Peter van den Berg

sara ventura wrote:I've read somewhere that a 20% increase is the usual to add to the amount needed of bricks, is that correct?

That could be correct, or not, depending on what you are building. Better to count the bricks individually when the drawing is finalized.

sara ventura wrote:Also, I've realized while drawing I forgot there are 2 types of brick, not sure that I can lay both between them as I've done? Different expansion rates, perhaps?

I am unsure what type of insulating firebricks you have there. Better to use just hard firebricks for the entire core. The riser is the part that's heat stressed most of all, especially the liner in the lower half. Thin strips of insulating firebrick, I feel scary about its durability.

sara ventura wrote:I've drawn the top's firebox using the refractory slab G-23, which leaves three joints on the top. Would it be better to have a single piece instead?

Not necessarily, it could be done in two pieces as well, three is also possible.

sara ventura wrote:And the single piece that doubles as top exit riser's port and base of the riser's top, should be from the same material as the rest of the riser? Can I use a cut from the G-23 slab?

Yes, you can, no problem.
I"ve had a look at your drawing of the core, and question arose. The depth of the firebox, is that a fixed figure because of the bell depth?

thomas rubino wrote:Thank You Peter, from the rocket mass heater community!

<blush on>Thank you for the compliment, glad to be of help.<blush off>

T Cool wrote:In my opinion a pönttöuuni is a 2 bell stove with the second bell very inefficient, being too small!

I fail to see any bell in a pönttöuuni, let alone two bells. It's just an old-fashioned contraflow heater, most of the time with the upstream channel built-in.

T Cool wrote:I read also an opinion of Vladimir Efimovich Grum-Grzhimailo (Владимир Ефимович Грум-Гржимайло)  regarding the transformation of contraflow stove in FMG one, if it is of interest I can post the in link.

According to that article you need to add some pillars inside of Pepper Shakers! More mass practically.

No, I am certainly NOT needing to add some pillars inside the Pepper Shakers. First, there's no space for those, second, no need for it. The pillars are a traditional feature of the Russian heaters, just because they are specifically needed for to close the top of the heater with their large bricks.

Now, you are searching the internet for old drawings and old articles. Once you've found one or more, you are trying to convince me that I should adapt my design accordingly. Let me tell you, I won't.
I tried pillars in a bell as long ago as 25 years, used the dry seams promoted by Igor Kuznetsov, a separation baffle in a dead-end bench, double bells in different configurations and whatnot else. All of those details didn't add any value but complexity instead and some had a negative effect.

I have a briljant suggestion: you are the best person to build these different ideas yourself! Buy one of those expensive Testo analizers and lots of materials, take leave from paid work for, say, 15 years, start experimenting and publish your findings here. Doesn't sound this as a splendid idea?

Cerbu Ulea wrote:hello, I discovered that only the meter that portrudes the roof is 17 /17 cm , the upward chimney is about 190 mm square does that change the math  of the stove? there is no need to go larger , the actual 165 is very  good

This won't change the math of the heater, only the narrowest portion is the one to go for. How's the burn season so far?

sara ventura wrote:I've finally managed to draw something that makes sense with sketchup.

Firebrick - 230x114x64 mm

IFB - 230x114x64 & 230x114x30 mm

I'm I going in the right direction? Are there any crucial mistakes?  

Yes, this is right direction and yes, there are some crucial mistakes.
Namely: the liner opposite the port shouldn't be there, the top half of the riser box should be square, sides equal to 2B.

Your bricks are slightly larger than usual, not easy to adhere to the correct proportions if figure B is exactly 72.34% of the diameter of the chimney. What I usually do with this size (150 mm) of core is this: I'll take the width of the bricks, in your case 114 mm, and use that as the Base figure.

Don't worry too much about it, I'll draw you a core that is the right size and proportions, based on the bricks that are available to you.
Could take some time to find a couple of hours that aren't filled in already. I'll try to have it completed before the end of the week.

T Cool wrote:In book  Finnish Fireplaces: Heart of the Home by Heikki Hyytiänen, Albie Barden, and Aila Rapeli.
available for free, see link below, at page 17 you can see the temperatures in a Finnish ponttouunit.

