Open fire smoking back into the room
Well, the simplest and commonest is that their fire or appliance smokes. The solution is to get a competent chimney sweep, and ask his or her advice to rectify the problem.
A fire smokes back into a room for a number of reasons. It can either smoke persistently, or intermittently. If the latter, it is usually a wind related problem. If persistently, then there is usually an obstruction, which may be partial or complete, or it may be something as simple as the fireplace being too large for the flue, or the wrong terminal.
You can usually tell that a fireplace is smoking back into the room by the smoke stains above the fireplace, so when looking at a new house to buy, watch out for that tell tale sign!
How do I know my chimney is working?
So when you ask yourself ‘how do I know my chimney is working?’ the simple answer is, it is far easier to tell when it isn’t, and in those cases, smoke is the key. You should never be able to smell smoke venting into the living space.
In most cases a chimney will work well (unless someone has done something to it, or it wasn’t built/designed properly), but your best course of action is to get a certified chimney sweep to clean it. They can tell a lot by what comes down the chimney and advise you as to whether or not the chimney is safe to use as it is.
In order to test the draw and identify whether or not the chimney is blocked, you can hold a joss stick in front of the fireplace, towards the top of the recess. The draw of the chimney should pull the smoke up the chimney. If it doesn’t it’s like it’s blocked. Either by a bird nest, or it has been purposely blocked off.