Randy Repass

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since Oct 16, 2013
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Recent posts by Randy Repass

Satamax Antone wrote:Rebuild feed and burn tunel out of insulating firebricks, with 3" or 4" of perlite or vermiculite around, then you can cob the outsides. Everytime i've tried, and there's several others who have tried too, puting mass in the feed and burn tunel gives this result.

Ok, Satamax... will do... thanks for the feedback. It will be a little while before I can, as I'm in daily use of the system at present, but will give my feedback on the results once I do! Thanks again.
5 years ago

Satamax Antone wrote:Too much mass, not enough insulation in the feed and burn tunel.

Wouldn't this change the burn as it heated up? Meaning that once the burn tunnel was hot, and all that mass was hot it seems this would change the quality of the burn, wouldn't it?

How should I insulate a chamber that is 4" thick in places? I used about 4" around my riser flu of vermiculite, is that a bad choice of insulation type?

Thanks for your insights.
6 years ago
Hi, I posted here about a year ago, was blasted by a mad drive by response and retreated to my cave to rebuild and re purpose my RMH. I did this two more times, and on my third, I've tweaked and tweaked and am getting far better results than previous.

I have a relatively small space, so originally shrunk everything down to 4" pipes. I had a lot of problems and wasn't drawing well, so sized up to a 6" system following dimensions as laid out in Rocket Mass Heaters, by Ianto Evans & Leslie Jackson.

Presently my place is cozy, though by no means has any really cold weather crept in. It's fairly mild where I am in N. Ireland, between -10*f at coldest (for about a week or two) and warmest gets to 70-80*f in summer. Right now it's sitting around 45*-55*f which is a likely average. I'm in a roundhouse/yurt insulated with hemp-lime plaster and sheep wool insulation.

I have a couple hard turns in the MH side, and have done my best to remove any 90*, I do think my flow is not bottlenecking too bad anywhere. In general she's pulling a good draw with little or no heat in the morning in the system, when I go to fire up. But, I'm get a lot of ash buildup in the burn chamber and have emptied it three times in this build already, (since about early september) filling about a half gallon space each time.

I don't believe I'm getting secondary burn at the top of the riser. My temps at the top of the riser get to about 350-400*, which is half of what I've seen people describing in other threads. WOW! what a major difference that is!

So, I am looking for ideas as to my main issues.
-too much ash
-low burn temp

I only get blow back into the building if a storm is raging & it's very windy. I plan to resolve that soonish with an "h" cap I'll build, when I did this with the 4" system it worked a charm.

Here are some pics:

6 years ago
So, based on your thoughts (Peter) and my own meditation on the project I'm rebuilding the stove before the battery.

My first iteration of the project had the chamber built entirely of cast pipe from a large cook stove, still 4" but hardy stuff. I had this setup as a burner to heat my hot tub, another side journey I've been on. I'm redoing that job into a Rocket?snorkel stove which I'll talk about another time.

I've just cast an insulated base out of vermiculite and cement, about 4" thick. I used to make such casting for the top outer insulation of my glass furnaces; it's easy to cast very well insulating near hot temperatures.

I'll next set my 'J' pipe on that and cast over and around the entire bottom and feed tube while creating a base for the tank above. That is a much smaller chamber than before, an old propane tank I've cut the bottom off. I'm considering running a copper coil I've built inside it for my hot water. The inner dimensions of the tank are 13", my heat riser is 4 ½ od, about 1" insulation inside a 6" pipe. This leaves about 2 ½ inches of gap between the heat riser insulation retaining pipe and the outer tank.

Should I use more insulation in the heat riser?

I am glad to be moving forward! I've been living off a wood stove that just feels like a mass fuel burner!

6 years ago
Thank you Jeff, Peter & R Scott. I take all of your thoughts to heart and appreciate your thoughts on this.

I built glass furnaces, as well as taught furnace building here in Ireland for about 6 yrs, so I do come with some "unlearning" to do, no doubt, but also some knowledge of "playing with fire". I went through a series of designs, the best of which came at the end of that tenure for me. I gave it up as it was so expensive and in my eyes impractical for our environment. This is the first time I am considering melting glass again, using one of these cool stoves.

