Wood Fired Furnace Questions - Lots!

[WStayton]

I wasn't sure - there didn't seem to be any ideal place to put this, and it REALLY isn't an exact fit anywhere, but I'll try here!

Being someone who, apparently, enjoys self abuse, I'll pitch this little idea/plan out there and see what y'all have to say!  <g> (I can say "y'all", I am from the South . . . okay, its NY, but its still SOUTHern Tier NY!!!  <smile>)

As you have all figured out, I am in the process of planning and then implementing, a "whole house" energy system.

Location:  Southern Tier of the great State of Taxation - New York!!
  Think long cold cloudy (lake effect) winters, with lots of 15 F to 20 F     time,  and less than ideal solar collection conditions, in general.

Primary electricity = 20 Solar Panels, in fixed mountings, on the roof

Primary heat - hot water  = 2 ea 8' x 4' solar collectors, hopefully homemade

Secondary Electricity – Mercedes OM616918 4 cylinder, 2404 cc displacement, indirect injection Diesel Engine driving a ST-24 Generator with AVR.

Expected operation:  2 x 6 hours/week during "winter" conditions, 1 x 6 hours/week during spring/fall-conditions,  Summer:  On vaction (not needed), hopefully!  <g>

Tertiary Heat:  Heat recovery from the cooling water, oil cooler, and exhaust manifold heat exchanger of the Mercedes.

Secondary Heat:  Wood fired hot water boiler – specs are still a "work-in-progress" , so don't scream too loud!  <g>

It is this last item on which I would like some feed-back, and not seeing any place exactly suited to its presence, I stuck it here.

I have looked at several commercial whole-house type boiler's, both external and internal (my brother is a dealer for a couple of manufacturer's) and thought that for $5,000 to $10,000 I could do better AND way cheaper – but I want to make sure that my "cheapness" doesn't drive the bus over a cliff!!  <smile>

So, what I envision building is as follows:

A large steel box of exterior dimensions of approximately 30" wide x 48" deep x 66" tall., fabricated from 0.500"  hot rolled steel.  Finish is lousy, but cost is, more or less, reasonable.

Inside, this box would be basically divided into three sections:

I. Ashpit – approximately 12" deep (tall) with a door having controllable louvers for primary draft control.

Above that :

II. A fire Box approximately 30" deep (tall), again with a door having
controllable louvers for secondary draft control.

Above that:

III. Two reburn "layers" each having a depth (height)  of 12" and a footprint 6" less than the inside depth, front to back, than the overall furnace. So they would be 36 inches deep. No real segregation between the front and rear 6" entry/exit sections and the main, central body of the sections.

So, the stack-up would be as follows:

Top 12" – catalytic heat transfer area

Under that a sheet of 0.500 steel the goes from the front of the unit to the back of the unit.  Call this the "top separator"

Under the "top separator" there is a space 12" in height that also goes the complete depth (front-to-back) of the unit  Call this the "mixing chamber"

Under the "mixing chamber" is another sheet of 0.500 steel that goes from the front of the unit to,  to within 6" of  the back of the unit.  Call this the "bottom  separator"  The "bottom separator" is also the top of the fire box.

Under the bottom separator is the 30 " deep (height) fire box chamber.

Under the fire chamber is a grate of ¾ rebar, set on a 4" x 4" grid, so the spaces between the grate bars is 3.25" x 3.25"

And, under the grate, is the ashpit.

Ancilliaryies:

Running along slightly below the bottom of the bottom separator are 8 ea 1" diameter stainless tubes carrying secondary combustion air from outside the furnace, immediately above the firebox door to the back of the firepit and then bent into a smooth half circle to discharge 6" into the "mixing chamber", from the rear thereof.  These air tubes are fed from a common 3" diameter tube equipped with a damper capable of restricting air inlet.  (maybe individual 1" butterflies on one shaft, with one in each tube, is easier?)

