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Glenn Herbert

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since Mar 04, 2013
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Glenn Herbert currently moderates these forums:
Early education and work in architecture has given way to a diverse array of pottery, goldsmithing, and recently developing the family property as a venue for the New York Faerie Festival, while maintaining its natural beauty and function as private homestead.
Upstate NY, zone 5
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Recent posts by Glenn Herbert

I think we're all in agreement that all the joists need to be replaced. Digging out to give plenty of air space and even some crawl space if possible would be the best way to go. Just don't dig too far below exterior grade along the outside edges, so there is no tendency for the foundation to get pushed in by earth pressure.

What is the current foundation, anyway? Is there enough to shore up, or will it be easier to clear out and put in all new? It will need a shelf below the bottoms of the new joists (with flashing to keep damp from the joists).
1 hour ago
It appears that you don't have a secondary air supply. This is some added complexity, but may make a real difference in completeness of combustion. The best current practice involves a channel recessed in the firebox floor (so the air gets preheated) and a metal tube rising just in front of the port to inject the air where there is maximum turbulence. Look up "pre-port injector" for configuration and sizing.
6 hours ago
Glad it's working well for you! The black dust is soot, which means that you are not getting complete combustion, and it seems to be quite a bit for a short time in operation. It might be due to the burning properties of your softwood lumber, can't tell from here. Can you get some seasoned hardwood to burn a few loads? If you clean parts of the interior, burn as much hardwood as you have burned softwood so far, and inspect it again, you will get a good idea of the culprit. Either it will be cleaner, indicating the fuel as the issue, or not, indicating some problem with the build.
6 hours ago
The separate air intake at the base of the feed tube is generally an idea of people who haven't built RMHs for themselves. It defeats one of the first principles of the J-tube, the downward-rushing air that pulls flames down and keeps the entire fuel load from burning at once and making a strong competing chimney that would burn up out of the feed opening.

There is a common secondary air supply practice, called a P-channel (for Peter van den Berg who developed it), which consists of a way for about 5% of the cross section to be separated and protected from fuel blockage. It is generally implemented as a sheet of metal at the edge of the feed tube, extending down about 1/4-3/8" below the burn tunnel roof. This creates added beneficial turbulence and fresh air at a critical spot.

Operators generally find that at full combustion rate, the top of the feed tube can be blocked about 2/3 to achieve the best combustion.
19 hours ago
Part of waterproofing under a slab is giving the water an easier path to escape than up through the slab. A few inches of gravel under the membrane, with the ability for the water to drain away from the building on as many sides as possible, would normally work fine.
1 day ago
It's true that cob works best with a lot more sand than clay, but you first need to find out how much sand is in the clay you have. What is the source of your clay, and have you examined or analyzed it to find its composition?
When cutting dead trees, leaving the stumps taller could be useful not just to create microclimates, but to anchor the laid-down trunks and branches so they are less likely to get washed out of place by heavy runoff. In severe locations, I would anchor bigger logs, and lay small branches uphill to best trap sediment. A little sediment under and around brushy piles will give moister, shaded spots for pioneer plantings to get a good foothold.
5 days ago
I think it's a tricky line between helping to keep room air from escaping, and hindering exhaust flow at startup and possibly running. The prevention of downdraft is obviously a good thing no matter what.

In any event, I wouldn't use one that had plastic involved, but stick to all metal, just in case.
5 days ago
You need to have a height difference from feed tube to chimney for draft to work, but I think the main reason for the duct to slope is that you want to encourage the hottest gases to flow along the duct instead of pooling near the source. Bell technology has a large chamber where the gases don't flow in any particular pattern (ideally they become still and only move due to cooling and sinking to the exit, but that is not exactly true in ordinary sized bells); the hottest part of the bell is the top, which can be a tower or a bench shape.

I think it's not the barrel over the riser that causes the forced draft "push", but the riser itself. The barrel only secondarily adds to the draft; its main function is to get the exhaust gases down to bench level. If the core were to be below floor level so the exhaust didn't need to go down from riser top, it would have even stronger draft.
5 days ago
The RMH is actually a subset of masonry heater, with specific combustion core features. It also usually is owner-built with less expensive materials, but this is not a requirement.
5 days ago