That aside:
Since all these posts, and after "Big Al's" I persisted and got her burning fairly well. Kept it burning, but had backdraft that kept putting it out. After blowing on it, it started up again... lots of hot coals though. Partially I found placement of my sticks was helpful and towards the end of my testing when the coals were building up, covering the hole with a bit of brick increased the flow so it burned well, and resisted the backdraft. I had to leave before it completed, so I don't know yet how much burned up, or if there is a good deal of ash or charcoal left from the burn.

Thoughts on comments:
  • rough lines improved burn in a glass furnace, but I can see now how it can really mess up my system.

  • testing minus the barrel, then minus the flu is a great suggestion

  • Peter; there is insulation around the flu out of the burn chamber, where else would I need any? I don't see any description or sketches showing other insulated spaces-or did I totally miss something?

  • Can you clarify why you feel changing the brick thickness would matter Peter? my understanding is that we are dealing with internal spaces, not external?

  • I guess, Peter, you are suggesting a larger riser from the burn tube, so that the transition from square to round is better? I tend to think is flows well enough there, that that might be minor in consideration of other issues, or am I wrong about that? Seems the test with just that riser will help a lot to see how it does.

  • length of system, Peter: the guide says 30' for 8", 20-25' for 5", I went for about 15-20 for 4". But will test it with 10-12', as the last 8' is not built yet, just attached on for testing.

  • vertical chimney was very short initially, and had problems. I increased it with that last test burn and that made a big difference. I'll work on getting that properly setup.

  • barrel size: should I shorten it? Or is it too big around all together? Is it a problem with too much space between insulated riser and the OD of the barrel?

  • I went with 4" as that is what I had, as I said, but also, I want a smaller system. I have a very well insulated 23' yurt this is in, I'd like it to be warm but not overly hot. Thus a smaller system (in my practical mind) makes some sense. I know from furnace building and the origins of rocket stoves, small is very possible... so why can't we size down the mass heater? I am hard pressed to see argument saying it can't happen, but do agree R Scott that it is likely on the small side of draw, especially if I am too long. Filling with ash and reducing it hadn't come to mind (another important point I overlooked on some level). So, I need to introduce another access hole for sure at my 180 degree bend to deal with that I think.

    I am feeling that I will need to pull the rough flu... sadly. Thought that was so perfect! It's used as replacement chimney liner all over this part of the world, and jus't didn't occur to me, even though the mention of a clean straight pipe in the guide is there.

    Lastly, R Scott, I don't think, reading now, that "Big Al" was being cruel... but as a first response it was not a good one. I taught furnace building for years... I'd certainly congratulate efforts before pointing out problems... where ingenuity is in place. Mistakes are the pillar...

    Thank you all hugely for your input. I've been pushed by Al to prove him wrong (not a bad thing! we can all learn, eh?) and now have a lot to consider going forward and best of all, R Scott, practical testes to perform at this point.
    7 years ago
    I have built two rocket stoves, this is the second. The first is very simple, and is similar to something I saw a guy do on Youtube to heat water, my need on that one, to heat a hot tub. I am learning from all of this, and certainly would love for someone to help me understand where a 4" pipe, if that is the real issue (I'll be quite keen to know why), will not work when proportions to the 5 or 6" style do? In other words, I build the chamber and all of the stove to the proportions laid out in the larger systems, and it does heat, it just doesn't stay lit.

    If I can fix this, I will, if I have to tear it down... I will, reluctantly & sadly. But I am looking for insights here please, not newbie bashers.
    7 years ago
    Brand new rocket stove... used what I had to use... that's the idea right? I downloaded Rocket Mass Heaters and read up a good bit. Had 4" pipe to work with in good quantities as well as stainless flexi flu. Built her nicely... fired along the way, never a real hot or lasting fire, but decent enough to be darned excited and keep moving. Now well cobbed up and just can't keep a fire lit.

    I seem to get decent enough draw, but it just burns out. The wood isn't the driest, though it is fairly dry, just damp from the dampish air we have here in Ireland. It's wood that in a standard fire would burn like mad.


    Brick layout before cementing

    Flu layout on first layer of cob

    Refractory battery

    Junction at tank to flu

    Tank in place

    burning with a few smalls sticks (normally many more in there... this was a first light)

    The 4" pipe up the middle of a chimney liner with vermiculite insulation between.

    Video showing it burning and some other details... (sorry it's the wrong angle!)

    Any thoughts?

    Many thanks for looking.
    7 years ago