Glenn Herbert

"Stumps" is Australian for what we call posts in the U. S.

A gravel pad is not suited to point loads, but rather something like continuous sills.

Looks like a good plan. Just remember that when you join half barrels at 90 degrees, you will have to extend the top of one barrel over the joining one to cover the whole space. This means either shortening the run covered by the barrel, or adding a partial "triangle" of barrel to fill the gap. So for your plan, the best thing would be cutting filler parts from a third whole barrel rather than alter the shape of the layout.

With two planters separated by a walkway, it seems you would have to have two downspouts one way or another. How long is the roof edge/gutter, and how long are each of the planters? The double-sloped gutter would accomplish the dividing, and one gutter could run sideways under the eave before dropping to the second planter.

I would be concerned about the triangular holes getting blocked with leaves, and a gutter that does not drain freely accumulating leaves - unless there are no leaves to worry about.

Too bad it turned out to be impractical to build your RMH in this house, but I'm glad that you foresee acquiring a house more suited to the job. If you do end up with a well located masonry chimney which may not be reliably safe or code compliant, a stainless steel liner with perlite poured around it can work nicely. I did two of those last fall in my family house which my parents built, and it was a fairly straightforward process which works excellently. My wife insisted on reusing her nice Morso stove in the basement and buying a beautiful soapstone stove for the living room fireplace hearth. The interior sections (most of the length) had almost no ash or creosote deposits. I had to extend the living room chimney about 5' above the existing masonry chimney for sufficient draft, and that portion does get creosote deposits.

The original living room chimney is 12 x 12 flue tile, much too big for a stove and costly to fill with perlite around a 6" SS flue liner, so I surrounded it with 8" galvanized duct and poured in an inch of perlite all around.

The basement has an old cracked 8 x 8 tile flue which tenants had lined with now disintegrating 6" stovepipe. The fireplaces and chimneys are all contained in a 32" x 10' block core in the middle of the house, so I put in a 7" SS liner to handle a future large batch box I want to build using that core for the bell in the basement. The tile being cracked and partly displaced, I had to slightly flatten/square the liner to fit all the way down, and poured perlite in to fill the corners. I made a wooden trough about 6 1/2" wide to hold 7" flue sections and squeeze them to get the right shape. It was picky but not difficult. By the way, you can get good solid stainless steel flue pipe from a company called Supply House, currently about $90 for a 5' section - not cheap but not exorbitant. (It was $70 when I bought the first batch of it...)

Very nice! I would use the thinnest brick you have for the riser, as it will heat up quicker.

Lots of points to address. I will start with a few.

There is no need to build the whole bell from firebrick; most of it can be ordinary clay brick, with just the part above the riser top level firebrick. If you build a shorty core, it appears that you only need to have firebrick on the part of bell wall that the (horizontal) exhaust hits. The whole combustion core needs to be built of firebrick, with a possible exception of the riser which can be made from ceramic fiber blanket or Morgan superwool (safer to handle before firing).

The shorty core does not use a floor channel with its spalling risk, but it does require a specially welded door frame for controlled air supply.

The shorty core development is described in the Development of a Compact Batchrocket Core thread. There are links to construction drawings scattered through the thread.

All-barrel systems do not have thermal mass. Single-skin bells have decent mass, but will take some time to start heating the room (maybe a half hour). I would advise a hybrid bell with either a barrel or a good-sized steel panel built into the bell, for some instant heat delivery. The more often there will be gaps between occupation days and the more often occupation will be short like just a few hours at a time, the more I would go toward metal in the bell.

"Steps" refers to jumps in system size; these systems can be built in any size from small to huge and still work, using the same proportions. A minor jump in size gives a significant increase in power. Going from 6" to 8" might double the power (just a guess). 8" is a very powerful core, and 10" would be a monster suitable for extreme circumstances.

Jake's setup may work, but it will not be a closed system as you originally envisioned. No matter what, it will require input from outside, in the form of new water or other energy source.

I would say insulating firebrick for the riser of a core would be fine, getting hot faster than hard firebrick, but concur that hard firebrick is the best material for the firebox.

Look up youtube videos on making a shower floor pan. We had to replace an incompetent professional's 10-year-old floor in a 6' x 8' custom built shower which had rotted down into the floor joists. We rebuilt it with a proper sloped subbase, membrane, and tile bed, laying standard tiles on floor and some walls. It is still working well a dozen years later.

If you need to replace or shore up framing, setting the new top a couple inches below original level will make it easy to match the floor outside the door.

For the radiant floor temperature question, the water in a radiant system is generally around 90 to 110 F. This is easy to achieve with the normal controls for such a system, including a (nonelectric) thermostatic balancing valve that keeps the same temperature in the circulating piping no matter the source temperature.