Finally, we have come across a topic where “fun” goes aside and pure physics and safety come into play. While it is just fun with T-shirts with holes or blue eggs, a bad decision with a chimney can end in a fire or poisoning.
Installing a 90° elbow directly on the flue is considered a major offense in the heating industry, for several very logical reasons:
- Drastic reduction in chimney draft
The chimney works on the principle of pressure difference. The flue gases want to rise upwards. As soon as they encounter a sharp 90° angle, turbulence occurs and the gas flow slows down sharply.
Imagine it like a car that has to take a right-angle bend at full speed – it almost has to stop.
The result? The stove “doesn’t pull”, it does not heat well and smoke can return to the room.
- Soot and tar deposits (fire risk)
In a sharp bend, the flue gases cool down and slow down, which leads to massive soot deposits.
Soot is flammable. A deposit forms in a 90° bend, which can sooner or later start to burn (so-called chimney burnout).
Moreover, cleaning such a bend is a nightmare, because it is very difficult to get a brush over the sharp corner.
- Condensation accumulation
Flue gases contain moisture. Condensation occurs more quickly in a sharp bend. This liquid (often an aggressive acidic mixture) remains in the bend, corrodes the pipe material and can flow out through the joint onto the floor or wall.
What is the right way?
Instead of one “killer” 90° elbow, use:
Two 45° elbows: They create a smoother run-up (the so-called pants), the flue gases do not lose speed and the soot has nowhere to get trapped.
An elbow with a cleaning hole: If there has to be an angle, it must have an inspection door so that you can see what is going on inside.
The golden rule:
The fewer bends and the gentler the angles, the safer the home. If someone tells you that “we just dig in there at a right angle because that’s how it comes out to the wall”, you’d better send them to dye their eggs with turmeric.
Are you building a fireplace or just adding another important fact to your collection of internet wisdom?