Rocket Mass Forge

I think I came up with a novel idea, the rocket mass forge. It is a combination of a side blast, side draft forge and a rocket mass heater. I can do my smithing and heat the garage at the same time!

I built a side blast forge – one who puts air in from the side instead of from underneath in the hopes that it will direct the smoke towards the hood. This is the older style, it’s simpler, and works better for charcoal.

It’s a side draft forge, meaning that the chimney sits beside the forge fire and not over it. It draws the smoke in sideways.

It’s going to be a rocket mass heater, with the insulated inner burn chamber, the outer barrel chamber, and the horizontal ‘chimney’ that dumps heat into the room.

Rocket Mass Forge Concept Drawing
Rocket Mass Forge Concept Drawing

So far, I have… ~ $20 invested in the forge, discounting gasoline used to pick free stuff up. The block is retaining wall block and the fire brick is recycled red clay brick. Most of the ductwork was free, but I bought a few pieces of it. My dad gave me the blower, it was brand new – about 25 years ago. The barrels will be free. Oh, I did buy the perlite.

2 weekends ago I visited a local blacksmith for a few hours, and that really got a fire under my butt. When I got home, I built the base of the forge. I used probably 2/3rds of roughly 160 retaining wall blocks that will be used for a pond next year.

One of two trailer loads of free retraining wall blocks found on freecycle
One of two trailer loads of free retraining wall blocks found on freecycle

They are stacked in a circle with room for a 6 inch stove pipe to do down the back and out the bottom. It is infilled with a mix of block and brick to support the brick top. The brick top is layered in 2 different patterns and 90 degrees offset so I don’t have any seams that overlap. Less likely for hot coals to fall through down to the floor this way.

Start of base of forge
Start of base of forge
Finished forge bed
Finished forge bed
I will be staring at this for hours, just as well make it look nice, right?
I will be staring at this for hours, just as well make it look nice, right?
Initial brick burn chamber on top of the forge bed
Initial brick burn chamber on top of the forge bed

The brick burn chamber did not work at all. Too ‘open’, the smoke poured right out of it. It felt good to get a fire lit there though. The next thing I did was hook up my old pocket rocket to vent out the new rocket mass heater chimney system. This worked a little better. I was able to get it to burn in the right direction.

So I grabbed an old 5 gallon metal bucket of killz paint that had dried up – or so I thought, under about 2 inches of crust was white goo,  not quite paint – that was in the weeds in the back yard when I bought the house. I cleaned that out, burned out the goo, it burned OK once lit with a torch.

The First Iteration of the Rocket Mass Forge
The First Iteration of the Rocket Mass Forge

 

I made a hat hook on the first fireing of the Rocket Mass Forge
I made a hat hook on the first fireing of the Rocket Mass Forge

The forge didn’t really get hot enough for me, and the rocket mass heater didn’t want to draft for crap.

I need a 55 gallon drum so I have room inside to make a proper insulated heat riser. This should help it draft better. I need a different hose for the forge blower, as what I am using now whistles something obnoxious. I need to make a cold air intake for the forge blower and a mixing box so I can pull some smokey air as well if needed. I need to make a heat exchanger to pull more heat from the system before it leaves the building. I need to make the thermal mass yet too.

Lots of things to do for the next iteration. The important thing is that I got it working, if poorly..

Pocket Rocket Heater

This weekend I fiddled with my Rocket Heater some more. I put an outer chimney around the existing chimney so I can pull the exhaust down, then out the side, and currently am running it right back up. The elbow I am using I can adjust so I can run the exhaust any direction.

Rocket Heater
Rocket Heater

It surprised me how well this worked, pulling the exhaust down. The amount of heat coming off the top of the outer stack was amazing!

I will be playing with this some more in the near future.

Phase two of the Paint Can Pocket Rocket Experiement

So yesterday, I got to play outside a bit more. I worked on my Pocket Rocket Heater some more. I tore it apart, to see where it got hot, and where it did not and to add 1 more can to complete a burn chamber. I also insulated it with perlite.

The 4 cans, wire and perlite to rebuild the Pocket Rocket Stove
The 4 cans, wire and perlite to rebuild the Pocket Rocket Stove
The cans all come together to form a single burn chamber
The cans all come together to form a single burn chamber

I couldn’t find my baling wire (old timers will tell you it’s duct tape 1.0) so I used a bit of floral wire. Not as sturdy, and I expect it to be too light, so a good burn will melt it enough that it will break, but this is just a test unit, right?

I also poured perlite all around the inside cans to insulate the stove burn chamber area. Of course, I forgot to take a photo of this step. Bummer.

With the lid back on, I now have an insulated Pocket Rocket Stove
With the lid back on, I now have an insulated Pocket Rocket Stove
The wood tray is KEY to the workings of this stove, it allows the air to come in from underneith and thus through the fire
The wood tray is KEY to the workings of this stove, it allows the air to come in from underneith and thus through the fire
The wood sits on top of the wood tray.
The wood sits on top of the wood tray.
Shiney!
Shiney!
The whole unit as it currently exists.
The whole unit as it currently exists.

I am quite happy with how it all works. I like fire, and I like making things from junk.

My future plans for this particular unit is to either run a longish near horizontal 4″ exhaust out a window or maybe do the full on inverted chimney. This involves a 2nd, much larger chimney placed around the current one with a cap on top. A horizontal exhaust is then attached to the bottom of the outer chimney to vent the gasses. This allows the whole thing more time to release more air into the space that it occupies. It’s worth trying to play with, that’s for sure!