Using our old woodstove chimney/ flue for a rocket stove?

Hi-

We removed ourold, inefficient woodstove and want to build a rocket stove (and soon! Our house is cold!). We still have the old stoves flue in place (goes up through the attic and then up at least another 8-10 ft to clear the second story part of the house's roofline). I'd like to use it as our flue for the rocket stove, if I can, since it is already there, but am concerned about creosote and corrosion from water condensing in it. Is there a way that I can modify it to be safe and effective, or should I just make a different flue and close the old one up?

Thank you for any advice on this! I have Ianto Evan's and Leslie Jackson's book and took part in a short 1/2 day workshop on rocket stoves, but still feel pretty intimidated about building my own in an old wood framed house.

Noelle Marquis

Noelle Marquis : O.K., lets start off with what size stove pipe was the old wood stove set up with , any increases/decreases in pipe diameter before it enters your chimney, number of feet of what size stove pipe running horizontally, does it pass thru any walls before it goes in the chimney, any Elbows, If there were any dampers - you can run a Rocket stove with dampers but you will have to learn how all over again! What is the general condition of the stove pipe receiver of the chimney, is the chimney Insulated pipe, brick, or cinder block, does it have a Ceramic flue liner in the chimney !

Are there any other heaters, cook stoves, furnaces or water heaters piped into the chimney.

I just had a thought,- There exists a bastard chimney, sometimes called a 1/2 chimney that starts on the second floor or in the attic, the builder expected people to run stove pipe up to the second floor or attic and into the 1/2 chimney which then carries the smoke the rest of the way out of the house, out of sight, out of mind! If the house is old enough to have one of these bastard chimneys you can not be sure that it is safe to use without an inspection by your local fire dept., or local code enforcement officer ! (and it probably will not pass !) While i am scaring you , I need to know if your chimney has places where it has been covered with wallpaper !

With the exception of the Bastard chimney, any thing you find does not rule out the use of the old chimney just that you care about you and yours, and want to be safe ! Now is a good time for me to be here to answer questions, if that doesn't work for you just post your answers, someone here can help ! G'LUCK Allen L.

The chimney is insulated metal pipe. It looks like it has an 8"diameter inside and a 10" outer diameter. It has no horizontal runs or elbows... just a straight shot from where the stove was through the ceiling, attic, and roof. There doesn't seem to be a damper. The house is old (1920s), but the former owner used the woodstove daily up until a year ago.

Thanks for your help, Allen, or anyone else out there that has advice on this matter!

Noelle

Noelle MarQuis : Great news, hopefully there is a storm cap on top of your insulated pipe and it is in good condition. A Rocket stove burns much more efficiently than whatever you had, how ever it does send a lot of that heat up the chimney, we need to optimize the amount of the heat we get out of it .
We did determine nothing else shares the stove pipe right !
If you look up the pipe can you see daylight ?

The 1st thing we need to know is a Visualized measurement, from the approximate height of a 55 gal drum how many inches to the 8 ''opening in the pipe.
How hi is the ceiling in the room your old stove was in !

Our ceiling are 8' tall, and we will probably use a 55 gallon drum, but possibly a 35 gallon one, so I think there will be around 5' vertical distance from the top of the barrel to where the flue goes through the ceiling. We may still have the rest of the 8" insulated pipe in the yard that connected the old wood stove up to the ceiling... right now it is cut off at ceiling level. Nothing else is feeding into the flue right now, and you cannot see sky through the opening now because there is some sort of cover (storm cap?) on it.

Thanks Allen! I'm so happy to have found this forum, because I never knew where to go with my rocket stove questions.

Noelle

Noelle Marquis : Plan on setting your Rocket Stove up in the very center of your room ! if you want to move some hot air to an other room, then get a 3 speed box fan, and manufacture a door shaped / sized sheet of plywood, cut out a box fan sized square hole near the top, you can leave a gap at the bottom and hang it in the door way you are trying to pass heat through !

Due to the extreme amount of heat coming off of this you need to plan on dry stacking a wall of bricks and paving stones around your rocket stove waist high-ish, time and use will show you how you can modify this just be prepared , also it will need brick or paving stone or a poured concrete pad with an air gap under that for safety , you did see the rocket stove glow red at the bottom didn't you ! Allen L.

If I dry stack brick etc around the rocket stove, will the barrel still be exposed enough to give off radiant heat to quickly heat the room? Or is it worth skimping on the radiant heat in exchange for safety... I have a 3 year old? Do I place it in the center of the room in order to maximize the distance from any flammable wood walls?

