Josh Whited

Sean Fitzgerald wrote:Hi everyone, I am new to the site... I am working on a solution to heat my uninsulated studio.. We are renters so insulating is not really an option. I just wanted to lend some of my professional experience as a potter.. Also, to you folks living in MT you should call the Archie Bray Foundation its an old brick factory turned ceramic mecca. They do sell fireclay by the ton and should have a never ending supply at a good price. On average, nationwide, a bag of fireclay should cost $12-$15 per 50lb bags. Less if you buy more..

I wanted to give you some info on castable mixtures, I have been building kilns with this stuff since undergraduate school. In areas that are not going to reach (Quartz Inversion approximately 1000 degrees F in ceramic jargon) the fireclay will never make the magical switch to fired clay. So anywhere you put this stuff that will not reach Quartz it will always be susceptible to being crumbly and it will not be waterproof/freeze thaw proof. So if you expect your heat riser to actually reach these temps then you can reduce the amount of cement needed to form it. So when you are building your suitable mixtures you can keep that in mind. This bond is called a thermal bond. In areas where you will not be reaching Quartz you will need to have a hydraulic bond (like the bond you get from plaster and cement) in order to maintain its rigidity.

In the ceramic world we differentiate the bricks mainly by density and thermal properties. Firebrick is a specific term for Hard Brick. Insulated Fire Brick is a specific term for Soft Brick. Soft brick is relatively new... However, it is made with the same materials as Hard Brick. Its duty rating (heat resistance) is based on its purity and frankly I've never understood why they are more expensive. If you want to create Insulated Fire Brick, or Soft Brick, you need to create air voids in the mix. You can achieve this by adding carbon based material, sawdust, spent grains from a brewery, etc. The particulate size will give you variable size holes in your refractory mix. A word of caution here I have made castable with bigger sawdust and the size of the void does make the mix even more fragile. Now this will work if your mix, fireclay (or any clay actually--I can answer any questions on this topic) sand, cement reaches at least 451 F (this is when wood burns, all chemical carbon with burn out at Quartz Inversion). I see that a lot of you are using perlite which is a igneous rock--good choice as a fill material but it does carry with it issues too. One, it has a very low melting point. Two, chemically it releases its H2O with heat and expands which may be another reason I see that you all have a lot of steam/water collection. It does lend itself to being refractory so it is a good choice as a fill. Again, we potters totally geek out on this stuff so I could go on..

If you really want cheap insulation for heat risers and insulation is really what you want/need for a riser personally Id cast a core of a fireclay, sand, sawdust, cement (just enough to make it hard enough to move around before it is "fired" then wrap the whole unit in Kaowool. That stuff is amazing. I can line a galvanized garbage can with 1" and fire it to 2000 F in less than 20 mins with a propane burner and the can doesn't lose it zinc... The fireclay skin will prolong the life of the Kaowool... Just a side story, this is the stuff the "tiles" of the space shuttle were made of... Very fragile.

Thanks for all your info.. I'd love to hear more of some of the room temps you all achieve with your heaters. I hope this info helps you guys!

While a lot of this is mumbo jumbo to me, it has a lot of keys for Google and that means learning! I need to reach out to the local university as it is has a pretty good fine arts department and I'm sure they have a ceramic guru on staff that would get pretty hot and heavy for this stuff. Networking is what I need to do.

thomas rubino wrote:Josh; One 50# sack of fireclay and apx 2'of perlite should be plenty for a riser. however I would buy at least 2 bags(or more) of fireclay and a 4 cubic foot bag of perlite just to make sure. Also that way you will have a start on materials for your second rmh,lol. Build your core first ,in fact, fab it up(with no mortar) outdoors and try it first. Then build it indoors. After your core is ready then pour your riser next to it on the ground and lift it into place when ready. I've included some pics of mine. The first is brand new, next is at the end of the first season covered in ash and the last is after its mounted on the rebuild. Go to youtube look up (broaudio) this is matt walkers page (a respected rocket builder) watch his videos of cast core and cast core part two.

