Permaculturing in Portugal

One family's attempts to live in a more planet-friendly way

Bread oven/rocket stove/masonry stove construction workshop?

PLEASE NOTE THIS POST WAS A PRELIMINARY ENQUIRY ABOUT WORKSHOP INTEREST BACK IN 2010 AND CONSTRUCTION PLANS SUBSEQUENTLY CHANGED (see Comments section below)

This post is a preliminary enquiry to see if there is likely to be enough local interest to make it worthwhile planning and running this construction as a series of workshops. The construction will be going ahead anyway. (If you’re interested, please leave a comment below rather than responding on eg. Facebook. Comments on this page won’t get lost or superceded by more recent news.)

I’ve looked at several options for our cooking and winter space heating, but all have ultimately been filtered through a single criterion: efficiency. Most conventional woodburning stoves are not very efficient. A compromise has to be reached between combustion efficiency and comfort since so much of the heat generated is immediately radiated from the appliance. Efficient combustion = a room too hot for comfort. Conversely, a comfortable ambient temperature = inefficient combustion. That inefficiency has a number of downstream consequences; a large annual firewood requirement, creosote and tar build-up from incomplete combustion, increased frequency of cleaning, fire risk, etc.

A big AGA-type cast iron woodburning range with a back boiler is a wonderful thing to be sure (I grew up with one), but it’s a bit like one of those all-in-one printer/copier/fax machines: does all of those jobs, but none of them particularly brilliantly. It takes several hours to bring up to running temperature. Heat your water for a bath and you can’t bake at the same time (forget about running radiators – they really don’t work too well). Cook too many things on the top of the stove and the roast potatoes go soggy. If you’ve got good dry hardwood, it is possible to stoke the fire well enough to do all 3 but you’re down to your underwear and sweating into the frying pan. And in summer, a cooker like this is far too hot to use in comfort, so some alternative is needed.

Having gotten on a roll with the KISS principle in the renovation of the building, I started questioning the convenience of the single heat source and wondering whether it had eclipsed a more balanced assessment of the total energy input involved. Firewood takes a lot of effort to fell and chop (or alternatively a lot of money to pay someone else to do the felling and chopping). If we could halve our annual firewood requirement by lighting a fire only when required, maximising its efficiency both in terms of heat production and delivery for the purpose required and by storing surplus heat for later release, it ought to far outweigh the inconvenience of having to light and tend more than one fire.

Just as importantly, burning efficiently means minimal build-up of toxic deposits and virtually no greenhouse gas emissions.

So I have a cunning plan. We are going to remove a section of the upstairs wall between the two rooms and rebuild it as the core of a masonry heater, fed by a firebox in the living room. The use of the wall itself to store heat from the stove means that we need only burn one stove-load of firewood at maximum efficiency every 12 hours to keep a constant comfortable heat in the two upstairs rooms.

Masonry stove design

Below it, in the kitchen, a rocket stove will serve as our cookstove. With much greater efficiency in delivery, a rocket stove takes far less time to bring to running temperature than a cast-iron range and does not store heat so can be used year round for cooking. It has the additional advantage that it runs on much smaller pieces of wood, so harvesting the wood to run it can be less labour-intensive (it can even be done easily enough by hand rather than using a chainsaw). Last, but far from least, a rocket stove can be built for a (very) small fraction of the price of a cast iron range cooker.

A separate (possibly also rocket) baking oven will be built on the exterior of the building. Both rocket stove and bread oven will vent into an external chimney above the oven which, in winter, can be diverted via dampers into the masonry matrix upstairs before returning to the chimney.

I’m also considering running pipework for winter domestic hot water through some part of the system at the same time.

So. Question. How interested would you be in attending a series of workshops based around the construction of this integrated cooking/heating complex? The way I’m thinking right now is that we will have separate workshops based around each component of the system – the masonry stove, the bread oven and the rocket stove – with the option to attend any or all. The response I get to this post will determine whether or not we do this.

