Eric Bristol

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since May 06, 2013
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Recent posts by Eric Bristol

I would just like to give an update my testing.  

I created 3 test bricks of 3 different ratios.

#1 - 75/25 refractory to perlite
#2 - 50/50 refractory to perlite
#3 - 25/75 refractory to perlite

#1 was extremely strong and had the most mass. In the mold I used, this mix ended up to be 1.5" thick. I couldn't break it by setting the brick half way over the edge of the table and using all my weight (230#) to break the brick.

#2 was strong and ended up 1.25" thick.  I was able to break this brick using the method above. But I had to put all my weight on the brick.

#3 was weak and ended up 1" thick.  I was able to break the brick in half with my bare hands without much effort. I also used too much water in this mix so there was a thin layer of refractory settled on the bottom of the brick.

My original plan was to cast the base and riser tube as one unit.  But after doing some general estimating, I think the entire mass will be too heavy.  So I will cast them separately.  

For the riser, I plan on using a 40/60 refractory/perlite mix. For the base (wood feed and burn chamber) I plan on using a variation of 25/75 to 75/25 refractory to perlite mix in the different zones of the base.  

2 years ago

Glenn Herbert wrote:I think you have been misled by a lot of youtube videos, which are not made by people who build rocket mass heaters regularly, but by experimenters who are familiar with woodstoves and maybe rocket cooking stoves.

I'll start with this because you are 100% correct. I've also read about 30 build threads in this category so I'm meshing the information together. As you can understand, it's easier to comprehend the information presented in a visual vs text format.  

Glenn Herbert wrote:I'm sorry, but you seem to have misunderstood the way a RMH core with the 1:2:4 proportions is supposed to work. The 8" dimension is the vertical wood feed AND air intake; the 16" and 32" dimensions are correct. There is no front air intake. Also, the feed works better completely vertical than slanted.

Okay. I thought by separating the air intake from feed tube it would give me control over the amount of air to fine tune the burn. Are you saying that controlling the amount of air entering the heater isn't important?  

Glenn Herbert wrote:
If you think that a front access port is needed for ash cleanout, I can assure you that it is not (unless maybe you have gorilla-sized arms). I have cleaned a 6" x 6" J-tube with my bare hand, and with a sardine can on a short handle, easily.

It was primarly to be able to control the amount of incoming air.

Glenn Herbert wrote:A 5" x 5" core would be trickier, but for a 6" duct size system, a 6" x 6" core would be fine.

I planned for a 5" x 5" core based on the information I found on this site in reference to matching the area of the 3 components of the J tube design. 5" x 5" square tube has an area of 25". A 6" round tube has an area of 28.27". Where as a 6" x 6" core has an area of 36".  It's possible I'm also confused about that concept as well.

Glenn Herbert wrote:Can you give us any information about your plans for the system? What kind of mass, how long, what size of space and how insulated, how you use the space, what your climate is like?

I don't plan on heating a mass with this design. So it should be considered a rocket heater. I apologize if there is a rocket heater category on this forum and I missed it.  

I plan on using the rocket heater in my 1400' garage. The walls have fiberglass insulation rated @ R13 and the ceiling has 8" of blown cellulose rated ~R24. I like to spend my evenings tinkering on vehicles or building projects.  I live in North East WI where the heating season is relatively short and there are very few days where the temperature falls below 0 degrees Fahrenheit.  

I don't need the entire garage heated to 70*. I plan on positioning the rocket heater in a location where the radiant heat from the drum will be near the area I work in. It would be nice to fire up the heater 30 minutes before I plan on working in the garage and run it for up to 4 hours a night.

I plan on using a 30 gallon steel barrel as my bell but they are hard to find in my area. The local scrap yard sells 55 gallon drums for $10 but crushes 30 gallon ones for some reason. Brand new they are $45.  I'm hoping that the thin gauge of the steel barrel will be great for radiating heat into the space.

Glenn Herbert wrote:It may be helpful to explain that having the wood feed capped off and air coming from the front will let the wood get hot and char up into the feed tube. When you open the cap to add more wood, you risk a puff of smoke or even flame bursting out of the top and singeing your eyebrows off. The air intake pulling down from the top keeps all the fire and smoke moving in the right direction, and you can clearly see when you need to add more wood.

