What were living conditions like for a chimney sweeper?

In the early 19th century, more and more homes with chimneys appeared, and with them came an increased need for chimney sweeps.
For a chimney to work properly, it needs proper air flow, as this draws more oxygen into the fire, supporting combustion. However, soot and other residues could build up in the chimney from the smoke, causing blockages. These could be extremely dangerous—some particularly poor constructions could explode from the pressure (as happened in some old Tudor/Elizabethan era homes), and the residue itself was flammable, so it could lead to house fires. It was the job of the chimney sweep to stop this by removing the buildup.
With the rapid increase of chimneys during the industrial period, there was an equally rapid demand for people to become chimney sweeps. However, despite what the dance scenes in Mary Poppins might suggest, it was perhaps one of the more derided jobs of the period.
It was low-paying, difficult, and incredibly dangerous. The U.K. in particular had some of the more hazardous conditions (due to differences in construction and regulation), and children were often the ones doing the riskiest part of the job. Chimneys were narrow and often filled with twists and turns that needed to be cleaned as well. It was simply impossible for adults to do the actual sweeping, so the younger and smaller the child a "master sweep" could take on as an apprentice, the better. They would literally climb through an environment filled with noxious dusts and gases, sure to result in later health problems if they didn't simply suffocate in-chimney (many master sweeps would have two children, one right behind the other, just so one could literally poke the other to consciousness). Sometimes the chimneys might still be hot from fire—or literally still on fire since the residue they were planning to clear was flammable and could still potentially burn after the main fire was put out. Many also went in naked due to the cramped spaces, so there were plenty of opportunities for burns. Combine this with tight, often twisting spaces, and it was entirely possible for a child to get stuck. This is not even getting into long-term conditions such as stunted growth, lung problems, or other medical conditions.
Slowly, child labor laws were put in place, for example stating the minimum age for a chimney sweep was eight years old, but it wasn't until mechanical methods of clearing chimneys appeared that demand for the job began to fade.
All in all—not a fun job.
https://www.ncbi.nlm.nih.gov/pubmed/1399014

https://www.parliament.uk/about/living-heritage/transformingsociety/livinglearning/19thcentury/overview/childrenchimneys/