Zero Fossil Fuel Rocket Stove Heater

The ZeroFossilFuel Rocket Stove Heater

Theory of operation and assembly details.

©20! ZeroFossilFuel ZeroFossilFuel This document may be freely distributed" only free of char#e char#e and unedited.

$et me start this document by sayin# that" if you intend to replicate my Rocket Stove" it is hi#hly unlikely that any t%o replications %ill be e&actly alike. That is as it should be because" if no one tried anythin# ne%" development %ould cease and there %ould never be any pro#ress. 'f you(ve #ot an idea that you think %ill improve on my desi#n" build it) 'f it %orks" please share it) *hat ' %ill do here as best ' can is take you throu#h the steps ' %ent throu#h to determine all of the critical dimensions for buildin# your o%n stove based on the ra% materials you may have found or bou#ht. The photos in this +,F document are fairly hi#h resolution so they can be -oomed in to see finer details.

So what is a Rocket Stove Mass Heater? There is a %ealth of information re#ardin# Rocket Stoves all over ouTube and the %eb" and numerous variations on the basic desi#n. ' encoura#e you to do some research. /ood places to start are http11%%%.richsoil.com1rocketstovemassheater.3sp and http11%%%.ernieanderica.info1rocketstoves. 'n the strictest sense" it is #enerally a %ood fired heater %ith an internal flue or riser" covered by a barrel of some sort %ith a lon# e&haust pipe that runs throu#h a cob 4mi&ture of clay and stra%5 thermal mass %hich acts as a heat battery" #ivin# off stored heat in bet%een burns usually bet%een evenin#s and mornin#s %hen family are asleep and you don(t %ant to be burnin# %ood then any%ay. 6ey benefits of a Rocket Stove over traditional %ood stoves are • •

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7s little as 10 the consumption rate for the same effective heatin# to your livin# space" 8irtually no smoke or carbon mono&ide byproducts" 3ust carbon dio&ide and steam" 8ery little ash buildup %ith easy cleanout.

8ariations on the desi#n include the 9+ocket Rocket: 4'(m not terribly impressed %ith these5 and mini Rocket Stoves intended for cookin#. ' %ill not discuss either of these here in any detail because neither of them conform very %ell to the ori#inal concept despite that they %ere named Rockets. 6ey features that truly define a Rocket Stove are •

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8ertical %ood inlet to a small firebo&" Hori-ontal burn chamber" 'nsulated internal flue or riser" 7 drum or barrel over the riser for #ases to cool and #ive off heat" 7n e&haust at the bottom that often e&tends throu#h a cob bench to slo%ly store ; release heat.

How does it work? 8ery %ell" thank you. or more of the heat created by the fire up the chimney flue and out" #ivin# off only left over radiant and convection heat transferred to the body of the stove and into the room. 7 Rocket Stove" by contrast" is able to scaven#e almost all of that previously %asted e&haust heat %ithout buildup of creosote or other deposits. Here(s ho%.

©20! ZeroFossilFuel This document may be freely distributed" only free of char#e and unedited.

*hen a fire is started in the firebo& of a Rocket Stove" all it should take is a puff of breath or t%o do%n over the firebo& to #et the hot #ases to start travelin# throu#h the short hori-ontal burn tube and up the internal riser.
All of the draft necessary to make a well designed Rocket Stove function properly is created inside the internal riser.

' cannot stress this point enou#h. From the moment the #ases e&it the top of the riser and do%n the sides of the barrel they be#in to cool. The draft created by the riser behind the coolin# #ases should be so stron# that" not only does it pull in fresh air behind it" it also pushes e&haust #ases out ahead of it %ithout the need for any additional draft created by a typical chimney flue. This is %hy it is so critical that the internal riser 4and even the hori-ontal burn tube5 be as insulated as you can practically make it. ?y so doin# it •

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@reates a super stron# draft in a very small space and +rovides the environment for secondary burn of any unburned #ases

Some say it creates a plasma burn but that(s 3ust not possible at the temperatures %e(re dealin# %ith here. Aven still" the combustion is complete and that(s %hat counts. Smoke and odor are byproducts of incomplete combustion. 7 %ell desi#ned Rocket Stove produces virtually no smoke or odor at all" has very lo% flue temps #oin# outside and e&chan#es most of its heat into the livin# space.