I know the book, I have the original Finnish publication, can't read Finnish by the way. But... I'd think you are mistaken, the numbers showed aren't from a pönttöuuni, but from the large nineteen-eighties heater built and tested in Tampere instead. In general, Heikki's large contraflow heater wouldn't pass the EU confirmation test of today by a long way, the requirements are much more stringent now. As such, the overall design is well outdated after 40 years, in my humble opinion.

T Cool wrote:What is your opinion regarding the combustion temperatures?
Seems to be higher than in a classic Swedish tile stove, the kakelugn.

I haven't seen any numbers for the pönttöuuni (page 29, picture 40), neither for the kakelugn, so I am unable to compare those.

T Cool wrote:Please consider also to view this video https://www.youtube.com/watch?v=znVxrKN0XVs

Funny, I know the guy who's presenting the pönttöuuni build. I've met him in France during the AFPMA annual meeting, three times. Last year we discussed the pros and cons of the Pepper Shakers as opposed to the pönttöuunit. No conclusion was met at the time.

It might be a good idea to shape the seat's back wall with a generous layer of plaster, this will make the transfer and the top temperatures flatten out somewhat.

sara ventura wrote:Can the thickness be done with clay / sand render or better to shape it with cob and render on top?

Best to shape it with cob and lots of straw. Th render is just for looks then.

sara ventura wrote:This gives me high hopes of real comfort when the Shorty is finished and the floor installed again 😊

Even people who tend to know what the effect of a mass heater would be, are surprised what it can do in the long term. The Mallorca build was one of those, it turned out the house wasn't just warm, but also dry. You have an awful lot of mass there, in the house itself. which means you probably start having a fire once in two days, later one per day. In about two weeks, the buffer of the house itself will get saturated and the indoor environment will stabilize.

In short: it may be so that at the start of the heating season the heat seem to disappear, until all the walls and part of the mountain that is behind one of the walls is finally warmed up.
I've seen it happen, a long time ago, high in the French alps in the Vallée de la Clarée.

sara ventura wrote:- I've found this product, would it be suitable for tiling top bench and bell? https://www.unistara.com/en/product-/
I'd prefer to avoid high temp silicones as I imagine in case of repairs it's more difficult to get rid of.

I'd say it is a suitable mortar for this application, yes.

sara ventura wrote:-The bell wall facing the riser's port exit - It will also be the face of the exterior bell that will serve as back support when sitting on the bench.
With a double skin of firebrick and red brick, what can be expected temperatures outside? Too much to rest your back on?

It greatly depends on how often the heater is fired and how many refills are done. As a guess: one fire (batch) every day could result in 30-35 ºC and two fires a day in 50 ºC. It might be a good idea to shape the seat's back wall with a generous layer of plaster, this will make the transfer and the top temperatures flatten out somewhat.

sara ventura wrote:Would it make sense to help gases flow through the exit pipe to cut the last section of the funnel? Like in the picture below

No, not at all, definitely.

sara ventura wrote:The left wall it's underground but it must be well drained and insulated because it has no moisture issues at all, the back wall is open to the kitchen and the floor it's a slab on top of the lower floor, wild guess it's probably more than a meter of concrete foundation underneath.

So the left wall is really, really massive. It's going to act as a huge thermal buffer, evening out temperatures and close to ideal! No insulation at all between bell and wall then.

sara ventura wrote:Given the size and height the top of the bell will have, I'm considering making it also sitting place like the bench.
Would it make sense to extend the heat shield of IFB to the first layer of the top? If it's two layers of red brick, it will get hotter than IBF and red brick on top?

I've been thinking about that IFB as heat shield, it's not very sensible there. Better to use hard firebricks for the shield. The idea is that the firebricks are better to pass the heat on to the bell wall itself. If you want to make the top of the bell as a seat as well, best to have one layer of bricks extra, separated by a layer of 12 mm superwool. It works wonders like that with my red bell heater, the top didn't get as hot as it was before, with insulation only.