I notice your rebuild picture the riser has a much thicker lip on the top. Is this on purpose? Why the rebuild?

Wow, thanks guys. I am not sure when the build will start. I was hoping to get it done this winter, but it may just have to wait. It seems the brick core and cast riser makes a good combo. I haven't looked around really locally for fireclay. There is a refractory supplier about 40 minutes away.

How many bags of fireclay would one need? Is it better to cast in place or off site and move to it's permanent resting place?

Still researching and reading on building the core. So far there are two methods that stick out. The typical build with fire brick which is well documented. There are also others who have cast the core and the riser using fire clay. A quick search brought up a fire clay that you can purchase called Hawthorn Fire Clay. Looks like 50 lb. bags shipped come out to about $40 a bag. Would casting the core and riser be a cheaper option than building with brick? If the riser is cast into a thick tube shape with say a 6" or 8" ID and an outer OD of something like 12" to 14" negate the need for insulating around it since it would have such a thick wall?

Thanks. There's a local scrap company (think American Pickers-ish) that I have an email out to to see if they might have any used fire brick from where they might have demo'd or scrapped something like an old pizza place, or a boiler somewhere. Hoping to score some cheap fire brick. The book states 60-70 bricks for everything. Is this about right? I have been asking for 100 at various places.

Any advise on where to find cheap fire brick?

Well at some point in time the built onto the back of the home. So the back wall in the basement is about in the middle of the house. There is crawlspace behind it so the heat would go into the crawlspace and seep up into the kitchen and master bedroom. The RMH is just for supplimental heat. While yes, it would be giving heat away it's not a complete loss. I want to do a RMH to burn for maybe an hour when I get home from work and let the mass keep it nice and cozy in the basement and keep my gas bill down. I am installing a hybrid heat pump water heater that will be close to the RMH as well so the heat from the RMH will also help heat my water in a sense. The heat pump water heater will be very efficient extracting the heat from the air during the winter and putting that into my water. If the basement is 75 to 80 degrees then the water heater will thrive extracting that heat. I will most likely follow Ianto's book very closely to build a tried and true RMH.

That makes too much sense to measure and compute how much mass I will need.

I have heard it is better to have the burn chamber slightly smaller than the feed tube and riser.

Been reading all I can for a while. We are in process of renovating a home we just purchased. Pretty excited due to the prospect of being able to have a wood burning something. Planning on putting a RMH in our basement as a place to hang out around, read books, and gather when friends come over in the winter. Plans are pretty much "by the book". Fire brick stove, 55 gallon drum, insulated riser, cob mass bench, and feeding that into the existing centrally located chimney. Chimney is pretty normal at probably 30 feet ish. Planning on putting the J style burn box and barrel near what used to be the exterior wall made from cinder block as an added mass for heat absorption. That will feed into a bench of about 8 to 10 feet long and then exit into the chimney. Fire brick will be sourced from a local refractory (45 minutes) supplier for the main feed, chamber, and riser (price is about $2.50 per brick, 2700 degree brick). Have a friend who is an excavator and says he hits clay all the time and can give me all I need and then some. I have no idea the quality of the clay, but it's free clay and a good starting point for my mass. I am currently building a "proof of concept"flue size in our back yard out of regular masonry brick that was demo'd from inside our house (gas fireplace surround) just to see if I get the idea of building the guts.

Current questions are:

Would an 8' truck bed of clay be enough for the whole mass?

Can the guts be built well using clay slip instead of mortar? (Donkey on that forum stated just dipping each brick into clay slip during the build)

I think my flue size entrance to the chimney is only around 8", so would 8" flue in the mass be sufficient or should I use something like 10" and neck it down to 8" right before the chimney.

I have taken university physics a year ago so the concepts of the laws are still somewhat fresh. (Changed my world BTW)

FULL DISCLAIMER: I am aware of basement RMH being frowned upon. It's the best I can do. It won't be for whole home heating and not really supplemental heating, but more so heating to keep it toasty warm in the winter months.