So where do I start? 7t the be#innin#" of course. ,uh)
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Bi# %elder 4flu& core is fine or #as if you can afford it5 Sheet metal bendin# brake. Bine is !0:. Tin snips. 7n#le #rinder %ith #rindin# %heel and cuttin# disks. ,ry%all sCuare. 2: bubble level Sharp indelible marker.

De&t consideration is overall si-e. 7sk yourself 9Ho% bi# of a livin# space do ' need to heatE: 'n my case it %as 3ust a 20 sCft %ell insulated %orkshop %ith about 2G0 cuft of air space. So" ' scaled do%n the overall si-e accordin#ly from typical %hole house heaters that use !0 or GG #allon drums. *hile scaven#in# throu#h a couple of scrapyards ' stumbled across a discarded  #allon air compressor tank. +ARFA@T) So... •

Step 1. ind your own perfect !arrel" drum or tank.


This compressor tank for me %as the ideal choice. Dot only %as it the ri#ht appro&imate si-e" it %as ru##ed havin# 1=: thick side%alls. By tank measured 2: diameter and about !: lon#.
Step #. $etermine the internal si%es of your riser" !urn tunnel and feed tu!e.

@ollectively this is kno%n as the JTube. 7 typical GG #allon drum heater desi#n uses a =: inside diameter riser. 7 typical !0 #allon drum heater uses a K: inside diameter riser. Therefore" ' e&trapolated that mine should be about :. ' had read about others %ho had tried makin# : systems %ith mi&ed results. @onfident that ' could make it %ork ' for#ed ahead despite the naysayers. ' kne% that ' %as #oin# to use some sort of firebrick for the firebo& and hori-ontal burn tube. By first concept for the riser %as to use a : & 2: #alvani-ed vent pipe as the inside %all of the riser %ith a K: & 2: #alvani-ed vent pipe for the outside %all and : of fiber#lass insulation in bet%een. Several people e&pressed %hat ' later decided %ere valid concerns over this choice ' had made. They %ere •

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Amission of poisonous #ases from the -inc #alvani-in# burnin# off" Short life span from rapid rottin# under the e&treme hea t" Beltin# of the fiber#lass %ool.

*ith the su##estions from others and kno%in# that many Rocket Stove builders use firebrick for their risers too" ' decided to %ork throu#h the desi#n usin# firebrick as a liner and retain the #alvani-ed pipe outer %all. To do so ' %anted a crosssectional area as close to a : round pipe as ' could #et %hich is 2.GK sCin. ?ricks arran#ed to #et !.G: & !.G: sCuare tube ended up bein# 2.2G sCin. @lose enou#h for #overnment %ork. The final dra%in# illustrated belo% sho%s e&actly ho% ' arran#ed my bricks to achieve this openin# si-e.


Averythin# else about the internal dimensions is all about ratios and crosssectional areas. 'n a nutshell" the crosssectional area that the hot #ases must pass throu#h should be the same or increase sli#htly at every point alon# the path %ith the e&ception of the area bet%een the riser and inner tank %all %hich is often much #reater. So" startin# %ith my riser of !.G: & !.G: •

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Hori-ontal burn tube area should be L or M the riser. Bine is !.G* & !.2GH 4.!G sCin5 Firebo& openin# also should be L or M riser but not L than the burn tube. Bine is !.G: & !.2G: 7rea at the top of the riser should be bet%een .G& to 2& the area of the riser itself. 7rea of the e&haust port should not be L area of the riser. Bine of : round or 2.GK sCin.

The area at the top of the riser is calculated by the circumference of the '.,. & distance to the top of the barrel. Bine is !.G: &  & 2: or 2= sCin" a hair over 2& the riser area.
Riser hei#ht should not be L !& the hei#ht of the firebo& tube" 2& the len#th of the hori-ontal burn tunnel" or & the hori-ontal burn tunnel plus the feed tube. Bore is better here.

