WIND, PUSH-BACK, and Black Lungs

EXPERTS, Please help...

I have a gravity fed pellet stove at the moment... eventually going to build an RMH, and seeing these have more draft, more pull, more drive, or more power than a typical fireplace... I want to make darn sure I have no smoke-back problems... as I quit using my existing arrangement at 30 MPH, not the best scenario for survival, but OK for now, given the high cost of the next size of pipe.


How often do you have smoke come back into the house in a typical RMH (I'm seeing plenty of wind problems with my gravity-fed pellet stove... it has nowhere near the pull, or draft, I would expect from an RMH)

Do you design for an abundance of heat leaving the house, if you are designing for a windy location, or for my 7 K foot, extra-high elevation (less oxygen, less drive power, right)?

What methods do you use, in design, to give yourself some latitude for wind problems?

When experts say, This is the typical size, length, and diameter, what do you find you would do differently at altitude, or say, in windy Wyoming?

Thanks in advance.

You can't really compare the draft from an RMH to the draft from a woodstove or fireplace; each installation has so many variables that you can only effectively compare two specific installations. A woodstove running flat out may have very strong draft because the chimney is very hot, while the same woodstove damped down to satisfy the actual heating need on a mild day may have weak draft.

If you have smokeback issues with your current woodstove, connecting an RMH to the same chimney is not likely to be more (or less) reliable. The location and configuration of the chimney have a huge effect on how well it works in various weather conditions. Ideally you will have your chimney rising through the interior of the house and up through the roof, to at least three feet above the nearby roof and two feet above any roof within 10'. If you have unusual roof conditions, you may need the chimney to be taller.

So what are the details of your chimney, and the stove location? Pictures would help.

GH,
I'm sorry for any confusion.

I'm not meaning to compare them...or even use the same chimney. I'm looking to compare a typical RMH at sea level... maybe in tall pines VS. an RMH in a windy, and even a very high elevation, which would change the need to push the design in the right direction a bit.

If anyone has experience in adding in a little fudge factor, I'd love to hear from you.

Dean, as i see, you're living quite high. What's your building like? How's the chimney? Flat land? Or with mountains very close?

I'm living in a 2-story A-frame site-built home, high on a Southwest Desert mesa, surrounded by Juniper, Pinion pine, and some cedar trees, but not enough to shield me from high winds, often above 30 MPH. The beautiful White mountains of Arizona are nearby, but only a factor in that the Mogollon Rim Country is full of mountains, as the low desert shifts to high plains, along a broken cliff face that is over 100 miles long. Many weather disturbances are created from this.

Many RMH's are built with pipe exiting a home with little, or no vertical chimney. I'm in a very rural area on 10 acres, so I'm not worried about using a non-vertical run and having much smoke for my neighbors. My main concern is high winds, and the extra chimney height I may need to overcome smoke from being pushed back into the house, and the possible changes in design criteria given my altitude and windy conditions. I thought about building a standard 8 inch RMH, and just shortening the pipe run that the smoke is pushed through, in order to have a little extra push against such winds. I would lose a small amount of heat available to me, but I would rather not have smoke be a big part of my life, from not having adequate power to push against it, as it leaves my home. The other factor, in my opinion, is altitude, and the loss in power derived from less available oxygen. It would be interesting to know how much a person has changed the standard RMH system to arrive at a comfortable, working system for these conditions.

Just for fun, I've also considered building an external RMH that pipes through my cinder block stem wall and into the crawl space under the house, heating only the crawl space, and under-house thermal mass, exiting on the opposite side.

- Just to clear up 1 small point that might confuse a future Newbe visiting these pages for information- English is a slippery language and can mean different things to two

different people! In The quote below I know Glen was Referring to not Re-using a chimney that had already shown to have problems !!!

Glenn Herbert wrote: -If you have smokeback issues with your current woodstove, connecting an RMH to the same chimney is not likely to be more (or less) reliable.


