do you have recessed lights?
are a/c supply boxes in each room sealed to
attic flooring?
do you have cellulose insulation?

I usually find that these things are the
cause of 'dust'.
and I don't recomend duct cleaning.

best of luck.

I get a ton of dust from my recessed lights. I know of two solutions... the best way to seal them is use cheap styrofoam coolers like 12 pack coolers and cut the cooler to fit over the light housing if anything is in the way. Make sure the housing is toward the middle of the cooler. Foam the coolers in place and set a brick on top of them. Rearrange the insulation around the cooler.

The other way is to buy new recessed light trim kits to seal them. This method helps but does not seal as well as a styrofoam cooler can. The coolers might not pass a thorough builders/electrical inspection because they are not flame retardant.

Coolers 2.00 each at wal-mart
Can of foam sealant 5.99

Recessed light trims 7.50 ea and up.

The can of foam will do 2 or more lights usually.

check your return air for leaks. If your return is located in an unconditioned space and has a leak, it is under negative pressure and will 'suck' in the dirty unconditioned air.

could you please tell me where the return air would be. I am drowning in dust also and anymore helpful hints would help me pinpoint where it is coming in. Regards, P.K.

return air is behind the filter you should be changing
monthly.

is this in the ceiling, bottom of a heating system
closet or on the lower part of a return air chase
in the wall??

best of luck

Where is your furnace located? Attic area? Crawl space? Basement? Main floor mechanical area? Laundry area perhaps?
All of the previous posts have pertainent locations for dust entry. If you have cellulous insulation ceiling to attic penetrations are a good place to look. Also look for disconnected return air lines in the attic. Air handlers located in crawlspaces can transfer dust as well if connections aren't sealed.
And this may sound really stupid ....but I've found it before ..... is your DRYER vent connected!
With all due respect to previous posts, I don't know why anyone would not recommend duct cleaning, especially if it's an older home and they've never been cleaned. For people who complain about dust and allergies I recommend they have them cleaned every three years or so. In extreme cases I've found dust mats laying in return ducts in old homes nearly an inch thick that pull out like a blanket.
And I don't know about the styrofoam coolers over the light cans in the attic. They can get quite warm and many of them have overtemperature switches for that purpose. Typically they should have insulation shields around them anyway if they are exposed to blown cellulous.
Honestly the first place I would look is for leaks or disconnects in your air distribution system.

Deciding Whether or Not to Have Your Air Ducts Cleaned.

https://www.heatingair.org/

Knowledge about the potential benefits and possible problems of air duct cleaning is limited. Since conditions in every home are different, it is impossible to generalize about whether or not air duct cleaning in your home would be beneficial.

If no one in your household suffers from allergies or unexplained symptoms or illnesses and if, after a visual inspection of the inside of the ducts, you see no indication that your air ducts are contaminated with large deposits of dust or mold (no musty odor or visible mold growth), having your air ducts cleaned is probably unnecessary. It is normal for the return registers to get dusty as dust-laden air is pulled through the grate. This does not indicate that your air ducts are contaminated with heavy deposits of dust or debris; the registers can be easily vacuumed or removed and cleaned.

On the other hand, if family members are experiencing unusual or unexplained symptoms or illnesses that you think might be related to your home environment, you should discuss the situation with your doctor. EPA has published the following publications for guidance on identifying possible indoor air quality problems and ways to prevent or fix them.

The Inside Story: A Guide to Indoor Air Quality

You may consider having your air ducts cleaned simply because it seems logical that air ducts will get dirty over time and should occasionally be cleaned. While the debate about the value of periodic duct cleaning continues, no evidence suggests that such cleaning would be detrimental, provided that it is done properly.

On the other hand, if a service provider fails to follow proper duct cleaning procedures, duct cleaning can cause indoor air problems. For example, an inadequate vacuum collection system can release more dust, dirt and other contaminants than if you had left the ducts alone. A careless or inadequately trained service provider can damage your ducts or heating and cooling system, possibly increasing your heating and air conditioning costs or forcing you to undertake difficult and costly repairs or replacements.