Heat Riser Design - Middle Drum

I'm just about to make my first RMH and I've acquired 8" stove pipe and a 55 gal drum. In many videos I've seen that the 8" pipe is placed into a barrel (looks like 16 gal?) with cob or some other type of insulation, and then capped around the insulation with a hole for the 8" pipe. How important to the overall system is this 16 gal drum? The main reason I ask is I've been monitoring Craigslist etc for some time now and I haven't come across any for sale. And buying them online is about $70.


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Are there good alternatives to this drum? Some kind of rolled steel or something?


Thanks,


Matthew

Anything can do, sheet metal. Wire mesh, if it's for holding cob. Some have used chicken wire for batt insulations. But your best bet is go to some digging compagny, usualy they have Smaller barrels. There isn't any dumpyard in your area you can get into?

Thanks. There is a landfill in the area, but apparently they are against taking anything out.

Matthew Weir wrote:Thanks. There is a landfill in the area, but apparently they are against taking anything out.

Sometimes a pack of beer or proper bribing eases things nicely!

Do you think one off those small silver trash cans would work?

If it's the right diameter it should work fine, but "silver" means galvanized, and there will be enough heat in that area to burn off the galvanizing and release toxic fumes. It is recommended to use black iron/steel in the high heat areas, and consider it a sacrificial form as much of it will burn out or corrode sooner or later (sooner in the combustion core).

Sections of round duct can be combined as needed to make the outer heat riser form to hold the insulation.

Glenn Herbert wrote:If it's the right diameter it should work fine, but "silver" means galvanized, and there will be enough heat in that area to burn off the galvanizing and release toxic fumes. It is recommended to use black iron/steel in the high heat areas, and consider it a sacrificial form as much of it will burn out or corrode sooner or later (sooner in the combustion core).

Sections of round duct can be combined as needed to make the outer heat riser form to hold the insulation.

http://donkey32.proboards.com/thread/373/afraid-galvanized-pipe-anyways

Late-night typing... I didn't get into the inertifying (!) effect and how to make sure there is no further danger. I had read that thread a while ago. Best to save posting for when you can answer fully sometimes

Matthew Weir : Their are more than a few Technical problems with the build recorded within the video, I will attempt to list most of them.
Be advised that the tears in my eyes as I attempted to watch this probably caused me to miss a few errors in the unit we see built !

As a proof of concept build it was a success! Otherwise, the builders quickly fell into error and never recovered. To err is human, and I am
human, but not as willing to show certain lack of understanding of the concepts willingly to my peers!

For a proof of concept exercise the use of iron/steel in the Feed tube and Burn Tunnel and Heat Riser is acceptable ONLY when it is
announced for all gathered, and all that will see this video that this is a temporary build that will quickly fail as made! Many people watching
this will now falsely believe that iron and steel can be used in these locations, this is completely false, as has been repeatedly shown !

The use of sand to make-up the thickness of the Heat Riser is totally inadequate, and when the 8'' pipe that makes up the inner wall of the
Heat Riser fails the sand will pour down into the burn tunnel, probably while the unit is being used, filling the room with smoke and the Feed
Tube with flames !

The Barrel in question is a 16-18 gal grease drum for lubing cars and light trucks, you should be able to get one at at Oil change shops,
muffler, and brake repair shop chains!

Both the grease drum and the 55 gal drum need to have the paint removed, I still prefer burning it off and also changing the way the
galvanizing is bonded to the 1st 4-8 feet of the galvanized pipe used within the horizontal pipe run through the Thermal Mass !

The Transitional area where the vertically falling gases meet the opening into the Thermal Mass is inadequately small the opening should be
3xs the size as shown in the video, gently sweeping the hot exhaust gases as they turn their 90 degrees to flow though the Thermal mass !

Stated in the demonstration was the material used to hold the bricks together was 'cement' generally this would be a sign that the material
was a Portland Cement based Mortar, this is the wrong material to use on a Rocket Mass Heater RMH, it should be a Clay sand based Mortar!

