Alaska RMH!

You guys I’m new to Permies and also new to Alaska. Also I have never built a RMH. I am very excited to see how it does up here. I have asked around and people seem to like the masonry heaters and only one person I know has a RMH. I would love your thoughts on an RMH in Alaskas cold winters. I’m so excited to try it out what a perfect place to try one right?

Welcome to Permies, Dick!
If people know and like masonry heaters in your area, they will like RMHs also when they become familiar with them. The rocket mass heater is just a subset of masonry heater with a few particular design characteristics. Alaska is indeed the perfect environment for an RMH, with its continuous heat reservoir and ability to burn wood, even softwood, efficiently and safely (no creosote). I have heard that some parts of Alaska are deficient in clay, so you might need to use more brick masonry versus cob, but use what you can get. I would advise you to make the biggest mass you reasonably can as the heating load will be constant for months, so no need for fast response. Just make sure the system size is adequate to get that mass up to temperature. Probably an 8" J-tube would be the minimum for a normal sized house, maybe even an 8" batch box would not be overkill.

I have ordered the book on RMH and am waiting on its arrival to figure out the correct “model” to use. I’m sure I will have questions once I am set to start. We will be in a 14x24 house with 2x6 studs and hopefully r-30 insulation if we can get it. We do have a decent amount of wi does however. My plan is to build the mass as big as we can get (like you said) in that small space. I think it will be well worth it for the long winters. Needless to say I am very excited about it. I will post pictures this summer of the build and will most likely have lots of questions. This seems like a great community. Thanks

Hi Dick, are you locked into building a 14x24 house? I.e. using standard 2x4 foot sheets of plywood, OSB, siding and etc., it's not much more expensive to build a 20x... (5x sheets of 4x8 ply/OSB/etc.) instead of 14x...

Building in cold climates obviously means close attention to construction and insulation methods. Are you planning on doing "double-studded" wall construction? An exterior wall R-value of 38 is easily obtainable with a 12" thick "double-studded" (to limit thermal bridging)  2x4 wall construction. Some neat info is available on this site comparing single vs double-studded exterior wall construction and typical R-values:  https://www.bpcgreenbuilders.com/what-is-double-wall-construction

I built an 8" RMH into a typical small 900 sq. foot stick-frame (2x4, R11 exterior walls) house and have been working on shoring up the insulation, in order to extend the thermal mass heating flywheel effect. Winters are fairly mild here, and on a day where the lows hit the mid 'teens (F) and highs into the mid to upper 30s', the house will stay around 70 degrees (F) for 12 hours after the fire is out, and I usually fire the RMH for 4 to 5 hours to warm up the 40-inch wide x 10-foot long thermal mass. My RMH is patterned after Ernie and Erica's Cabin-8, modified to use a Peter van den Berg 6" batch-box combustion unit.

Best of luck with your build. Sounds fun.

The cabin is already built unfortunately. We had a company build the shell so we wouldn’t be “racing” against winter to get everything done. I have never heard of double insulated walls I will definitely check that out. We used 2x6 studs for the frame to achieve better insulation. I am still waiting on the book to come in and once I read it I will have a better idea of what size and style RMH we are going to build. I will keep you guys updated though.

I’m hoping if this goes well and cuts down severely on wood burning I can spread the word up here and get lots of people on board. Lots of people already build alternatively up here. It’s crazy the amount of wood some people need to keep warm though. We will be filming the process and putting it on YouTube so everyone can see. We are very excited to try the RMH as well as, cordwood building, rammed earth, and cob. And eventually I’d like to try a straw bale house 😁 anyway I’ll keep you all updated!

Hi Dick;
I agree with Glenn that you want as much mass as possible.
I have both a piped mass system and a brick bell system.
Both work extremally well.
I have found the brick bells simpler to build than the piped mass.

As far as style and size.  
In your location if you want a J tube than I would consider nothing smaller than an 8" .
J tubes are the original style.   They work great, give that throaty roar that people expect from a rocket stove.
However with an 8" you need to feed it every 45-60 minutes...    Or  relight it  (very easy with a warm mass).
If someone is home all day this is not a hard chore but if your gone  for long stretches than you might want a batchbox style instead.

