Please visit our home site at www.TRILOBOATS.com.

Anke and I live aboard WAYWARD, and wrote about it's design and construction at ABargeInTheMaking.blogspot.com.

Access to the net comes and goes, so I'll be writing in fits and spurts.Please feel free to browse the archives, leave comments where you will and write... I'll respond as I can.

Fair winds!

Dave and Anke
triloboats swirly gmail daughter com

Tuesday, December 5, 2023

A DIY Rocket Stove Smoke Hood

 


Eco-Zoom Rocket Stove with DIY Smoke Hood




Somebody who claims to speak for the ‘hood don’t need no private jet.

– Chuck D



A DIY Rocket Stove Smoke Hood


About half of the energy in wood literally goes up in smoke, and with it, a good deal of our own! If the smoke can be burned, efficiency nearly doubles. The corollary is that only half as much fuel produces a given amount of heat.


Rocket Stoves were developed as a low-tech solution. At their heart is an L shaped, insulated tunnel, wide open at both ends. Fuel is fed horizontally, oxygenation and combustion burn hot at the crux, and what little smoke is left is pushed vertically, up and out the top. Typically, a pot directly atop the stove absorbs heat from the hot, gaseous outflow for cooking.


We’ve been using an EcoZoom Rocket Stove for years as a nearly smoke-free, otherwise open deck fire for outdoor cooking in hot weather, an evening blaze in nice weather and to heat metals for various projects (it easily takes ferrous metals to red-hot). It runs on limbwood from about thumb to wrist size, the former for cooking and the latter for longer, more subdued heat. In short, perfect for easy wood-gathering, especially as we age..


In planning MUSTELID, we hoped to bring this marvel indoors for cooking and heating. It requires far less wood to gather, dry and store within her small volume. Being insulated, wood can be dried directly alongside the stove, warm but nowhere near wood’s flashpoint (we can touch the stove sides without burning!).


To bring it indoors, we must gather and direct combustion gasses outboard, like any other onboard stove. The solution is a smoke hood fit snugly over the stovetop with a stack, which has the extra perk of increasing the cooking surface area. We wanted one more feature… we wanted to easily install and remove the stove for outdoor use on deck or ashore. So we went for a swing-up, cantileverd variation.


This called for some head scratching…



Note (black) fire-blanket to protect carpet from sparks, 

Grate spacer for airflow under,

Ash tray…

Whole thing slides aft behind bulkhead lip

And between heat / splatter shields.



Near end swung up to remove / install Rocket Stove




Not to Scale


Smoke Hood Elements


At it’s simplest, the hood is a flattish box made from sheet metal (in our case, stainless steel from and old stove’s grease trap… a heavier top plate has better thermal mass for cooking, if available. A large hole in the bottom fits closely over the Rocket Stove top, while a smaller hole in the top has stovepipe fit into it, which leads to a standard deck-jack and smokehead. If you leave the stove in pace, this is all you need.


For a swing-up top – allowing removal of the stove – we broke the hood into two boxes, each with an open end:


  1. The far box is fixed (in our case to bulkhead and flanking heatshields), with the flue let into its upper surface. Its near end is open, with rounded shoulders and an under-lip. This part is female, slightly larger than the second part.

  2. The near box is cantilevered (stops may be additionally fitted to help support heavy pots). Its far end is open, with a partial rounded shoulder fairing to 45deg… extending an over-lip, while the angled section limits upward swing. This part is male, slightly smaller than the first part. Insert its open end into the female’s until their respective hinge-pin holes align.


Other parts:


  • The long hinge pin (alternatively, short, opposing pins) are let through paired holes centered on the shoulders. If it binds while swinging upward, grind away from the lower male shoulders till clear.

  • A vertical smoke collar can be used around the stove-top cut–out (not sure it’s necessary). We used a strap of sheet metal, its edges doubled over just short of its outer mid-line (result about one inch wide) and tabbed around its outer mid-line (tabs bent alternately, slightly away from cut-out). When pressed into place, it ‘snaps’ in to lock. It works best to cut the tabs before bending.

  • Rims, rails, bars and what-have-you may be added to secure pots while cooking underway. In our case, we added a low front rim and let that and tall heat / splatter shields along each side contain pots. Watch for swing-up clearance.


Notes:


  • Any gaps allow air to be drawn into the hood. The closer the fits, the more energy is available for cooking and heating. Once the stove is drawing (seconds) there appears to be no leakage, even from wider gaps. We didn’t use gaskets, but they can’t hurt.

  • We sized our male part to be 1/16in smaller than the female’s inside dimensions. Given our crude techniques, we managed between 3/32in and 1/8in. So long as it slides in without undue forcing and the gaps are small, it should work fine. Thermal expansion binding isn’t a problem as we only ever move it out once cool.

  • In both cases, the lips should overlap the opposite part to help close the gap and contain ash. Small tabs may optionally be bent along single edges to help minimize warping with heat.

  • Sizing can be more or less according to your available space. We sized around our frypan plus our small teapot, to cook and heat water at the same time.

  • The smokehead can be lower to the deck than is usual. Although it does induce some draft, Rocket Stove’s generate expansion in their combustion chamber, and actually push gas about 40ft. Still, an efficient draft smokehead hedges our bets in some gnarly conditions.

