So Jerry the rocket mass heater is STILL steaming away and not really getting hot after 2 weeks plus of daily firing, each lasting an average 6 hours. I'm seeking advice on how to get the mass dried out quick because, well, it's friggin cold and I'm sick of watching my peas and spinach get nailed with frost damage!
Here's the setup: we have a 26ft 5th wheel camper trailer with a 24ft long, 10ft wide "half" polytunnel "sunroom" attached along the SSE. The mass heater is an 8" system (galvanized ducting) - larger than CSA manifold into ducting tee, 90* turn with one end capped for cleanout, runs straight line angled slightly upslope 15ft to 90* elbow, up 5ft stack set at apx 5* offset to final 90*, exiting sunroom with tee set horizontal to reduce wind issues. The heat riser is 39" tall perlite/slip - 8" round inside with 14" ducting as surround. Drum is 55 gallon. The feed tube/burn tunnel portion was built with clay brick rather than firebrick due to money and time constraints. It takes a bit to get Jerry rocketing nicely with the extra mass in the brick, but once he's up to temp, he runs nice and loud, sucking down about three 5 gallon buckets of mixed birch, aspen and sugar maple over a 6 hour period. The one time I measured the barrel top temp I got a reading of 650*F, top of the scale for the oven thermometer I used - exhaust temp is warm on the hand, just a bit above room temperature, and very wet with barely any smoke smell.
The mass itself is onsite clay and offsite sand - no structural cob as of yet - plus a fair amount of aggregate/large rocks. Currently the bench is all of 6 feet long, 2 feet tall and 2 feet wide, plus a covering about an inch thick surrounding the remainder of the duct to the vertical stack.
First off, is it normal to have fired nightly for over 2 weeks and still have this much moisture in the cob? The first 2-3 feet of the bench is dried out most of the way at this point and gets up to about 160*F with a blanket thrown it. The rest is still steaming like crazy and doesn't even get warm to the touch (in fact, it's downright cool to the touch lower down near ground level). Second, I'm sure the temps are up to where they should be when the exhaust gasses get to the bench, and the exhaust is only slightly warm, so that heat is definitely going somewhere, but is ALL of that heat being used up in generating steam? And finally, should my exhaust be wet enough to literally drip out the end of the pipe?
I'm at a loss here as to what I should do to speed the drying process up and get the mass hot. We're getting temps down to about 10*F already (17*F as I write this at 7:30pm) and we're struggling to keep the temps 2 feet away from the bench above 40* with Jerry firing full throttle. My spinach has about had it and I gave up on the rubarb chard last week - the snow peas might stand a fighting chance if we can get this bench dried out quick.
I've been thinking that the wood might have just too much moisture in it. Most of this was saplings up to 8ft that I've been clearing from the property since august this year, so though it's mostly thin and dried out pretty well, it's not really well seasoned - with the amount of rocketing I hear and the area around the manifold getting up to 160*F through 4" of thermal cob, I'd think we're doing at least somewhat ok. I know wood pellets are dirt cheap so would maybe throwing a handful of wood pellets in to the feed tube to bring the overall fuel to moisture ratio down burn ok in the beast?
I not only really want this thing to work, we're partly relying on it for our winter heat (propane gets expensive).
Tristan; Keep burning ! it will eventually dry out and heat up. Keep it going for 12-15 hours at a time, if you can. A few days that should get your mass heating. If you are not sure about your wood being dry than try construction waste ( 2x4,2x6 cutoff pieces) buying a cord of seasoned dry wood, or at the least preheat your wood before putting it in the feed tunnel.
Tristan ; I completely agree with Thomas R., you should be heading in the right direction ! Due to your description i am guessing that you do not have much in the way of perlite
surrounding your burn tunnel area ! This is Very Early Ianto Evans and should work well for you once you get it up to temperature !
At this time you are just trying like the guy in the swamp up to his ass in 'gators- to remember he was there to drain the Swamp ! You are fighting 3 streams of water, the original
used to make up the Cob, the % of water in your fire wood which can be 15% or higher, and all of the water made by the recombination of Hydrogen 'released' during your woods
consumption of your woods hydrocarbons !
Once your Cob gets dried out your wood consumption will drop a lot!
For immediate protection a second layer of plastic over the immediate top of your vegetables should allow the unfrozen ground to keep your plants above freezing !
In addition to construction waste/cut offs look for pallets behind stores in strip malls, They are piled there because it costs money to throw them away ! They may have been
promised already but not picked up -so ask ! You may find that you are part of a 3-way deal which pays you for delivering- take first pick !