I never considered that.  I was more concerned with having control over the amount of air entering the burn chamber. As I have observed on Youtube, the burn can be dampened to optimize wood use and output temperature.  I've also observed the "capping" of the feed tube and use of a front air intake on several RMH/RH that were converted to run pellets.  I have no plans on running pellets in my heater.

Glenn Herbert wrote:The 16" burn tunnel dimension is a maximum, and if your barrel clearances allow, you can make it shorter and get better draft.

That is great to know. I can make it shorter and would prefer a shorter design to safe space.  I've seen other builds on this forum at 1:1.5:4 or 1:1.3:3.75 ratios.  I tried to find a thread on the general concept of the ratio minus the specific detail of build but fell short.  

So "In General"

If the equation is 1:X:Y
X can be <= 2 but has to be > ?
Y should always be as close to 4 as possible?

Glenn Herbert wrote:Keep the feed vertical, though. The best method I have found (also recommended by everybody I have read) is to lean the sticks away from you so that they lean against the burn tunnel roof, and air has to go down on your side of them or through and between them to get to the fire. This keeps the tops of the sticks a bit cooler and helps preheat the air. If you lean the sticks back toward yourself, the air can flow down on the far side of them and leave some of them starved for air, while a lot of air goes into the burn tunnel without meeting the burning coals.

I understand what you are saying. I think I have seen an image on this forum demonstrating the concept.  It's like the sticks are stabbing the fire vs the fire flowing from the sticks.  
2 years ago
Would you mind critiquing my design plans?

I hope you can see the image well.

Using the 1:2:4 strategy, the intake is 8" long, the burn tunnel is 16" long, and the riser is 32" long from the center points.  

For the intake I plan on casting a 5" x 5" square tube. The riser and exhaust with be 6" round stove pipe.  The wood feed is going to be 5" x 5" 1/8" steel tube capped off at the top.  All the air will come from the front of the stove. I plan on installing an adjustable plate to control the amount of air flow.

Pardon my paint!  
2 years ago
Thank you for the responses.

thomas rubino wrote:That's not a bad price for refractory. Way more than fireclay but should be more durable than the FC mix Your going to want to experiment. Try a small batch at 50/50 then try a batch at 70/30 I think a 50/50 mix might be to fragile in the feed tube but  be fine in the burn tunnel and riser.  The fireclay mix is known for wear issues in the feed tube (trying to push wood down) When casting a core you should be able to vary the amount of perlite, using a refractory heavy mix at the feed tube end and then add more perlite as you form the burn tunnel . The riser can be cast with a "fragile mix " heavy on perlite.  

I went out and bought a bag of the Hi-Cast and perlite last night. I made bricks of a 50/50 mix and a 75/25 mix to test them out.  I want to let them dry for 48 hours before handling them.  Thanks for the advise.

Glenn Herbert wrote:I would suggest making a richer refractory mix for the inner surfaces of the feed tube and burn tunnel, and surrounding that with a highly insulative mix.

That sounds like a good idea.  

Glenn Herbert wrote:The riser can be mostly perlite with just enough refractory to hold it together (make test bricks with various ratios).

I'm going to make a 25/75 refactory/perlite mix tonight for testing.

Thanks again.
2 years ago
Hello everyone.

This is my first attempt at a Rocket Heater so keep in mind I'm very new to this.

I would like to build the burn chamber and riser tube of my RMH using Fire Clay and perlite.  Unfortunately, I can't find Fire Clay (Motar Clay) anywhere.  I called all the fireplace and stone dealers in my area. I called all the material suppliers and all the places they recommend and no one carries it.  There was one place that was willing to special order Fire Clay for me but they said they would only do it when they are ready to place an order with that supplier and after they order it would still take 4-6 weeks for delivery.  However, they recommended a product they carry as a substitute. Alsey Hi-Cast 45 Refractory Castable.

I was hoping to get some input from the community on if this product to determine if it would make a good substitute for the traditional Fire Clay/perlite mix.  If not, how could I modify it to make it work.  

I had the retailer send me the data sheet on it.


Dry, hydraulic setting, high duty refractory castable. HI-CAST 45 is a general purpose 2700°F castable effective for most standard operating service conditions.


