Maybe the HVAC ducts needs to be cleaned out professionally or a new filter replacement.

Thanks to you both. We've had a new construction home before, but this is a new level of dust. Like a blanket of it only a few hours after cleaning. I have a chair that I clean and vacuum every couple weeks and it has cobwebs and dust as if it's been neglected a year. We did change out the filter a couple times after th HVAc work and had a company check to see if we need our ducts clean but they said we're fine.

If, the concrete floors are sealed and coated. Dust is finding it's way in from outside.

I seldom can see problems from thousands of miles away but this one I do. The hvac was put into service BEFORE construction was complete. Dirt and debris stirred up by workmen rapidly clogged filter causing lack of hvac performance. Having seen this many times before the workmen removed clogged filter and system went back to working,,,,,,,,,,until dirt and debris clogged coils. Hvac stooped preforming again and "SOMEBODY" decided ducts were undersize so they were replaced. Now dust hung up inside system is blown out and onto everything inside home. If it were my sister's home I'd have her issue builder an ultimatum of having a licensed ac contractor dismantle and thoroughly clean air handling system or she will hire one and sue builder for expenses,lawyer fee,pain and suffering and possibly replacement system if that's what her contractor recommends. How can you prove or disprove what I just said? You or anyone with a little mechanical ability can easily remove one or two exposed panels. If you find dirt inside hire a contractor at your expense or diy to remove remaining panels on air handler to expose blower wheel,coil and plenums for pictures. Mine are as clean as when installed,yours should be also. How's that for long distance xray vision?

It's best practice to commission and run a home's HVAC system during construction--we typically get the system operational right after drywall installation and prior to installing trim, hardwood floors, cabinetry, etc. which need a stable, conditioned indoor environment. While dust can be generated from construction activities, frequent inspection and replacement of filters as needed should be sufficient to keep dust from accumulating on the coils or being circulated throughout the home.

If your concrete floor is not sealed, considerable concrete dust can be generated just from traffic.

Leaky HVAC ducts can pull dust-laden air from attics and crawl spaces. If you haven't already had a duct blaster test performed to measure leakage, I'd start there.

Op if builder starts to tap dance with shudda,wudda,cudda, ask him who bank wrote checks to,him or subs. It is 100% builder's responsibility to complete work up to standards and lick all calves that must be licked a second time. It is NOT homebuyer's responsibility to have "blaster tests" preformed in order to see if work was done right.

Also check the venting for your clothes dryer and make sure the connections are tight. Lots of lint can be blown around if something isn't sealed properly. There have been so many threads about this on this site. The Houzz search function is junk, so I googled it to try to find some of the other threads. Take a look here: Houzz excessive dust threads

"It is NOT homebuyer's responsibility to have "blaster tests" preformed in order to see if work was done right." No, it's not. I'm not sure what building code applies in your area, but there's a pretty good chance the building code in the OP's area requires a duct blaster test during construction if the code is based on the International Residential Code-- which forms the core of most statewide building codes.. Section R403.3.4 of the 2018 IRC specifies the mandatory leakage performance testing required.

When my home was built, after ducts were put in, but before drywall and vents, the workers covered up all the openings to each air duct while they worked. They also did a complete clean of subfloors before putting in any

(sorry hit wrong button) was going to say before putting in any flooring. I still had minor const dust issues in first month. But not bad. This is a whole level. Seems like combo of not cleaning the const environment before installing finishes, and not properly sealing.

Is your environment causing this, e.g. do you live in a dusty area?

Klem1 - we went through all the checks you‘ve suggested prior to getting the HVAC fixed. The filters were changed and the ducts were checked to see if they needed to be cleaned. The HVAC was also not turned on until the house was completed. Its a custom home, so we had a lot of control over thay and didn’t even turn on service to the house until just before moving in. We hired an great HVAC engineer who did a full room-by-room calculation, which showed all rooms were not getting the flow required because the ducts were severely undersized. The plenums were also replaced.

The jobsite was kept horribly dusty, so im leaning toward that and poor sealing.

Since you say a tight rein was kept on construction process and you hired "a great HVAC engineer" you present an preplexing set of circumstances that causes me to think we are missing information that is key. Did you happen to hire and oversee trades instead of hiring a builder? Parts of this sounds familiar to a protracted build two or three years ago where there were on again off again with cabinets and trim work. Every possibility I can think of would surely been noticed by the "great HVAC engineer".