  • We didn’t have a brake (sheet metal bender), so clamped sheets over a piece of sharp-edged hardwood, then hammered it over. Cutting was with a thin-wheel grinder and touched up with a mill file. We used bent tabs with (copper/stainless) pop-rivets to join. Wear gloves, eye, ear protection and work safe!



Looking Ahead


One of the intriguing possibilities with Rocket Stoves is to make our own from a substance that insulates, absorbs and radiates thermal energy. In other words, which acts as a thermal mass or ‘sink’. Such are easily made from brick, firebrick, concrete, clay, cob and other materials. 


Perlite (pumice) is a light, inexpensive insulator, and can be mixed with concrete for a lightweight aggregate with decent thermal mass. The combustion chamber can be lined with refractory clay. A thick, steel cook surface is easy to install over a lipped smoke chamber for a full sized stovetop / smokehood. Sand makes a good gasket between plate and stove. Alas, this doesn’t sound very portable!


But we keep on thinkin’.


12 comments:

  1. Well done solution! Liked a lot rocket stoves, have here one conventional stove that wants to transform on a rocket one. Lot of axe and chainsaw work this winter that can be avoided.

    ReplyDelete
  2. Hi Lucas,

    One of the things we've thought about is to insert a rocket stove into our wood range on WAYWARD. It would probably work well for the summer, and we'd switch to the regular firebox for winter. But ya never know!

    Dave Z

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  3. Wow, a clever way to use a rocket stove inside!

    I've been interested in a Eco stove but your reports that you can touch the sides while its burning is a keeper.

    Clearly not a Rocket MASS Heater. So limited heating capability unless your cooking all night?

    A belated Merry Christmas and a Happy New Year to you both!

    Michael

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    Replies
    1. Hi Michael,

      Happy Holidays to you, to, of all persuasions!

      It's definitely not a Rocket Thermal Mass Heater, though we're thinking about one. Can't easily take them out, once in, though.

      The EcoZoom does well with a cast-iron pot or two to amass and radiate heat, but as goes the fire, so goes the heat.

      We don't leave the fire on past bed-time at any rate, and it's seldom going during the day, so heat is definitely up and down. But when it's on, it's nice and toasty!

      Dave Z

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    2. The success of a Rocket Mass Heaters ability to carry heat all night is MASS.

      My Deer Camp RMH heats a space not much larger than your 32 foot barge (maybe less) and I estimate the mass involved is over a ton.

      Might be hard on the Waywards ability to sail?

      Warm the human, that's boat camping to me.

      Delete
    3. Yeah, we think that our all night heat had better come from our own, internal combustion (beans, beans, them magical fruits!), with a lot of blankets.

      But any thermal mass is a plus, and helps to even out ups and downs of the burn/attentention cycle.

      In our case (on a MUSTELID type vessel), we're thinking of a couple cubic foot mass within a space that is 5x10x4ft max. We'd have no chance to heat the person not the space (as Iago recommends).

      It's true, I fantasized briefly about a cobbish thermal mass/ballast for the living platform, but it doesn't pencil out.

      Compromise and doowhatchakan is the rule. Sigh.

      Overall, we adapted the function of the Rocket Stove (e.g., using larger wood for a less efficient, slower burn for space heating) and would be adapting the Rocket Thermal Mass concept to squeeze what we can out of it, well short of its full potential.

      I do think that, on larger vessels and especially barge hulls, the full implementation would be interesting to pursue. Check out Dmitry Orlov's QUIDNON concept... he was proposing a variant on the concept.

      Delete
  4. Question Dave, have you ever used that 5 briquette small boat stove you have the 10.00 PDF for?

    Since your current craft is insulated (and most small craft are not (burr) I'd expect it would keep some of the chill off?

    A sack of briquettes would last a lot of months I suspect, and I wonder if a GI style steel canteen cup could be placed against it for a tea water cup?

    ReplyDelete
    Replies
    1. Hi Michael,

      We have NOT tried the Lenihan Heater (though its inventor, Peter Lenihan, used it on his live-aboard MICRO on the St. Lawrence... chilly!).

      I have thought of them as small space heaters -- heads, cabins, etc. -- and think they'd only take the edge off of a larger space. MAYBE if we really pumped the charcoal through, but then the bags wouldn't last long?

      We have a model of an 'improved' prototype that we've never finished to try. Tests and plans pending.

      I've wondered how to make a water heater for them, and sometimes imagine a Kelly Kettle reservoir high on the stack.

      I like your idea, especially of the type that have a hollowed 'saddle' on one side.

      So much to try out, so little time!

      Dave Z

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  5. That’s great Dave, been trying to figure out how the stove works since watching the series, now I know.
    Thanks again.

    ReplyDelete
    Replies
    1. Hi Tim,

      Pretty simple, once I got it well visualized. But I'm kinda slow that way. 8/

      Dave Z

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  6. Don’t know why, but the images on this article aren’t loading for me. All your other entry images do load just fine.

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    Replies
    1. Thanks for the heads up! The links are broken for me, too. I'll go refresh them as soon as I can (a few days?).

      Dave Z

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