so heres the rundown, built your L bench 6" rmh, did it in my basement, for a few reasons, slab floor to support the weight, center of the house footprint with existing center single flue chimney, un insulated floors for radiant heat transfer etc... only a couple variations on your design, a 55 gal drum, un insulated fire brick heat riser, and a pretty sizeable rock wall perimeter for visual effect and added mass... heres the thing, finished cobbing 5 or six weeks ago, cob is hard as a rock with surface cracks, cooked that thing for 15 hours thanksgiving day, the bench was meh, warm. mayybe 65 degrees. my concern is that theres is too much cold thermal mass in the hollow block foundation and uninsulated slab. now, i put down a 3" slab of portland stabalized perlite before bui'ding to shield the thermal mass from the cold slab, but i seem tp be losing the battle, also, frequently get condesation running out of my final cleanout, and the stovepipe exhausting to the chimney, which is, 10" from my barrel, is cool enough to put your face to, just looking for input thanks guys-mike from maine
also, i know, i get the whole, make it the heart of your home thing, put it in your living room... i have a 1952 cape with a 10x14' living room, trust me the beast would not fit. also, if i f-ed it up i didnt want a 8000 lb paperweight in my livingroom.
I also built my mass directly on a cement slab. I did a calculation and found that about 50% of the heat going into the mass is heating the cement slab. The slab will eventually heat up but it will take a tremendous amount of energy to heat it. My bench will get warm as it is only 2.5 tons of material.
Are you interested in modifying, rebuilding the bench? If you isolate the bench thermally with insulation it will heat up much faster. Can you put down a layer of supports and then insulation in between the supports?
Mike ; Despite cracks ,if you're not heating up ... and you're getting lots of moisture at the cleanout... Then ... your cob has not finished drying on the inside yet. How hot is your barrel top ? How long is your mass ? Are you using a digital temp gun ? What are the temps ? My RMH is in a greenhouse, was built slowly at the end (hot) part of summer , being in a greenhouse it gets burned every day, almost all day ... and it took at least 3-4 weeks or more before the mass temps started rising at the far end. As your moisture problem is at the last cleanout I suspect you haven't gotten the whole mass up to heating temps yet. Bottom line ... KEEP BURNING, it will get better !
thanks tom, yes, burn burn burning lol, few things, it IS insulated from the slab, with a 6 to 1 perlite to portland slab 3" thick, i knew before building that was a must or all id have are happy worms under my house. i for all intensive purposes built e replica of amy and ernies 6" L bend "code" bench they made, theirs was brown with reclaimed tile here and there... anyways, about 25ft of horizontal run before a 5ft vertical pipe near the barrel dumping into a single flue mason chimney in the middle of the house. the drum is a 55 gal drum, and she rockets like a champ, havent heat gunned it yet, but the barrel puts out some serious heat, have floor registers cut in the first floor right above it. one mod i did that was for asthetics but did change some function was add a hand hammered copper top to the drum, which looks boss, but also adds a thin layer of airspace between the copper and the barrel, thus insulating it, so much less heat comes off the top than before the copper, BUT, sends more heat down into the bench, which i dont mind, and was hoping that would aid to make the bench super toasty.. plan on heat gunning soon. id say currently the barrel gets about 600, the bell of cob around the barrel gets to be 100 the bench seems to get to 70? maybe not that much, and the final stove pipe, which is only about 10" from the barrel may only be around 90 after hours of burning... just gunna keep it crankin, i just hope it wont be this much of a struggle until i finish and insulate the basement in a couple years. thanks guys.
Another thing you might want to try is covering the mass with furniture blankets, a sleeping bag, or something else to insulate it - that will help get that mass hot faster. If you notice there's dampness to the material you use to insulate, it's coming from the bench still. You'll be amazed how much moisture will come out of these beasts before they're really bone dry. It's a battle to get them dried and warmed up as you have a lot of mass there to heat...thermal inertia...but once the ball is rolling it's easy to keep it hot.
I wont even estimate how many tons our bench is now but more than half of it is *still* drying now. We (re)built it over the month of August. Over and around the manifold area, I put in a HUGE amount of cob as well as several large rocks that I could barely lift - that area was only getting up to about 90*F internal temperature (so said the meat thermometer) just a month ago, and still steaming away visibly on colder nights even though it appeared dry and showed some cracking. We covered this once the visible steaming stopped with an old sleeping bag for a few weeks to help get it up to temp. We're now keeping temps between 120 and 140*F internal with the low range being after 8-12 hours since the last burn. 10 feet down the run, however, we're still battling the 65*F mark as the final bit of moisture gets driven out.
Good luck and be sure to update as things get toasty