Homeowners should check their chimneys once a year, either at the end of the current heating season or shortly before the start of the next season.
If you don't want to hire a chimney sweep to check out your flue, you can do it yourself if you take some precautions. Climbing up on the edge of the roof to peek down a chimney can be a risky business, especially if your house is two stories or more high. Make sure you have a very sturdy ladder and an assistant to help you. The assistant can hold the ladder securely while you are climbing to the top. You will need to take up a flashlight for looking down the chimney, and a long, heavy chain if you see a creosote buildup.
If you have a long rope, you can make a pulley by looping it over the ladder rung closest to the top of the roof, and tie one end to a pail with the chain and flashlight inside. When you get to the top of the ladder, your assistant can pull the rope slowly, allowing the pail to rise to you, and anchor the rope to one of the bottom rungs. This way, you won't need to carry the pail up as you climb. This is very important when working on high roofs, as you don't want anything to make you lose your balance. If the chimney is at the edge of the house, you can stay on the ladder. If it's in the middle of the roof, you'll need to carefully work your way across the roof to the chimney to look inside.
When you are at the point where you can look down the chimney, point the flashlight into the opening and see if you can look all the way down. Shine the light on all four sides, and see if the chimney has dark areas in some spots more than others. If it looks good, just dangle the chain down its chamber, not letting the chain fall in, to knock any residue that may have accumulated on the sides into the lower part.
Once you've finished and are safely back on the ground, find the lower part of the chimney and remove it from the base of the furnace, pulling out any debris that fell down and checking the base for more buildup. You should then be able to use a mirror or just peek yourself and see if the light is visible from above. If so, your chimney is clear and has no blockage.
If you have a wood burning stove, however, and it has a heavy buildup of black waste, you will need to scrape that out and clean the chimney walls, making sure there is ample open spaces for the smoke to be drawn to the sky. If there is a small build up that loosens easily, tap the chimney until all the residue falls out before putting it back together.
If you have a wood burning stove or fireplace, it would be a good idea to periodically burn a creosote-dissolving log to take away the dangerous buildup before it becomes too thick. A fire inside a chimney gets extremely hot, and it could burn the house down before you have a chance to call the fire company.
When you put the chimney back together, make sure all seams are tight and if they are screwed together, make sure the screw heads go as far in as possible. If not, smoke could leak out into your home, causing you to suffer from carbon monoxide poisoning or destroying your furniture and walls with a smoke smell and residue that may never come out. Also, anyone with a wood burning stove or oil-based heat should purchase a carbon-monoxide detector, for the optimum safety in case a chimney backs up into the house.