If you are trying to thin a patch of saplings then now is the time to become an expert on Coppice-ing and Pollard-ing your young tree stock as a perpetual way to keep your trees forever young, and have easy to split small wood tat dies fast! Less desirable 'weed' trees can be allowed to start making young leave and then girdled to allow them to dry out
as standing timber, and then cut up after the worst of black fly season ! Time will tell all! Sorry the answer is not more positive For the Good of the craft ! Big AL !
Success has a Thousand Fathers , Failure is an Orphan
Big thanks to both of you. Yesterday and last night I fired for about 12 hours straight, finally putting it out about 3am, and started toasting my wood on the top of the barrel - mostly split pieces of 1-2" diameter saplings. Jerry really started to get going on the pre-dried/pre-heated wood - got the sunroom temps up to about 50* while we saw 7* outside. About 5 feet down the bench I was starting to see surface temps up to 85-90*. Today, there was a wonderful brown icicle hanging about 3 feet off the exhaust outside - the first 3 feet of mass was still warm to the touch (at least 100*) by 3pm and we got it fired up again by 4pm with plans to fire until around 2-3am again. I scouted for some good dead standing wood and brought back about a week's worth of dead, dry maple and fir that I'll be mixing in with split/toasted saplings. I'm about an hour from the nearest city and the local towns are small enough we don't even have strip malls, so it's definitely a back-to-the-land thing when it comes to wood - pallets and construction cutoffs are basically non-existent and grabbed up by the locals faster than they come in. And with every house in the area running 2 or 3 wood stoves, prices for even a cord of green wood are ridiculous.
Al: you're right - I sort of skimped on the perlite around the burn tunnel - had a little less on hand than I planned due to a mixup when ordering bags so only put a 1-1.5" layer around the bricks with the rest going to the heat riser. The 3-4" layer of the cob around the burn tunnel gets HOT hot when firing and I've been worried about cracking, but so far so good and we've had some darn hot fires going in there especially last night. And right on about the coppicing - as I clear areas that are destined for pasture, savanna and various "themed" forest guilds (walnut/black cherry, oak/apple, etc) I'm purposely leaving behind stumps for the sugar maple and white/yellow birch to sucker, plus I'm pruning poles for future years firewood. I plan to keep some rotations going, focusing mainly on maples, birch and willow (property is pretty wet), all of which should eventually double as goat munchies I think the best thing about this RMH thing is that I can harvest firewood for a year with horticultural shears, loppers and a hatchet - no toxic petroleum gack or noise pollution necessary!
Good idea on girdling trees for future firewood harvests - hadn't thought of that one. I've been thinning a lot of fir, the one nearly useless tree we have in abundance, but taking the entire tree down - would be a lot easier to not have to lug those around to piles.
Wanted to post an update on the stove. It turns out that we're just really really wet here and this is leading to continuing issues. The majority of the mass is steamed out dry at this point and heats nicely, but moisture from the ground continues to wick back up into the mass about as fast as we can dry it. Dead standing timber harvested weeks ago, stored in a shed off the ground, is still loaded with moisture. The latest discovery has been that the ducting in a portion of the bench slumped a bit at a joint allowing water to accumulate. Every few days, I shove a mop in there and take out a gallon or so of water to get things dry.
In such a wet climate, I guess a RMH in a polytunnel isn't the smartest course of action.
That said, we're seeing temps of 180*F during firing on the surface of the mass, just above the manifold where it's about 4" thick pure cob, when everything's "dry" and we've fired daily for 8-12 hours at a time. Farther down the bench where it's about 1 foot of cob and rock, we're getting temps to about 100*F at the surface. The polytunnel, now bubblewrapped for extra insulation, is seeing air temps during firing that reach the low 70s on nights that drop to single digits (-14* was our coldest so far and our temps in the polytunnel were in the low to mid 60s). The barrel throws off most of this heat of course - temperatures stabilize around 45-50*F once the fire's been out for several hours.
The real kicker is in positioning of the system and the dramatic effect we've had on comfort levels and propane usage. The barrel is apx 4 feet from the side of the RV and we have a window directly in line with it. Temperatures at the window have reached the 90s at times during firing while outside temps are in the single digits. The mass is run along the length of the RV and the chill we'd expect on especially cold nights is all but gone, even hours after shutting the system down for the night. So far, for the month of December, with overnight low temperatures that were below zero for about a week straight and enough wind to chase a polar bear to his den, we've used about 40-50lbs.