Glen was definitely Not talking about using the same chimney for any two wood burning heaters. This rarely or never works, and is not worth even attempting as it adds

lost time, money, and lots of frustration to anyones build !

Dean Howard : When Ianto Evans used a string of observations on ancient heating/cooking practices going back thousands of years to create His first Rocket Mass Heater

(RMH) He sought out and found a place on our west coast where there was a nearly unvarying climate pattern and stable winds that blew from one direction during a

modest heating season.


At this location he built his ''Colony'' With the rocket stove built 1st, and then the Houses were built around Them.

These were usually open plain/or single room, low, single story, Button Mushroom shaped Houses, and always had his RMH's exhaust exiting low through an outside wall

to the Lee or Downwind side of the House !

This combination of purposely executed steps is the major reason RMHs quickly got a reputation as Great Heaters that were efficient , used little wood, and heated entire

houses and were incredibly reliable !

Retro-fitting pre-existing houses with any Woodstove will always require some compromises. In most cases with a realistic plan and a generous Final Vertical Chimney a

Well cared for RMH delivers almost every time.

Placing any wood stove in a remote location needs to be carefully considered from a safety aspect; but it most be noted that due to the RMHs Freaky high Combustion

Temperatures and greater efficiencies we use much less wood and much less wood to sustain our present burn.

This is an important reason for the RMH to be located in the very Heart of the home where it is easily tended to during the normal daily household duties; because of the

smaller load or Charge of wood present at any time -any remote location will result in missed Audible signals that Your Rocket needs attention !

When located within the heart of the home and used as a piece of integral furniture it becomes much like an Ample Bank account into which you make small deposits of

wood fuel and receive generous disbursements of Heat, soul warming/bone thawing -relaxing heat With no more conscious thought than a person uses to adjust a pair

of glasses on his nose !

Because every Rocket Stove built today is a hand-built D.I.Y. project it is difficult to clearly define every area that needs careful attention in a build, a generously tall

Heat Riser and Final Vertical Chimney located on the lee side of the house are always good investments !

I hope this was timely and useful, for the good of the crafts ! Big AL


These comments are specific to the J-Bend style RMH, and only generally apply to the Horizontally-fed, batch-loaded Rocket , which is ( I Think )an advanced build;

and is undergoing rapid development and improvement, both shrinking in size and going to resemble a masonry stove more and more ! A.L.

Thanks Big Al
I pay homage to those who have gone before me, experimenting, and developing. This post was meant to glean wisdom from them.

New Readers: If you have the appropriate knowledge and experience... Please respond to my original 3 questions, if you have any input for me.

Note: These are not trick questions... I know there are too many variables to mention and would rather stay on the path of learned experiences shared.

Experimenters first hand knowledge is always welcome, though it muddies the waters a bit.


Who has reliable, ongoing knowledge of standard builds? Anyone? I realize there is tweaking involved with every build, and hope to limit my endless tweaking and nip it in the bud, if I can

I can't see where your current chimney is in the photos, but a properly placed chimney exiting the house near the peak will only help the draft in your RMH, not require reduced mass storage. I might consider a shorter mass run given your extreme conditions, just as insurance, relative to what I would do in a mild climate. But a properly located chimney with a good cap (I can't tell you what will work best, as I haven't had to deal with this) will only draft stronger in high winds.

The chimney is the main factor specific to the RMH that needs to be tailored for the environment. Other adjustments are more related to interior layout and usage, not to climate.

One thing I can say given your exterior photo: the chimney really needs to be near the ridgeline to be reliable in all wind conditions. With the steep pitch of your roof, a chimney, even one taller than the ridge, that is remote from it is likely to be subject to unpredictable turbulence in any direction including downward. A chimney at the ridge will pretty much always have the wind being deflected upward as it passes, aiding draft.

Also, in an extreme heating climate, keeping the chimney inside as long as possible has the dual benefit of not wasting any heat, and keeping the chimney warmer to aid draft.
I think sacrificing a bit of interior space for an internal chimney would be worth your while.

