Sunday, March 3, 2013

Maintaining an Even Oven Temperature in a Wood Cookstove, Part 4

What I Do
This post is intended to be an accurate and detailed account of what I do to keep the temperature of my wood cookstove ovens steady.  Remember, however, that every stove and every chimney is different, and it is entirely possible that for another wood cookstove user, none of this information will prove useful.
The first steps in baking in either of the cookstoves that we currently use is the same: start the fire.  The process of establishing a steady fire should result in a bed of coals being present in the bottom of the firebox.  A bed of coals serves to prevent the oven temperature from fluctuating drastically, but I find that coals alone provide insufficient heat for baking.  Furthermore, it doesn't take long--especially in the Margin Gem--for the coals to "ash over."  "Ashing over" is my own term to describe the process of the outer layer of a glowing coal becoming ash as combustion of the burnable material is totally completed.  If you've ever burned charcoal, you are familiar with this situation and know that the bed of charcoal needs to be stirred a bit when you can no longer see the glowing coals for the layer of ash that has accumulated on their outsides.  Once coals have ashed over, the heat which radiates from them is significantly diminished.
Before I go on with the next steps, it is important to understand another characteristic of the wood-fueled fire: the amount of heat radiating from the fire is determined by the amount of surface area of the burning firewood.  The greater the surface area which is burning, the greater the heat radiated.  Suppose you have a log which is four inches in diameter and eighteen inches in length.  If that log is put into the firebox and ignites, the maximum surface area which will be radiating heat is approximately 251.2 square inches.  Now suppose that the same size log is split into four smaller pieces and all four pieces are put into the fire at once.  The same volume of fuel has been added to the fire, but the surface area of those four pieces is now 539.2 square inches.  Thus, the four smaller split pieces will burn hotter than the one whole log, but they will not burn as long.
This whole geometry lesson is important because once you have established your bed of coals, you control the temperature of the oven by adding appropriately sized pieces of firewood to keep the oven at the temperature that you desire, using larger pieces for cooler temperatures and smaller pieces for hotter temperatures. 
Managing the baking fire in the vintage Riverside cookstove and managing the fire in the new, airtight Margin Gem cookstove are two distinctly different processes, so I'd like to talk about the two stoves separately now.  We'll start with the Riverside.  Maintaining the oven temperature in the Qualified was basically the same process, by the way.
A small log burning in the Riverside Bakewell.

The firebox on the the Riverside (and the Qualified) is quite small compared to wood stoves which are built for heating.  Once the fire has a well established bed of coals and the oven is near to the needed temperature, I would add one fair-sized split piece or whole log--there isn't room for much more--for a moderate oven.  This needs to be quite dry and ready for burning.  This should be sufficient for keeping the oven at a moderate temperature.  Once this log has perhaps burned to about half its useful life, I would add another piece of similar size.  While the second log is igniting, the first log is finishing its combustion.  This keeps the second log from suffocating or significantly cooling a fire which has completely gone to coals. 

If a hot oven is needed, then I would continually fire with smaller pieces of wood which would be added at more regular intervals.  Since the firebox is small, large pieces are not really an option, anyway. 

Riverside Bakewell firebox full of small pieces of wood.  A fire
like this would be needed for a hot oven.


Managing the oven temperature on the Margin Gem has proved to be quite a bit more challenging for me than I had expected.  We have used the Margin Gem exclusively for our baking since August of 2012.  I haven't ruined anything, but the Margin Gem's firebox operates on an entirely different principle of combustion than that of older style stoves like the Qualified and the Riverside.  Basically, in the Margin Gem, air enters the firebox above the fire rather than from beneath the fire.  Also, since the firebox itself is so much larger than the Qualified or the Riverside, I've discovered that adding only one piece of wood at a time is not sufficient for keeping the oven hot.  Instead, I always have to add at least two pieces of wood at a time.

Two pieces of wood burning in the Margin Gem cookstove.
In the Margin Gem, it has been my experience that more logs or split pieces make a hotter fire, and fewer makes a cooler fire.  However, I have encountered some challenges.  If the bed of coals in the firebox is quite deep, it can sometimes take quite a while for wood which has just been added to the fire to begin burning, and the oven cools because the new wood is preventing the heat from the coals from moving through the stove. 

I mentioned this to Mrs. Detweiler, an Amish acquaintance who has a Gem Pac cookstove.  She understood exactly what I meant and advised keeping the bed of coals to a minimum and making sure that they were frequently stirred down.  This causes the firebox to operate more like older style cookstoves where the oxygen enters the fire from beneath.  This certainly works, but it is not always easy to get the coals stirred down sufficiently.

What seems to work best is to make sure that I have plenty of small pieces of wood available when I am baking because they offer a more controllable heat.  The small pieces not only burn hot, but they burn quickly which provides an added measure of control.

