I proclaim the rocket stove “not working”

by ziggy on February 3, 2010 -- 15 comments -- Follow

I have officially proclaimed the rocket stove “not working”. The stove simply does not draw on days without the right wind direction/intensity. It is unreliable. Even when the wind is right, the stove takes too long to heat up (even the barrel itself!) At times, it smokes into the house, which is added frustration.

Something is not right, unfortunately. The stove just does not keep the house warm. When April was home alone in December, she struggled to keep the indoor temperature in the 40s! That is not really livable.

When we got back in January, the temperature inside was in the upper 30s. The house temperature dropped below freezing on a few occasions while we were away. (All of the canned goods had to be moved out.)

Within that first week back, we decided to move a temporary woodstove into the house. It’s a funny little thing – I think it was originally manufactured for chicken coops (the manufacturer name is Buckeye Incubator Co.) and intended to run on coal. It’s a really tiny little thing, and we ran the stove pipe out the window on the southeast side of the house. The whole setup screams “rinky dink” but it works!

We’re able to get the house up into the 60s in under an hour (in the furthest area of the house away from the stove — of course it’s warmer nearer the stove.) The house temperature drops to the low 40s by morning when it’s under 20 degrees outdoors at night.

Without the stove going, the house remains in the low 40s during the day, but like I said… we can get it to the low 60s in under an hour of firing the stove. It’s not bad. My body is pretty okay with less than ideal indoor temperatures, thankfully.

I am now reconsidering the whole rocket stove setup, and I’m pretty nearly set on tearing out the entire stove and cob bed, which is no small task! But seeing how well this little woodstove performs in the cob house, I imagine a nicer stove (such as the compact Jotul F 602 CB) might be a reasonable choice.

It feels like a cop-out to get rid of the rocket stove completely. I really want a working rocket stove, but I’m unsure if I am willing to get through the effort of rebuilding it. I think the bed is a lost cause and would have to be removed anyway. (It’s wayyy too much mass for the stove!) So it’s a lot of work either way. I love the concept of a rocket stove and think it’s ideal for a massive, completely cob house such as my own — heat storage is a huge benefit when you don’t have much insulation! But I think a nice, little and efficient wood stove such as the Jotul might not mean that we have to burn that much more wood for the heat we gain.

It’s sad to say that the rocket stove is a failure, but it’s a learning experience, for sure. I have learned a lot through building it and using it (when it did actually work). I would love to build another one again, but I don’t foresee that happening in the house. It looks like we’ll be going the cast iron wood stove route.

More on this later…

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Grant Wagner February 4, 2010 at 11:30 am

I’m sad to hear that your rocket stove didn’t work well. I know it’s hard to admit when something you put so much work into just isn’t working out.

I know several others at DR use rocket stoves. Are they having the same issues? I was really looking forward to having one in my own tiny house, after how great the “Rocket Mass Heater” makes them sound. Should I even bother? Is there someone on site which can at least give you an idea as to why yours failed if it is a unque experience?

More importantly, is there anyone who is interested in buying all of that good stove pipe you have left?!

Grant Wagner February 4, 2010 at 11:32 am

Also as a side note, can I subscribe to comments? I’m not seeing a link.

Michael Janzen February 4, 2010 at 1:29 pm

So back to kiln design. In college I helped build and fire several different wood kiln designs. I looked at your older posts and I think there are some things you can probably do to salvage your work. I’ll draw up a google sketchup illustration tonight to show you but I think the main problem is the length of the run, number of turns or your pipe. The stack isn’t tall enough to draw that length of pipe without some kind of assistance when it’s cold.

A quick ‘test’ fix would be to add more height to your stack on the outside of the building. Since an incredibly tall stack isn’t practical long-term eventually you’ll want to shorten and straiten the pipe run under the bed (which would be a major pain but so is pulling it out) so you can shorten the stack and still have it work. In fact you could test a modification to your stove design while in the process of tearing it out… and if you find the design change works… stop tearing it out and start rebuilding the bed.

If you decide to go with an EPA stove, which is an excellent idea too, leaving the flue imbedded in cob will help you heat the thermal mass of the house, but like all stove/fireplace designs, keep the flue as strait and vertical as possible.

I’ll post my proposed modification tonight on tiny house design and send over a link.

Michael Janzen February 4, 2010 at 2:42 pm

OK… pulled out my old copy of “The Kiln Book” by Olsen and he says

“There should be 3 feet of chimney to every 1 foot of downdraft pull (note: this is the space in the kiln chamber, which is like your rocket stove’s fire box height), plus 1 foot of chimney to every 3 feet of horizontal pull.”

Too much chimney draws too fast, so test your stove by adding sections of pipe to find the optimal. Chimneys should also be 1/4 to 1/5 the diameter of the chamber, which I think you have correct. The air inlet should also be the same as the air exit. So if your air intake is too big or small it would effect the draft.