As shown the rocks placed on ether see of the horizontally run pipe probably performed a function to stabilize the pipe! I like to use short
sheet metal screws, at least two at every joint ! The proper use of the rocks in question would be to increase the density and heat handling
characteristics of the thermal mass this also greatly reduces the amount of 'Cob' that must be made !

Here again sand is just not the material to use at this location.

At 5:25 In the video the builder states that the drum is to tall for the Heat Riser, and we are shown that the drum has been cut down! This
seems to work- but the more efficient solution is to raise the height of the Heat riser to with in 2'' to 2.5'' of the underside of the drum, Raising
the Heat Riser has the additional benefit of improving its ability to draft ! Occasionally a gap 3'' or bigger has proved to help!

the final vertical chimney was never plumbed to the outside of the building -ending some 4' over the peak of the roof, a storm cap is always a
good idea !

The use of galvanized roofing as shown in the video must have been a preexisting installation to keep dripping water off of the roof of the
g'house from creating standing puddles on the wood, as a source of protection from high temperature heat loads the roofing would not have
Helped those wooden exposures at all!

I now have a headache and need to lie down, Let me close by saying there is a LOT OF CRAP on You-tube ! For the crafts Big AL

Wow, Big Al. That's quite the post. I hope your tear ducts have regained their strength

I appreciate the hint about the 16 gal drum at a lube place. I was able to walk down the street to Jiffy Lube, and sure enough they go through them all the time. They said they'd set one aside for me and to come back Saturday. This will allow me to return the 20 gal silver trash can and save $20.

As for the rest of the video, I only used it because it had a good view of the riser. I'm actually probably going to go closer to a design for the "portable" RMH that Paul Wheaton has on Youtube. I'm trying to heat a 16' x 7.5' greenhouse to grow through the winter. The biggest question in terms of design, is should I bury this all under the floor of the greenhouse, or use the portable box-like design that's above ground and use the box as shelving.

Matt W. : The Paul W. Heat Riser is a copy of a design best referred to as'' Yesterdays !'' You already have my opinion on the other design

1st ) Pauls !
This is a 6'' pipe inside an 8'' pipe, packed I believe with Perlite and clay 1 : 1! As the clay reduces someof the insulating effect of the penlight -3'' would
be better! 3''+ 6'' + 3'' = 12'' outside diameter!

The video you liked because of a clear picture of a barely workable Heat Riser doomed to failure with its steel component.

2nd the other system!
We can use an 8'' RMH system and still provide adequate flow of the cooling/denser gases as they fall vertically through the transitional area and flow
horizontally into and through theThermal Mass When a 55 gallon drum is used !

Scenario #1 an 6'' system and a heat riser made with~3''~ of Clay/Perlite the inner wall made with a sonotube or heavy duty cardboard tube often used
as an outside form for a footer of poured concrete! this will burn out in the 1st couple of firings! The outside wall is a length and a part length of 12''
stove pipe that can be expected to eventually fail without destroying your Clay/Perlite Heat Riser !

Scenario #2 an 8''system with an inner sonotube core, and a modified grease barrel as the outside wall with the Claypperlight 1 : ! ratio Heat Riser !

O.K. this is one of those physics things you can take on faith or work to understand ! For the 'magic' of the RMH to happen and push the hot exhaust
gases sideways 50' an RMH with a Small barrel and a RMH with a larger Barrel must Radiate of the same Number of BTUs of heat energy to work !

Counter intuitively the Smaller barrel with a smaller surface to volume area MUST do this at a higher Temperature than the Larger Barrel with the
greater surface to volume area !

This is the reason why when your 3 -4 year old is tired and wants to climb into your lap they are such a great cuddle, with their lower surface area to
volume, to maintain their 98.6, they must radiate their 'heat of respiration' at a higher Temp ! Same number of units of heat energy higher temp !

I hope this was clear , timely and helped ! Big AL