I am interested in comments on Successful Horizontal Venting :)

Hello,

 I read through a bunch of posts on this subject. I haven't yet seen a clear answer.  I am likely in same boat as plenty of people; To vent through roof I would need close to 10 M of vertical rise , so I am looking for a viable horizontal solution. I see that people have done it.. I'm brain freezy on which method to use. I see that protecting the exhaust from wind on the outside is important, but am fuzzy on other details.  I am assuming the classic drum can J tube thing with a internal riser made of a acetylene cylinder or possibly fire brick..  thanks for thoughts

A horizontal exhaust is only viable if you have a very reliable prevailing wind direction in the heating season, and you can exit on the downwind side of your building. If you ever have wind hitting the side where the exhaust is you will get smokeback which can fill your room with smoke.

Ianto Evans who originally developed the rocket mass heater lives in a coastal Oregon valley with consistent westerly wind, so he was able to use horizontal exhausts successfully.

A heat riser can be made of firebrick wrapped with blanket insulation, or a 2"/5cm thick perlite-clay mix cast inside a metal outer form, or a "five-minute riser" made from 1" ceramic fiber blanket insulation inside a metal outer form, or a few other variants. An acetylene tank or other metal on the inside face of the riser will quickly spall and corrode, and may fail in less than one season, probably at the coldest part of the winter. If not wrapped in insulation it may last longer, but will be inefficient and may not work well at all.

what do you think of building a shield for the exhaust to mitigate wind?

It's not so much the wind blowing directly into the flue. It's the pressure gradient from one side of the building to the other. In a steady wind situation, the windward side is a high pressure zone, with a low on the leeward. This makes the RMH work harder to push its exhaust gases out, and the low on the opposite side can set up a vacuum through any gaps in doors or windows. Put together, these factors can make the draft go backwards pretty easily.

Thanks,  So is exhaust above roof peak the only option or is there some other way of sorting it?  

Getting it above the roof plane might be good enough if you can't get it above the peak, especially if your winds tend to be from opposite directions and the ridgeline of the roof is aligned with that axis.

For example, our prevailing wind here is NW and our storm winds are nearly always SE, so a ridgeline running NW-SE would allow a chimney exit lower than the peak to still escape the pressure gradient. Not ideal but still workable if the system has good internal draft in still conditions. What I observe with the RMH in my glasshouse is that it's not the steady winds that cause problems, but the turbulent and gusty conditions that we get with storms. The main effect is that a fire will be a little harder to light from a cold start and prone to occasional puffs back up the feed tube. This is a 4" J-tube with the flue going up just above the E-W  ridgeline but affected by a dense feijoa hedge immediately next to it.

Horizontal outlets are problematic, no doubt about that. It's actually a sort of urban legend.
As an alternative one could use a chimney fan, I've installed one of those (not at home by the way) and all problems vanished like snow in the sun. The fan I used is of the injection kind, the fan blades aren't in the chimney itself.
https://darco.pl/en/category/offer/chimney-cowls/chimney-fans/#opis-produktu
These are made in Poland, I am aware you are half a globe away. Don't know whether these are for sale somewhere a little bit nearer, sorry. To solve your problem it's a real chimney or this solution, the rest is cutting corners the wrong way.

It MIGHT work to have a sort of horizontal tee along the outside wall that reaches to a corner of the building, similar to a variety of chimney top. The wind would blow through the tee across the end of the exhaust and maybe help reduce back pressure. I would want to test this before actually using it for a fire.

The building shown is an uninsulated, steel garage with a rocket heater inside against the north wall of the building.  Although wind-break tree lines help reduce northern winds out of Canada, it can still get pretty gusty on certain winter days.  Originally, I had the outside stack rising up to just under the roof lip (soffit) with no angles in the external chimney pipe, but had the cap on the chimney as shown.  That actually worked fine, but the exhaust discolored the soffit and since many soffits are perforated to allow for roof line 'breathing', some exhaust ended up back in the building.  Again, the building is un-insulated and a bit drafty so for the work I was doing in there, it was fine as an experimental rocket heater set-up.  Having added on the mild elbowing and extension above the roof line, the stove does draft better and now I'm not getting exhaust back into the building.  My guess is that, depending on height of chimney, height of roof line, cap design, and safety/aesthetics, you *might* be able to get away with a horizontal vent as long as there is some vertical chimney to provide that 'reverse siphoning' effect on your air column and exhaust.

