I need some help from the experts! My RMH doesn’t seem to be rockety. The first two burns went okay. I observed some rocket effect but not enough for my liking. Sticks that were longer than the feed tube had a flame that would smoke back into the room. The “rocket effect” was not very loud or strong (my Fisher wood heater is louder). There was smoke that would “puff up” and out of the feed tube from time to time.
The third burn was a doozie! After putting a lit newspaper in the burn tunnel, then burning paper and sticks in the feed tube, the RMH began a back draft. Warm air from outside coming through the flue pipe back into the room. The flames were about six to eight inches above the feed tube! Wow….what a sight! A reverse Rocket into my room. Good thing the room is isolated from the rest of the house. I covered the feed tube hole, waited for the fire to go down, and then was able to blow, blow, BLOW, until the draft reversed, and the flames went in the direction they were supposed to go…I’m not a happy puppy.
So I need some input from y’all. Since the RMH isn’t rockety enough, there may be some build issues? J-Tube Dimensions (built with new firebrick): 5.5” x 8” Feed Tube-14” deep, 6” x 8” Burn Tunnel-15.5” long, 6” x 8” Heat Riser; into an 8” x 31” Steel Heat Riser; Approx. 2.5” gap to top of 55 gal Drum; approx 3.5” between drum and insulated heat riser; Insulation for heat riser is a vermiculite/horticultural perlite mix; the vermiculite was mixed with a thick clay slip, more like clay putty, and made into a dry as possible mix, then the horticultural perlite was added to the vermiculite mix (so it would not take on a lot of water); the transition area/ clean-out, from the drum to the stove pipe, is a LARGE area. My thought at the time was to make it large for easier cleaning, but being a novice, could this be a problem? From the clean out, the 8” flue pipe goes 2’ to a Tee, and goes through the wall, makes a 90, up 2 feet to a Tee where it ends. Approx 8 foot distance. This is a temporary arrangement for now. Later there will be 16 feet of bench added and the exit will be on the opposite side of the room. There is no insulation on the bottom of the J-tube brick work. My floor is 2’ deep, insulated, with a clay/sand fill. There’ll be a 3” thick earthen floor built later on top of that. I wanted heat from the RMH to go into this area (that’s why no insulation on bottom of RMH brick work). There is a 2” thick layer of vermiculite/perlite insulation on the outside of the J-tube.
Other hints of problems. I saw a video that had kids toasting marshmallows over their RMH’s feed tube. The comments were that they shouldn’t be able to do that. I can only hold my hand over the feed tube for 10 seconds before it’s too hot to hold. I probably could toast marshmallows too. Also, after all this work, it bothers me that my good old faithful Fisher still makes more of a rocket sound when it sucks air then my new RMH. Something HAS to be done about that! Everything is still pretty wet, meaning cold. Does it take awhile for a “good rockety effect” because the heater is colder than the outside temperature? Will the rocket effect get better when the heater dry’s out? What steps should I be taking? My plan, for now (until I get more input from yoz) is to do short burns each day to dry out the heater. I’m hoping that a dry heater, that retains some heat between burns, will be a better heater for draw and start up.
Earlier post have had a bunch of pictures of my RMH build. Alas, this weekend when I finished my RMH, got ready to take pictures of the deed, my digital camera broke down. To be used no more. Wonder if it got too much smoke in it’s lens?
Your comments from Hugo’s problem have helped me formulate my questions, etc.
yea you definitely need to split your wood down into small sticks. i would personally increase the height of the outside pipe to at least double what you have should increase flow.. you may want to experiment with 2 more t/s for a chimney topper should cut down on wind blow back... make it look like an H out side
Kevin & Brian: thanks for your comments. I kept the feed tube surround short (7 inches) so I could get my arm into the burn tunnel for cleaning when necessary.
I'll do the H thang to see if that helps.
I see all kinds of RMH video's on YT where people put large bundles of sticks, that reach all the way out of the feed area, and the flame and smoke get sucked back into the feed tube area. I saw one RMH video that had a 4" x 4" x 6 foot post sticking out of the feed tube.....whether it was burning correctly, who knows?
I follow the book when starting my fire. Put burning newspaper into burn channel, put second burning newspaper into feed tube, place very small sticks on top of burning newspaper, then small sticks, then medium size sticks, then larger sticks. I hope one day to be able to burn three to four inch pieces of hardwood. So far most of my start up wood is pine.
I am new to rocket mass heaters and just started reading the forums and started learning everything possible about rocket mass heaters. I have not built one yet, but I am a engineer by training.
I looked at your previous posting and watched all your videos of the rocket mass heater and believe you have two problems:
(1) your steel pipe "riser" is too short
The longer this pipe is the more 'chimney effect' you will get. The steel pipe should be one to two inches from the bottom of your 55 gallon barrel. Since a 55 gallon drum is about 3 feet tall you will need a riser pipe that is about 2 feet 10 inches.
