## New Barrel for Rocket Mass Heater/Forge

I got a new barrel for my Rocket Mass Heater/Forge (RMH/F) from my neighbor. The new barrel is over 10 times bigger then the old one. This should give me a performance improvement.

The current barrel is too small to work, really. There is no room for the insulated heat riser they need to work. I folded up a metal sign to use for my heat riser. I have to cheat it by putting a pair of inline-duct blowers at the far end of the heater. This forces the draft to work in the direction I want it. Works well for the forge, it sucks all the smoke out of the building, not so good for a hot fire, I have to keep the fire a bit held back or I overheat the blowers.

There is a bit of math that is required to build one of these. Not too much though. Area of a circle is pi time the square of the duct diameter, all divided by 4.

I am using 6″ ductwork as that’s what I got for free on freecycle. 8″ would probably work better – that extra 2 inches gives me twice the air volume, but, I don’t have it. This gives me a cross sectional area of 28.2 inches. I want to keep this 28 square inches minimum throughout the length of the system. Especially critical are the areas around the burn tunnel. You can get bigger than this in places, such as with the burn barrel, but everything up to the burn barrel had better be pretty close to 28 inches or this thing will smoke.

The space between the top of the heat riser and the burn barrel is one of the few spaces where you can ‘tweak’. I guess going smaller will actually make the heater sound more rockety. I am going to try to maintain my 28 square inches. The circumference of my 6″ burn tunnel is 18.8 inches. So I need to gap the top of the heat riser from the inside of the barrel an inch and a half.

This is primarily a forge, so that means I need to forgo the burn tunnel. However, I can lay a dozen bricks or so and make a quick, loose burn tunnel for the times I am wanting to heat the shop to do woodworking, or some other project.

I want to be able to ‘peel back’ a few of the ‘layers’ so to speak, so I can show people how these things work. The barrel I got is conducive to such abuse. It has a lid with a bolt-tightened band to hold it on. I will make it so I can take the outer barrel off so I can show people the insulated heat riser inside.

So, All I have to do is cut two 6 inch holes in the barrel lid, balance the lid upside dine precariously on some uneven brick, and then somehow sling the barrel up over the top of the heat riser which tops out near 6 foot off the floor.

I have a hunch I won’t be taking the barrel off for show and tell all that often..

## 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.

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.

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.

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 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..