Batch RMH build in Sweden

Chimney is 250x130mm plus or minus a few mm. Area 325sqcm. The 200mm pipe is 314sqcm so quite close. It is probably not the best chimney ever made and is not exactly straight. The stack effect is probably not best now in late summer with wet weather outside and cold/damp chimney but at least it is confirmed not too small as I understand it. Removed the plunger and will make that a bit higher now and a smoother transition to the chimney.

Owww... Here you go, your assumption that a rectangular chimney's cross section area is the leading factor is not correct.
That's because in the center of a vertical (chimney) pipe is a fast streaming, hot core. Closer and closer to the walls velocity is slowed down and the last half millimeter or so, called the boundary layer is effectively at a standstill. Keeping that in mind, a rectangle of any arbritary size is not as good as a circle of the same csa, aerodynamically speaking.

There's a simple rule of thumb to compare those. Multiply length by width, muliplied by two. Divide the result by the sum of length and width and you've got the fictional diameter of that particular chimney size.
In your case: 2 * 250 * 130 : (250+130) = 171.05 mm as the equivalent circular cross section chimney.

Conclusion: your chimney is too cramped to drive that particular heater system size, I'm sorry to say. In case the chimney is not smooth inside it will make matters worse.

When applied to a square chimney you'll see it's circular equavalent's diameter is just the same as one of the sides of the square. Despite the fact the square is bigger csa-wise.

Oh. So that's the end then. Bummer... 😩

Thomas Holm wrote:Oh. So that's the end then. Bummer... 😩

Not necessarily.

For example, i run a 220mm round riser, in a 200mm squarish, well square with rounded corners.  

Do what i was saying, cut the front of the chimney, and face it with bricks. Up to the ceiling. Or another easy way. Pipe up to the ceiling, and then plunge in the chimney. But  plunge with a 250mm pipe, so your transition is not too bad.  25xpi is 78, 53 cm circumference. By 13cm ; you end up with 1021cm² of ring projection  Since the gases go up. there"s 1/2  of it which works. So that's 510.5cm² for the transition. Not too bad. Even if it's a third, that's 340cm².

So imho. Not all is lost. You could even make your 25 cm diameter into a metal plate which affixes to the front of the chimney with gasket. And cut a bigger hole behind. 250 mm x 500 mm, and put the tube at the bottom. So for the first twenty cm above the pipe, your chimney section would be  if the bricks are laid flat, 24 x 25 cm.

You can then if needed, grind the top brick with an angle grinder and diamond disc. So it makes a funnel, instead of a shelf.

Thanks Satamax. But I cant cut the chimney, too much work for an already bad implementation of this. I should have done my homework from the start. I read everything on the internet (or so it felt) before I started but apparently did not absorb the right information and did a poor job at implementing the information that actually got absorbed. My mistake. Maybe someone can learn something from this.

Satamax, you have been a true hero in helping me. Thank you so much! Your kindness, knowledge and creativity is a true inspiration.

Satamax Antone wrote:

Thomas Holm wrote:Oh. So that's the end then. Bummer... 😩

Not necessarily.

For example, i run a 220mm round riser, in a 200mm squarish, well square with rounded corners.  

Do what i was saying, cut the front of the chimney, and face it with bricks. Up to the ceiling. Or another easy way. Pipe up to the ceiling, and then plunge in the chimney. But  plunge with a 250mm pipe, so your transition is not too bad.  25xpi is 78, 53 cm circumference. By 13cm ; you end up with 1021cm² of ring projection  Since the gases go up. there"s 1/2  of it which works. So that's 510.5cm² for the transition. Not too bad. Even if it's a third, that's 340cm².

So imho. Not all is lost. You could even make your 25 cm diameter into a metal plate which affixes to the front of the chimney with gasket. And cut a bigger hole behind. 250 mm x 500 mm, and put the tube at the bottom. So for the first twenty cm above the pipe, your chimney section would be  if the bricks are laid flat, 24 x 25 cm.

You can then if needed, grind the top brick with an angle grinder and diamond disc. So it makes a funnel, instead of a shelf.

Why you can't cut the chimney.  50x 25, with a 230mm grinder, might take you an hour!

Looking at the work you have already done. For fuck sake, do it!

And as i said, do a temporary bypass with some shit pipes or whatever, between your two cleanouts. That would be the first thing i would try.