RMH Longevity

Back in the early 1950s, my Dad built our camp and fireplace complete with Heatilator* (Metal box that sat between the firebrick and the outside red brick shell, including fresh air intake at base, small integral fans and outlet grates at top).  The place was summer only, so that method of heating worked fine for the conditions.

I recall twice in my lifetime where a mason came and repaired or repointed the firebrick.  The last time, an delightful gentleman came, mixed his mortar in a "flying saucer" snow toy and told me to watch very carefully as he proceeded. "I won't be around next time this needs work, so pay attention!" were his words.

As I prepare to build an RMH in place of the old heater, I'm wondering about longevity of BB RMHs.  I see where many of you experienced contributors show us the wear, ash buildup and soot - or lack thereof. And it seems that rebuilds are very common.

Well, that concerns me a bit.  I want to build this thing once - and if my kids or grandkids have to do some work on it, okay.  I looked, even using the search function, but I don't find any threads where the longevity of RMH is discussed.  Is it realistic to think I can build it, feed and care for it properly, and NOT have to rebuild every few years?  Thanks!

Hi Randy.
That’s a sweet anecdote you shared. Thank you.

The wear and regular rebuilds you talk about, can you be a bit more precise?

So far the only parts that I’ve read about giving out after some time would be the bell (in case of using a steel oil barrel) and the first fire brick in the “bridge” (I.e. the roof of the burn tunnel).

So as far as I’m concerned I would say you could avoid some of that by building a masonry bell or make changing the barrel easy.
As for the bridge, I’ve heard someone mention a pice of sheet metal that provides some protection. Forgot the name. Something Peter?
Also it’s possible to design the build in a way that this particular stone can be replaced rather easily.
I’m sure some of the rocket masters here have a lot more to offer on the topic.

Oh, I totally read over the “bb” before your RMH… no idea about those yet

Hey Randy;
The majority of builds you read about on Permies are first time builders.
Being excited about their first RMH and not taking the time or having the finances to build a proper stove, they do the best they can.
A common issue I see, is taking "shortcuts" to make building easier or less expensive , almost always those shortcuts come back as a problem later.
Then there are the folks who think they can "improve" on a proven design... they too are rebuilding... to remove those improvements.

Then you have folks who have built a successful RMH but want to upgrade to a larger size or a different design.
I currently have 3 RMHs on line. Two have changed from J-Tubes to Batchboxes, both have been "rebuilt" several times over eleven years as I experiment or fix problems (like firebricks that do not have a high enough temp rating)  Each time I make changes I create a better build.  Although I have plans to further improve those RMHs, the core units are a solid build using a tension frame rather than mortar to contain the bricks, it is the bells or piped mass that I will modify sometime in the next few years.

My third RMH is a onetime build.  A Walker BBQ that I call a black and white oven.
I have no need or desire to make any changes or improvements, it is  perfect as is.
Also a "dry" stack build on the core, but due to it's design no tension frame was needed.
https://permies.com/t/164923/rocket-ovens/Build-Black-White-Rocket-Oven

My fourth RMH is being built this summer in our 100 year old cabin.
A 6" "Shorty"  Batchbox that I will encase in a brick bell.
The Core is already built and test run out in my shop.
https://permies.com/t/254283/Shorty-Core-Montana-Version-burn
https://permies.com/t/254292/Airframe-Construction-Shorty-Core
This core build is different from my dry stack cores.
A similar tension frame is used but 1/8" Morgan Superwool gasket is placed between every brick surface.
This method will allow the bricks to thermally expand and contract.

My experience is that all mortar will crack over time due to thermal expansion.
My dry stack cores may ultimately crack the firebricks in the core and require a rebuild.
I will mention that my experiments with refractory mortar and 1800F temps inside a core resulted in a rebuild, and the bricks were not reusable without grinding off the old mortar.
I will never build a core with refractory again.
My bells have been and will continue to be built using a clay/sand mortar.

Here is a link to another recent build,   https://permies.com/t/248275/Batch-Rocket-Double-Skin-Bell  (see link to the build itself)
Glenn took the time to build properly, he did an outstanding job and he will not be "Rebuilding" anytime soon.
He did use a refractory mortar on the core, and perhaps he may be making a repair or a rebuild, in ten years or so.

The bottom line, follow a proven design, build it carefully with quality materials and you will get proven results.
A true Masonry heater is only fired a few times a day unlike the old wood burners that are lit in october and stay lit 24-7 until spring.
Document your build with photo's and video.  
Your grandchildren might need to make repairs after you are not there anymore.

Oh my, Thomas.

I wonder if the general audience (and lurkers like me) understand just how much of a guru we have at our disposal. THANK YOU!

Your response gives me a bunch of immediate answers, and after I study the links you provided, I suspect those will lead me to both answers and more questions.

But you can understand that many folks may want to have an RMH, but certainly don't look forward to rebuilds.  

I hope that the response you provided here will allay the concerns of new heater builders like me.

Your points about shortcuts and "improvements" are good to have enumerated - I don't think I realized just how many of the rebuilds were triggered by these.

I shall go and dig into the links and again, thank you so much!

I know it’s been posted before but I can’t find it now and it does relate to this thread….

How do you plan for repair. I know the feed bricks on the J take a beating and will need to be replaced fairly regularly if you aren’t really careful. What other bricks tend to fail and what tricks can you do to make it easier to replace them without tearing it all the way apart?

The first brick in the burn tunnel roof has a lot of uneven heating and thermal shock, and is supposed to be the quickest to crack in a gently handled J-tube. If you are rough with the wood feed, you may damage the whole top of the feed tube if made from red brick or poorly braced. A cure for most all of that is to fabricate a steel liner for the top 6" more or less of the feed tube, incorporating a P-channel in the face nearest the burn tunnel.

Aside from that, if you use good firebricks for the whole core (possibly insulating firebrick for the riser), it may well outlive you.