We are trying to work out the best materials to trial building a movable rocket stove/thermal mass.
- We have the 55 Gallon Drum (So I guess we are making an 8 inch core chamber to match this)
- We have free "haul your own" supplies of river stoves and sand and really cheap timber to make a box to contain it to make the thermal mass
The core material is what we are struggling with as we are in New Zealand:
- We have sourced Perlite for $35 + $25 freight ($85 locally) for 100Litres (almost 4 cubic feet)
- The cheapest fire clay we can find is $55 plus unknown freight for 10 kg (22 lb) (I know anything more than $15 for 50lb is considered too expensive in the USA)
- We have an almost full 20kg bag of potters clay that is dried we could use That is rated to 1000C bisque and higher firing - it http://potterysupplies.co.nz/shopexd.asp?id=160 It costs $48 to replace - but has not been used on 4 years ...
- we are on the coastal sand dunes, so clay is not a local to our area, we could try digging from where we get our river stones - but I would rather not waste $55 of perlite on wrongly made clay
We happen to be in a tiny town that manufactures this product: http://www.mastermix.co.nz/pdf/Fire%20Mortar%20.pdf I am have yet to find their direct price - but a retailer 8 hours away sells it for $80 for the 30kg bag.
Otherwise - the only refractory cement I can find is $31 for a 1.5 kg bucket of pre-mixed.
If we get a sack of the fire morter - would this and perlite alone be a good mix? Is there benefit to the clay being there - or is it just a cheaper option to the refractory cement? What proportion would we mix the fire morter and the perlite?
TWO OTHER QUESTIONS
- The drum is one with a lid - do we just turn it upside down, or cut out the bottom and use the lid to access inside the chamber?
- We can't source second hand flue - and so we would be paying $88 for 1.2m (4 ft) of stainless steel flue, and $37 for glavanised flue. Is it worth the money to get stainless steel all the way - or could the second half of the thermal mass be glavanised without burning out too fast?
Using the drum lid as a removable access panel is a really good idea. The one downside to it would be that nobody has arms long enough to reach all the way to the bottom, if that should become necessary. You could always get a vacuum wand in, though. The alternative is to make the drum connection to the core base such that it is easy to remove the whole drum.
One section of stainless duct should be sufficient in the mass; if you can get black stovepipe, that is generally heavier than galvanized and what is usually used in the initial part of the run. Another possibility is to substitute half-barrel bells for most if not all of the duct run. This gives more heat transfer surface in a shorter distance, and is said to be more efficient. If you can get steel drums inexpensively, that would be a good option.
posted 3 years ago
One place we were wanting to use this is in the green house with the most heat sensitive plants over or round the thermal mass box. Would the bells give out as good a heat over time to as big an area?
I used perlite and refractory cement when I built this portable unit. It's a rocket mass heater on wheels, with just the right amount of mass. Check it out! It one of my favorite rocket stove hybrid builds/designs that I basically designed and built myself with help from others here on permies.
Hi, I will read the posts in detail later. I can source fire bricks for $2 each plus $1 freight - I had thought of using them, but did not know if I would have to cement them together and if I did - if this would make them too heavy to move.
Bricks are great, but you specifically asked about perlite and refractory cement. If you read my link, that specific model I designed and made from perlite and refractory cement. Check it out! I also have micro batch box models made from bricks on my YouTube channel if you don't want to read the link, you can watch videos instead