Batchboxes;
A 7" batch will burn for 1.5 hrs and have coals for 2.5.
A 6" is apx 1hr and coals for 2.
Not having built an 8" myself I can only assume it would follow the same pattern.
Batchboxes burn hotter.
They use larger pieces of split wood than a J tube, plus they lay  horizontal.


You will not find much info about batches in the RMH book.
All the current info can be found here at Permies.
At Peter Bergs site  http://batchrocket.eu/en/  
Or at my site     https://dragontechrmh.com/

Just came across this thread. I too just moved to Alaska and hope to build an RMH (probably won't be for about a year as we need to get a place to build it first). Wondering if you have made any progress on a design, Dick?

Quick update for everyone! I have read all your replies but haven’t had a ton of time to be on my phone replying, we have been extremely busy trying to get our house insulated, wired, etc. thank you guys for responding and giving me insight/advice I appreciate ALL the help and wisdom I can possibly get so thank you!!

We have decided to go with an 8” J box style with 16’ of piping if we can fit that much in our tiny house. 14x24 feet. We are currently debating whether to go through the roof or the wall for the exhaust. I have read many different points and it seems the roof is the better option but I just hate to put a hole in the roof if I don’t have to. But anyway we got most of our material today and will begin building either this week or the next! I will keep you updated thanks everyone.

Hello to all-
Dick and Eloise, what parts of Alaska are you each in? I am out in Talkeetna. We are planning to build our place with a RMH as well. Have taken a sort of class here. Was very hard to follow, but the end of the class was a hands on putting together a RMH out in the parking lot of the school where the class was held.
Was not a permanent build, just a dry fit but we were able to fire it up in the parking lot.

Vickey,

I am in Wasilla. That’s awesome you are in AK as well I love talkeetna! We have never built an RMH before but are very excited to give it a shot. We hope to start building this weekend. What class was it? I had no idea anyone did RMH out here(besides a handful of people) let alone having classes about it. Will you be building this summer?

Quick update!

Hi Dick, neat start on the combustion unit. I'm not sure if it's the photo angle etc. but it looks like the burn tunnel may not be tall enough inside. From the floor of the burn tunnel to its ceiling, is it the same measurement as the span / diameter of the wood feed opening?

That is an excellent question I was so concerned with getting the width correct at 7.5 I don’t think I ever checked the height. The riser is 46.5 (should be 48) and the overall interiorlength of tunnel is 24 and both openings are at 7.5 or very close. But I forgot to check the height of the feeder which should be 16 I think I’ll have to look at the book for reference. Other than that is there anything else that looks odd? We used the clay slip to seal everything up. As always I appreciate all the help I can get thank you all 🙏🏻

Also that cement board should work fine as a base layer underneath the fire brick right? Under the burn chamber?

Hi Dick;
I would stop your build now and consider raising that whole core and cement board on clay bricks laid flat.
Sitting tight to the floor, that core will burn thru the cement board after? one season maybe two? After that, it's your flooring itself that chars.
If you raise your whole core build 2.5" or so, then your flooring is safe.
If left as is, you will have trouble down the line.
After the core the temps are low enough that you could sit cement board on your flooring if needed.

Hi Dick;
When I say to raise the core on flat bricks.
Not a solid base but just enough to support the core with plenty of air gaps for cooling.

After consideration with my wife we will be taking it all down and buying a wood stove. No just kidding we will be taking it down and insulating the floor better and then we will build it again. I hate to take it down after just getting it done but it is much easier to fix it now than later when it is totally finished. Thank you for the tip!

Perlite mixed with clay would be a nice base for it correct? On top of the cement board?

If you are building a 7.5 inch system then the whole inside needs needs to remain exactly the same i.e. 7.5” x 7.5” from the top of the loading port to the exit at the top of the riser.

