I also wonder if it would be a bit waisted in this application: if you are using propane burners and placing metal in the forge, that is quite a clean environment compared to a woodstove combustion chamber. I wonder if its ability to reflect the heat back into the stove would be limited/neutralised by the ash and soot and general blackness of a wood burner?
Also not sure how long it would last with bits of burning wood scraping on it? Any ideas as to how abrasion resistant it is?

Thinking about it, it might make a good lining for the secondary burn chamber though…

Sounds like a great project and with your climate, quite necessary. I’m no expert on stove design, but I did just build a propane forge for blacksmithing. I’ve found that ceramic insulation covered with refractory cement and coated with ITC-100 works wonders for insulative material that can with stand very high temperatures (over 2000 degrees. The ITC-100 is a high temp coating that significantly increases the life of the refractory material and increases temp by reflecting “radiant heat back into the furnace or forge to achieve high temperatures quickly and efficiently.”

You can get the ITC-100 here http://www.budgetcastingsupply.com/ITC.php

I have read there is another product called Plistix 900F that is cheaper and works as well as ITC-100, but I do not have any experience with this product.

I thought that this might be helpful if you are worried about melting your metal, as the ceramic insulation with with refractory cement and ITC-100 has worked well for blacksmiths working at very high temps. Just a thought.

You are right about the soot build up, that will be one of the design challenges of the heat exchanger. Really to get the best efficiency the air wants to be running through very narrow flat passages, where as much it ‘scrubs’ the metal walls as possible. Now the trick will be in having such an arrangement without adding too much air resistance, eddies and all that. I guess we will need one or more removable hatches so it can be cleaned – but we don’t want to be doing that too often!

Again the fans will help here – hopefully they will keep the air moving enough that this wont be a problem.

I suspose the desgin for the work shop is influenced by the fact that in many ways the workshop is more insulated that the average house, certainly more than ours, and a short efficient burn should warm up the space quickly and then remain so due to the insulation.

what diameter flue are you considering using? as this can influence the soot build up if there are dramatic changes where the transit through the flue drops in a sort of eddy effect.

In many ways a fan mounted near the end of the flue, which pulls the air, would be superior. But you then need a pretty robust and heatproof blower. Not sure how easy that might be to get hold of / hack together??
Fans at the inlets that push air in could possibly be mounted outside, at the entrance to the inlet pipes, so you wouldn’t be able to hear them inside. I can think of a few potential sources for suitable scavenged fans that should work for that…

Like your sterling engine idea, would be a nice project, but think the noise may cause mild insanity after a while. A peltier one would be good.

As for the stove base, i was planning to have it insulated to protect the metal (which probably wouldn’t deal well with the intense heat in the combustion chamber), and lined with a hard refractory cement, and the actual stove up on little legs, to hold it off the floor. I guess the idea of putting heat into the floor is what the rocket-mass stoves are all about.. I just think the time delay between lighting and getting heat out of that kind of system might make that less convenient for the workshop?

Agree about the glass – would be very useful!

Good conceptual plan so far, now I have seen the bulked out diagrams i see how the self feed will work, previously I was confused about how it was going to seal or whether it was going to seal at all. I like this self feeding fuel aspect very much, currently burning thin(1/2″ to 3 “) stuff in my conventional stove and getting good results in comparison to the open fire we had last year, but the reloading frequency is quite high. I wonder if all goes well you will be able to produce fuel ‘fagots’ held together with twisted split lenghts of stick ready for quick loading?

I’m liking the idea of the viewing windows from a control and learning point of view alone.

You will see when you pick up the stuff we ordered from the internet the other day that I have included the CO2 detector we looked at, not that I doubt the design will work but better safe than sorry. Control and correct function of the fans will be the tricky issue, as there is going to need to be some cut off system on the fans when loading fuel or the workshop is going to get smokey quickly. I can however voucher for the effectivness and consequent loss of effectivity of a conventional wood stove pulling cold air into a room while running, since the new windows have gone in at masion dave the draft under the door has become comical. And our stove is rated at below 5kw the point at which a air vent is legally required.

In regard to the heat up of the base issue, what hearth material are you considering as some of the heat build up could be disapated into the floor if configured right, obvisously not directly sat on the floor as the concete will prob crack up? I’ll do some learning on this…

All in all looking forward to warm workshopping, wouldn’t a stirling engine heat exchange fan look good, if potentially noisy.