Creosote remover. It comes in a variety of options. We heated a 20x20x16 plus the adjoining dining room/kitchen with a fireplace.
My situation is a little tough to explain.
I have a soapstone wood stove. The design is different than a regular cast iron wood stove.
-There is a ceiling in the firebox that slants upwards towards the front of the stove.
-It joins a horizontal plate that leaves a couple of inches of space between it and the top of the stove.
-There is a gap between the front of the stove and where that horizontal plate begins.
-There is also a gap between the back of the stove and the horizontal plate.
So the fire burns, the heat rises with the upward slope of the firebox ceiling, and it gets drawn into the flu through that airspace between the horizontal plate and the top of the stove. That hot air heats the top of the stove, while the firebox ceiling and the horizontal plate protect the soapstone stovetop from direct flames.
The problem isn't creosote...the problem is that soot falls down the flu and deposits on top of that plate and piles up (and I assume some falls down the back inside of the stove.) When enough soot piles up on the plate, airflow is blocked. A couple of years after I started using the stove, enough soot piled up so I could not get enough of a draft to start the thing.
I've gotten the stove to burn more efficiently, and only clean the flu and the horizontal plate every 3 years just to be safe...it really doesn't need it that often. But in order to clean it, I have to break the flu free where it enters the stove. This allows me to put a bag on the end of the flu to capture the soot when I brush the flu from the roof, and it gives me access to run a small hose hooked to a shop vac to suck up the soot that's deposited on that horizontal plate inside the stove.
It's a little frustrating because I think with a normal stove I could just brush the flu from the ceiling and the stuff would deposit in the firebox for me to collect through the door. It's even more frustrating because the manufacturer does not have End User Support and they push you back to the dealer, who is not trained and does not care once the sale is made.