I really hope this helps.

Grant Wagner February 4, 2010 at 3:20 pm

Always trust your local potter.

Joe Cook February 4, 2010 at 9:51 pm

http://www.gimmeshelteronline.com/masonry/

YOU MAY WANT TO CONSIDER BUILDING A SMALL MASONRY HEATER FOR YOUR DWELLING- IT CAN BE BUILT TO NOT ONLY HEAT BUT AS A BAKE OVER, AND ALSO TO HEAT THOUGH A BED/BENCH ETC.

ABOVE IS JUST ONE SOURCE OF INFO ON THEM- THEY ARE NOT DIFFICULT TO BUILD- EASIER IF YOU CAN FIND SOMEONE WHO HAS DONE IT TO HELP.

Littlest Jotul February 6, 2010 at 2:00 am

I have had one of these for over 30 years. Heated my 18×24″ house in the Adirondacks at the lowest of 25 degrees below zero Fahrenheit. I hauled it to the west coast on the airplane, it is so light, and hooked it up on a 1200 sq ft house in the NW US and with unnecessary parts of the house closed off, it did a terrific job keeping the main living, kitchen and bedroom areas of the house comfortable even on the coldest days, even with the cathedral ceilings.
Great for cooking on, too.

heather February 7, 2010 at 4:28 am

Rocket Stove? They look like ‘hippie killers’ which is what my landlord calls them. He was a hippy back to the lander and there have been many cottages on his land over the years. Some burned down because of dodgy stoves. I have not read about the rocket stove actually, but if it isn’t working I suggest that you get a good energy efficient eco standard woodstove and make sure the stove pipe is set up properly. Woodstoves can be found used and make sure it has a flat top that you can cook on if need be. A modern woodstove should be efficient with wood, have little smoke leakage and produce very little smoke pollution.

Sean February 9, 2010 at 2:02 pm

If you are looking at the Jotul, you may also want to look at the line of marine stoves from http://www.marinestove.com/sproducthistory.htm. They are EPA certified but built for small spaces (sailboats) and some are even cookstoves.

damon February 25, 2010 at 4:25 pm

The problem with rocket stoves is that they are designed to make the most use out of a small amount of heat, concentrating it in a small area. Great for cooking, not so great for warming up a room. Traditional metal woodstoves are probably a better bet.
I just came across mention of tile stoves on this website: http://www.lowtechmagazine.com/2008/12/tile-stoves.html
Not much how-to information but it utilizes the same idea of thermal mass as a cob house does. Probably too big for your home, but seems like it would be great for larger structures, especially if the home was built around it.

Melissa March 19, 2010 at 1:24 pm

Hi,

I’ve really enjoyed reading your blog as my husband and I are currently building a cob cottage. Since it gets pretty cold where we are, I was little worried about the cob keeping warm. We plan on having a “real” wood stove and it is nice to read how your makeshift one gets the job done. Do you think adding extra straw to the mix would help with the insulating? Sorry about the rocket stove :-(

Melissa West

Kaj Lauritzen March 20, 2010 at 5:57 am

I am planning to build a rocket stove and have read your pages with great interest. Some of the advice I got from other builders is that the horizontal channels (inside the heat storing mass) must not be longer than the vertical smokestack. And that the diameter of the air intake should be slightly less than the diameter of the stack. My wife and I have lived with a 2.5 ton masonry heater since 1995 and really love the heat storing capacity. If you can´t get your stove working I think that a masonry stove could be fine for your house. Here´s some inspiration for you, http://www.stenovne.dk – I think it has en english version, otherwise have fun with the computers translation…

marina April 9, 2010 at 12:15 pm

Sorry to hear that your rocket mass heater didn’t work out. I agree that it has too many turns and too long a run for the size of the stystem. I would have recommended making the stove part of it bigger (larger diameter everything and a taller rocket burn chamber), but you’ve made a decision to get a different heat system installed and that’s hunky dory.

However, I’m going to dampen your excitement about how warm your house will be with the addition of a modern radiant heat woodstove. The problem I see is that your house is constructed out of a material that has virtually no insulating properties.

Cob is strong and beautiful thermal mass. In the winter, you will always be battling the fact that the exterior portion of the walls are cooled by the outside air temperature, and that there is no insulating barrier to help maintain a warm inside air temperature. The walls of your house will always be cooling off in the winter, and drawing the heat of your interior living space outside. This is why a heating system that makes that thermal mass heat up makes sense for your space. I can see why you were attracted to the rocket heater.

So, to help the effectiveness of a radiant heat cast iron stove, I’d consider putting a layer of insulation on the inside walls of your home. Even a few inches of something with insulation properties – light straw clay, perhaps? felted wool? – will help you greatly in the effort to keep yourself warm. Best of luck!

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