Hi everybody,
Thanks for writing in with so many good questions!
We just had a nice, loooong talk with Paul, and answered a big whack of these questions. But we had to let him go on to his next destination.
So most of you can eagerly await the podcast.
There were a few specifics that were in the later part of the questions, that we didn't address, and that I can't recall addressing in other forums.
(Sorry TK - - general questions about length, etc. are part of the basic design, and I think we've covered those well enough elsewhere. The text of the book is in the public domain, so you might see about getting a copy from someone else and buying the whole PDF or book later on. )
Dale, Christian, John M - thanks for looking at our other posts, and it looks like the Ernie fairy has already visited Dale's additional topic.
This is part of why we asked Paul for a woodstoves forum, so that it would be easier to find the large amounts of information already discussed on this subject. (And as many people are 'calling their crazy a rocket mass heater', and other people may quite legitimately prefer another appropriate solution for their particular needs, we brought the whole wood-burny-things along without prejudice.) I like how the forums work, but if you wanted to help us develop the existing info into another format, like a wiki or e-book, that would be fine. Especially if people are willing to pay a couple of bucks for the extra work involved to edit what is, essentially, a re-telling of an existing book, or its sequel.
The link to our website:
http://www.ErnieAndErica.info. (The whole address navigates best).
Aaron and others - As far as tipis - it's possible to build an RMH in a tipi, the main issue is keeping it dry if the tipi is moved or leaks. A hot, wet mud floor is
nobody's a weird idea of luxury. I guess it beats a cold, wet mud floor.
But if it's an established year-round dwelling that is keeping the rain out fine, and just happens to be conical, then putting in a mass heater would be reasonable. It would basically be the same steps as any other installation, you'd want the barrel inside and the exhaust to the outside, or straight up the middle, given the tipi's draft profile. I'd take the tipi down, dig drainage, and make a compacted gravel (or concrete) support pad. I would probably lay ducting in a thick cob pad to make a higher, entirely heated floor, with no contact with the tipi walls, to maintain maximum flexible space. You will probably have to shift your lifestyle to fit around the barrel and
feed tube. I would be tempted to put the barrel near the middle, and make sure there's good air to the feed tube (open door or floor vent opening nearby, but not directly into, the wood-feed.) You could also try one of Paul's more portable mass-heater-in-a-box, with rocks or gravel added at each site for mass.
John C - sorry, never worked with calcium silicate, you'd have to look into its properties. Resistance to thermal shock sounds good, but it would also need to withstand the high temperatures that occasionally go well over 2000 degrees F; Ernie suspects as high as 3000 in some outlier dense-fuel-plus-draft situations.
Jess, Daniel, Michael: Building on a suspended wood floor involves two considerations: shoring up to support the weight (including water weight while building), and insulating to protect the wood from the heat especially in the burn area. We've done a raised stove on air channels that provide passive air circulation under the stove; this is a nice elegant touch but not absolutely necessary. About 2" of perlite should do it, and I believe we've gone into more detail elsewhere. We certainly have a plan for an 8" system on a wood floor among our offerings for sale.
Building on concrete: A concrete pad should not be the floor of the burn tunnel itself; it will cool (and dirty) the fire, and the fire will erode the lime out of the cement over time. But it is fine to use ordinary concrete pad for a footing, and insulate above it. Insulating below it also is ideal, but not practical with a pre-existing slab. I believe we've already talked about lengths in the other forums.
Clay questions are fun, but infinite variety makes it a hard topic to address in a public forum. In general, stickier is better, low-shrinkage is also good, and any old clay will work fine with the right proportions of sharp sand or other suitable aggregates. Silt, talc, and other 'softeners' are not as ideal.
We have no interest in working with refractory cement - it's an expensive and relatively low-temperature solution that is not re-usable like bricks or cob.
But we have been seduced into playing with refractory ceramic board and fiber-mat materials, and we are probably going to keep playing with those for certain applications. A 1" slab of duro-board or fibrefrax board, plus a half-firebrick to take the impact of
firewood, would probably be a good substitute for the perlite and brick in the burn tunnel. Any masonry insulation will have the potential to make dangerous fine dust, so you want to avoid smashing it up into lots of little fibers at any stage while coexisting with it.
Lori, Jesse, and TK:
Yes, Lori, stick to the stove dimensions for the exhaust.
And yes, technically, you can drop the diameter about 1" for better flow in the last part of the system, but for Pete's sake don't enlarge it, it will slow down too much as it cools.
Tight turns are not a problem if they are 90 degree elbows paired into 180 degree turns, we usually use one elbow and one Tee to make a cleanout at each sharp turn. HVAC guys will tell you this slows the flow down like an extra 5 to 10 feet of pipe, and they may be right. All the systems we've built include at least one sharp turn and work fine; this is an expected feature and factored into the general design.
For the work space: think about how often you use it. Heat penetrates cob at about 1" per hour, so if you are only in your shop a few hours a week, you may not get much heat from your mass. A non-cobbed ducting heater is not a good idea for smoke leakage and chimney-fire problems. So, either make a very small mass, or consider a more quick-heat system. Ernie's dad was tickled with a pocket rocket that burned 'stickers' (scrap wood) as a substitute for his old propane shop-heater. Obviously, vent to outside like a normal high-temp chimney.
