Is your furnace or air handler located in the attic?

The only thing you should be concurned about is leaking intake/return air. It will cause problems more serious than odors so you should have returns tested for leaks. If you are super handy and phically fit we can tell you how to diy but it take's time and determination.

mike_home, No the unit is located in our garage. But I can tell you that I believe the section of roof decking replaced was obviously on the roof but above or in the general vicinity above the furnace. I was thinking maybe they dropped something and caused a tear in the ductwork, but I cannot figure out why it would smell like sawdust only when the A/C is on and not the furnace.

klem1, Thank you we are NOT handy at all. I might note ALSO that we have off ridge air vents on the roof. They added a piece in front of it to try to block hurricane driven rain from blowing right into the attic. I don't know if that is helpful, but still I would not think the duct work should be picking up the smell. But we are baffled why it is only when the A/C is on and not the furnace.

If sawdust fell on a return duct it could have been sucked up through leaks in a connection joint. Have you looked at your filter? It may have collected sawdust.

mike_home, we have an electronic filter. I'm not sure if I would see anything there, but I will check.

Update: cleaned the electronic filters. I about fell on the floor when I looked at them. I'm going to try to attach a photo of the pre-filter. Always they look clean when I take them out to wash them. This time they were horrible. Dusty and had pieces of what to me looked like insulation. Had the A/C guy crawl through the attic and check the duct work for tears. None found. But how did all this yuck get into into the ducts? We've been here 14 years and never ever saw anything like that. So anyway, I washed the pre-filters and cells really well. I turned the A/C today to see if it made a difference and it smelled up my house. Not the saw dust smell this time, but smelled like an old vacuum cleaner bag that needs to be changed. Doesn't smell bad when the heat is on, though. How do you explain any of this?

"How do you explain any of this?"

Noone is in as good of posion to answer your questions as the AC guy who crawled through the attic. The fact your filters were so much dirtier than usual confirm's what everyone here is saying "the ductwork has hole(s) in it". Worse still is that performance will be diminished and equipment life shortened as result of sucking in more and running with that crap inside.

Since the heating and cooling guy cannot visual find a leak and doesn't really have an answer, is there some kind of test that can be performed to find where the dust and whatever is getting into the ductwork?

The fact your filters were so much dirtier than usual confirm's what everyone here is saying "the ductwork has hole(s) in it".

If duct work has holes in it, the filter would be clean because air (dirty or clean) will take the path of least resistance which would be thru the holes in the ductwork. The blower wheel and evaporator coil would then be the dirtiest part. (My opinion based on science.)

If the filter is dirty, it is doing it's job.

As far as smells go, this is a very subjective type thing. I am not there so I have no comment at this point on that.

Yes,a competent technician can find where dust is getting into the ductwork. We could go on forever telling you what "it might be"but since this isn't a diy project,that's only wasting time while more is pulled in. It has been 5 days since you cleaned the filter,how does it look now?

How carefully did the HVAC guy check the attic returns?

Mike the attic (in most cases and designs) does not have any air returns.

Air returns all typically all within the envelope of the home. Attics tend to be either hot or cold depending on OAT conditions, it would be pointless not to mention profoundly ignorant to install a attic return that draws any significant amount attic air.

Given that some installations may have fresh air intake in the attic, but these are typically filtered by a whole house filter not to mention strategically placed and cycled closed via a powered damper when conditions are unfavorable.

If duct work has holes in it, the filter would be clean because air (dirty or clean) will take the path of least resistance which would be thru the holes in the ductwork. The blower wheel and evaporator coil would then be the dirtiest part. (My opinion based on science.)

Austin Air Companie,why can't you leave well enough alone because you certainly do yourself nor your reputation any favors with this kind of behavior. You should just set back and listen sometimes instead of trying to disparage others. You might learn something. Now,for the benefit of those who listen with their ears instead of their mouth,here's something for your consideration(My opinion based on common sense). Return air often involve's several feet of duct from grill to the filter rack at or near air handler. There are in fact several in large homes that connect to one central location. This is done so that one filter location can serve several returns from various rooms in home. If and when one of those duct runs is torn or disconnected in attic,insulation as well an extraordinary amount of dirt is sucked into duct and deposited on the filter. This is common sense rather than science sourced from Ouija board,oddball,screwball or other sort of ball. Questions are welcome and I will expound if anyone doesn't understand.

An average homeowner is going to mistake what you are saying if it's wording is misleading.

There are a myriad of configurations as in how or where the filter is located within your HVAC system.