Running within the "mixing chamber" and the "catalytic chamber" in a loop, from outside the rear of the unit to outside the rear of the unit and looping back outside the front of the unit are the  1" stainless "water heater" tubes and are fed from a 2" (3"?) manifold at the lower back of the furnace and recovered into another 2" (3"?) manifold at the upper back of the unit.  So, each of these loops has two legs, with a smoothly bent loop between them and at an angle of 24 degrees to each other, so when they are installed, the slope is 12 up from the entrance in the back to an, almost,  180, to another 12 degree up slope to the collector.  The thought with the 12 degree upslopes is that I would have "some" flow by natural convection, even when I did not have a circulating pump engaged.

The top separator has six 3" diameter holes in its front 6" section into top of each of which is inserted the feed end of a 3" x 5" oval by 6" long automotive catalytic converter, which simply dumps out into the top of the front of the 12" catalytic heat transfer area, which has the return half of the heat transfer loops.  Automotive catalysts were selected due to my own famialiarity with them and their relatively inexpensive procurement possibilities – think $70 each.  The catalytic converters come with a stainless inlet and outlet cone that goes from 2.5" tubing to the 3" x 5" oval of the catalytic substrate.  They will be cut down for total fit and to increase the inlet area to the catalyst without thereby requireing any forced convection (think combustion blower)

  There are also a set of  "dampers" in the back of the "top separator" so that they can be opened to allow exhaust smoke to bypass the catalyst so that during light-off they will not be over-temperatured due to excess smoke/unburned HC/CO.

Note:  Maybe a set of shut down dampers is required at the inlets to the catalysts, so that it can be assured that there will be no flow through the catalyst during furnace light-up and/or during ovetemperature (attempted) control???

My experience has been that new fresh catalyst coated substrates are something like 100 times more reactive upon initial light off than they are after they have been operated a few times and some crud has built up and the initial very reactive surface area has been scrubbed off a little by exhaust flow so the "First Fire" might be exciting!!!  <grin>

Exhaust from the unit is in the top rear, via conventional 6" stove pipe, again, with a damper.

Obviously, this system needs a lot of tweaking, but this is my first cut to start the process.

Physical construction is probably grossly excessive, with 0.500 steel plate for everything – something like a ton of it, more or less and 3/8 would probably be more than enough.  But, I wanted to build it out of something that wouldn't need any internal supporting structure to hold its shape.

I envision all of the plate connections of the box and section dividers to be made using a 1" angle iron as a reinforcement, through bolted in both directions, every 6" with ¼ x 20 stainless bolts.  Seams to be sealed with furnace cement.

Tube connections to be made using compression fittings, drilled out to allow the tubing to pass through them, at the outside where the tubes penetrate the periphery of the assembly.

Feeds of water  to be done with "offset" feeding, so the cold liquid comes into the distribution manifold, again made with drilled compression fittings, and then goes out in the other direction, so that every tube has the same path length

My SWAG for the cost is something like $3,000, total, vs about $5,000 for the cheapest off the shelf unit that I could find that I thought would work.

Weak areas:  Well, just about ALL of it is a pit of unknowns but I do see a few areas of concern right off of the bat, like 1) Is ¾" rebar substantial enough to stand up to the heat, long term?  Rebar is relatively cheap, but changing it every summer, when not in use.  would be a hassle because something (1" angle iron?) has to hold it in place and unscrewing and rescrewing a couple of dozen ¼ " x 20 stainless machine screws, where one person can't get to both ends, will be a supreme PITA.!  <grin>  And, God help you if the rebar pukes after ten fires and you have to change it during the winter while the house is freezing due to no fire! <smile>

So, what say you, am I NUTS, yet again, still more, already, or am I at least started down the right track?

Comment is hereby solicited – I'll put on my asbestos BVD's!!!   <grin>

Regardz,

Wayne Stayton

[mike90045]

would automotive catalytic converters even work with the wood fire fumes ?  And they are sure to die in 3 years, just like wood stove cats do. I'd just leave them out.

