Jonny Clothier wrote:...However, on the thread about small RMHs "Peterberg" - who clearly does a lot of this - seems to be using a square section tube for the riser made of insulating board...
Jonny Clothier wrote:So my list of to dos is...
1. Block holes in feed tube.
2. Leave tunnel as it is.
3. Possibly add steel liner to the inside of the riser.
4. Shave outside of riser to standardise riser-barrel gap.
5. increase manifold size to increase the stream profile there.
6. Lift outlet to a decent level.
What I can see of your riser it looks like it's made of fire brick. That's a better solution than steel, because the brick will reflect part of the heat. The riser slightly wider than the tunnel is not really important. It's obvious, this stove hasn't been in good working order before so it will not burn the soot off the inside walls.
Jonny Clothier wrote:The only one of those I'm not sure about is the lining the riser. Do you think the difference in mass between mine and yours makes that worthwhile.? The resulting, slightly reduced riser csa would certainly make the line of csa's more consistent...
Don't care about the top gap being too large for half an inch or half a yard. Too small is bad, it will hamper the running of the stove.
Jonny Clothier wrote:Last point. Is the barrel-to-top-of-riser gap too much? If so a new steel riser-liner would take care of that if it pokes up half an inch...
That's even better than fire bricks, more of the heat will be reflected this way. The soot will burn off once the stove is running properly, don't worry. The surface of those bricks will be very much hotter than the inside. My vermiculite board riser has always been clean within one run, no mass to heat up will create a very hot, fast streaming core inside the riser.
Jonny Clothier wrote:However the riser is nto made of firebricks. They are fireproof insulating blocks - so they don't heat up like normal firebricks. Quite the opposite in fact.
Yes, I am afraid you are.
Jonny Clothier wrote:Or am I talking rubbish?!