Ok, that's flatland!

Dean, thoses claiming to have an horizontal chimney pipe, don't know what wind is. And i'm ready to bet that their house get smoke filled every now and then!

So, if any of thoses stubs are your chimney, no wonder nothing works.



You need to lenghten that chimney to about 70cm 1m above the roof peak.

You could do a guyed chimney, all metal, with a bow (like a boat hull bow, or snowplow bow) above, so the snow doesn't push it.

I merged your stuff with the following thread. I hope that is okay by you.

I'm starting this post to talk about WIND problems only...
I'm looking for specific answers, not long-winded answers, pun intended, ha, ha... Some of us are challenged and simply can't wade through all the replies, so please keep on subject and be concise.
Thanks


[1] Standard RMH: How often do YOU have wind blowing smoke back into your house, or greenhouse? For a new user, what is the expected norm?

[2] Standard RMH: Do YOU have trouble in high elevations, with wind and smoke-back into the house?

[3] Modified RMH: What have YOU (and others) done to modify your RMH system (chimney included) to overcome a design consideration for excess elevation and wind problems?

you are confused.
the high cold windy place is actually helping the draft. (in a proper designed chimney)
you can do a longer mass

shilo kinarty wrote:you are confused.
the high cold windy place is actually helping the draft. (in a proper designed chimney) you can do a longer mass

Help me out here... Am I confused?
High = less oxygen to burn and lower temps of exhaust gas achieved for the same amount of fuel...
Cold = less heat, more cold to overcome in heating the chimney... maybe the hot air rises faster in general is your point?
Windy = I'm not seeing that as being a help... without wind, my smoke goes outside just fine up to about 30 MPH for the pellet stove...then I've got blow back, which I would expect in an RMH, as well.

So, are you speaking from your own experiences, or just blowing smoke (sorry, I could not resist the pun)?

High = less oxygen to burn and lower temps of exhaust gas achieved for the same amount of fuel...

no. you have plenty o2.

Cold = less heat, more cold to overcome in heating the chimney...

no. colder outdoors temp = bigger delta T (the engine of the chimney). (if most of your chimney is inside the house)

Windy = I'm not seeing that as being a help... without wind, my smoke goes outside just fine up to about 30 MPH for the pellet stove...then I've got blow back, which I would expect in an RMH, as well.

if your chimney location, high and cap are good, the wind help to suck the smoke by creating low pressure zone. search for Bernoulli low.
my experience is based on Israel - a country with a relatively wide range of conditions. -400m to 2000m +45c to -10c no wind to 100kmph. but we don't have a real high or real cold conditions so take me in skepticism.

Dean, Shilo is right. I assumed you understood from the first place.


https://en.wikipedia.org/wiki/Stack_effect

https://en.wikipedia.org/wiki/Bernoulli%27s_principle


It's simple. Difference in temperature leads to difference in density of the gases. Would they be air or otherwise. They are, at ambient presure, pretty much incompressible, so that one point out of the equation.

Hot gases, being less dense, are pushed upwards by the colder denser gases.

In a properly made chimney cap, the air going through, in windy condition; accelerates because it is blocked by the solid portion of the cap and chimney. Creating a venturi, and "sucking" the gases out of the chimney. CF bernoulli's principle above.


Your problem, the height of the chimney. If your chimney doesn't go above the apex, what happens?

When the wind comes from the opposite dirrection, a "vortex" forms on the chimney side, like what you see after a plane wing, in damp condition. Making the draft unpredictable. If the part of the vortex going downwards is right above the chimney, it pushes back the gases in there. Despite the underpresure generated by the vortex.


But the worse part is comming. If the wind comes from the chimney side, what does happen. The wind sees an abstacle. Ok, not a straight wall, but an incline. And not a tiny one in your case. The wind keeps pushing against that surface, untill enough presure is created, that the "incompressible molecules at ambient presure" can escape on the apex and sides with increased velocity. Thus pushing everything back into the house. Get it?