I also have to remember that I cannot let each load of wood burn quite so far into its total combustion time as I would have in the Qualified or the Riverside before adding more wood.  Because the ignition time on new wood is longer in the Margin Gem, it is important to add the new wood to the fire sooner than what I was accustomed to.

I have also tried filling the firebox to the top and then controlling the amount of heat which the fire emits through the use of the drafts.  This method has not been as successful as I would like because the fire tends to eventually burn quite hot.  I'll continue to experiment and update the blog as I learn more.

Hmmmm.  I feel that I must again say that baking in a woodburning cookstove looks a lot more complicated in print than it is in real life.  Don't let any of these posts intimidate you.  They are merely well-intentioned help for those wondering how to manage the heat of a cookstove.  Each wood cookstove cook will develop his or her own techniques which will work best for each stove.  The biggest key is to pay attention to what gets results and to be observant.  Besides, the rewards of learning to bake in a woodburning cookstove are great.  For some reason, when I cook on a modern range anymore, it just doesn't feel like cooking.  That sounds funny, I know, but I can't describe it any other way.




7 comments:

  1. Great post. I've done some learning about wood and heat and fires over an open fire during maple time. You're right about paying attention to the situation you have now. You develop a feel for it - it's not as hard to do as it is to talk about, but it takes serious experience.

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  2. Great post, I've just put in a woodstove range cooker and I've never cooked with a range before. We've had a woodstove which is now in another room and I quickly learned how to burn efficiently and achieve an overnight burn and love our little stove but really wished for a range cooker...my wish came true! It is heating all our radiators and does so effortlessly but I couldn't figure out how to get the oven temp up and steady and this post gave me some great tips and I've just made 2 lemon cakes and a batch of date bars (your apricot bar recipe modified :-))
    Thanks!

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    1. Hi, Anne! I'm so glad to be of service to people. I think that putting dates in the apricot bar recipe is a brilliant idea. My mom would especially like that, so I'll have to try it some time. Thanks for sharing!

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  3. Hello Jim

    I have started using my Everhot Deluxe 204 now that I am retired. I used your method of using small pieces of wood to get the oven temperature up. The highest I can get it is to about 160.

    The slow combustion cooking range( as it is called in Australia) was in the kitchen when I bought the house about 16 years ago and it hasn't been used much in that time. I'm wondering if there is some maintenance I should do to help the oven get hotter. It also heats the hot water through a reticulated system.

    Thanks a lot for your blog. It is really helpful.

    Gerri

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    1. Welcome, Gerri!

      Wow, you presented me with a challenge! I'm not at all familiar with the Everhot Deluxe 204, but I've done some research on the Internet today (and some thinking on my own), and at the risk of sounding totally ridiculous, I'll make some suggestions.

      First, if you haven't already done so, thoroughly clean the areas around the oven box, paying particularly close attention to the surfaces of the oven box itself. Creosote deposits can prevent ovens from getting hot enough to be useful.

      Secondly, make sure that the flue which exits the stove is clear also.

      Finally, are the levers on the upper left part of the stove set properly? It is my understanding that these are what determine if the smoke and heat are traveling around the oven.

      In my research, I discovered the following thread which gave what I thought was some pretty good information about the Everhot Deluxe 204s. Perhaps you have already read it, or perhaps you were the one who asked the original question. However, I am going to share the link just so that the information is shared here on my blog.

      http://forums.permaculturenews.org/showthread.php?5547-Everhot-204-deluxe-Instruction-Manual

      I also ran across this blog which belongs to some fellow Australians of yours who also own and use an Everhot Deluxe 204. Perhaps you could comment on their blog and receive some better advice.

      http://yungalife.blogspot.com/2011/08/old-benny-slow-combustion-stove.html

      I also found where Jacqui and Sven, the owners of the blog, had asked questions about their stove and received some information that looked like it might have been helpful.

      http://www.fixya.com/support/t9147609-bought_house

      I hope that some of this information proves helpful because it sounds like your stove could be great if it will work properly for you. Keep me posted on what you find out!

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  4. I suspect that the added effort in managing heat for baking - which I have also noticed with the Gem relative to the older stoves I've used - is a trade off that comes with added tightness and efficiency of modern wood cookstoves in general.

    As you pointed out, the ash bed has a big effect on how the wood burns in these stoves. If you want to regularly stoke the stove well for heating into the night at a slow burn, thick beds of coal and ash are very helpful for damping airflow. For cooking and temperature control when you are around and able to add wood regularly, less ash allows more air to come through from below so that wood ignites faster and air moves more freely through the firebox. I notice that when I have a nice bed of ashes, that air comes through the holes in the sides rather than through the bottom - the recirculated gases from the right hand side can be sen as hot jets of flame from the vent holes as recirculated volatiles ignite - another nice benefit of modern, efficient design.

    So when you're both cooking and heating, one needs to manage the ash levels in the firebox for the application.

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