Warm climate low power aryan shoebox type cookstove

[fishalive12345]

Hello forum members and readers,
thanks for the wealth of information posted here.

I'm about to start a project to replace the traditional wood cookstove in a small house just above the coast in Liguria in Northern Italy.  It was how the house was heated in winter and how the food was cooked all year round until a gas cooker with bottled gas was installed probably in the 50's or 60's.



I plan to replace it with a stove approximately the same size though a bit taller but with a cooktop and a separate oven. The original stove has a pizza oven domed fire box and has a large aluminium cooking pot sitting with it's base in the firebox. It seems strange that there is no cooktop so it looks like the people lived off baked stuff and soup.

As the climate is warm most of the year We don't need a very poweful heater. The original chimney is about 15 by 15cm internal made of concrete blocks lined with some kind of refractory mortar and then plastered on the outside so it's not really insulated.  I plan to line it with single skin stainless tube, either 12 or 13cm in diameter and to fill the remaining gap with perlite.  I will have to drop the lining in from the top, put some kind of insulating wadding in near the bottom then pour in the perlite. The size of the chimney and the fact that the replacement stove will be much more efficient than the original mean that we can, I hope, use a smallish stove (in terms of power)  to heat the kitchen and adjoining room and to cook and bake if we choose to use the woodstove instaed of tthe gas stove.

There are a number of cookstove plans here on proboards but I really liked the look of the Vortex stove as soon as I saw it.  The proportions are right. Firegazing is given its due importance, even more so with viewing window into the secondary burn chamber on the aryan shoebox version. But no oven and a different climate from Ireland so different heating requirements. It would be nice if Trevor's stove had been tested with a combustion analyser but until they get cheaper or more widely available which may happen with the current emphasis on air quality.

So I have decided on the combustion system but still have doubts, questions and so on about the heat recovery side. The following sketch is where I am with that.

imgur.com/81qJiDt

The aim is to have half the stove as combustion system and ceramic glass cooktop and the other half as black oven and heat storage. The sketch shows two bypasses, one for startup and cooktop only operation and the other for cooktop and oven operation. When both are closed the heat recovery labyrinth is also in the smokepath with the option of cutting out the oven by opening a shortcut in the smokepath on the right hand side of the oven floor. Too many controls I'm sure but it's at the idea on paper stage.

I haven't really got to grips with the ISA calculations at all and that's the next thing I need to do. I really like the idea of a bells but the volume, even including the oven is too small I think. I plan to make the internals of the oven/heat recovery side independent of the outer brick skin and to make the horizontal elements including the top out of cast concrete (refractory?) or, if it doesn't cost too much, soapstone.

My first job is to get together the materials and then to try out a scaled down aryan shoebox system in the garden as a preliminary to actually building in september hopefully.

I'm kind of hoping, initially, for comments on the oven and heat recovery side but welcome any comments.
Thanks
 

[Vortex]

One thought reading your post, you don't say what type of pipe you intend to line the chimney with, but I don't recommend the stainless flexible pipe. I've had problems with stoves using it and so has Pat. The wrinkles seem to create a lot of resistance to gas flow.

I look forward to seeing your 5" garden test stove, hopefully it will spur me on to build mine

[gadget]

So this heater is only going to be used when it is cold to heat and cook since there is also a gas cook top for warm days?

I am curious on how you are going to do the chimney with perlite insulation. It sounds like you plan to place it between 2 pipes? Why not just have air between the 2 pipes?

Take some pictures when you tear out the old heater, I would love to see how it was made and how well it held up.

I'm not an expert on this type of heater compared to others on this board but will be reading on how well this goes.

[fishalive12345]

Hi Trevor and Gadget,
thanks for the responses.

The stainless flue is made up of straight rigid 1 metre lengths so it shouldn't really create any resistance. I guess you're talking about the flexible corrugated tube. I think the regulations in Italy say that you're not allowed to use corrugated flues for wood or pellet stoves and any new external chimney has to be insulated. You can only use specifically approved and marked flue liners I think. In my case I'm renovating so as long as I make improvements it should be ok. But I'll make sure that I've got photos of the what I'm doing and the materials I'm using just in case anyone asks.

