Are there good alternatives materials for the exhaust?

I was given 26 gauge spiral wound 8" duct and suggested maybe using aluminium chimney flue liners as a cheap alternative to stove pipe. Does anyone know if either of these Items will suffice as thermal mass piping?

The spiral wound duct should work fine as mass ducting. Aluminum flue liners may work fine also for that (as long as they are not flexible corrugated material), but not for the first 5' more or less after the barrel, as there is potential for more heat than the aluminum can handle. Black stovepipe is recommended there, as it is strong enough to stand up to hard conditions.

Is the spiral galvanized able to be used within the first piping in the thermal mass?

Philip BAldwin : It is possible to make a Heat Riser using a combination of Perlight and a clay slip often with "Water Glass" mixed in as a hardener, It is then possible

to consider using any piping as a sacrificial form around your Heat Riser -Think Heat Riser thickness of 2'' minimum - otherwise no nothing short of Titanium

( and I'm not real sure about that ! ) Big AL

My heat riser is fire brick abd schedule 40 combo.
stove pipe is super expensive. I am snooping for alternatives inside the thermal mass.

Talking about the horizontal thermal mass ducting and not the heat riser, you may be able to use the 26 ga ducting for the whole length, but black stove pipe which will be 24 ga is recommended for durability for the first few feet. Also, galvanized ducting will be affected by heat, with the bright galvanizing potentially offgassing zinc which is NOT A GOOD THING. You could heat-treat a length outdoors in excellent ventilation until the galvanizing turns a dull gray, at which point it is said to be inert and stable and would be safe to use.

You could use a length of this as the sacrificial inner form for your heat riser to be packed with a perlite-clay mixture (just enough clay to make it self-supporting if/when the liner burns out).

Philip Baldwin : My bad, I posted an answer to the subject line and not the question asked ! Color me red faced ! You Didn't post your location, so none of this may apply.

IF you have Habitat for Humanity in your location, they often get some ductwork and piping ! Or try any Craigslist Clone ! Houses being demolished are good candidates

here in the States where most home heating units are Fossil Fuel Fired Forced-air Furnaces with yards and yards of ductwork, 6'' and 8'' are common, and the

ductwork directly under a floor register (called a Boot ) can often can be a potential Manifold !


Look for houses showing fire damage, windows boarded up with plywood, and a large dumpster/skip in the yard - I scope out the dumpster then talk with the job site foreman

often I can talk my way into major salvage Often if the house is getting fixed up after a fire the furnace is considered water damaged and is replaced !


Sometimes this is a major remodel, then old ductwork might go back "to the shop'' but I have had good luck dumpster diving there too. Aa case of cheep beer to the foreman

is a good trade if the picking is good

Most spiral ductwork is classed as HVAC piping not "Smokepipe" You can try local heating contractors, quite often there will be HVAC Pipe that is shopworn, damaged which

is fine for you ! For the Craft ! Big AL !

I am considering building a RMH in my basement and have a nice stainless steel 55 gallon drum and an 8" SS pipe that I am considering using as the heat riser that will be insulated inside a 12" heavy gauge steel tube. I have access to a lot of bricks and understand from reading all of the postings that the the first 5' or so of the exhaust will be very hot so I will use the appropriate pipe for that and incase it with cob (I am in N.J. and I think I found clay under a huge uprooted tree that would be enough to mix with sand to create cob to cover that 5' of pipe) My question is after that 5' can I not use pipe at all and use just the bricks mortared together to create a turn around Chanel with the same cross sectional area a as the 8" pipe? At the 90" bend, I will have a sealed removable 3' by 3' stone for clean out purposes.The exhaust through my above basement window will have to be experimented with to have an appropriate draft. Will this work enough to be a good mass?

Your 8" stainless steel pipe will corrode quickly as the heat riser liner; I would use a piece of sonotube (cardboard concrete form) or an old metal duct for this, purely as a sacrificial form. Pack around it with 2" of a perlite-fireclay mix (just enough clay to make it hold up on its own). Your stainless duct will be great as the first 4-5' of mass ducting after the manifold. People have built air channels in mass out of brick. It would have more friction than smooth duct, but if you make it a little bit larger you should be fine. You need more than one layer of brick to be safe against leakage, and also to absorb enough heat.

It sounds like you are building this in your basement, so we need to ask some other questions. Is this a frequently-used living space, or are you hoping to heat the upstairs from the basement? An RMH needs to be in the same space you will inhabit while the fire is going so you can pay attention to it and tend it properly. An RMH works best by radiation and direct conduction, not so well as an air heater.
How tall is your house? A heating appliance in the basement of a two-story house will have to fight with the house for chimney draft, and you must have a good chimney rising through the interior of the house to make this work. A stovepipe running out the basement window, even if it runs up to roof level, is chancy and in some conditions will not work at all, backdrafting with any change in the wind.

Dackle Shephard : Welcome to Permies.com and our sister site Richsoil.com, and a Big Welcome to the Rocket and Wood stoves Forum Threads . Among the ~35,000~

Fellow Members World-wide you can come here 24 / 7 and talk with someone who wants to talk about what you want to talk about, this includes several hundred Fellow

Rocketeers. We all started where you are now !

As you have not shared a Geographic location/local weather conditions, or the size of the area you are hoping to heat most of our answers will be guesses!

To make your searches and your future Forum-Threads a little more Productive Here are a couple of Helpful threads /// Links below :


https://permies.com/t/43625/introductions/Universal

https://permies.com/t/34193/tnk/permies-works-links-threads


The original discoverer of the various separate techniques that combined make up the Rocket Mass Heater RMH Whole built sculpted his houses, making

them small, low, single story, Mushroom button shaped, in a super stable climate near the west coast ! These units nearly always work flawlessly.

