flue system height, and slope?

I see in most designs the flue system height from the floor is roughly at the same level as the burn tunnel height, can the flue system be lower? for instance 5" 10" or could this create backdraft from the longer vertical distance from the barrel?.

Another question, can the flue system have a slight slope upwards as it starts from the bell? would it help against potential backdraft? or would it maybe just accelerate the exhaust and not heat the thermal mass as much?

Two things to consider:

1. The exhaust temperature from a stove is low enough that you can put in a fan at the exit port to help your draft. I would be tempted to do this with a 4" pipe, entering an 8" pipe from the side, with a right angle bend. The fan blows air into the 4" pipe and it entrains air to push out the end. My guess is that you would need the fan for only 5 minutes when firing the stove.

2. Running a slope up should help even out the heat on a long run, but much depends on the air flow speed. A rocket stove has a pretty fast exhaust. Convection effects are going to be minor. However, having it closer to the surface of the bench at the other end, will make that end warm up faster, but it will also cool faster, since the heat isn't as deep in the mass.

Leonard Allen : Part of the magic of a good working Rocket Stove is the heat gain in the system as the 'flue gases' cool down below 212 F.
At that point we gain the rather surprisingly large heat of condensation. Due to all of the variables, it would be nearly impossible to tell when
and where in the Thermal Benches Stovepipe that this condensation begins. This should be one or more threads all to thereselves ! The point
here is that approximately the last 1/4 of the pipe should slope slightly downhill to allow water to drain out of the pipe to the out doors!
Any slope that is enough to be visible is enough slope !

There are out there high efficient, Home heating, Forced air oil and gas fired furnaces that for a variety of reasons have a 'booster fan' inline in the
exhaust pipe, The failure rate for the 'booster fan' in oil fired furnaces runs ~5 years~, thats three replacements in the 20 year warentee'd life of
the Furnace, the failure rate for gas furnaces seems longer, none of these fans are like what S.G. B. suggests and would be a D.I.Y. build 1

For the good of the craft, be warm, be safe, PYROmagicly - Big Al

allen lumley wrote: Leonard Allen : Part of the magic of a good working Rocket Stove is the heat gain in the system as the 'flue gases' cool down below 212 F.
At that point we gain the rather surprisingly large heat of condensation. Due to all of the variables, it would be nearly impossible to tell when
and where in the Thermal Benches Stovepipe that this condensation begins. This should be one or more threads all to thereselves ! The point
here is that approximately the last 1/4 of the pipe should slope slightly downhill to allow water to drain out of the pipe to the out doors!
Any slope that is enough to be visible is enough slope !

There are out there high efficient, Home heating, Forced air oil and gas fired furnaces that for a variety of reasons have a 'booster fan' inline in the
exhaust pipe, The failure rate for the 'booster fan' in oil fired furnaces runs ~5 years~, thats three replacements in the 20 year warentee'd life of
the Furnace, the failure rate for gas furnaces seems longer, none of these fans are like what S.G. B. suggests and would be a D.I.Y. build 1

For the good of the craft, be warm, be safe, PYROmagicly - Big Al

I'm just building the flue system so the pipes are still in the open, it will be only 15' horizontal run, but i'll do some testing before covering it all up for good.
i'm making it about 4" from the bench top, which might be made from wood boards instead of just adobe.

To All : I know I'm overstating the obvious here but, We have a design that is capable of great efficiency in turning wood, ESPECIALLY small wood,
into heat energy, it has a name and that is - Rocket Stove ! After we have created this minor(!) miracle, we still need to deal with this gift properly

If we make a serious effort to use this great gift and not squander it the way that conventional Wood Stoves do, we are given a second miracle. When
we use this boon from mother nature as we must believe we were intended to use it, (and store it for later use ) frugally, it's name is Thermal Mass .
Its use reveals this second gift, the latent heat of vaporization, which we 'get back' and use or store as the flue gas temperatures drop back below 212F!

And what cost do we pay, what burden must we bear to be given this benison. Its simple, we properly design our thermal battery/mass to use all of the
heat energy to a point near 150 F or lower at the outdoor chimney, and allow for the drainage of condensed water vapor in the last 1/4 of the Thermal
Mass! For the good of the Craft, be safe, keep warm, PYRO magically -Big AL

allen lumley wrote: To All : I know I'm overstating the obvious here but, We have a design that is capable of great efficiency in turning wood, ESPECIALLY small wood,
into heat energy, it has a name and that is - Rocket Stove ! After we have created this minor(!) miracle, we still need to deal with this gift properly

If we make a serious effort to use this great gift and not squander it the way that conventional Wood Stoves do, we are given a second miracle. When
we use this boon from mother nature as we must believe we were intended to use it, (and store it for later use ) frugally, it's name is Thermal Mass .
Its use reveals this second gift, the latent heat of vaporization, which we 'get back' and use or store as the flue gas temperatures drop back below 212F!

And what cost do we pay, what burden must we bear to be given this benison. Its simple, we properly design our thermal battery/mass to use all of the
heat energy to a point near 150 F or lower at the outdoor chimney, and allow for the drainage of condensed water vapor in the last 1/4 of the Thermal
Mass! For the good of the Craft, be safe, keep warm, PYRO magically -Big AL

Is it worth to insulate the outdoor chimney?,i'm making the exhaust go out horizontally then the vertical part outside rises almost from the floor to about 3 meters, someone told me it would be good to insulate that maybe with some glass wool around all the outdoor part of the exhaust.


Can't the downhill slope in the last 1/4 hinder the flow ?. could it all be uphill instead and drain the water back to the ashpit in the manifold ?

