Our House

I’m having a bit of a difficult time finding an inexpensive solution for my rocket mass heater riser. I stopped in a Moerke well drilling yesterday. They were willing to offer me a piece of well casing at cost, just under $10/ft. That would make the cost of the riser ~$50. Ouch. With the increase in metal prices, an inexpensive riser is a bit like hens teeth. All the scrap is being turned in for recycle. I’ve been haunting the recycle yard with no joy.

I could use round flue liner at ~$15/18″ length. I’d need 4 lengths to get the total height I need. The total $ for flue liner eclipses the cost of the well casing at cost from Moerke. Plus I’d have to figure out how to join then cut the resulting mess to 53 1/2″. Hmmm.

Alternatively, I have the option of pouring the riser using refractory cement. I have all the ingredients. I’m a bit hesitant to do this as I’m already veering quite a bit off the straight and narrow in building this rocket mass heater. I can test fire the constructed riser to ensure it doesn’t explode or disintegrate or . . . well, you get the idea. And if I’m pouring the riser, why am I not pouring the burn chamber . . . You can see if I’m given an inch I’m gonna try for the mile. It’s just the way my brain works.

The weather still sucks. Wad’s off work tomorrow and we’re going to start on the foundation for the sun porch. I hope we have nicer weather. The forecast is for rain both Friday and Saturday. I want to try and get a batch of refractory cement mixed so I can see how it works. I don’t need to mix much for testing . . . a little over a gallon total, I think, just enough to see how it holds up to being toasted. I will need to pack it firmly into whatever I use for a mold. Air pockets are a bit of a guarantee it will end up in bits when fired off.

Our Barn

It’s a bit chilly today.  Not bad.  I don’t have the heater running, but I do have a quilt wrapped around my legs to cover my bare feet.

Last weekend a crew showed up to work on the barn.  The weekend’s crew was Lorr (our son) and two of his friends, Austin and Roy, and Terry’s brother Walt and my friend Mindy’s husband Wayne.  My friend LouAnn came to help with feeding the workers and Mindy came as Wayne’s chauffeur.  Terry stayed on the ground and ran the tractor, Walt ran the crew and Austin played gofer.  We’re close . . . there’s a bit more to do before the sheathing, tar paper and metal can go on the roof, but it should be just another weekend’s work.

Once the roof’s on I’ll encourage Terry to get some walls in and move everything from his shop.  I’ll have to do some fancy electrical stuff to make it happen, but getting rid of his current shop makes this a value added task.  His current shop is an old rotting leaky building parked on bricks in the middle of what’s supposed to be additional parking.  It’s got to go.  I can build another rocket stove in the new shop to keep him warm when he needs to work out there.

Mindy, in her supervisory role

On the house rocket stove front, I lit off my test stove to show a couple more people how it works.  Pretty cool!  This week I purchased more things to play with.  I now have a couple sheets of 6-6-10-10 wire and two more sheets of cement lath.  Also, a sack of silica sand, three sacks of mason’s sand and a bag of portland cement.  Once I get the riser pipe (6″x53″) I will cast the curved brick for the end of the burn chamber.  I’ve been debating how I’m going to set the riser, whether I’m going to weld on tabs or a flat circular collar or . . . haven’t decided.  I’m liking the collar idea but even that has some drawbacks . . . we’ll see.   I’ve about given up finding a water heater core to use as the container for the riser insulation.  I think I’ll swing by Ace today and pick up enough hardware cloth to do the job and stop trying to find something to suit at the recycle yard.  They’re starting to roll their eyes at me which is never a good sign.

The weather’s still pretty crappy, and I’ve got an infected toe (way too much fun at the cob workshop), so I’m filling time by doing more research.

I ran across a rocket mass heater where the exhaust flue leaves the cob bench and travels through the floor to exit the home. When you get to the site, the stuff on their rocket stove is almost halfway down the page.

I stopped in at our local supply place and ante’d up for fireclay, concrete and sand.  Wad’s picking it up on Friday after work.  I stopped in at the recycle yard to get a tall 40 gallon hot water heater to use the water tank as the container for the riser insulation.   No joy.  I’ll try again on Friday.

James (cob workshop) is planning an interesting rocket mass stove using a gas hot water heater. I hope he’ll continue to share his progress in designing and building his system.

My meeting with James this weekend provided lots of food for thought. This post is mostly just ideas, with a bit at the bottom regarding plans.

My brain doesn’t stop processing ideas. Something James said yesterday triggered an extension of my thought on a kickoff fan for hypocaust (obviates the need for a priming fire and solves the draw problem until the burn chamber heats up). To get a fan that will provide the proper amount of airflow (enough flow to keep the air moving but not so much it will put out the fire), the fan will need a potentiometer/rheostat. If you haven’t been following my posts you won’t know about my interest in hypocaust floors. Check out my original house site for more information

Because James mentioned cleaning difficulties for exhaust run through the floor, we had a brief discussion on air to water heat exchangers. I talked to Dan (brother) yesterday about water based heat exchangers. We kicked some stuff around, but the visit was too short (time enough for dinner and a rub for all the dogs) and we ran out of time. I’ll hit the topic again when we’ve got a bit more time and the two of us aren’t quite so tired. I’ve got to run up in the next week to get the last drive shaft parts for the mixer. Dan is a pretty amusing guy. Here’s his solution for a bucket brake (mixing cement for ferrocement).