I wish that it was as easy to adapt the RMH into an existing structure, often we are stuck will some compromises !

Congratulations on Scoring a S.S. 55 gallon Barrel/Drum.


The Heat Riser is best made out of a high temperature refractory material, At this location the freaky high Combustion temperatures 1300ºƒ + will cause the rapid

destruction of all metals -due to Oxygenation and ''High Temperature Hydrogen Attack'' also called ''Hydrogen Embrittlement". The barrel which comes after the

Heat Riser and has a large radiating surface is safe, and will last you for many years !

A Refractory Firebrick backed by a blanket of high temp insulation is satisfactory, I can recommend that you use a sacrificial form out of an 8'' pipe and a 12'' pipe

and fill the gap with a mixture of perlight and clay slip to D.I.Y. your Heat Riser. always use the lowest grade and cheapest piping you can find, as any metal used to

make the inside form of a Heat Riser is temporary! This saves your 8'' S.S. pipe for the 1st 5 feet or more of the Horizontal piping that carries the hot exhaust gases

through the your Cob Thermal Mass Bench !

The reason that we use piping through the thermal mass is for its smooth walls, unless you are an uncommon master mason who has worked with surface coating

bricks the difference in the distance you can flow your hot exhaust gases horizontally will be greatly reduced.

See my comments just above on ''finding'' used Piping !

The RMH was created to be located in the very heart of the home ( the more open the houses building plan the more it can provide comfortable heating ) where your

Rocket can be tended to easily as part of your household duties and daily living, it can be tended to totally by ear, with no more thought that you wood take to adjust a pair

of glasses on your nose !

Locating the RMH in any remote location where it is out-of-sight, out-of-mind is like all wood stoves a safety issue, and leads to the need for interruptions to your daily routine

- especially early morning routine, to stop what you are doing and check up on your RMH, this can quickly interfere with other duties becoming a drudges task to be ignored-

Your RMH can only Serve you as well as you serve it !

Basement locations are very problematic, please take the time to Google ''Stack Effect'' and "Whole House Stack Effect'', This is not a nice to know search but something you

will need to understand clearly, As several whole house conditions like an upstairs window open can cause major backdraft; filling your basement and house with smoke !

Other problem areas / conditions include running a nat.gas or propane water heater vented to the outside, or a clothes drier vented to the outside, and even the

range hood/exhaust fan for your cooking stove or that bathroom exhaust fan Have been The cause of smoke -back into your house !

I hope this is timely and useful For the Good of the Crafts ! Big AL

I live in a 2 floor house in N.J. with a basement and was hoping to be able to heat the basement with this RMH at least enough to keep our old cat warm and happy as he can no longer stay upstairs unattended since he is old and can't hold his bladder. I was also hoping that it would help heat our first floors floor somewhat to help reduce our electric bills. I am now having second thoughts if I have to raise the exhaust stack above our roof. Thank you for the information as I would have wasted the nice 8" SS pipe that I acquired. If I go forward I will find 8" piping for the exhaust and clay somewhere to make cob around the exhaust and mortar the multiple layers of brick on top of that for more mass. Thanks again.

Dackle Shepard :O. K.Take a couple of deep breaths, and let them out slowly, and just relax! While we are here for you and will try and explain why we like /don't like

doing something one way or the other -Basically its because we started where you did and made all the mistakes and foolishly spent moneys for shit we didn't need !


Here is a pretty good link describing how to test your Clay for suitability to make Cob and Clay slip. /////link below :

https://permies.com/t/32204/cob/Backyard-recipe-making-cob


Is your basement a full basement below grade, or is it a ''Walk-out Basement'' sited on a Slope, the latter is generally better !

Glen is right about an interior chimney rising to a point 3-4 feet above the peak of your roof ! However if you realize that the Heat Riser is your 1st Vertical Chimney,

then adding height there can work to improve your draft !


I have a special place in my heart for old cats, my mothers cat 'Little Orphan Annie' (a rescue kitty) came to us as an heirloom from a grandparent and lived an incredible

27 years, she had old cat dignity and all her teeth and claws to the day she passed -and wasn't opposed to testing them on friend or foe.

Our present rescue Cat is named Mithril -the name says everything, is just over 1 year old and is huge - Main coon somewhere in the family tree?

Membership has its privileges , we have Free-to-members 6'' RMH plans on-line here if you want to proceed !


This is where I recommend you go to Rocketstoves.com to download your PDF copies of the brand new 3rd Edition of Rocket Mass Heaters, This is ''The Book'' and will

save you time, money, and frustration in selecting and using the correct material to build your Rocket. It will also help you understand the length ratios of Feed Tube :

Burn Tunnel : Heat Riser and the need to create a Constant Cross-sectional Area for all sections And the orientation of all parts to themselves and each other !

For the good of the craft ! Big AL

Thank you Big Al. Our unfinished basement is full on a slope with a walk out. The bottom of the basement window that I wanted to put the exhaust through is 7' above the basement concrete floor and about 6" above the ground outside. Our cats name is Chance as I found him by chance by my work when the mother feral cat ran away with all of her other kittens. Chance just stayed there and meowed and let me pick him up. His eye was badly infected so after the vet visit that day we gave him the antibiotics daily and had to put drops in his eye every 3 hours for 2 weeks. Either way, we and our vet did the best we could do but we couldn't save his eye and it had to be removed to avoid future cancer and his eye lid was sowed shut. He didn't seem to notice as he played like a normal kitten. It just took him a while to learn how hard to jump up on beds and chairs etc.