Now, get back to my previous post, and act accordingly.

Nothing else will work, with any type of natural draft burner. And remember, when you go out the house, use insulated pipe, to avoid a condensation plug.

Is that short enough and not verbose enough to keep you happy? Better than my previous answer?

Shilo, and Satamax...

I think half the appeal of the RMH is the high drive of the furnace, and less worry about an expensive, well thought out chimney... though I can see your points now. I sounds like you are coming at this with a good knowledge of physics... I definitely am not. Isn't the powerful "drive" of a typical RMH, what prevents most of the push-back from wind, despite what RMH chimney experimenters seem to use?... because many people were not using a traditional chimney in my reading, taking that out of the equation, and some barely having any vertical run. I'm pretty sure I'm not alone trying to understand this. Thanks for the physics lessons guys.

shilo kinarty wrote:

High = less oxygen to burn and lower temps of exhaust gas achieved for the same amount of fuel...

no. you have plenty o2.

Cold = less heat, more cold to overcome in heating the chimney...

no. colder outdoors temp = bigger delta T (the engine of the chimney). (if most of your chimney is inside the house)

Windy = I'm not seeing that as being a help... without wind, my smoke goes outside just fine up to about 30 MPH for the pellet stove...then I've got blow back, which I would expect in an RMH, as well.

if your chimney location, high and cap are good, the wind help to suck the smoke by creating low pressure zone. search for Bernoulli low.
my experience is based on Israel - a country with a relatively wide range of conditions. -400m to 2000m +45c to -10c no wind to 100kmph. but we don't have a real high or real cold conditions so take me in skepticism.

Like many permies, perhaps, I'm looking at it from a practical view... Even my BBQ does not work well at this altitude, whether summer, or winter. And, there is seldom humidity here to consider. My chimney people may be wrong, but they have told me it takes more chimney to overcome this lack of O2. Heck, I'm not doing well at this altitude...I'm winded, and only feel good after much exercise...



Now, to hear back from the practical side: Are there any actual RMH operators out there having Wind push-back problems in windy, high altitude conditions?... just so I can get feel of what may be normal, despite the "good physics" argument...

many people were not using a traditional chimney in my reading

many people report they have excellent stoves but when you see it you wonder if they going to wake up next morning or not.
make a good chimney and have a good stove!

To repeat because it seems needed... Your chimney (if the upper fixture on the roof is it) needs to be taller than the ridge, and preferably right at/next to the ridge, in order to work well. This is irrespective of altitude, it is simply an effect of wind physics. That chimney does not even come close to meeting generic building code for wood-fired exhaust, let alone being properly configured for reliable results.

It would be nice for some people to share their own experiences, but you have already gotten the expert advice from several directions.

The experimenters you saw with minimal or no chimneys are getting their RMHs to work due to mild conditions. It is true that an RMH has an internal draft "push" that ordinary woodstoves do not, but this cannot compensate for a good chimney without cooperative weather. Any woodburner will work better with a good chimney. It may be "normal" to have smokeback on occasion, but that would be due to either an inadequate chimney or external conditions like tall buildings, trees or hills that that are beyond individual control. You have no significant external issues; wind itself is not a problem to a well-built chimney, and the ridge of your roof is uncommonly clean and well-positioned to host an excellent chimney.

Dean Howard wrote:Shilo, and Satamax...

I think half the appeal of the RMH is the high drive of the furnace, and less worry about an expensive, well thought out chimney... though I can see your points now. I sounds like you are coming at this with a good knowledge of physics... I definitely am not. Isn't the powerful "drive" of a typical RMH, what prevents most of the push-back from wind, despite what RMH chimney experimenters seem to use?... because many people were not using a traditional chimney in my reading, taking that out of the equation, and some barely having any vertical run. I'm pretty sure I'm not alone trying to understand this. Thanks for the physics lessons guys.