On the heat exchanger topic, water based cooling systems for computers use air to water heat transfer. I’ve looked at a bunch of those systems while researching cooling for my computers. There might be some concepts of worth there. Radiators are fairly easy to come by and would be no problem to chain together. It would be worth experimenting to see how plugged they would get . . . As the system I’m planning doesn’t run to the need for heat exchangers, anything I come up with is strictly conceptual.

As to the whole concept of heat exchanger and rocket mass heaters, every idea I come up with ends in a complex multi-staged system. I don’t see that as being value added. Any system that transfers heat more than once isn’t going to be very efficient. I think it would be far easier/less expensive to plan how to clean the hypocaust portion of the exhaust. I know there are ways to vacuum all the hot air ducts in a home heating system. It shouldn’t be too hard to adapt that concept to cleaning a hypocaust exhaust system. And with welding skill, it would be possible to add cleanouts in appropriate places.

I think the rocket stove would burn better/cleaner if the burning end of the wood is held off the ash pit by a grate. The test I tried certainly did. Toward this end, I’ve been researching grills. I want to plan my rocket mass heater feed tube to accommodate a grate. I’ll have to do a bit of experimenting to find the right depth in relation to the feed tube. While doing research on grates, I ran into a great paper on the longevity of different materials for downdraft grates. As I can’t afford (and can’t find) RA330 alloy, 304 stainless, or any of the other really effective materials tested, I’m going to have to stick to what’s already formed, inexpensive and will work . . . hibachi grills. I should be able to find them at low to no cost and will plan my rms accordingly.

Nori

I met a fellow rocket mass heater fan at the cob workshop this weekend. It was great to have someone who knew what I was talking about. James is also interested in hypocaust heating, which was a double bonus.

Our current challenge involves wall penetration. I’ve been thinking and studying and working through what if‘s trying to get the best solution. With James’ council, I think I’m pretty close to a final solution. I’ve got to collect some material and do some testing, but I’m close.

One of the issues I have is dimension. Because I’m doing a wall penetration, and because I’m using a tall radiating container, I’ve got to do some calculations to get the proper dimensional relationship between the rocket mass heater elements. My radiator (pictured at right) is 55″ tall at the shoulder; 20″ taller and 1″ wider than a 55 gallon drum. The rise from the shoulder to the center of the radiating tank is 3″ and the curve is continuous from the shoulder to the center.

The Rocket Mass Heater book provides relational guidelines. A few key relationships are noted here:

• The feed tube should be rectangular or square, not round and the cross sectional area must be smaller than the same measure for the burn tube and the feed tube. The height of the feed tube should be short.
• The burn tube should be wider than tall and no part of the riser or exhaust cross sectional area should be smaller than the burn tube.
• The burn tube should be half the length of the riser.

I’ve got some testing to do ensure I maximize the burn.

I spent part of yesterday at an excellent cob workshop put on by Brina and Darin at their home in Stanwood. Along with four other participants, I learned much about cob. I also had the opportunity to compare notes with another rocket stove afficionado. It was definitely a red letter day.

My goal is attending the workshop was to acquire the knowledge/skill for mixing the cob I will need in the construction of our rocket mass heater. Mixing cob is pretty easy, but can quickly resemble hard work. Fortunately I won’t need a large volume, and my cob won’t contain straw.

We got the snout flap hinged today. We’re planning a swing arm that will keep the snout closed until we need to empty the tank. I don’t know how well it will work . . . time will tell.

We also got the snout added to the tank. For the inside of the tank we cut a ring flange that was stuffed into the end of the inner tube before the inner tube was run through the hole in the tank. The outer flange is the same material as the inner, but other than trimming the edge that wanted to stick beyond the back side of the tank, we did nothing additional.

The bolts heads are on the outside and are slotted and almost flat. I don’t know how good the seal will be. Again, time will tell. It doesn’t have to float, so I’m not going to worry about it.

I had to skip off to a friend’s yesterday to play computer games, so I dragged the auger assembly for her husband to play with.  He is an absolute wiz at machinery stuff.  Terry had been unable to detach the drive shaft from the auger gear box.  John found a painted over pin that held the drive shaft to the gear box if the shear pin failed, one of those handy safety things.  With the pin removed the drive shaft slipped right off.  Progress!

We tested our initial rocket stove design today, and it works great. It’s still out there burning away. The burn is really clean, which is great. In the picture, the bottom (insulated) stove pipe isn’t part of our planned setup, it’s just there to assist the draw.

For this stove I’m using two different sizes of fire brick. The light colored bricks are the salvaged bricks I got for 50 cents apiece. The buff are new (larger) bricks I picked up at our local redi-mix plant for $1.50 each. Between the two I can configure the layout to give me a good 6″ burn tube. I probably have enough brick to build a riser, but I’ll get better draw with a round riser tube.

I still have to get perlite, mortar and something to use for the grate. I’m using light stainless screen in the test setup for the barrier between the cleanout/ash chamber and the feed tube, but that will hold up for only a short time so there’s no point in using it. I’d love to find some heavy 316 stainless stainless screen as that will keep the embers in the burn area and allow the ashes to drop through. 316 stainless will hold up for about 4000 burn hours. Steel will last less than 1/4 of that time for the same material weight, so the expense of stainless is warranted. Finding stainless screen in the configuration I need may not be that simple, so I’m planning to use something else. Hibachi grills are fairly common. I’d have to replace it every year, but it’s affordable and available. We’ll see what I can find.

Terry and I were discussing the ash clean out access under the feed tube. I’d like to use 6″ square pipe with a cap. I don’t have a lot of room under the stove for ash clean out, so I may see about making a 6″x2″ slot with a tray. We’ll see what we come up with. This isn’t the only ash clean out we need, but it is the most critical.