I am new to this forum, and have been reading a lot of the threads with interest. I have wanted to build my own wood stove for a few years now, and recently discovered rocket stoves. What I like most about them is that they are capable of burning wood completely, without producing creosote. I have lots of good wood to burn, but it's mostly big logs. Has anyone experimented with applying rocket stove principles to burning big logs? I want to try building one as an experiment, unless someone can convince me that it can't possibly work. I have ideas on how to do it, and wonder if anyone else has tried.
Thanks,
Steve

Look into the batch burn style. You load up a decent amount of wood at the start and it burns it all hot and fast.

On my 5" Batch Batch Rocket I normally start with plenty of small kindling pieces. Once this fire is roaring I fill up the firebox (with a 50mm gap at the top) with progressivly larger pieces.

The firebox on my 5" BB is quite small, though built as per Peters specifications. Once a fire is established quite large logs can be added and provided they are dry (sub 20% MC) they burn very well with no noticeable smoke. When adding larger logs I will often increase the air intake to the firebox to cope with the extra gassification of the larger fuel load.

Hi Steve. Welcome to Permies.

I think one of the reasons that you might not see it discussed much is because it has been touted as a way to not have to chop large trees, or so you can use coppiced wood, branches, and trimmings for heat, and use the larger logs for lumber.

That said, I know that batch box designs exist that will take logs of reasonable girth, cut to length so as to fit in the burn tunnel with the door closed. It can be done.

My concern would be that, if you need to fill the box to get a proper burn, and that box is too large for the system or the room, you could be heating much more than is comfortable or necessary, and you could negate some of the efficiency that is one of the biggest draws for those seeking to heat with RMHs.

I would, in your case, providing the large logs can't be used better, cut them to length for a batch-box-style RMH sized to the house you want to heat. I would then build said RMH, and perhaps concurrently with this, I would spend time splitting the rounds, probably by hand, with a maul, because it's one of my favourite, most relaxing outdoor tasks.

When it would come time to load the batch box for a burn, I wouldn't have to wrestle a giant round into it (if I went with a design with an open, gravity-fed burn tunnel, the sizing would be even more difficult, I suspect). I wouldn't have to worry about obstructed airflow, or about feeding smaller fuel around the giant log as it burns from the outside of one end to the core. I would be loading the box evenly, with similar-sized pieces, to form a stack that air can move through (well, after I start the thing with kindling and progressively larger material).

As I said, it can be done. I just think it's important to keep in mind what it is RMHs are designed to do well, how it is they do that, and the reason people have historically split their round logs for the fire.

-CK

Welcome to permies!
I personally don't have any experience with RMH, but there is a video available on the subject.

Also for other stuff about RMH, here is Paul's video list: paulwheaton youtube videos He is currently sharing various RMH videos (and thus how I got to learn about RMH); how they work, myths, some sections from DVD's, do's and don'ts. Enjoy!
Edited to add: In the description section of the video there are links to related permies topics. ;)

I suppose part of the answer to your question depends on your definition of "large". Are you talking 6" split wood, 8" round, 12"? Is it knotty wood that is not practical to split? Is it already cut, and if so, how long?

Unless you are heating a small space that would be overwhelmed by a large RMH, I wouldn't worry about overpowering it. One of the features of the RMH is heat storage, and if you have a large firebox with corresponding mass, you may need to burn only one batch a day.

The J-tube design is actually capable of using larger wood than many people describe; if at least two or three pieces can fit in the feed, you can get a good inferno going that will last quite a while (after the fire is established with kindling). My feed tube is 7" square, and using 3 or 4 16" long split pieces at a time, it can burn hot for 40 minutes before needing reloading.
A larger system could handle even bigger wood handily.

Thanks for all your responses. You have encouraged me to want to continue with my experiment. The video was enlightening. To clarify, when I said "large" wood, I meant round pieces up to 6-8" in diameter, and anything bigger than that would be split.
A little background: I live in northern Indiana where the emerald ash borer has killed most of the ash trees, so I have more dead wood available on my land and the neighbor's land than I'll ever be able to use. I heated my house with an Earth Stove for about 35 years. When I had to replace it about four years ago, I got a Voglezang Ponderosa stove. Big mistake. Although it was rated the same BTU's as the Earth Stove, the firebox is so tiny i can't build a big enough fire to heat the whole house like I could before. That's what got me started with designing my own stove. I think maybe I'm on the right path.

Hi Steve. Over here in the UK I've had my 5" Batch Box lit for around 40 minutes and recently added a 6" diameter very dry ash log to the fire. It's burning well and I could probably fit a few more in the firebox. Your 'large' pieces should work fine - provided they're very dry of course

In my particular BB (5" sidewinder) it seems to perform best when using different sizes of fuel and also a mix of hard and soft wood. We've mainly got oak, ash and sycamore but larch and sitka spruce burn very well in the system. Broken pallet planks work well, especially when mixed with the hardwood.

Hi Steve. Over here in the UK I've had my 5" Batch Box lit for around 40 minutes and recently added a 6" diameter very dry ash log to the fire. It's burning well and I could probably fit a few more in the firebox. Your 'large' pieces should work fine - provided they're very dry of course 

In my particular BB (5" sidewinder) it seems to perform best when using different sizes of fuel and also a mix of hard and soft wood. We've mainly got oak, ash and sycamore but larch and sitka spruce burn very well in the system. Broken pallet planks work well, especially when mixed with the hardwood.

Thank you John. As a newbie here, I need to ask, when people refer to a rocket stove or heater with a single dimension (in this case 5"), what is that referring to? The diameter of the riser?

Yes Steve - 5" refers to the diameter of the riser. All the other measurements are in proportion, see Peters  Batchrocket.eu site    Batch Box Dimensions

Yes Steve - 5" refers to the diameter of the riser. All the other measurements are in proportion, see Peters  Batchrocket.eu site    Batch Box Dimensions

Thank you, and thanks for the link, an excellent resource!