Now, to hear back from the practical side: Are there any actual RMH operators out there having Wind push-back problems in windy, high altitude conditions?... just so I can get feel of what may be normal, despite the "good physics" argument...

Well, it's rather funny, because all the guys telling you their horizontal exhaust works wonders, and they never report back. Then there's the many ones, using that arangement, and coming here for troubleshooting, having poor draft and smokeback problems.

And i live up high, 5000ft, snowy southern french alps. Cold, extremely windy at times. Sometime real damp too. Or real dry most of the winter.


I've used all sorts of contraptions, and funky chimneys before having my own place. The real answer is, use a proper chimney. The proper solution for your house, i would say, guyed metallic double layer insulated chimney. With a bow to protect it from being pushed by the snow.

Something like this!

http://www.fumisterie-pro.com/produits/kit-de-haubanage-galva-poujoulat/

Glenn Herbert wrote:To repeat because it seems needed... Your chimney...

Sorry, bubba... this is an old picture... someone asked to see the house and terrain. As told in my very first post, I'm thinking about a future RMH.

I do appreciate all the expert testimony on chimney, believe me, I do, thanks. But it takes time to realize who the experts are.

Glenn Herbert wrote: Any woodburner will work better with a good chimney. It may be "normal" to have smokeback on occasion but...

Hence my original question... as I was looking for real, or anecdotal evidence in a similar altitude and climate situation as mine.

Something like this!

Great picture Santamax... I'm agreed this is the best route, by far, to have a working chimney, though I'm sure the "low budgeteers" would build the RMH, and probably not bother with the higher cost of a chimney, once they have tuned their RMH outdoors. This may be a good time for the experts to warn us of exhaust gases... even for an RMH. :}

I'm thinking about a future RMH

so for your conditions, I'm strongly recommending that your 1 meter insulated chimney will leave the house very very close to the roof peak. if you don't love troubles.

Gotcha...Thanks

Dean, you can also make it on the cheap.

If you have access to a metal brake, you bend 15"x15" metal boxes out of galvanised sheet metal, stuff roxul around black stovepipe in there. "et voila" you have an insulated chimney. Cables shouldn't be too hard to find. And making a chimney cap shouldn't be that hard either.

You paint the metal sections of the color you want. And you're done. You could also use HVVAC spiral pipe for teh outer layer. If it's just to check the feasability, before you buy anything, even 30gal metal barrels could do the job temporarily.

Dean Howard wrote:
I think half the appeal of the RMH is the high drive of the furnace, and less worry about an expensive, well thought out chimney... Isn't the powerful "drive" of a typical RMH, what prevents most of the push-back from wind

Now, to hear back from the practical side: Are there any actual RMH operators out there having Wind push-back problems in windy, high altitude conditions?... just so I can get feel of what may be normal, despite the "good physics" argument...

One thing to keep in mind is that the rocket drive is only strong once it is going well. When you are just starting a fire the drive is weaker. I have had a few times where when I was starting the fire a strong wind gust pushed back so hard it put the fire out and spewed massive amounts of smoke back into the cabin, making the smoke detector go off. I have a chimney that goes out the side and then goes up just short of the rooftop - I think I need another 5' section to make it better.

Thank you for your reply of a real-world RMH. I would be real surprised if this wasn't the norm.

I would love to hear from you builders, who have built 10 plus, and are familiar with the type of feedback you are getting from your customers. Ernie? Erica? PW?...Ianto?, surely there are many more... Anyone got a direct line to these folks, so I can get a lot of feedback in one place?

Especially notice Ron's comment:
"I have a chimney that goes out the side and then goes up just short of the rooftop - I think I need another 5' section to make it better."

This is the classic case of an inadequate chimney (no offense Ron). It may even technically meet building code, but because it is apparently far from the ridge, it gets interfering turbulence in the right (wrong) conditions. What you need, aside from builders with long experience, is analysis of whether the reported good or bad smoke behaviors are connected with ideal chimneys like we are advising, or ones with issues whether avoidable or not. You have a situation where you should be able to build an ideal chimney, right at a clean ridgeline.

