While I do not know the exact makeup of all of this black marking of the ceiling on one side of the garage, I am quite sure that a very large percentage is bits of tires and brake linings from the highway on the other side of the fence.
The boiler gets its combustion/dilution air from the garage and the garage gets its air through this crack where the ceiling joins the house foundation wall.
Years and years of cars braking at the bottom of the hill on the highway, and years and years of the boiler sucking air out of the garage, has created this nice picture of what air infiltration looks like.
I don’t even need my infra-red camera to see what is happening here.
It does make one think about how such stuff like this can affect indoor air quality.
It is contaminated infiltration like this where HRV’s and ERV’s are not only a good idea but may become essential as we continue to impact our environment.
These devices filter the air exchange between indoors and outdoors. However, opening windows, using fireplaces and running exhaust fans will still create pressure differentials that will result in pulling this dirty air into the home.
Providing combustion/dilution air to the immediate vicinity of the boiler would be a huge improvement in this home. And sealing openings and filtering other sources of incoming air would be a good idea.
Even the house’s own stack effect can result in pulling this dirty air into the home. It is things like this where control over how air moves into and out of our homes becomes so important and in some cases critical.
Especially if you need to keep your ceiling from getting “tired.”
Charles Buell, Real Estate Inspections in Seattle
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WA State, Home Inspector Advisory Licensing Board