P.C.E............................................................................... 31-31½
Temperature Equivalent (melting), °F ......................3061-3090
Service Temperature (max. recommended), °F................. 2700
ASTM C-20 after 2500°F
Apparent Porosity, %.......................................................... 25.9
Apparent Specific Gravity g/cc ........................................... 2.71
Bulk Density lb/ft3
............................................................. 125.2
ASTM C-113 Schedule B % linear
Reheat Change at 2550°F ..................................................... 2.2

TYPICAL CHEMICAL ANALYSIS, Wt. % (calcined basis)
Silica (SiO2)........................................................................ 46.25
Aluminum Oxide (Al2O3) ................................................... 44.88
Calcium Oxide (CaO)........................................................... 4.30
Titanium Dioxide (TiO2)....................................................... 1.90
Iron Oxide (Fe2O3)............................................................... 1.65
Potassium Oxide (K20) ........................................................ 0.60
Magnesium Oxide (MgO).................................................... 0.32
Sodium Oxide (Na20) .......................................................... 0.08
Total.................................................................................. 99.98

Recommended water content is 9-12%. [2.5-3.5 US Quarts / 55lb bag.] Actual water content may vary depending on job site conditions. Coverage 55lb sack = .44ft3 Stir dry mix thoroughly and add the correct ratio of water. Return unused portion to the bag. To avoid moisture absorption, store HI-CAST 45 in a cool dry place. Under normal atmospheric conditions, set will occur 8 to 10 hours after HI-CAST 45 is mixed. Heat can usually be applied after 24 hours; however, starting temperature must be held below the boiling point of water to avoid the formation of steam which will result in excessive cracking, spalling and lower strength.


The two main chemicals in the mix are Silica and Alumina.  As I understand (in general terms), the Silica and Alumina work together to create the "Fire Rating" and "bonding agent" for the mix.  I believe I could this mix in it's raw form to case the burn chamber and riser tube for my RMH.  However, I don't believe this mix will have the insulating properties that are necessary for the burn chamber and riser tube.  Is that correct?  

If so, what other materials could I add to this mix to get the insulation properties needed?  If I add perlite to this mix at a 50/50 ratio, do you think it would cause the mix to be too brittle?  Are there any other readily available materials I could add to the mix to increase the "bonding properties"?

As of right now, the Alsey Hi-Cast is the only option to get my project started this year.  They charge $48 for the 55# pound bad.

2 years ago
I would like to thank everyone for their replies. It is very helpful to get opposing viewpoints on topics.

Interestingly enough, there is a local ICF manufacturer who specializes in Vertical ICFs I have been in contact with.

They has provided me with a materials quote for their vertical ICF system and are looking working on getting subcontractor bids.

However, my focus has switched from ICF to Traditional Stick construction. The R25 upgrade my builder provides is a Blown in Blanket. They also spray foam around all ceiling fixtures and the floor joists. They have an energy expert who blower tests the home for Focus on Energy (Energy Star) certification. He has a computer modeling solution where he will be able to estimate the energy performance of the home before it is built. He can different models to determine the RIO of increasing or decreasing insulation.

Insulating a home properly can have a huge payoff but chasing the last bit of of inefficiency can be expensive. At least at that is what I am finding out.

My new contractor is well aware of my energy efficiency goals but I feel like he is still missing the mark on some things. I asked for 3 options for Windows. My builder has their preferred Jeld-wen Premium Vinyl windows they put in the majority of their homes. These are considered Jeld-wen's 3rd level of their window offers. I was also provided a quote for Pella 25 series (cheapest product from Pella) windows and an Anderson Fiberglass window. Price wise, the windows were ranked:


Performance wise, they were all about the same because they are Low E, Argon filled, double pane windows. But there was a $2,000 increase in price going from the Pella's to the Jeld-wen and $2000 from the Jeld-wen to the Anderson because the windows are of different quality and build. The Uvalues are:

Pella - .26
Jeld-wen - .27
Anderson - .29

The cheaper windows had the best energy performance.

So they still have a little to learn!

I am going to do some serious research on the Pre-cast concrete panels.
5 years ago

Jay C. White Cloud wrote:

Good luck and if you really need to, give me a call...these long emails kill me as I tend to be long winded.



Thanks for the offer Jay. I'll keep that in mind!
5 years ago

Rufus Laggren wrote:our at least an overview and some understanding of what kind of process you're getting into and the different viewpoints, motivations and constraints on the participants.

Some general rules of thumb:

1) The way it starts (with any associate) is the way it's going to continue. Forewarned.

