We clean fireplaces and chimneys. The cost is $150 for most one-story systems and $200 for most two-story systems. More if the access is unusually difficult or if there is a heavy creosote build-up. (Creosote is a form of soot that is physically hard and which adheres to the inside surfaces of chimneys very tightly. Hard to remove.) If the creosote is heavy we might leave a tube of catalytic powder with the customer, for the customer to spray up into the flue between several fires. That will (hopefully) soften the creosote to the point where it can be brushed out when we come back for a second visit.
If you have had around 50 fires since your last cleaning, it probably needs cleaning again.
Or, if you shine a flashlight up from the firebox and look upwards, from the firebox, and you see the soot getting to be a quarter of an inch thick, or more, then it’s time for a cleaning.
Note that cleanings will not remove the black stains you might have on the inside walls of your firebox. If you want to have a uniform “look” to the firebox walls, instead of irregular soot stains here and there, some customers have us paint the inside walls with a flat black, hi-temp paint. Then the walls look black all over.
When the chimney is cleaned, our chimney sweeps will close off the fireplace opening with plastic and tape, and will use a vacuum to help contain the soot and dust that is stirred up. Drop cloths are laid down on the floor in front of the fireplace. There will not be any impact on the house from doing the chimney sweep. That is, you will not have soot getting on the carpets or furniture, etc.
If there is a soot build-up inside the flue, it is considered a fire hazard, because the soot is combustible. If there is creosote in the flue or smoke chamber, that is more combustible than regular soot.
Also, a heavy soot build-up reduces the size of the flue opening, and the irregular surface of the soot can result in a flue that offers more resistance to the flow of smoke up the flue, which can cause smoke to spill out of the fireplace opening into the room.