Basically I'm just going to put a single pipe made up of 1 metre sections as a lining into the original chimney. The old chimney is a rounded square but it's too big and not properly insulated as it's outside on the side of the house. It will also make it easier to clean as I can put a cleanout at the bottom of the straight section just before it goes through the wall. The reason for using perlite is mostly to insulate the chimney but also to stop mice and wasps from colonising the empty space round the flue during the summer when the stove won't be used (much?). We've had hornets regularly in summer and also a lone mouse. It didn't come down the chimney. It just took up residence in a cleanout above the stove.

I meant to ask about flue size. I'm assuming a chimney that is oversized with respect to the stove, ie 6" inch chimney on a 5" stove, would create too strong a draught. Is that right?

Will definitely document the demolition of the original stove as I'm quite reluctant to do it. From what I can see the firebox is a dome made of red bricks. The top is tiled and there is an iron bar frame round it.

Trevor, not sure I can live up to the responsibility of spurring you on to experiment! I feel the weight already. I'll have to do my best.

[gadget]

That makes sense on your chimney. I know in the US they run new pipes in old chimneys. They call them chimney liners. They just run 1 pipe typically.

I believe allot of the standards for chimney pipe have to do with how the seam is made. Usually it is designed so that if the chimney pipe gets really hot from a chimney fire the seam does not open up like a zipper letting all the chimney fire flames loose in the house and attic.

I have seen many people use vent tubing for chimney pipe that has a very weak seam but get away with it since there is practically no creosote build up in most rocket/masonry heaters.

I know allot of these heater designed are tuned so for maximum draw correct diameter is good to follow but there is a window to work in. Its allot like running a car, if you run a larger camshaft then your need to increase the size of the intake, exhaust, etc... so it is a matched/tunes system. Length, turns and insulating values also come in to play. Your probably fine going with a 6" but someone else can confirm that

[fishalive12345]

It makes sense to have chimney liners that can stand up to eventual chimney fires. Another advantage of stainless is that it will stand up the acidic flue gases and condensate.

Seems like fine tuning a system, as Peter V. D. Bergh does, can be quite unpredictable. Small changes can have a big effect. My main concern at the moment is to try not to overlook anything really essential in the general setup. Any tuning that I might be able to do will have to be based on my five senses as I don't think I can afford to buy a combustion tester and I certainly couldn't afford to have it regularly calibrated. It would be really nice if you could call someone up to come and check out your woodstove. In fact in Germany when you build a stove I think you have to call a certified chimney sweep to approve your system. In Italy you have to get your gas heating system checked out once a year or once every two years. It costs abot 80 euros and they fill in the logbook for the system. Considering how much more pollution woodburning causes you'd think someone would think about a similar system for woodstoves. Not that I want to pay 80 euros but at least I'd get to have my system tested and the technician's flue gas analyser would get intensive use and so justify its costs and the environment would benefit.

Looking through the site yesterday I found a link to a woodheat.org page,
www.woodheat.org/all-about-chimneys.html
which answered my question. A good chimney is, among other things, "the correct size for the appliance, which is usually the size of the appliance outlet collar". I'm taking that to mean the system size or the real or hypothetical diameter of the heat riser. This system size should be the smallest restriction in the system apart from the port which is deliberately smaller in order to speed up gases and promote mixing with oxygen.
The woodheat.org pages have so much good, clear and brief information. Now I know much more about why an exterior chimney is a bad or a really bad idea, depending on how it's done.

Thinking about scaling down Trev's Vortex stove, I'm going to take my measurements based on the ratio of the area of a 13cm circle (the hypothetical heat riser) to the area of a 15cm circle. That means the measurements for the combustion system, fire box, throat, secondary burn chamber etc should be 75% of the measurements of Trev's system. Does that sound right?

That also means that the ISA of a 13cm system should be 75% of the ISA of a 15cm system? I was looking for information about calculating the ISA of a smoke labyrinth but can only find information about sizing bells. It seems that the main thing to be careful about is oversizing the heat recovery system as that will bring the temperature of the exhaust down below the point at which creosote and eventually water will condense, stalling the system. A good indication is if the system is difficult to light. The problem can be avoided if you have a bypass which allows you to heat up the chimney and to increase draw.

My understanding is that undersizing the combustion part of the stove and oversizing the heat recovery side would be a good idea in our situation as we get cold (-5c) for a few weeks a year and wet and windy weather for a few months a year. As long as we have a startup bypass this will allow us to fire the stove more often when it's cold or wet and only occasionally when we just want evening heat or to cook or bake in the warmer months.

