6" RMH in northern Idaho

[Nirky]

This is my 6" build so far. I will for sure have it running by Sunday as it's supposed to get a little chilly here by then.

Just finished the core, put the steel cover over to measure clearances. Didn't like the idea of having a 55-gallon drum inside my small home, so got a 4x6 ft sheet of 20 gauge and bent it twice using a brake I built from a YT video. Actually bent it 90 degrees and then formed a prism, thereby making the sides rounded instead of straight & flat.


It's a work in progress, just like my home.


Another view of the tower/rounded prism/cover thingie


Had an idea to make extensive use of clay bricks for uniformity in supporting the rounded prism. Will clay slip the bricks, then will put the cutout sheet metal over, then prism on top.


Wider angle view


Overhead of the unfinished core

[DrewInToledo]

Ho nirky! That looks great!! Question, if i may? Why did you choose 6 over 8 inch? Just curious, thats all.
Boy, every time i see one of these go in, i want to rip out some carpet and start a project like yours!
I see great skill already. im excited to see where this will finish.

[matt walker]

Hey Nirky, good to see you. I love the prism! That's going to be a neat heater, very cool solutions you have come up with there. One thing I'm not seeing is insulation. I imagine you know this, but you have to have it around the riser and hopefully the core as well. Otherwise, it looks fantastic, I can't wait to see it come together. Thanks for posting it so far and please keep it up, I love to see new builds!

[ByronC]

Ah man, super cool design! With the tight triangular "barrel" to heat riser clearance, so it appears in the photos, I assume there's still room for insulating the heat riser's exterior with a minimum of 1" thick ceramic wool blanket wrap? The same ceramic wool is excellent for insulating around the feed and burn tunnel too.

What's the core sitting on, a thick insulated layer made of clay/perlite, or something else? Or maybe there's insulating kiln brick in the "floor" of the J's burn tunnel?

[mannytheseacow]

Nirky, great to hear from you and glad you are sharing your project! What a cool idea, I really like the steel prism, too. Are you going to weld the cover on it or how do you plan to do that? So cool to see something other than a barrel.

I'm curious about the floor, too. You'll want to get that duct work off the floor in addition to the core, as Byron suggested. It's great that you have a 6" because you can elevate it and still not be too tall for sitting on. In Matt's latest work on his home heater he has a good gap under the bench and behind it. I can really see the advantage of this, especially with a 6" stove. You might consider something similar. And if you could do the same thing with the core... man, you'll have one heck of a heater.

[Nirky]

Drew--I chose 6" because I already had the 6" vent from my wood stove. Additionally, my home is small, only 500 sq ft. My Quadra-Fire heated the place very nicely, except in the AM it would be chilly. I expect the mass to keep the place above 66-68 for at least 12 hours.

Matt--I have the perlite on hand but did not use it on the riser because of the clearance, the thickness required. Needs 2" I'm told, noticed I may not have enough room. I want the exhaust gasses to freely exit the system, no restrictions. The existing prism may be too small for a perlite-encrusted riser. Will look at a 1" ceramic blanket, but will perlite+fireplace cement cover the core. The blanket is not cheap at around $60 + shipping. Either that or get another $50 sheet of metal and bend a larger prism. The current prism has 21" sides and is 48" tall. I have a decision to make about this.

Byron--the core has one layer of firebrick between it and my concrete slab; that is, the floor of the burn tunnel is that one layer of firebrick, slab directly beneath.

Manny--don't own a welder and was considering getting one for this project. But money is tight, so I have cutout a top (14 gauge sheet) and it will be held up by 6 protruding stainless screws--two per side--and then there will be a bead of fireplace cement around to make it air tight. The prism will sit atop of that other metal sheet, which will have fireplace rope glued to its top in the prism's outline, making the prism easy to simply lift off for maintenance. For the hvac duct, why do you think it ought to be off the concrete floor? What better mass could one have than an existing concrete floor to add to the cob mass of the system?

[ByronC]

The firebrick core really needs to be insulated underneath (and on the sides), if you want a RMH that both works well and quickly comes up to operating temperature. And there is a concerned about the concrete spalling over time at the area directly under an uninsulated J-core.

For building on a concrete base or floor, the common practice is to first lay down a 2" thick base pad of clay stabilized perlite, both under the J-core and under the bench. Otherwise the concrete floor will sink or pull to much heat from the RMH, resulting in poor performance and insufficient heat to the living space, especially for a BTU limited 6" J-core.

Your firebrick splits riser also needs insulation, and a 1" thick wrap of ceramic blanket, contained with 1/8" or 1/4" square holes steel hardware cloth commonly sold as "rabbit wire", will save space there. Going that way, would you still have a minimum of at least 1.5" riser to "barrel" sides clearance? Or if you have to remake the "barrel", I'd be tempted to make it square, or maybe even hexagonal, to increase the heat shedding surface area.

Hope this info. is timely.

[DrewInToledo]

I agree with byronc. get that monster off the floor if its not to late Nirky. Think of the floor as a huge heat sink coupled to the cool earth rather than a thermal battery.

Good building practice on new home will add rigid insulation around the outside of the foundation to decouple the structure from the earth to create a thermal break. This results in less heat loss allowing one to become more "green", if you will.

[mannytheseacow]

Hi Nirky. It's good to know that you have a concrete floor. I couldn't tell from the photos if it was wood or concrete. At least with concrete you won't have fire issues. Is it insulated under the slab?

I think you are right that a 6" will heat you 500 sq.ft. space very well but Byron and Drew are right, you will need insulation around the core and riser. Personally, I would not couple any of the stove to the concrete floor. I'm saying this from personal experience. My own rmh is coupled to the slab and I agree with Byron that it is just a huge heat suck. My bench is 3 1/2 tons and a 6" was hard to heat that mass. Your slab is closer to 30 tons, and if it's not insulated under it..... You're fighting some big forces there. It might be frustrating to change for plans at this stage but I'm just speaking from "if I did it over again these are the mistakes I made".

[matt walker]

You've gotten great advice from the gang here Nirky, listen to all these guys please. I would do everything recommended above if I were building there with you. You will be so glad you spent a little more time and money to make it right. The one thing I will reiterate is the insulation around the riser is mandatory, the thing will not work at all without it. You are on your way to a great heater with a really unique look, keep at it!