Leonard Allen : With a good clean highly efficient burn we are reducing the wood to it's basic elements, if this is truly happening, then ALL of this mineral ash
will have a feel on the fingers just like talcum powder. Any feeling of grittiness should be considered to be proof that there is Lye remaining in the ashes,
until a ph test proves other wise ! Lye and water from condensation is not good for lots of things, two of them are iron/steels and mortar, and one of the
reasons most stove pipe is galvanized.

Having said that, any slope even 2-5 degrees down slope will always be preferred, besides, we want to gain the latent heat of vaporization, not re-create it !
The stovepipe should be oriented within the horizontal thermal mass with the male end pointing towards the "T" ditto the vertical!!
Not knowing your location/climate, house location in relationship to prevailing winds, and averaged temp of your flue gases at discharge, And being con -
servative, I would recommend a flush mounted, Double wall or insulated "T" connecting to the vertical stove pipe (also double wall or insulated), you can
try operating your Rocket Stove with only 3 meters of vertical pipe, but, be aware that you may have to add enough additional pipe to a point 3' - 5 ' above
the tallest part of the house and install a storm cap!

Insulation wrapped around the outside of the stove pipe will become wet stove pipe, this time the latent heat of vaporization, will cool the pipe, not protect
it! Does it get cold enough to freeze where you are, then you also have to deal with the latent heat of thawing ,Or sublimation again cooling not insulating!

For the good of the Craft ! b.s.,k.w., PYRO AL

Please help me to understand...I am summarizing what I have gathered about the flue chimney and I'm doing it in this thread because I don't mean to make people repeat themselves.
So the latter part of the horizontal pipe is tilted slightly downwards to remove any condensation water. Goes through the outer wall of the building and ends in a vertical elbow/vertical tee. The vertical pipe does not need to be kept inside as it already cold and so the bend is located outside to vent the toxic gasses. In order for the condensation to get out of the pipe, use a vertical bend (From the picture in the "Rocket Mass Stoves" book-pg26), you leave a little space in the pipe to bend connection and the water drips out this space. I assume with a tee, the water drains to the bottom part of the tee...but how does it get out? And I live in a horrifically cold place (Alberta, Canada) where any water dripping out a crack is guaranteed to freeze 9 months of the year. Allen mentions insulation on the outside pipes not doing anything.
Perhaps in my climate I should: tilt the pipe downward, add the bend but keep it inside, let the water drip out the bend, and keep the vertical pipe within the room till it reaches the ceiling, where I can put it through a ceiling box, then use heavy duty insulated pipe to go out a pipe hat in the roof and 5 feet above the ridgeline.
But the book is very adamant about creosote and toxic gasses that are better leaked to the outside rather than kept inside. How do I let the water out and keep the gases from escaping?
Thank-you!
Meagan

Meagan Poisson : The only advice I can give you that I can guarantee will always be effective would be to move south 1,000 Km. .

Due to your potential for long periods of extreme weather you probably will be happier with an inside insulated chimney, I want to invite you to go to

permies.com/t/25435/rocket-stoves/great-working-rocket-mass-heaters#215410

Here in extreme Northern new york we are north of the populated parts of Ontario, and Northeast of LaKe Ontario so We have experienced a frost
every month except Aug for as long as I can remember, and have even lost police cruisers in snow drifts 100 Km inland from the Lake !

Enjoy the videos, please come back to these forums and start a new topic with any questions and someone will get you a good answer !

Be safe, keep warm,comments and questions are welcome and solicited Think like fire,flow like gas, don't be the marshmallow ! Pyro - AL

Helpful stuff on Leonard's second question (though not a definitive answer), but how about the first question of a flue 10" lower than the burn chamber? That actually might help the flow if some of that extra height is from a larger manifold to make the turn from the barrel to the flue. Has anyone built a RMH with the burn chamber higher than the flue?

Elliott,
i had to build it lower and in my case there were no problems, see this thread

https://permies.com/t/26748/rocket-stoves/level-horizontal-flue-feed-chamber

D. Elliott :Exterior insulated pipes are a good thing, if sealed! Wet or frozen insulation will drop the temperature of the chimney and reduce its ability to draw.

Your 2nd question was a very good question, and I am glad you asked it! If you look at Videos in You Tube Land at the CRAP that are often called Rocket
Stoves, And some times even Rocket Mass Heaters these 'Flaming units of Death' rarely show the build and most of what are shown are definitely under
insulated !

Because you usually want to insulate all the way around your Combustion Chamber to increase temperatures quickly, for maximum efficiencies ,and (Usually)
you want the horizontal pie low in the mass to help conserve the heat, this is the most common way a rocket mass heater is built, not necessarily the 1st R.M.H.
built, but then all after that ! Hope this helps and is timely ! For the good of the Craft!

As always, your questions and comments are solicited and are welcome. Think like fire, flow like gas, Don't be the Marshmallow! PYRO - Logically Big AL

wouldn't a sink trap (that is filled before first firing) keep the gases out?

in case my terminology is off, a sink trap is that u-shaped piece under a sink that always stays filled with water to prevent any bad smelling gasses from the drain pipes coming up through the sink.

Andrew Ray wrote:wouldn't a sink trap (that is filled before first firing) keep the gases out?

in case my terminology is off, a sink trap is that u-shaped piece under a sink that always stays filled with water to prevent any bad smelling gasses from the drain pipes coming up through the sink.

Your terminology is correct, Andrew. That would be a reason to be careful that water never gets in the flue. We want the flue gasses to pass easily through the mass.