It looks like you’re using split fire bricks, they should be fine if they’re good quality just bear in mind that the exterior of the brick, after one hour of burning, will be 500°C or more!

As Thomas points out you need to offer some form of insulation between the base of the unit on the floor.
You can use a ‘five to one’ mix of cement and perlite (vermiculite is easier to work with) but it will take an age to dry out hard enough to support the weight.

What do you plan to use to insulate around the J tube core?
obviously the more insulation and the better quality it is, the more effective and efficient fire will be.

Dick Winters wrote:Perlite mixed with clay would be a nice base for it correct? On top of the cement board?

Insulation does not prevent heat transfer, it only slows down the process. Best practice when building on a wood floor is to have air circulation (air gap) under the J-tube combustion unit.  I.e. lay down parallel and evenly spaced rows of common brick, the rows spaced far enough apart that they can be "bridged" with a layer of horizontally laid brick that form a platform the same square dimensions of the cement board base. No mortar is needed. Then build the combustion core on that elevated brick "bed". Have a careful look at the diagram on pages 43 and 45 of The RMH Builder's Guide by Ernie and Erica Wisner.

Notice in the diagram's insert on page 43 the exact detail, which includes a thermal reflective layer of aluminum foil on top of the elevated brick bed, then an insulating layer of Perlite/clay mix, then the combustion core brick work.

Edit: more details for clarification

Fox and Byron,

Thank you for telling me this now before we start our second attempt. We would have been in big trouble. I will look at the book today and see what you mean Byron. We were going to insulate the whole J tube with clay perlite mixture. Is this okay?

Also (NOT trying to be a smartass) does it make a huge difference if the dimensions are a half inch off here or there? I assume the CSA, precise dimensions, are to ensure the “thermo siphon” works and the unit drafts correctly. Is there any room for forgiveness at this stage or is perfect 7.5 the only way? We are not masons so it is real tricky trying to get the bricks “perfect”. We can get them very close. Anyway thanks again!

Dick Winters wrote:...does it make a huge difference if the dimensions are a half inch off here or there? I assume the CSA, precise dimensions, are to ensure the “thermo siphon” works and the unit drafts correctly.

The vertical wood feed, then the horizontal burn tunnel, should be as close as possible to the same dimensions, for best draft performance. If one must be slightly less CSA than the other, make  the one with slightly less CSA be the vertical wood feed.

Before encasing the J-tube combustion unit with Perlite/clay mix, wrap it in high-temp fiber blanket insulation, about an 1 inch thick. That will serve as both insulation and an expansion joint between the combustion core and the outer skin, which can consist of your Perlite/clay "encasement mix".  On my build, I used two inches thickness of high-temp blanket insulation to encase the core, then over the top of that went straight to a decorative brick work (also serves as thermal mass) for the outer skin over the combustion unit.

There are several ways to build these combustion units. The high-temp blanket insulation technique is the best I've personally used for preventing heat expansion cracks from forming in the combustion unit's encasement masonry.

Hi Dick, these threads can get a bit confusing when you get mutable folk trying to help and as Byron points out there are different approaches as to how these stoves can be put together!

Do you have access to high temperature insulation like ceramic fibre products?

It is possible to use clay, straw and pebbles and other organic materials but more high tech materials will make your build far more efficient and easier to build but of course will cost considerably more money to purchase!

There is no doubt a rocket stove is a Wonderfull thing to own but they do require quite an investment in time or money or both… so having a good plan and construction method is going to be important.

Okay I understand what you guys are saying thank you. Unfortunately we can not find anyone who has high temp ceramic blanket that’s why we were hoping to use the clay/perlite mix around the whole combustion unit.