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9 Comments

  1. Quinta do Vale August 22, 2010

    Ah no … we will only use the rocket stove when we’re actually cooking something on it! Ditto the oven. The masonry stove takes care of space heating in winter.

  2. michelle August 22, 2010

    Hi 2 interested folk here its a good concept and certainly ,as you describe, very efficient ….Paul reckons that the rocket stove would require constant feeding of fuel which means you are tied to it in winter?Do you anticipate this being the case… he thinks that it would be a great demand on ones time.
    I like the plan as it appears that it would also be cheaper than other alternatives.So yes we would be very interested in all 3 developments but not if we have to pay to be honest (with cash anyway!)as cash is in very short supply.keep us posted and see you soon!

  3. michelle August 23, 2010

    I see.We are thinking of something similar like an adobe stove ,heated seats etc and the stove being double breasted so that it warms more than one room.But as you know we are a long way off so am very interested in what you are trying!

  4. Kim August 5, 2011

    Oh I just ran across your site, and I love the way you think!! I am sure you have finished your heating system by now and would love to know how it turned out. I was actually looking for information on a outside rocket stove oven, when I ran across your site. Please let me know where and how your plans went.
    Thanks!

  5. Quinta do Vale August 5, 2011

    Hi Kim. I wish! No we haven’t finished the heating system yet. We haven’t started it. We’ve got to complete the exterior of the building first, so there will be more to say on this as time goes on. My original ideas in the post above have changed a bit. I’m not now going to dismantle the wall. It was going to be a massive and complex undertaking that risked destabilising the building – dry-stone walling has much more interdependency than a mortared wall – but we are still going to use masonry to absorb, store and radiate the heat from a cast-iron woodburner with a small back boiler to serve a single radiator in the room the other side of the wall. It won’t be quite as efficient as a purpose-built masonry stove, but it should be ‘good enough’. I’m still going to build the rocket cook stove, but have changed the plans for venting the flue gases. They’ll now rise up through a heat exchanger to heat a small volume of water for washing up, then continue to the roof through the same masonry construction as houses the upstairs woodburner. The outside bread oven will have its own short chimney at the front of the oven like many traditional bread/pizza ovens. Shared flueways don’t work too well and in this instance, since the oven is outside, it’s not essential to use anything longer.

  6. Yolanda Schudel December 2, 2011

    I realize this is after the fact for the opportunity to view the construction of a masonry oven or stove, but will there be another opportunity to learn about this? I am starting to look into this so that I might learn to build one..not now, but to gather enough information to get it done later. Thank you for your response

  7. Quinta do Vale December 2, 2011

    No we haven’t built it yet! I am hoping to be in a position to next year, but we’re still getting the building wind and watertight. Plans have changed a bit (see comment above) from what I outlined in this note I put out to see if people were interested in a potential workshop, but there will still be a rocket cookstove in the kitchen. Also a separate rocket water heater along the lines of the one they constructed at Milkwood Farm for the bath-house which will be in a separate building and integrated with a greenhouse so the two work together in a kind of symbiotic relationship. There will be posts in the blog if we’re going to turn it into any sort of workshop.

  8. Adrie De Maesschalck May 3, 2015

    hello,
    This one i want to build , it looks like a full enegy and wornth source.
    do you got blueprints of this super rocket stove?
    Do you have more blueprints of other rocket stoves, because i want to buiild 2 rocket stoves in my house.
    Love them how they work and dont or a little get lost and also good for the envirement.

    Thankss in advance,
    Best Regards,
    Adrie De Maesschalck

  9. Quinta do Vale May 3, 2015

    Hello Adrie. As noted above in the comments, the plans changed. The building is still being worked on to get it wind and watertight nearly 5 years on now. Sometimes things go a bit more slowly than expected … So there are no blueprints and I don’t have blueprints for any other rocket stoves. The stove designs are in my head. There’ll be more about this when I get around to building it, but that’s not going to be for a while yet.

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