By riser is about & the len#th of the burn tunnel or the feed tube" each measured at the shortest dimension. The lo%er portion of my Jtube %as first si-ed up by stackin# fire bricks in different confi#urations on my bench top until ' %as happy %ith the ratios. Startin# %ith the firebo& feed tube a#ainst the tank outer %all or very close" ' made sure the burn tunnel %as lon# enou#h to center the riser in the tank. The dimensions for me seemed to 3ust fall into place by themselves. ou may or may not be so lucky dependin# on %hat si-e tank you end up %ith. The point is be a%are of placement for all components %ithin the tank as you e&periment %ith brick layout. 't(s not a terrible thin# to place the riser off center in the tank if you must. Just be a%are that more heat %ill radiate from the side %ith the #reatest #ap bet%een the riser outer %all and tank inside %all. There is one very special rabbit cut ' had to make for everythin# to fit to#ether precisely as seen to the ri#ht and in the dra%in# belo%. By bricks are all assembled free floatin# inside a %elded heavy sheet metal enclosure that is open at the top at both ends.
By brick riser is three #roups of  firebricks locked into place %ith a small bead of furnace cement alon# all inside ed#es of each #roup formed %here they overlap. The three #roups are not cemented to each other. They simply sit atop each other. Dotice in the dra%in# belo% that the middle #roup 425 is a mirror of 4"!5. This %as done so that brick seams crisscross each other %hen stacked instead of ali#ned parallel. This inherently reduces the tendency for #ases to escape %here they ou#ht not. To keep them ali#ned %hile the furnace cement almost fully cured ' simply strapped them usin# rubber bands and maskin# tape around a uniform & piece of lumber 4%hich actually measures !.G: & !.G:5 then tapped them out" set the bricks upri#ht and allo%ed the furnace cement to finish curin# overni#ht. The ne&t step %as to cut my tank. ' kne% ' needed t%o thin#s • •

That the top of the burn tunnel cover be perfectly flush %ith the top lip of the lo%er section and That ' %anted 2: spacin# bet%een the top of my brick riser to the top inside of the tank.

7ll ' did %as assemble all the bricks to my lo%er brick carrier" stack the three riser sections" measure from the top ed#e of the riser to the top of the top burn tunnel metal cover" add 2: and %ith a dry%all sCuare mark that point on the side of the tank every couple of inches from the top. That ended up bein# e&actly 0: from the bottom. The ori#inal platform for the compressor that %as %elded to the side of the tank %as cut off and reused as the base to hold it vertical. 7 bubble level %as used to ensure the tank %as plumb before %eldin# the ne% base into place. The openin# for the metal firebo& enclosure needed to be a close fit at K ; 1=: so ' cut it K: & K:" #round it slo%ly to fit" then tack %elded it in ! spots on each side and t%ice across the bottom to secure it into place. $ike%ise" a bubble level %as used to ensure the bo& %as level so the riser %ould stand strai#ht in the center of the tank before %eldin# it into place.


'n this photo '(ve tack %elded the fire brick carria#e into the sCuare openin# cut into the lo%er tank half. Dotice ho% %ell centered the riser is inside the diameter of the tank. *ith the top half assembled it 3ust brushes up a#ainst the front feed tube brick. 7lso notin# that the burn tunnel top cover plate is as flush to the top ed#e of the lo%er tank half as ' could #et it. The fiber#lass rope %ill be #lued all the %ay around to seal the top half %hen assembled. Here '(ve cut the : openin# for the lo%er e&haust port" added 2 supports to the brick carrier corners and  $ brackets made from small pieces of !1: an#le iron. They %ere drilled first and preassembled to their upper mates %ith threaded rod. The top half of the tank %as set into place" then the $brackets %ere %elded. This helped %ith positionin# and ensured they %ere vertical so that the top half %ould slide freely off the lo%er threaded rod studs. To the ri#ht you also see ' tack %elded more !1: an#le iron to make a flan#e that the burn tunnel end cap bolts to. The intent %as to make the bricks entirely serviceable.


Here is a closeup of the e&haust port starter pipe ' made from a dryer vent adapter pipe. +refab units %ere not deep enou#h to accommodate the curvature of the tank. The pipe %as inserted into the cut openin# first. 7 line %as marked around the pipe to follo% the curvature of the tank %all. Then slits %ere cut every 12: or so all the %ay around up to the line creatin# tabs.
Here(s a look do%n inside the =: #alvani-ed vent pipe at the st #roup of  riser bricks. 'nternal #roups are stacked one at a time. Fiber#lass is stuffed do%n bet%een the brick and pipe %ith a thin piece of %ood trim" 2: ruler" %hat ever you have on hand. Hi#her sections are simply held to#ether by #ravity" friction and fiber#lass" centered by the =: #alvani-ed vent pipe a#ainst the corners of the bricks. The bricks do not cave in because of the lip created by the furnace cement.


