytem before the air handler, than afterwards iin the plenum?

Unless the internal of the plenum is insulated and old? Hmm just thought of that.

[SandShark]

You would be correct that dust in the home would stand a greater chance of entering through the return air (before the air handler). Not that an internally insulated supply plenum with old insulation that is breaking down couldn't contribute to dust issues, but the return side of the system is the likely cause. In addition, inadequate return air along with leaky return air duct work can significantly increase dust in the home, especially if the return air duct work is after the filter and is located in an attic or another unconditioned and dirty space.

[stardotstar]

Thanks!

Would a simple fix be the installation of a media filter and forget the return air one? rather than trying to figure out how to seal the return air chamber?

[mark beiser]

It would be highly unusual for dust to be entering the home through the duct system. The dust streaking you get around supply air registers is usually dust that is already in the room air that gets flung out of the air stream when the room air mixes with the high velocity air coming out of the register.

A high efficiency air filter, even a media air cleaner mounted at the equipment, won't reduce the visible dust in the home in any significant way.
The particles of dust that are big enough to see are heavy enough that they fall out of the air before they can be pulled into the return duct and make their way to the filter.

[stardotstar]

It would be highly unusual for dust to be entering the home through the duct system. The dust streaking you get around supply air registers is usually dust that is already in the room air that gets flung out of the air stream when the room air mixes with the high velocity air coming out of the register.

A high efficiency air filter, even a media air cleaner mounted at the equipment, won't reduce the visible dust in the home in any significant way.
The particles of dust that are big enough to see are heavy enough that they fall out of the air before they can be pulled into the return duct and make their way to the filter.

I am talking about dust that accumilates on furniture, dont see any on the registers.

[mark beiser]

I am talking about dust that accumilates on furniture, dont see any on the registers.

The dust that accumulates very rarely ever comes in through leaks in the HVAC ducts, but leaks in the supply ducts, including where register boots penetrate into the conditioned space, can cause the inside of the house to be at a lower pressure than outdoors.
This causes air to leak into the house through every available opening, so a lot of the air, even most of it, comes in from or through some very dirty areas.
If you have recessed light fixtures, they are a huge leakage point from the attic, unless they are specifically manufactured and installed to be air tight.

Other sources that should be looked at are old carpet, leaky vacuum cleaner, poor dusting techniques, pets, people, etc..
In some homes, most of the visible dust is dead skin cells from the people living there.

Again, no air filter mounted anywhere in the HVAC system will do much of anything to reduce a visible dust problem.

[stardotstar]

The dust that accumulates very rarely ever comes in through leaks in the HVAC ducts, but leaks in the supply ducts, including where register boots penetrate into the conditioned space, can cause the inside of the house to be at a lower pressure than outdoors.
This causes air to leak into the house through every available opening, so a lot of the air, even most of it, comes in from or through some very dirty areas.


If you have recessed light fixtures, they are a huge leakage point from the attic, unless they are specifically manufactured and installed to be air tight.

Yes, will look at.


Other sources that should be looked at are old carpet, leaky vacuum cleaner, poor dusting techniques, pets, people, etc..


No carpet, super duper vacuum, dusting weekly and yes a dog.

In some homes, most of the visible dust is dead skin cells from the people living there.

Again, no air filter mounted anywhere in the HVAC system will do much of anything to reduce a visible dust problem.


So what good are they?

Thanks

[SandShark]

The circumstances I was referring to would apply if, as I said, the return air duct work wasn't sealed properly and it was located in a dusty, dirty and unconditioned space, like an attic or a basement. I've worked on many systems where dusty, dirty and hot attic air was being introduced into the poorly sealed return air duct work. In some cases, it was happening for years. I'm not saying this is the case with your system because you've told us nothing about how or where your system is installed, but it can and does happen.

[mark beiser]

So what good are they?

They do a fantastic job of protecting the equipment, and filter out most of the very very small particles that don't fall out of the air.

Coincidentally, those very small particles that don't fall out of the air include most of the things that cause allergies.

[stardotstar]

The circumstances I was referring to would apply if, as I said, the return air duct work wasn't sealed properly and it was located in a dusty, dirty and unconditioned space, like an attic or a basement. I've worked on many systems where dusty, dirty and hot attic air was being introduced into the poorly sealed return air duct work. In some cases, it was happening for years. I'm not saying this is the case with your system because you've told us nothing about how or where your system is installed, but it can and does happen.

Thanks, you have pretty much hit the nail on the head as far as the attic description.

[mark beiser]

The circumstances I was referring to would apply if, as I said, the return air duct work wasn't sealed properly and it was located in a dusty, dirty and unconditioned space, like an attic or a basement. I've worked on many systems where dusty, dirty and hot attic air was being introduced into the poorly sealed return air duct work. In some cases, it was happening for years. I'm not saying this is the case with your system because you've told us nothing about how or where your system is installed, but it can and does happen.

Usually the stuff pulled in through return leaks ends up stuck to the evaporator coil though, as a wet evap coil acts like a >MERV 6 filter.

If you have leakage in both the supply and return duct, sealing just the return leaks can actually make the dust problem in the house worse.

Return air leaks tend to cause the conditioned part of the home to be at a greater pressure than outside the conditioned space, and can actually result in less visible dust in the home.
A tightly controlled return air leak, aka fresh air intake tuned to maintain a very slightly positive pressure in the home, is one of the things that can be done to combat dust problems caused by infiltration into the home.
The major leaks in the building envelope, and the duct system, must be sealed before using such a strategy though.
Otherwise the amount of air needed is way to high.

[energy_rater_La]

seal both return and supply leaks.
address the recessed lights.
cooper lighting has retrofit inserts
for recessed lights to make them
air tight from inside the house
rather than from the attic.

what type of insulation on the
attic floor do you have?

best of luck.

[stardotstar]

Thanks for your help and suggestions. At this point, the old batt insulation is the only thing ther, not much. That is why I was wanting to address the ac issues so we would not have to mess up any newly installed insulation.