Noelle

Noelle : I'm a little ahead of you because I want you to have an idea of what you will need as you look at your project !

You are going to want an air gap of at least 20 inches below your ceiling ! Because you are going to have to move your rocket stove to the center of your room for safety, You will need to go up towards the ceiling with your stove pipe and then just above your head to a " T" where you connect to the insulated pipe !

Okay. Thank you! So helpful, Allen!

Noelle : yes, its a safety issue , don't worry we will work hard to maximize the heat that you can use , your 1/2 wall of dry stacked bricks will re-radiate the heat out to the room at a slightly lower temp and do it for longer so you are getting some benefit of thermal mass ! allen

Noelle : it works out that a smaller barrel will radiate out all the amount of heat that its surface- think the skin of the barrel, will let it ,a bigger barrel will actually radiate the heat out at a slightly lower temp- safer !

A good example would be your 3 yr old, when he/she wants to snuggle in your lap you get the benefit of all that heat energy radiating out from his/her smaller body !

We will also need to think about a long narrow strip of reflectix say 36 inches wide hanging down from the ceiling making an air gap to protect the ceiling of the room !

Noelle : by now you should have a picture of the rocket stove walled in - in its own little crib, 6 '' stove pipe rising up to an elbow or '' T " ( to be determined ) then along below the ceiling, which is protected with a super reflective material - think bubble wrap with a reflective layer of aluminum foil, into a second " T" or elbow then an adapter to the 8 '' pipe .

If you try your local freecycle, or Craigslist you may be able to get additional materials for free or little more, also try your local "Habitat for Humanities" RE-store, where they sell al kinds of used /servicable building materials. - Allen L.

Noelle : you will also need to determine if the 8" insulated stove pipe was installed with the correct orientation, the last piece of stove pipe should have a short lip of crimped stove pipe that the next piece of stove pipe will slip over, if the next piece of stove pipe will slip into rather than over , thats the way I was taught to do it and its wrong, check it out and let us know !

I forgot to ask, can you deal with over head stove pipe down to 5' 10'', we may need to make-up two layers of reflective material and even then have a low speed fan blowing through the gaps !

Cleaning out the rocket stove, I know two ways to clean a rocket stove 1) wait for it to be cool to the touch, reach in with tools, clean . And 2) wait for it to be cool to the touch, disassemble, clean, put back together !
Hopefully that is the worse news you are going to get on this project !

Just one last thing for now ,make sure to keep the open end of your 8 '' stove pipe blocked off until you need it ! Allen L.

Thanks for all the tips, Allen! I'll check that the stove pipe was assembled correctly. We have it covered now so that ash/etc doesn't fall into our living room. It probably needs a good cleaning. Not much in our house was well maintained when we moved in.

I understand that I need the rocket stove in the center of the room (although my dad is still questioning whether we could'nt just use a couple layers of cement board and fire brick between the barrel and a wall... do you happen to know the temperature that the surface of one of these barrels will reach, so I can convince him?) However, couldn't I just make my built in furniture wind over toward where the old flue is so that my new flue can just go straight up rather than using "t"s. My husband is 6'3 and I'm 5'10", so pipes at 5'10" is not ideal if I can avoid it.

Noelle

One more question... I think we got inspired by all those lovely pictures of benches against walls and had a similar design in mind, forgetting that those were all cob houses. So... what if we replaced any wood studs within a few feet of the combustion chamber with steel studs so we weren't close to anything flammable. Could we then put our rocket stove by the wall? We have lots of free brick too, so we could face the wall with brick over the sheet-rock too if it would help (we'd put a couple of inches of pumice or vermiculite between the thermal bench and any wall containing wood.) Would that work?

Thanks again,

Noelle

My fast answer is you need a thermal barrior, and insuation, AND air spaces, steel studs hidden behind sheet rock is Not a good idea Old wood will pyrolyze or 'out gas' flammable wood gases at lower temps then new studs, you would have to insulate the studs from floor and ceiling ! I am looking for some of the you tube type videos where they show the barrel glowing red, You did see that when they used clay slip and paper mache to burn off the old paint off of the barrels didnt you !
I am 6' 3'' myself so i understand that having to 'duck' can be a big pain - but you can always walk around it.
A rocket stove is equal to the best of the wood box stoves for efficiently and cleanly burning the wood but a lot of the heat goes up the chimney, the rest gets radiated out into the environment and you have little No control over your fire 1 second after you add 'just one more stick' till it burns out !