Regarding upcoming workshops:
Thanks for your interest, everyone. Here are some upcoming dates, in various regions:
Will confirm within the next 2 weeks: Looks like a March quick intro, and a June full build, near Reno, Nevada.
An April introduction (1-2 days instead of a 3-day weekend) here in the Okanogan, and possibly another full workshop later in the year.
July and August will most likely be boat-related and private workshops, unless the owners decide to open these installations to a public workshop.
September we are in New England - in Vermont for Yestermorrow workshop the weekend of Sept. 15th (Friday-Sunday), heading up to Maine the next week or two with an installation at NewForest Institute the last weekend in September.
We know others are interested on the East Coast, and in the Great Lakes region. The question is, how interested?
We could use about 4 people who want to do the groundwork to organize and/or host additional events.
This could be committing to host a full workshop or pay us to supervise your work-party on an installation project. Or it could be a few phone calls and emails to introduce us as guest presenters for a
local venue. We can do a slide show in your local library, or a fire science night in someone's backyard firepit; or a Do-It-Herself demo on emergency heaters. Obviously, a larger site with shovels and bricks and
kindling lying around, will get you a much more hands-on learning opportunity. Might be worth drumming around your local forums or bulletin boards to see if there's enough interest that you could make a buck by selling tickets to see us in your town.
In my ideal world, we'd come across and do a workshop in the Great Lakes area the very first weekend in September. (Host needed)
We'd continue east, with a couple of private site visits or speaking events on the way, do a bang-up job at Yestermorrow mid-month (confirmed), and smaller events as available the following week. (Hosts for smaller events?)
The third weekend in September we'd visit the Common Ground Faire; install a working model in Maine the following weekend; and then we might need a week off before we hit 2 other destinations on our return.
We could easily make a detour southward in early October, if the North Carolina and Virginia folks could get together to coordinate a good strong location that can host overnight visitors from the whole region.
I'd love to stop off in Montana on the way there or back, too. Again, hosts needed to set up a site or event forum for these extra stops.
We prefer homestay hospitality over hotels, both to meet nice folks and to reduce travel costs.
Then we hightail it for Australia in whatever part of our winter is their almost-wet season. And stop by New Zealand to see some great friends of mine.
If our itinerary does not include your area, we are also happy to do phone consultation or email plans back and forth. We generally ask about $300 for either a site visit or a detailed long-distance planning session. This can double as your workshop deposit to reserve a later date for installation help. Long-distance planning sessions include scale drawings; on-site visits can include whatever you want us to look at for a couple of hours, rockety or otherwise. Note that our 45-minute podcasts often become 2 or more hours, so our 2-hour site visits can stretch to include lunch, dinner, supper, or occasionally all three.
and I've completely ignored Paul's questions.
paul wheaton wrote:I would like to hear stories of rocket mass heaters used in scenarios that were utterly illegal and how they got away with it. And I want to hear about how insurance companies hate them - and people that then express their love for insurance companies by building one anyway.
I prefer to cultivate a reputation for discretion where other people's fifth-amendment rights may be involved.
I will tell my own stories, as I did on the podcast, and I will tell other instructors' stories that I've heard them tell in public.
A good one is Ianto's surprise visit by a local inspector, who sat on his rocket bench for half an hour drinking
coffee and chatting before he asked about this thing he was supposed to look at. Ianto pointed out he'd been sitting on it for the past hour. He looked it over and decided that as it wasn't this, one rule didn't apply, and as it wasn't the other, it must not need to meet that code either, and went away perfectly happy to do nothing at all.
(We've mostly forgotten the details, but it went something like this: it's not a woodstove, and the wall wasn't combustible, so you don't need the woodstove clearances or permit. It wasn't a fireplace or open fire, so the chimney and foundation codes didn't apply either.)
Technically anything over 900 kilos (1860 lbs) has been exempt from EPA regulation by weight alone; they may change this ruling to specifically describe masonry heaters, but you could build a Rocket Mass Heater to meet the ASTM code for masonry heaters, it's just more expensive and slightly less efficient that way.
I suspect the building code offices would have to know something about rocket mass heaters before they can make them illegal. They fall tangentially under guidelines for heavy objects, or hot ones, but nobody seems to know for sure. Most of the people we've worked with, it's either in an outbuilding, or is the sole heat source for a non-flammable building, which is yet another reason for exemption from most applicable rulings. So I can't swear to it that ANY owner has done ANYTHING illegal in installing one.
The story I want to hear one day (hasn't happened yet that I know of): someone building a house on a hillside with a traditional Chinese or Navajo or Roman hypocaust (a slowly rising masonry channel under the house to heat the floors, lit from the outside) and having the conversation with their insurance company about how it is not a violation of the policy to light a fire under their house. What can they do if you keep lighting it, yet it never burns down? Stop letting you pay the premiums?
Owner-builders can get away with a lot more as they scrabble together their first home, than could a renter, mortgage-debtor, or a landlord of rental units. In a sense, if you are paying a
mortgage, you are essentially renting from the bank without them assuming any of the landlord's legal responsibilities.
Ernie will do some digging to see if the replaceable-filament
light bulbs still exist. I've seen scrappy kid-science projects to build one, and I suspect it could be re-created that way using a mason jar as the bulb, and installing a filament-holder and vacuum-valve in an ordinary seal-able lid.
And that's all.
G'night, and thanks for stopping by!
-Erica W
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