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Question DetailsAsked on 6/11/2013

dark soot on wall edge of carpetingEnter your question...

also dark lint build up around seal of basement door

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4 Answers


Bet the lint buildup on the basement door is on the inside and your gas or oil fired hot water heater and furnace are in the basement, right ?

This usually means your heating system (and hot water heater) is pulling air from the house for combustion air, and because of the continual airflow through the flooring gaps around the perimeter of the room, and bypassing the basement door, you get dirt buildup.

If the lint buildup is on the inside of the basement door, then the heating system is overpressuring the basement relative to the house, so dirt and dust is being pushed into the house around the door, and around the edges of the flooring and carpet.

You may have either (or several) of three problems - one might be inadequate airflow to the combustion chambers (fixed by providing an outside vent in the room the furnace/hot water heater are in).

HVAC system airflow may be unbalanced, causing a significant pressure differeential between different parts of the house.

If can also mean you have a leaky (to air) basement, so the HVAC system is pressurizing the house (a bit of which is normal), and the easiest place for that higher pressure air to escape is through the basement, so the return airflow is going that way. If this is happening, you may need return air vent modifications, and/or weathersealing the basement.

Either way, you need an airflow assessment by a certified HVAC contractor who is certified in energy efficient HVAC system design.

Answered 6 years ago by LCD


Dark carpet perimeter is generally an indication of air infiltration under an unsealed base-plate of exterior walls(your carpet is acting as a filter of outdoor air entering your home).

Answered 6 years ago by AirTekHP


This can also be caused by burning candles, particularly ones with inexpensive wicks.

Most people don't believe it, but it's true.


Answered 6 years ago by BayAreaAC


Good point by BayAreaCool - if you burn candles, use an open-heartyh (not sealed outside combustion air unit) fireplace a lot, or smoke - that can cause this too, though that would still be an indication of significant airflow through that area. The lint buildup around the basement door still indicates an airflow issue - either excess leakage between rooms, or combustion air starvation.

Answered 6 years ago by LCD

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