2) Expect and budget your time to talk with a LOT of people. When you can't personally develop total expertise in a particular area you must rely on as much research as you can afford and then spend time talking with at least three and as many as 7 or 8 contractors (or other people) in that field. Talk with as many people as you can afford the time for and take good notes so your time is well spent. You start to see common threads, agreements, recognize certain types of business practices that you like (or don't); you also develop a feel for and start to recognize people who a) _know_ what they're talking about (not all that common actually, even w/a major degree after their name); b) Are willing and able to work with you in a worthwhile way; c) evince good business practices that you can have confidence in; d) relate well with you.

If you can't be deeply involved (it will consume your life for the duration of the project) you may want to use the services of a management agency to monitor the job of the GC. This is not a very satisfactory situation - it's expensive and it _will_ involve some conflicts. But if you can't spend the time needed to oversee the job on at least a weekly basis it's something to consider. Again, read some books about the residential home building process to pin point alternatives and key players that might help you.

If you work directly with the GC, expect to visit the job site at least weekly and inspect everything carefully as you can. You _must_ raise issues you see and get them remedied or clarified to your satisfaction as soon as possible - that's _your_ job and it's a LOT of work. You need to have at least bi-weekly milestones and generally conform to good project management process - you _need_ to know when there's a problem to attend to. The specific methods you use to manage the project (manage the GC) depend on you and the GC but you must actively manage it IMHO. You will likely spend 15 to 20 hours a week (if you're working a "day job" full time, otherwise a lot more) on this and other aspects of the build for some months preceding the build and some months after the job is technically finished - as well as during the actual build. Try very hard spend a couple hours a week personally inspsecting the jobsite. You're not an engineer or architect or builder so you don't expect or try to confirm _all_ the details of a build; that's not realistic.. But you _can_ look closely at everything, focusing on the latest issues and milestones, get an overview of the job, show the GC and others that you _are_ most interested and paying close attention and perhaps most importantly give yourself a feel for the actual physical house which in turn will influence your real time decision making. And of course you will often see things that don't line up with your expectations and need a little clarifying.

Nobody got this far in life w/out having some smarts and you absolutely have the right and the need to apply any and all intuitions, skills, training, energy and any other advantages you might accumulate to this project. You more or less owe it to the house and yourself and the world in general. You mention your wife and if she can join actively in the project you'll be way ahead. Don't hesitate for one second to play good-cop bad-cop with the people you have to work with. Only remember they're human too and we're all in this together.

Best luck. It's a damn fine challenge and you're sure to learn a whole lot.


Good tips.

I do have time to get deeply involved. My new home will be built on the same road my current home is one and it is on my commute. I will be there often because I drive by at least twice a day. The home is going on a 2 acre lot. Half of the lot is covered with trees. I have spent many evenings and weekends clearing the lot for construction.
5 years ago

R Scott wrote:You are ONLY out a couple grand and a couple months now. Once you are in the middle of a build, you can be out A LOT MORE--tens or hundreds of thousands and years of time can be lost to a bad GC (or sub). Been there, done that. I know many that lost everything because the builder shafted them and then the bank took the land to recoup their losses.

Very true. I am not too upset about the money. I am more upset about the time. My money could have been spent a little better but I can not get my time back. In the grand scheme, a few thousand bucks and 4 months is not that bad considering the amount of money and time some people put into planning their new home.

R Scott wrote:You need to be 100% in agreement with how the GC has built other homes, because most don't like to do anything different--not out of pure stubbornness but a matter of "stick with what works" when money is on the line. They are liable if your ideas don't work in many states. In the same vein, you need to listen (not necessarily follow, but consider carefully) to the experts as they know more of local conditions and experience of past failures in the area.

I liked the ICF builder because he never once used the terms "Curb Appeal" or "Resale Value". I am building my dream house and I plan on living there for the rest of my life. I am building a 1650sqft 1 bedroom home on the first level. Then there will be two bedrooms with a total of 1000sqft of finished space in the basement. Everyone in my area is building 1800-2200 cookie cutter 3 bedroom split ranch homes. I have gotten mixed responses about building 1 bedroom on the first level. But in my opinion, it is not much different then building a two story (above ground) home with all the bedrooms on the second level.
5 years ago

Brian Knight wrote:Hmm funny you should say that about builders. Ive heard IT folks are like professional engineers and should be avoided because they are too difficult to work with.

There is some truth to this.
5 years ago