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Question DetailsAsked on 2/29/2016

Had a new ac/heater put in the house, last year its becoming very dusty and the filters are extremely dirty whats u

Have a new ac/heater in the house. Since last year the house is getting more dusty than ever, and the front filter gets extremely dirty so much sooner than before, what can be going on?

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2 Answers


First, it's not any dirt that is in your ducts,what is there stays there.

It is likely that the new system moves more air then the old one. New system has a clean coil and blower, if the old one was dirty(very likely) the new system moves more air. If you have duct leaks the air that is moving causes an imblance which brings air in and pushes air out any plkace the home "envelope" has leaks, cracks,windows, doors, recessed lights, etc. for duct leakage test and repair.

If you started vacumming more often and your vacuum doesn't have a HEPA filter on the exhaust, every time you vacuum, you put more small particles in the air.


Answered 4 years ago by BayAreaAC


I have to differ with BayAreaAC - he is right that dust/dirt in ducts generally stays put - i.e. if it dropped out of the airflow under existing airflow conditions it is not going to kick back up unless disturbed by duct cleaning, earthquake, something hitting the ducts hard, or a MAJOR airflow event through them like a tornado passing by. Also occasionally when a heavy build-up of lint cake of matte falls off because it gets too heavy to stick to the duct any more (which is probably usually due to a door being slammed or someone jumping on the floor or such, you just may not recognize that) you can get a short-term surge of dust of lint.

However - I have seen new systems kick out a lot of dust and lint from ducts for a substantial period after installation - weeks - because the system puts out a lot higher airflow, so the velocity in the ducts increased in general, and also commonly forms vortices art corners and at the bends leading registers where dust commonluy accumulates, caussing it to be mobilized. This can be particularly pronounced - to the point of blowing clumps and "scabs" of lint buildup out the registers or even blocking them if the new system has a dramatically higher airflow. However, even a relatively minor increase can cause noticeable dust accumulations at the registers.

Installation of a new system also commonly causes increased dust in the very short term (a few days) because the installation commonly disturbs the ducts in the vicinity of the furnace enough to knock some loose. Ditto to repair of ductwork, and also cleaning of an A/C evaporator if it is not the slide-out type but rather requires some duct panel removal to get at it.

Other causes as he implied - a furnace with more air throughput (assuming ducts are not upsized), if it does not have adequate makeup air for combustion or for makeup ventilation air if a model that blends in outside air with the return air, can create a partial vacuum in the house, which results in air being pulled in through any openings in the "envelope" under doors, air leaks around weather stripping and windows, in through non-operating bathroom and kiitchen fans, from crawlspaces and basements through the floor, etc.

And of course - has there been any construction or farming nearby creating dust, unusually dry climatic conditions or higher winds than normal, etc. Also - if in a drought area, citiesw banning lawn watering have noticed significantly increased dust as people pull up their lawns and go with dry yard landscaping.

Additional or new garage uses can also create dust - parking in garage (especially in winter when you track in slush/mud on tires that then dries to dust), using garage as workshop for woodworking or such, etc.

Carpets that have not been cleaned in a long time can do this too- the accumulate dirt off shoes and out of the air over time, and with walking some of that dust gets mobilized back into the air, so without carpet cleaning periodically your house dust issue can get worse over time despite vacuuming.

New dog or dog door resulting in tracking in of more dirt ? Ditto to kids reaching the age where they actively play outside, tracking in dirt on shoes and clothes. Sand in a sandbox that is not washed can contribute GREATLY to household dust - sandbox sand (though it does not pack and hold its shape as nicely) should be thoroughly washed before use, or be a bagged washed masons sand.

Also - check your filter(s) - are they correct size, installed snugly all the way in AND correct side to front (many are NOT bidirectional), is the filter cabinet properly closed, no access panels left open on filter, humidifier/dehumidifier or furnace, etc.

I presume the filter is changed as soon as it shows signs of getting significantly dirty - because letting it go too long can result in the furnace not getting enough air through it, so again it starts trying to pull air through any gaps it can find in ducts and panels and recirculates that unfiltered air through the system. Look around, and maybe use a smoke pencil to look for any signs that air is bypassing the filter - open joints in ducts, open panels, even panels left completely off. Saw one unit once where a panel on the unit was left completely off during installation, so it was pulling unfiltered air from the room in preference to taking air from the return ducts, totally bypassing the return ducts and filter because the airflow resistance down the halls and stairs was so much less than via the return duct and filter.

And as BayAreaAC said - have there been changes in how you clean the house or change of vacuum. And on vacuum - there are commonly two filters - an inlet or outlet air filter for motor cooling air as well as the bag or cyclone to trap the vacuumed up dirt - if that other filter gets too dirty or is out of position you can end up with improper airflow and added vacuuming dirt in the air.

One other afterthought - have there been any changes regarding attic (non-living space part) - like maybe an access hatch or door not airtight, so dust from the attic is getting pulled down to the house when it is windy. Most attics (typical peaked roof type) develop quite a dust layer on top of the insulation which is kicked up in windier conditions, and if the furnace is pulling a slight vacuum min the house that can be pulled down into the house through penetrations or access points.

Ditto to any ducts in the attic - is there a chance a duct (especially return duct) has developed an open joint or rust-through that is letting dusty attic air in ?

Answered 4 years ago by LCD

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