Again, big thank you to Thomas and Al I was getting pretty discouraged there for a while but things have definitely improved
I've rebuilt the heat riser twice due to the sheet metal ducting warping from the heat, so this last time I added a significant amount of clay to the perlite/clay mix as well as a small amount of peat moss (figured it'll burn off much like sawdust) and I packed it TIGHT. Total clay to perlite to peat moss was probably 5 parts clay slip to 10 parts perlite and maybe 2 parts peat moss. Lo and behold, it's holding up beautifully and Jerry runs stronger than before!
We have a significant problem with the ducting running through the bench where the ground subsided and caused a valley about 10 feet in - water collects there and we need to drain it every day or two. Late this summer, we're going to tear the bench apart and rebuild to hopefully correct this because it's become a major pain in the butt. We'll also likely be adding another 10 feet or so of ducting before the exit stack as there's quite a bit of heat in the exhaust at this point. I'm planning a 5-7 foot dead-end bench extension as well to hopefully keep the east wall of the hoophouse from icing up at night.
We've switched to burning about 80% larger split wood as the saplings are just too time consuming to prep in quantity at this point. I can split twice as much as I can clip up in saplings, so for this winter at least, I'm cutting and splitting logs. We're able to get away with full rounds up to about 4-5 inches in diameter without choking the air flow, but anything over 3 inches tends to cool the burn down a bit.
We've burned probably around 2-3 cords of wood so far since this fall, the majority of that during december and early january, and as we burn it's like the thing just gets more and more efficient. I can see burning maybe 4 cords total during a NORMAL winter with the way it was running but maybe only 2-3 cords with how it's running now. With more bench, another 55 gallon drum or two of water and some hay bales stacked strategically around the east and west walls of the hoophouse, we might get that under 2 total.
I really wish we could have built it right in the living room because running in and out for hours on end every night is pretty frustrating. We burn about 6-8 hours nightly and have generally kept the hoophouse/sunroom above freezing even during temps down to -15*F. With temps 0-10*F, we're averaging about 55-60* air temps and with low 20s outside, we can get it into the 70s some nights. Rain and snow really puts a damper on the draw I've noticed. The colder and dryer it is, the harder the draw becomes.
The bench is staying nice and warm day and night now, reaching some 140*F near the manifold on a regular basis and averaging in the 100* range over the rest. We moved the BSF bin up on the bench to keep them warm during the cold snaps - even had to put the red worm bin on the bench (way down near the exit stack) after three nights of -15 to -20 readings.
Currently, the woman of the house is complaining because the feed tube area is getting so hot after a few hours of burn that she's burned herself on the outside of the cob (knew I should have put more insulation around everything). Every time she puts a piece of split green birch in the feed tube, it bursts into flames instantly she says. I keep telling her that's a good thing!
The other night, we successfully baked a 14lb turkey on the barrel top with a makeshift foil dome covering it as an oven. Took about 4 hours
Tristan Vitali : Thanks for the Report, If your W.O.T.H. is willing to load Your RMH, be a Sport and buy her a pair of welding gloves! Glad to Hear about the coppicing
plans, it definitely requires re-tinking how to handle the small wood !
I may have mentioned an aversion to all things U-Tube, There is a lot of crap out there and lots and lots of unsafe use of chainsaws Recorded for posterity and for
viewing latter in a court of law !
BUT, if you want to go looking for Saw horses Saw cribs, saw bucks, or Redneck wood holders There are lots of ways to make Holding racks that let you you use up
old 2x4s to make Frames to stack Small wood (Coppice!) into to allow you to process cords of 'cut to length' small stuff quickly !
Its worth repeating, to get out there and check things early, it won't be long before your neighbors are hanging buckets on maples, The small stuff you girdle between
now and Black fly season will be very dry by fall !
I think that the drainage issue is sometimes forgotten by those of us who had good luck with one or two builds and are sitting on our asses feeling proud, I think it
Depends on your options, With an insulated outdoor vertical chimney I would just as soon see it drain that WAY ! E& E Wisner have had good luck in letting it drain
back towards the Transitional area, Soon to re-evaporate and maybe make it outside the next trip !
It is always a weird sight to see a yellow birch sapling or lager that Coppiced or volunteered as a seedling off of a stump, and now the stump is long rotted out,
making the Sapling look like an ENT Caught in the Act of Pulling up Roots to go for a walk !
Keep warm, stay Safe ! For The Craft ! Big AL !
Success has a Thousand Fathers , Failure is an Orphan
LOOK AT THE " SIMILAR THREADS " BELOW !
You showed up just in time for the waffles! And this tiny ad:
rocket mass heater risers: materials and design eBook