My Strong suggestion is that you contact Ernie Wisner, or Erica Wisner who are moderators/ stewards in these wood burning stoves forums and get a second opinion ! I am much more concerned about your safety than I am about being Right
Irregardless, you and your family are the reason people like myself are here, please stay in touch and let us know how the project worked for you and what you did to change it, good or bad - I'm off looking for that information now Allen L.

Noelle : your Dad is 95 % right, what he is calling cement boards, are all that is allowed for sale now, the same thing in the exact same size used to be sheet asbestus (sp) Going out from the walls you need a dead air space then something like his cement boards but with a reflective surface, then the bricks and/or the pavers then in closer to the rocket stove itself a something to baby proof your rocket stove that can be mostly air like bricks stacked to allow air flow, How you do that and build a child proof stable wall i leave up to you. It would be very nice if you could come up with one of those blower units that has a fan and is the length of a standard stove pipe !
both do to safety reasons and to get more heat out of the entire heating system which includes the stove pipe as additional heat radiating area, I suggested you move your rocket to the center of the room, dont for get that you will need a dead air space then a layer of bricks or a layer of sand under the heater due to the amount of heat escaping from the bottom of the stove !

Off on an other hunt Allen

Hello Noelle,
I have just built a rocket stove for my greenhouse, the design is a bit unconventional, in that I connected a 16" barrel to a 22" barrel on the base, the insulated flue pipe that I used is meant for a wood burning stove, it measures 7" on the inside diameter and 11" in on the outside diameter it is filled with a mineral type of insulation. I fired it up with with a 16" length of horizontal flue and lo and behold it functions very well. However when I tried to extend this flue to 32' I had a problem not getting the draught, I believe this problem is linked to the two 90 degree short radius elbows that I introduced into the system. As soon as I get the chance I will replace these elbows with long radius elbows to see if this caused the problem.

Incidentally when I fired the stove with the short run of horizontal flue (16feet) , I over ranged my heat sensor gun, it limited out at 680 deg I think the temperature reached in excess of 800 degrees in the centre of the barrel. This temperature was achieved in approx. 15 minutes.

I will attach some pics for you to review if you have a question get back to me

Regards
Fred
In the heart of the rockies

Hello Noelle,
I have just built a rocket stove for my greenhouse, the design is a bit unconventional, in that I connected a 16" barrel to a 22" barrel on the base, the insulated flue pipe that I used is meant for a wood burning stove, it measures 7" on the inside diameter and 11" in on the outside diameter it is filled with a mineral type of insulation. I fired it up with with a 16" length of horizontal flue and lo and behold it functions very well. However when I tried to extend this flue to 32' I had a problem not getting the draught, I believe this problem is linked to the two 90 degree short radius elbows that I introduced into the system. As soon as I get the chance I will replace these elbows with long radius elbows to see if this caused the problem.

Incidentally when I fired the stove with the short run of horizontal flue (16feet) , I over ranged my heat sensor gun, it limited out at 680 deg I think the temperature reached in excess of 800 degrees in the centre of the barrel. This temperature was achieved in approx. 15 minutes.

I will attach some pics for you to review if you have a question get back to me

Regards
Fred
In the heart of the rockies

Thanks for sharing your experience, Fred, and your sketch. I'd love to see pictures and hear if increasing the radius of the 90 deg. elbows works to get a draught again. Good luck!
Noelle

Hello Noelle.
First a correction ..... where it states 16" should read 16' feet. I am also attaching photos for you to look at.

Regards

Fred

From the heart of the Rockies

Hello Noelle.
First a correction ..... where it states 16" should read 16' feet. I am also attaching photos for you to look at.

Regards

Fred

From the heart of the Rockies

Hello Noelle.
First a correction ..... where it states 16" should read 16' feet. I am also attaching photos for you to look at.

Regards

Fred

From the heart of the Rockies

Fred lightfoot : Hi ! I have created the forum thread Rocket Stoves in greenhouses, there are 20-25 members who have self identified them selves as interested in Rocket stoves in green houses.this is an attempt togive 'our' group their own forum thread - check in, check often Allen L.

Hi there,
I wonder if you ever did get your rocket heater built from  8 years ago, and did you use the existing flue from you old wood heater?
How did that work out for you?

Any pics or progress or retrofitting tips?

Hi Joyce;
A wood burning chimney is good for box stoves or for rocket stoves.
The only detail is the chimney diameter.
A 6" rocket uses a 6" or larger chimney.
An 8" rocket needs an 8" chimney .

As rocket exhaust is so much lower temperature than box stoves, insulated pipe is only needed near wood framing at the roof jack and outdoors.