(2) you need an insulated riser (a pipe within a pipe with insulation)
If your riser is hot on both sides it will decrease the chimney effect in the rocket mass heater.
I believe these reasons are why your RMH is not 'rockety' enough compared to your wood stove. Your wood stove has a good 8 feet or more of chimney (riser) and that is why is pulls so much air from the room. Your wood stove chimney is really hot on the inside but room temperature on the outside.
Since the chimney is "trapped" inside the 55 gallon barrel you need to make sure the 'inner part' of the chimney is separated from the 'outer part' of the chimney. I was thinking you can think your riser like a doughnut: the inside of the doughnut hole must be separated from outside edges by delicious foamy doughnut insulation.
Brett: My drum is 33" tall and my steel heat riser pipe is 31" tall. that's a 2" distance from top of pipe to top of drum. here's a jpg of my built RMH. I'm not the greatest at SketchUp so it's not exactly to scale:
Oh, and I used a vermiculite/perlite mixture to insulate between the inner and outer drums.
Thanks for the schematic. It looks like you had already built-in my suggestions. I had two other thoughts on inadequate air flow, but thought they were unlikely:
(1) The basement area may be really well sealed against air leakage. Not enough air flow is present to allow for RMH to pull combustion air.
I am wondering where the fresh air exchange in the basement comes from and if it is restricted in any way. When you burn the RMH can you discover where the fresh air is coming from and if it restricted (closed door, closed vents, air tight basement)? Does it help the RMH draft to open a door or crack a basement window?
(2) There might be an occasional wind-ward back pressure on the RMH exhaust that reduces or reverses exhaust flow.
Do always get the poor rocket burn and black smoke back flow? Is it only on windy days? Is the wind able to directly enter the RMH exhaust?
Brett: this weekend I'm going to make some changes to the stove pipe and chimney configuration. Your air back flow suggestion is most likely the answer. A few others have come to the same conclusion. I'm going to make the flue longer and add an H shape with TEE's for the chimney cap to prevent any air back flowing into the flue pipe! I'll keep you posted on my progress.
Pack : I am sure that you come complete with a wife and family, For me even after 35 years of marriage you can't always tell by my remarks, However, there are three things
that living with a spouse means you have little control over, The Clothes Drier , we rarely use one (clothes lines are still legal in most places, giving you 'the Right to Dry') if you
are discharging this bad boy at the same time you are trying to run the Rocket Mass Heater RMH, you will get an Automatic smoke back condition !!! Unhook it from its connection
with the outside, and put a pair of panty hose over the end, for the next few months you probably need all the water vapor in the air that you can get !
Any time you get smoke back you should check to see of your wife has just turned on the Fan in the Rangehood over your Kitchen Stove, install a two or better yet a three speed
fan and never use high in the middle of the heating season. put a pot lid on all boiling liquids, the energy (and smoke back ) you save will be your own !
With a really marginal system ether turning on the exhaust fan in your bathroom or opening an upstairs window will cause smoke back, go to a two or three speed fan and raise
the height of your vertical chimney 5 ' above the peak of your roof !
I will not guarantee that any one but the 1st one will cause smoke back most of the time, however eliminate the possibility by ether covering with tape or a sign, if this is your
problem a very short test will prove it, pop open a cellar door or cellar window, and a quick disconnect of the offending appliance will restore things to normal ! Hope this helps,
I know it was not timely enough ! Big AL !
Success has a Thousand Fathers , Failure is an Orphan
As well, i'm prety sure your heat riser isn't dry yet. That vermiculite/clay slip mix takes forever to dry. Even with added perlite, and putty dry. I'd say it will take a good 40 hgours of burning before it's dry (this is a completely random number btw!)
Great comments from everyone! I may be jumping the gun on my smoke problem. Several things have changed. I'm getting better at loading wood into the feed tube. All I had in the beginning was large wood (for my Fisher Grand Dad Wood heater). Now I'm cutting and splitting smaller, more manageable wood for the feed tube. I've noticed that when you start at burn, it's important to fill the feed tube up with small to medium sticks. This starts a good rocket effect. Then, as you can, you can add larger wood. Tonight I had a fire for one hour. The temp in the house went up from 62 degrees to 72 degrees. Also, today I added 25 feet of flue pipe which include's 8 feet of chimney. I had a short chimney while I was having the smoke back problem. Tonight's video is below:
I am still curious if you are getting good air flow (new combustion air introduction for RMH) in the basement area. Perhaps when you are optimizing the setup you can find where your fresh air is coming from and if you need to open a basement window a tiny bit to get more air flow.