As for the foundation we plan to put 2” of sand on top of the cement board and then add a second base layer of firebricks underneath the core. It is more costly but I’d rather overbuild it once than have to build it twice. Hopefully this is a much safer and better way to go. What do you guys think? You have far more experience with these than I ever will. Thanks

Good morning Dick, I started building rocket mass heater 'sin 2018. One thing I learned is when all of  the people that have been building these units and all of the you tube  videos out there and they say how hot an rmh or in my case rmhf they burn hot at least mine does. Unless you have seen one in real life burning and operating you can't feel the heat from a video. I would really look hard online or where ever for ceramic fiber insulation blanket or ceramic fiber board insulation. Both work well and have a place for each to be used. Seriously these stove's are awesome. I think it's the future for wood burning. Just remember  if you build it right it is going burn HOT. Listen to a guy that learns everything the hard way. Thanks

P.S. you can see my build on the permies thread huge batch box rocket stove.

Dick Winters wrote:Unfortunately we can not find anyone who has high temp ceramic blanket that’s why we were hoping to use the clay/perlite mix around the whole combustion unit.
 

You're in luck, it is readily available by mail order from Thomas Rubino: https://dragontechrmh.com/morgan-superwool-plus-non-ceramic-fiber-blanket

Shouldn't require more than about $30 worth of morgan-superwool to insulate the combustion unit. While you're ordering, might get a little extra to use for insulating the "heat riser".

Why not just use rockwool around the stove? Can you get rockwool? I believe you can peel layers off.

I have contacted Thomas Rubino via e-mail to see if he can ship to Alaska and how long/expensive it would be to get here. Home Depot does have mineral wool it looks like but no ceramic insulation unfortunately I have called all locations of Lowes as well. Winter will be here shortly so we do not have too much time to wait for shipping etc otherwise I would just order it. I’d say we have about 3 weeks maybe 4 to get this built before temperatures start to dip into the 30*F. We have no heat source at the moment so time is of the essence.

We will check for rockwool today but if they don’t have it is there another working alternative? Thank you all for your help 🙏🏻

Hi dick. I've never used rock wool so not sure how easy it is to use .I purchased most of my ceramic insulation on Amazon. Usually kicked off at my door within four  days. Might be different in Alaska. I really do urge you to look into it. Easy to work with and it works. Hate to see bad things happen to a beautiful build. Thanks

That seems like a tight time scale for a first build, perhaps it might be better to buy a basic metal box log burner while you study the form and get the materials together.
There are many detailed build threads on this forum showing the most basic builds right up to the most up to date methods.
It would not cost you much if any more to build a batch box, that requires a bit of metal work and more time to construct but the end result might be a more effective stove for an Alaskan home?
If you did not have a time limit then you could think about a stove that offers instant space heating, cooking and storage heating all on one unit but you are not going to build that overnight!

This thread is very detailed and I think it might be worth a few hours of your time reading it to see what you might be up against and how effective ceramic fiber can be…… https://permies.com/t/122458/Advice-RMH-build-Hokkaido-Japan

Hi Dick,

You may have already chosen your course, but I thought I'd share this in case its helpful. Another permies user mentioned difficulty sourcing materials in Alaska on a thread I had started a while back. https://permies.com/t/173455/Rocket-Masonry-Cook-Stove-Home

He mentioned Distribution International in Anchorage, and said they have all sorts of refractory materials in stock (that was 6 months ago). Maybe give them a call and see if they have what you need? Also look for a ceramic or pottery supply store in your area or in anchorage. I have not done too much looking for one yet myself, but there is enough local made pottery here in Alaska I imagine there has to be one somewhere. They will have supplies for kiln building, ceramic blankets being one of them. If you can't find something local, you can also check into any online ceramic supply shop (bailey's pottery, sheffield pottery, or big ceramic shop, to name a few) and shop around for the best shipping rates/times. Again, I have not looked into sourcing these items for myself yet, so hopefully I'm not sending you on a wild goose chase. Just some suggestions on where else to look. Put in as much energy as you think its worth.

I am on the kenai peninsula, and am new to the state of Alaska.

Not to hijack your thread, but did you have any trouble sourcing firebricks or regular bricks for your build? I have not been able to find regular red bricks here.

Looking forward to seeing your progress, whatever route you choose! Best of luck!

-Eloise.