7t the left is the completed riser %ith all three sections. The metal strap at the top is bent rou#hly I0N every =.G: into an overlappin# sCuare" then scre%ed throu#h the =: vent pipe to hold it in place like a halo. This keeps the riser centered should the tank be tipped. @orner to corner is 3ust under 2:. 7t the ri#ht is the same vie% %ith the top half of the tank assembled. Dotice that the brick a#ainst the tank is raised sli#htlyE 't(s because a bevel has not yet been made to allo% clearance for the fiber#lass rope that seals the t%o tank halves.

This is a closeup of the fiber#lass rope sho%n #lued to the top tank half. ' later chan#ed this desi#n because the rope kept #ettin# hun# up on and ripped off by the threaded rods %hen ' lifted the top half off for service. ' later #lued it to the bottom half %hich %orked out much better.

And now the fun part. &ime to fire it up'


(AH)))))''' irst test fire was a total success' Time to position it inside and finali-e the installation.


Here '(ve laid out the location for my Rocket Stove %ith concrete brick pavers. The bench ultimately #ets moved further left to a safer distance from the stove. The %all corner is protected by t%o sheets of !( & G( cement board" secured to the %alls %ith nails throu#h !1=: thick %ood trim standoffs to insulate them from the %alls. They are also .G: off the floor to allo% cool air from the floor to enter behind the boards throu#h convection releasin# even more of the captured radiant heat into the room. To determine the hei#ht of the flue pipe throu#h hole ' assembled a standard len#th =: section of vent pipe to the T at the back of the stove then the I0N an#le at the top and let it rest a#ainst the %all. The actual location is a bit left of %here you see it here because a stud %as available to scre% my thimble plate to. By flue pipe thimble is made from t%o plain : vent pipe %all plates and a section of

K: vent pipe cut 2: lon#er than the %all thickness includin# the dry%all and outside sidin#. $ike the tank e&haust starter pipe" slits are cut to create tabs all the %ay around" fanned out to hold in place on both sides.

The outside plate %as scre%ed to the sidin# first" then a 2: hori-ontal section passed throu#h and : thickness of fiber#lass stuffed in to create dead air space and seal out drafts. The inside plate #ets slipped over the vent pipe and scre%ed to the dry%all. The three left hand scre%s all catch the stud and the others use dry%all mollys. Some%here alon# the line throu#h this ne&t series of photos ' spent several days strippin#" #rindin# and %ire brushin# the heavy red po%der coat paint off the top half of the tank and resprayed %ith hi#h temp flat black.


The flue pipe is completed on the outside %ith one last I0N bend up%ard and another =: vertical pipe %ith a rain cap. The photo sho%s only a 2: vertical piece but that %as later made lon#er to elevate the rain cap 3ust above the roof peak. 't is held stable %ith t%o straps scre%ed into the vent pipe and to the soffit fascia board. ?ecause this is not actual double %all insulated %ood stove flue pipe %hich is 8AR e&pensive" and because the Rocket Stove produces so much steam" condensation inside the pipe before the e&haust #ases #et out the top is a real problem. *ithout a %ay to drain them out they %ould literally flo% back into the inside vent pipe" pool in the bottom of the T and drain out onto the floor) To address this %hat ' did %as tilt the hori-ontal pipe do%n%ard sli#htly 4only 2! de#rees5 and drill a !1K: drain hole in the bottom 3ust before the I0N elbo%. That %ay condensation drains out" not in. 7lso note that ' took #reat care to ensure that all vent pipe seams %ere sealed %ith either aluminum vent pipe tape or furnace cement %here appropriate.

'n an ill fated attempt to #reatly e&tend burn times bet%een feedin#s ' made up this %ire loop frame from a piece of !1: flat bar and some coat han#er %ire %elded to the bar. This %orked fine for precut lumber but not so %ell for irre#ular lumber and dead tree limbs. ' %as also still not happy at this point %ith ho% Cuickly ' %as able to %arm up the room. *ood stoves need air to burn. That air has to come from some%here. *ithout a controlled fresh air inlet the only other place it can come from is cracks around doors" %indo%s and outlets because of the ne#ative pressure it creates in the room. From there it cools do%n the livin# space first before it finds its %ay to the firebo&. So...


Mod *1 + resh air inlet.

$uckily for me the shed is a raised structure. 7ll ' had to do to relieve most of the ne#ative pressure created by the stove and brin# in fresh air %hen and %here ' %anted it %as to pop a !1: hole into the floor %ith a hole sa%. ' then ran a !: fle&ible aluminum vent pipe up to a shroud around the feed tube that doubled as a small %ood hopper. This also confines the inlet air over the firebo& %here it is immediately sucked do%n for combustion rather than circulatin# throu#h the room first. ' believe this is a key point that many Rocket Stove builders miss. The inlet air should enter do%n and around the %ood in the feed tube" not from an inlet do%n lo% directly into the firebo& burn area. *ithout a lot of do%n%ard air flo%" radiant heat and hot #ases in the firebo& are allo%ed to rise up%ard" #asify the sticks in the hopper and can actually start smokin# and burnin# into the room) ou may have seen my mishap video. 't(s not pretty. @ementin# the shroud to the top of the firebo& feed tube %as a mistake because ' still need it to be removable for cleanin# out ash. 7ddin# the fresh air inlet %as a bi# boost for heatin# efficiency but ' still %anted more. So... Mod *# + Radiator fins

This is simply t%o =( pieces of aluminum roofin# drip ed#e cut into 22 sections 0.G: lon# each" corners #round out to allo% a lar#e stainless steel hose clamp to pass throu#h" sprayed flat black and clamped around the top of the tank. This one mod alone added almost 00 more sCin of radiatin# surface area" droppin# flue temps at the %all about 0NF and makin# it difficult to #et the top of the tank any hotter than G00NF" %hereas ' %as #ettin# almost 00NF. Do% '(m happy %ith the efficiency.


$aily operation 't takes about !0 minutes to #et my stove up to temperature. From there it raises my 2G0 cuft of shop space about G20NF1hour. ?ased on rate of temperature rise and heat losses throu#h four e&terior %alls it is estimated that my stove is puttin# out bet%een !0"000 and !G"000 ?TO1hour. 't does this %ith a %ood consumption rate of only about 0 cuin1hour. $oadin# the %ood is a bit of an art and takes a little practice. The main idea is to put enou#h %ood in the hopper to produce enou#h heat but not so much that you choke off air flo% and not so close to each other that flames can travel up%ard bet%een sticks. ' also find the sticks do not al%ays self feed but need a sli#ht nud#e every so often to #et them to drop do%n. Still thinkin# about that one. For ri#ht no%" to clean out ash ' have reduced the number of scre%s on the front feed tube cover from  to !" tacked the heads from behind and put %in# nuts on the front. ' lift the air inlet shroud off" spin off the %in# nuts remove the metal plate and the front brick. Then ' reach in %ith a hoe ' made from a scrap piece of drip ed#e and the !1: flat iron bar that ' took off the %ood hopper. ' can run the stove 2 ! days bet%een cleanin#s but" ideally" it should be cleaned every day. The only ash that #ets any further than the burn tunnel itself is e&tremely minimal" super li#ht and fluffy. Baybe once a month '(ll lift off the upper tank half and suck out the remains. So far ' have not even had to do it once. Still ahead ' definitely %ant to add a better ash collection and cleanout" and very possibly a %ood pellet hopper and feeder. ' 3ust don(t %ant to use an electric au#ur feeder because %hat happens if there(s no po%erE 7nd %ith #ravity feeders ' %orry about it burnin# back%ard into the hopper. Baybe a sprin# loaded hand crank that can run several hours bet%een cranksE Still thinkin#. 7l%ays thinkin#. ' hope '(ve #ot you thinkin# too) ?etter yet" buildin#) +lease share this document freely %ith everyone you kno% and if you found it useful" please drop a fe% dollars in my tip 3ar at +ay+al. Thanks. 7ll the best" Z

7nd of course the reCuisite disclaimers P The information contained herein is for informational use only. The buildin# and use of items described herein may constitute a violation of your local and1or state codes and re#ulations. The reader holds harmless ZeroFossilFuel and his family" friends" heirs" partners and assi#ns" and assumes all risk and liability for their use of this information.



Zero Fossil Fuel Rocket Stove Heater

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