Here are some examples:

I posted this one above mainly for the dangerous placing of a vent in a room with 2 gas burning appliances. Why do you suppose this is dangerous?

Because filter is at equipment any break in return before filter the air will be pulled into the filter.

Attic installation above with filter at equipment. Any return break the air is filtered before it gets to equipment.

Attic install above. This represents about 80-90% of my current market. Your location may be different. Notice there is no filter at the equipment.

If there is a break in the return, the blower wheel and evaporator coil typically become the filter of the system.

A broken return --- how they happen (typically not always).

As the picture says... an air return operates on the basis of blower suction. The blower sucks the air thru the filter. If there is a break in return there is little to no suction at the filter.

How could the filter get dirty? --- it can't.

If what you are saying on a board is confusing to me... how is it not confusing to a home owner?

That is the whole point of this board is it not. Confusion doesn't satisfy anyone. That is why I venture into what appears as an attack by me when it's not --- It's to clear up confusion that some seem to propagate as truth and try to paint me as the bad guy for speaking up.

What I have posted here are very basic type pictures of various HVAC configurations. Your system could be similar or vastly different, depending on a host of various factors.

Okay, I'm going to give some unconventional advice and perhaps this will stick...

Now... What's the difference between heating and cooling?

In the house, everything is run through the furnace module, even the coils for the air conditioner.

So... No smell of saw dust with furnace on and bad smell with AC on.

The difference between the AC and furnace circuit is simple.

The air intake going into the the furnace, if it's gas, it need fresh air.

There should be a flap gate that allows you to select between summer cooling and winter heating.

If you're running your A/C, give this a try, yes, it does take more power (just a warning).

Set it for open aka winter heating, this is on your duct work.

Now, on gas based furnace units, there's another vent on the duct work, usually right up above the summer / winter flap selector. Make sure that's open and not blocked by paper, wood or card board. Make sure it's clean, too.

If the smell goes away when it's set for winter vs. summer.

Then the problem is more than likely in or around the furnace unit itself.

Furnaces should be cleaned from top to bottom every year before they're fired up.

My guess is that it could be some rotting material on or near the vaporization coil of the air conditioner inside the furnace cavity. Now, there is bacteria that can give off this smell.

How does this work though?

Your coils can freeze up or get too cold and cause moisture to collect on the outside, this could be the trigger for this smell to fire up, so to speak. Have your HVAC / Furnace tech check all these areas. Sometimes it's hard to spot, have them use a black light to find colonies quickly.

I have the same issue with a saw dust smell. House was built in 1930, until Nov. 2021, never had HVAC. I am the first to live in the house after remodel and HVAC install. Duct work is in the attic. Clear sign of work in the attic and when I open the attic pull down door, I smell cut wood. This is my 5th month here and I am feeling worse by the day. I've taken myself to the emergency room because I continue to get a sensation of some type of fume being expelled in my office, which is the same room as the attic pull down. Dizzy, heart racing, dry throat, slightly nervous feeling, disoriented and the inside of my nose feels like the follicles are full of dust or sanding dust. All blood work is fine. I do smell the saw dust smell throughout the house but the dizziness and other symptoms mainly occur in the office and living room area, Any thoughts?

Hi, HU,

If you are experiencing health effects, you need to get air quality sampling and testing performed to identify whether the irritant(s) is chemical (e.g., VOCs emitted from new construction materials), dust, or molds/mildew. Those findings will help guide your next steps. In the interim, open windows to provide some ventilation in occupied areas of your home.

Hi Charles. Thank you for the response. How do I get this accomplished? Who do I contact? I live in Kannapolis, NC

If you do a google search on "indoor air sampling near Kannapolis, NC" you'll get a list of potential contractors.

In our house we replace filters like that on a regular basis…is that not an option in your case?

@btydrvn yes I can replace the filters and have been. Actually I've been here since May 1,2022 and have replaced the filter 4 times.

@Charles Ross Homes thank you. I will do that. My unit is still under warranty and my gut tells me the duct work needs to be replaced as I just do not see how so much debris and smells are blowing through the unit if the duct work is completely sealed.

''I have the same issue with a saw dust smell. House was built in 1930,"

Since you didn't mention a taste along with odor you probably don't need to worry about Chaetomium or Stachybotrys.

@klem1 no I cannot say that I have any change in taste. This is the most bizarre thing I have come across and it seems to come around the same time of day, late afternoon.

@klem1 when you say taste, can you describe what that might be?