Gotcha on the chimneys everyone, thanks!

Great chimneys will clear up a multitude of problems, as I'm learning from you all.
I'm still trying to get a baseline for the RMH systems we so frequently hear about in Permaculture.

I'm still looking for real-world RMH successes, or near misses, just to get an idea.

Dean, t think you've had the best advice you could get here. Shilo has a fair bit of builds under his belt. Glen too, and i have a few too.

Besides what Ianto Evans says in his book. He even states that he has the occasional smokeback too. I don't think i have heard of anybody really making one work without a proper chimney.


I mean, smokeback can be ok, during a fair'ish day, when you're at home, and can open the windows. But what would happen if that was an evening, when it's bellow freezing, and you realy need to heat the mass. You're burning all evening along. And then, it's time to go to bed. The burn is not finished; And you're dozing off. You realy need to go to bed. So you do. And then, your rocket, god know why, reverts. Fill the house with smoke, without anybody noticing.

Would you think you would like this?

Dean : I come to bury Caesar -not to praise him ! BUT the Caesar I want buried is the Idea of the near perfect and user-friendly Pellet stove!

When the simple pellet stove was developed to have a (mostly) insulated storage hopper And The Built-in Through the wall air to air Heat Exchanger

The Air to Air Heat Exchanger built into the exhaust gas discharge vent did save a lot of heat energy that otherwise would have been Lost to the environment !


Its sales exploded ! It was sold as Convenient, Cheap/economical, and safe ! Unfortunately the show room salesman made promises that the installer could

not Meet !


Often, the Installer was often overruled by the homeowner who Demanded the Pellet Stove's installation in the wrong locations. Further the 3'' or 4'' shine-y

Tin Exterior Vertical Chimney, recommended by the installer as a 'band aide' * was rejected or only reluctantly agreed to!

In my area of rural New York these units are universally condemned by Local Code Enforcement Officers and Local fire departments responding to too many

'smoke in house' / 'Smoke detector going off, - Real estate agents attempting to sell properties with pellet stoves want the siding around the stoves discharge

scrubbed back to cleanliness often suggesting the removable to the cheap ticky tacky exterior Tin chimneys referring to them as 'looking like they belong on

an out-house ! '


I certainly can understand if you have experienced conditions severe enough that you can not always use your pellet stove on your schedule or convenience

why you might be wary of any wood stove where This condition was quoted as a problem !


As every Rocket Mass Heater is a one-off D.I.Y. Project it is nearly impossible to promise that you will never have a similar problem with a RMH .


One of the most important tasks your Fellow Members and Rocketeers all share is a desire to 'tout' the safe operation of a RMH, with different Rocketeers

reporting individual experiences. Success is always the largest common denominator. The one thing we all want is finding dedicated D.I.Y. RMH Builders

to swell the ranks of all rocketeers . Usually I am the spokesman for caution, As this post has grown our fellow members are now showing their conservative

side !

Remember, as boosters we can make (many) proposals and suggestions for your future build, ultimately the build will be your creation. Knowing that careful

preparation equals good luck then good luck be yours indeed ! For the Good of All the Crafts ! Big AL !


* Some times the problem can be clearly be traced back to a damaged gasket in the area of the storage hopper ! a.l.

allen lumley wrote:Dean : I come to bury Caesar -not to praise him ! BUT the Caesar I want buried is the Idea of the near perfect and user-friendly Pellet stove!

a.l.

FYI to all: I'm a real advocate of the pellet stove, when properly installed. I ran for years at 7,000 feet and heated my entire house, venting my insert out a chimney pipe.

MY recent purchase of a "Gravity-Fed, NON-Electric Pellet Stove is another animal, and is experimental for me, and until I get an adequate chimney, it does have smoke back. I only brought it up because most people wouldn't even know they existed.

Dean : thank You!!! And do please keep us informed of your developments ! Big AL !