This is the roof line so you can see why I am trying to find an alt concept than through the peak of the roof. This corner doesn't get strong wind at ground level.. we have hills all the way around and the Ocean  is in a straight line through the image.  Once you get up a couple meters you get air movement. at sunset, the ocean sucks all the air out due to the temp differential out at see and the land cooling off.

I can see why you wouldn't want a chimney coming out of the roof. It's not a matter of can't, it's esthetics. But I also wouldn't want to have a vent/chimney at the ground floor where it is highly visible close up. As you apparently have frequently variable wind/air movement, I don't think it would be safe to have any vent that didn't have positive pressure. Just because the air isn't moving much at ground level doesn't mean there is not pressure variation at a given point on the wall. I think your best bet is to run a chimney up inside as inconspicuously as you can, maybe face it with something that will help it blend in, and exit near the peak on the least visible side.

I think the chimney is a very important aspect (if not critical) of a successful rocket stove, personally I think a twin wall stainless steel chimney pipe is a rather attractive feature and considering its cost, so it should be!

Agreeing with these previous two posts and was thinking of a compromise solution.  One hallmark of RMH conceptualizing is the horizontal run of piping, normally running through the mass.  Would it be sacrificing too much to run the exhaust pipe out of the house at ground level where it becomes "class A" double-wall and is decorated as a bench?  It would run straight outward and then take a 90 degree turn upwards past the edge of the roof line and attached to that edge. (In my photo above, I've attached it in a similar way, but it's risky in our climate as 2 - 3 ft snow drifting on the roof often will rip the pipe off when that mass of snow and ice gets 'restless'... ;-)  )  *If* that horizontal run out of the house would not be prohibitive to stove efficiency, I could see where the vertical class A chimney (code in Japan??) might not be too unattractive?  Was even considering how an access port at the 90 degree angle section could almost be a separate "ambience" stove.....closed off when running the RMH inside the house, but used as a patio fireplace when sitting outside on a cool evening.  The mock up below illustrates, among other things, why it was best I avoided a career in CAD and architecture.... :-)  ..... but hopefully provides a sketch of the idea.

As far as code, there really isnt any in a lot of places bc so much of the rural country is deserted so they are happy to see repairs taking place. They stay out of your business mostly. And I have made massive changes to this building. The original form is beautiful but largely dysfunctional to live in. Almost nobody likes the old house designs as far as actually living in them.  

Q: If THE RMH needs the same type of costly exhaust system to install, then what is the benefit over building a masonry Stove or using a old cast Iron with a masss around it? Just some efficiency? I guess it's still less expensive too. can I make the inner riser out of fire brick?

Hi Brendan;
Nice there are no codes you need to follow in your location.
As far as the costly exhausting of an RMH.
If there are no codes, you only need a safe roof jack.
One piece of insulated pipe out past the ridge line is nice but unnecessary.
The vertical pipes on both of my batch box RMHs are thin wall HVAC pipe (in the US a 5' piece of 8" is $11).
A class A roof jack with a thin wall pipe stuck thru and a simple (coolie) cap to keep out rain and snow.
No insurance company would ever insure this but like in your area, as there are no codes here, I can do as I see fit.
The truth about the vertical stack is it should run 130F- up to maybe 250F not hot enough to harm anything.

Plenty of RMHs have been run thru a wall horizontally and then go vertical with just a short rise.  
You will have condensation in the outdoor pipes, they may need to go higher.  
If the wind becomes an issue then you will need to figure out how best to deal with it.
You are the builder and the boss rolled into one.
If what you try runs backward and smokes out your house, then open the doors and windows to air it out, and tomorrow change something and try again.
You are the boss here, I guess you could yell at yourself if one of your ideas does not pan out.  

Now about masonry stoves.    Build your RMH as a masonry stove they work great!
Stacking bricks around a box stove will help hold heat BUT does nothing about the wood-gobbling creosote-creating chimney fire waiting to happen box stove!
Yes, a riser can be firebrick but it must have insulation wrapped around the outside.
It will take some time to heat up before your system starts rocketing.

All these responses are great and appreciated.  I am in process of trying to locate this thing intelligently in my space, its a trick. The best places for it have low wooden ceilings that make me uncomfortable to install something on fire... The other places are not in heavy use during winter and are really large... Has anyone seen something that uses some of this concept but is really compact?