Another thing I don't really understand is the effect different materials have in the heat recovery and radiation part of the system. A cooktop will give instant heat, the remaining heat wil be stored then released. The bigger the ISA the more heat will be stored and some materials store more heat eg water? though that's not relevant in my case. Dense materials store more heat so you could have a physically smaller heat battery using more dense materials? As long as you have enough space to get the heat from the exhaust gases into the material, so dense materials with a high surface area? But presumably all this is well beyond the possibilities of calculation so comes down to rule of thumb and experience?
So many questions.....

[Vortex]

5" stove on a 6" chimney is OK but not the other way around.

The scale factor for scaling a 6" down to 5" is 0.83 (83%). 6" is 153mm so going from that to 130mm is 0.85 (130 / 153 = 0.85).

Straight SS 1m liners surrounded with perlite will be perfect, the fact the chimney is outside should be irrelevant once it's insulated.

Different materials all have different heat storage characteristics and capacities, but as a general rule the more dense it is the more heat it can store. The magnetite storage heater bricks are perfect as they are designed for the job, can you get hold of them there? I designed my heat storage so if there is too much mass I can just lift off the top and take some out, or move them around to create more surface area etc.

[fishalive12345]

No chance for magnetite storage heater bricks here as off peak electricity was never a thing. People seem to use electric storage heaters in France , even today, in my limited experience. In Italy I think heating went from wood to fuel oil to gas. I suspect widespread use of electricity for heating was linked to nuclear energy.

Being able to adjust your heat storage elements sounds ideal. I think adaptability should be a design goal.

On that note, what mortar do you use for your experimental stove? I've seen clay sand being recommended as it makes it easy to reuse materials.

[fishalive12345]

Thanks for the scaling factor. I was trying to do something much more complicated but wrong!

[Vortex]

Aug 4, 2019 2:42:29 GMT -8 fishalive12345 said:

No chance for magnetite storage heater bricks here as off peak electricity was never a thing. People seem to use electric storage heaters in France , even today, in my limited experience. In Italy I think heating went from wood to fuel oil to gas. I suspect widespread use of electricity for heating was linked to nuclear energy.

Being able to adjust your heat storage elements sounds ideal. I think adaptability should be a design goal.

On that note, what mortar do you use for your experimental stove? I've seen clay sand being recommended as it makes it easy to reuse materials.

Dense firebricks are the next best thing that's readily available most places.

I used the recycled fireclay from my old stove on my initial garden experiments, then later I started using pure clay as I could get really thin joints with that.

[fishalive12345]

[fishalive12345]

Hmm. Tried to insert the image rather than the link but evidently having problems.

Anyway, gave up on sketchup and went with sketch!


Built with castable refractory cement (core) and fire bricks (22x11x5 . 5). Ceramic glass for the hotplate and firebox door. Also in various other places in order to ensure that the flue gases never come into direct contact with the ceramic fibre insulation. Double skin with an intermediate layer of superwool for the black oven and single skin for the lower part of the stove which is designed to extract, store and radiate the heat from the hot gases..

The combustion core is a highly efficient (clean and economic) double combustion system developed by Vortex https://donkey32 . proboards . com/thread/703/vortex-stove

[fishalive12345]

Demolishing and rebuilding the old wood cookstove. It was inefficient and had no hotplate.




The firebox and oven with the pan holder visible at the top. The pan holder held a large aluminium water pan, the bottom of which was in the firebox. Lots of soot! The exit to the chimney was behind the pan holder. The base of the firebox was a large and thick refractory slab. Good for making pizza.




A photo of dirt! The lower part of the stove was filled with dirt to act as thermal mass and hold the heat. The kitchen was still nice and warm in the morning.



The new firebox base made of refractory cement cast in a mould. You can see the tongue and groves for dry assembly.



The dry assembled base and side.



The new firebox top with wood pieces for tongue and grooves still in place. The large wooden piece is the firebox port into the afterburner. You can see the vermiculite I tried to incorporate into the casting. This piece isn't too crumbly. Other pieces I had to recast after I gave up on the vermiculite.




The dry assembled firebox seen from the back

[fishalive12345]

Can anyone explain how to insert images directly into the post as I haven't managed to do so?
Thanks

[Vortex]

[img]insert your link here[/img]
Like this:

[img]https://i.imgur.com/xf3g9i1.jpg[/img]
Displays like this:




I would recommend you cut the top into 2 halves like this, otherwise it will crack: