Glenn Herbert

I'm sure you could use the top of such a bell to hold a water tank and feed infloor heating from that. The height above the core would probably give safe moderate heat. Unless the upper floor is sprawling, I would think it could just heat the space(s) pretty well without the added complexity of infloor heating, especially as the floor would be warmed from the lower floor ceiling.

I have a couple of possible applications for a Shorty sidewinder. Can you share more information and photos of how you built the core, and how well it works?

In looking at the cut list and the assembly sketch, I am confused about the "B" bricks. In order for the exterior base joint lines to look as shown, the B bricks would need to be in the floor (rabbeted on three sides) rather than in the walls. Likewise, I don't see a purpose to making three sides of the lower end wall bricks rabbeted. I think you would want two B bricks, one cut in half and then rabbeted on three sides ("B2"), and eight A bricks (3 floor, 4 wall and 1 roof), all used whole. The rabbeting for stability is very nicely planned.

If your real to dollar example is relatively accurate, it sounds like the cast iron stove system would be very expensive. Building a Kuznetsov heater would probably be a much better option. I would plan to locate it in the wall between two major rooms, so that it could heat both at the same time. You would just need to make sure the wall had a masonry section for at least 10-20 cm in each direction from the heater. If  masonry is a typical wall material for your area, there is no issue.

From your climate description, I would say you probably only need a medium sized heater, unless your house is going to be quite large. The more open the floor plan can be, the easier it will be to use a masonry heater.

Kuznetsov gives exact brick-by-brick plans, but there is an alternative which may well give better efficiency: the bell-style rocket mass heater, specifically as developed by Peter van den Berg at batchrocket.eu. The firebox of the batch box needs to be built exactly as specified in that site (various sizes available, with a 6"/150mm diameter system size being most common), but the bell using Kuznetsov's principles can be any shape of simple masonry box you desire as long as the internal surface area corresponds to the system size. These have been scientifically tested to be extremely efficient, easily exceeding strict European standards.

The obvious answer is a small rocket mass heater. How cold do winters get? Do you need to give any heat to the rooms around it, or just account for ceiling losses? You might be able to make a tall skinny bell that would be only around 2' square, and not require wood stove clearances on three sides so it could be more out of the way than a wood stove. What is the floor structure, and access below if relevant?

If you don't want to replace the wood stove, you could stack bricks around three sides with a bit of air circulation space; a double thick brick enclosure would be stable even without mortar.

My bell-style RMH is at one side of the 25' x 26' main floor, and the entire floor is comfortable when it has been running, even the stone-floored entry hall at the opposite corner. Radiation from the mass makes all surfaces in sight warm, yet the heater surfaces are only pleasantly warm, not uncomfortably hot. The lofts are always the warmest places aside from right next to the heater.

I can vouch for the comfort of hydronic floor heat. When I built my house around 30 years ago I put in hydronic heat and a Polaris through-the-wall vented water heater. It was glorious to have warm feet all winter. But that came with the cost of propane, and when I discovered rocket mass heaters 11 years ago I built one and found that comfortable heat also, if not always the warmest feet... Wood from my land costs only some exercise and a bit of chainsaw gas.

As a potter who has moved to exclusively wood firing in medieval-style cob kilns, I have a lot of kiln shelves that I don't use. I saw that Peter used pieces of kiln shelf for parts of his Shorty development core. Would kiln shelves of appropriate sizes be okay to use for all the slabs? How much does thickness of slabs affect the function of the core? Obviously the riser box upper top thickness is irrelevant, but do the ports created with these slabs need to be a particular thickness? (The port at the back of the firebox can be made from standard firebrick.) I can easily double up layers of kiln shelf if necessary.

How far from the house is this pad located? The closer the better, obviously... touching the wall would be best, especially if you could take out a section of the exterior wall and have one side of the mass be the wall.

If you really want to use ducted air as the heat transfer medium, I would make the whole top of the bell out of metal as the bottom of the duct, then insulate the whole exterior of the bell as heavily as you can manage. Every bit of heat that doesn't go to the duct is wasted, aside from pizza cooking. There is no reason to make the bell any higher than the J-tube riser requires. Making it low and wide maximizes the ceiling of the bell for heat transfer purposes. I would add a piece of heavy steel above the riser to diffuse the heat blast on the bottom of the duct.

A low wide bell could have multiple stacks of bricks inside, even up to the ceiling (helping support the heat exchange surface), as long as there is still free airflow between stacks. Bricks inside the bell store heat which cannot be lost directly to the outside, increasing the duration of useful heating to the duct.

The pizza oven would work best positioned at the top of the bell cavity, as you want that very hot. A nice mild bake oven doesn't work so well for pizza.

One thing that is indispensable if you ever need to put screws or anchor bolts into concrete, or drill a hole through concrete, is a hammer drill. I have had a Harbor Freight one, the trigger broke and the tool was useless with no replacement parts available. A Makita corded hammer drill worked fine until I used it too hard and the motor brushes burned out, replaceable from eReplacementParts but I never got to it. I got a Makita 18v hammer drill, excellent rugged tool, but the chuck froze up a few years ago and I have not been able to open it even with a big pipe wrench and the drill body locked in a bench vise. Fine if I need to drill that size hole... I have a Ryobi 18v hammer drill that has been my go-to for several years now for modest sized projects. It is also a regular drill/driver for all purposes.

For serious drilling in concrete, a Hilti hammer drill is a professional choice, at a professional price. My best friend got one used at a serious discount, and it put holes through 8" thick granite boulders in a minute.