So I may have been a bit dramatic with the weather timeline. I think we still have a few weeks until we hit freezing temperatures. It has been rainy with 50-55 degrees F.

Eloise, I wish I would have checked back earlier we could not find ceramic blanket anywhere. We already have our heater built and we are currently firing it and filling the mass. We did find plenty of fire brick thick and thin at a masonry place in Wasilla.

We did go back and re-do our base layer with a sand perlite mix ( about 2.5 inches)on top of the cement board and then added and additional layer of the thick firebrick below the entire combustion unit. We used mineral wool for the riser/box insulation. After a few more firings we will take off the barrel and see how everything is holding up. So far everything is working great and we are having a blast building the fire and enjoying heat for the first time in our new home. We are still working on getting the “cob” mixture correct because it keeps cracking. We have tried more clay, more sand, and better mixing but it seems to crack regardless. But it has been a joy to build with mud and rock. Thanks again to everyone for your help and suggestions. This is a great community 🙏🏻

Looking good!
Glad to hear your enjoying the beginning of a long season of burning... may it not get old or seem like a chore during a long Alaskan winter.

Have you experimented using any form of fibre in your cob mix? Even if it’s something as fine as cattail fluff (normally reserved for a finish plaster) it may be all you need to keep the cracking to a minimum.

Some places that experience higher temps, joints or that are adjoining dissimilar materials may always want to crack but the beauty of cob is that you just mist the crack with some water and then smear the crack away like magic. Some cracks are chronic so don’t worry too much about those. Just consider them to be artistic expansion joints....like face wrinkles !

We are trying to figure out some sort of fiber material to use, that is a good idea I forgot how important the fiber can be. And thank you for letting me know about the cracks that makes me feel a lot better about them I thought we were doing something completely wrong! We’ve put so much work into it I would hate to see it crack to pieces. It has been lots of fun playing with the mud though. Thanks for the help!

Hey Dick I should have popped in here earlier but if you ever need any refractory materials in AK I highly recommend checking out Distribution International in Anchorage. That's where I sourced my materials for a charcoal forge I built a few years ago. They had everything I needed according to my applications, knowledgeable guys they were. I recently inquired about heavy duty fire brick as well as ceramic fiberboard and they had both in stock, but it has been about six months since my last inquiry.  They also have Kaowool, soft firebrick as well as castable refractory.

I just moved over to ketchikan Alaska  It might be a good idea to buy one of Paul Wheaton's shippable chores

If anyone here is interested in a solar dehydrator with rocket assist, take a look at this excerpt from Paul's new movie, Free Heat:

I am considering purchasing land in Alaska near the Kenai peninsula someday, as I abhor the heat and humidity at this point. It’s early April and I can’t go outside for 10 seconds without beading sweat.

I desperately want to put to use many of these permies principles afforded to individuals that own wooded land and have access to felling trees.

I love being cold, I spend 10 minutes in the Wawa beer freezer when I go there. It’s much easier to bundle up and start a fire than take your skin off because you’re too hot.  

Edit: this is of course a long distance away, but I do wish to pursue astrophotography near the top of the world sometime.

for now, I am greatly considering the Pacific Northwest.

There is work on a RMH that can produce electricity!! The people at Wheaton Labs are tinkering with that concept this July!! At the Permaculture Technology Jamboree. See https://permies.com/s/permaculture-technology-jamboree  and there is a BOGO sale for that event happening NOW! See https://permies.com/s/ptj-bogo-sale That is so exciting to me.  Just imagine - you can be off-grid and as long as you have a few twigs, you can be plugged into the world, but only when you want!

Monica Truong wrote:There is work on a RMH that can produce electricity!! The people at Wheaton Labs are tinkering with that concept this July!! At the Permaculture Technology Jamboree. See https://permies.com/s/permaculture-technology-jamboree  and there is a BOGO sale for that event happening NOW! See https://permies.com/s/ptj-bogo-sale That is so exciting to me.  Just imagine - you can be off-grid and as long as you have a few twigs, you can be plugged into the world, but only when you want!

Sounds quite remarkable.