What causes this and how would you write about it in your report?

Good read for you here;

As the air travels further from the diffuser, the air velocity drops, gradually causing the air pattern to lose its “cling.” It then falls toward the floor. This results in good mixing of the cool or warm air from the diffuser with the room air. This also results in the room air being pulled up toward the center of the diffuser.

Room air particulates are the most common cause of smudging. Dirt particles (dust, fine dirt) in the room become part of the air circulation created by the diffusers and are drawn to the ceiling by the creation of the low velocity pocket (Coanda effect).

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When I was little our whole family woke up with black smudges on our nostrils when the oil heat did a hiccup. :flushed:

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The dirt looks sooty, in which case if there’s a furnace, the exhaust may be passing into the supply air. If the dirt’s not sooty, the source still appears to be in the duct system from duct leaks or from a filthy filter, blower fan, or coil since smudges are accumulating in areas with reduced velocity. If the a/c coil’s too filthy to reduce the humidity in the return air, would the increased humidity cause that dirt to adhere in that pattern?

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It can also be caused by a combination of issues. If the house is in a dusty area, or if there is construction going up nearby or upwind, that can contribute. Condensation can cause moisture to accumulate around the register and that moisture can trap airborne particulates that accumulate as dirt.

Pay attention to the pattern that aligns in the direction from which air is emitted from the register. There’s no oil heating here in CO, but the guys familiar with it might have a good point. I know at least one of them does and that’s why he wears a hat.

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I have seen this, and taken in context with a little back story, it made sense at the time. Sooty stains on the returns and registers, but a brand new filter. Home was being inspected as part of a sell. Current owners threw in a brand new filter to avoid getting “gigged”

When questioned [politely] they admitted to running system without filters regularly and burning smell-good candles near the returns to “spread it around the house”…

Not saying that’s your issue, just that it could be.

Fuck is wrong with you (2)

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