[Tom Reed]

My solution for asbestos BVD's was to join the local volunteer fire department. Now I've got a full Nomex and Kevlar suit and a SCBA for when things get really hot and heavy. Also learned a bit about putting out fires too.

[WStayton]

mike90045:

  Automotive noble metal catalysts, generally made out of a mixture oif 4:2:1 Pt:Pd:Rh, and  will oxidize just about anything, no matter where it comes from - be it non-combusted diesel fuel, or unburned recycled fryer oil, or HC and CO from incompletely burned wood, i.e. smoke.  The problem is that they would like to have a sterile environment, except for the HC and CO  that they are oxidyzing and there is wherein lies the rub - lube oil that slips by the rings, leftover copper ions from the cracked chrime plating over the copper in the fryer basket, or the myriad of "junk" chemicals that are carried in on the wood you burn, will all, eventually, compromise your noble metal oxidation catalyst and turn it into something that has about the same catalytic activity as a hunk of lead!  <grin>  I figured, that with the auto catalytic converters being pretty reasonably priced, I could put a whole new set of them in for about $400 bucks, and, in my sort-of part-time, seasonal setup, I was hoping that I might get four years before I had to replace them.  If they last for four years, I've only got to get the equivalent of about 2 face cords of wood out of them, in heating value, and they have paid for themselves.  I think that I might save the equivalent of four face cords the first season, three the second, two the third and one the fourth, for a total saving over their life of 10 face cords.  IF they do last that long, I'm a couple of face cords ahead of the game.  My SWAG is that they should do a bit poorer than this but, like most everything else in life, its really a crap shoot.  In an effort to be a responsible member of society (and that's what I'm putting the paper work!  <grin>) I think that it is worth the gamble to at least SEE if it works, ONCE.  If, after one season, they are junk, I will just write it off as the price of experience - but, at least I did TRY to be a clean responsible citizen!! <grin>  That's my story, and I'm sticking with it!

  And, if it doesn't work, I can just take them out and use the whole two upper chambers as a "reactor" with the extra air added in, and I'm only out the first cost of the catalysts - seemed like a reasonable TRY to me . . . Doesn't sound like my usual save a nickel at all costs, huh?  Maybe you guys are a GOOD influence on me!  <smile>

  On the other hand, if the first cost of the catalysts was a grand, I would have already relegated it to the scrap heap.  I am a responsible citizen - as long as it doesn't cost TOO much!  <grin>

Tom:

  Unfortunately, after a moderate and a couple of mild strokes, I THINK any volunteer fire department would only be interested in having me oin the force in the position of "crash test DUMMY"!  <grin>

  I guess I'll have to stick to buying my own asbestos BVD's!


Jens:

  "Yup, you are NUTS ** 3, no doubt in my mind." 

   Uh, I THINK that comes under the heading of OLD infomation!!!  <grin>

  Any other comments, other than that I am, indeed, CRAZY???

  Thanx for the input so far!  (I think?!?!)

Regardz,

Wayne Stayton

[mobile_bob]

google

rocket stove and russian fireplace

neither use a cat, or need one in my opinion

also look into old boiler designs, that use "water walls"
they are really interesting in my opinion

you might also consider using some heavy wall pipe casing, some of it comes in very large diameters and you might find some drops
that are about the right size in length for your project

if you find one larger in diameter than the other, and have large end caps made up you could then encase the fire chamber with water, or with sand and a cooling loop or coil embedded in the sand?

the dual pipe design is the direction i am heading, rather than having to build up a square box from flat plate which takes a lot of welding, and
in my opinion likely not as structurally stable as the round pipe section.

just my opinion

bob g

[WGB]

Didn't read the whole thread, so sorry if I'm off!
I'll give you part of my idea.
I use old LP tanks all the time, get them for scrap price.
They already have a hole cut in them, so the safety Nazis don't have a cow!
Anyway put a 250 in a 500 or 500 in a 1000 gallon.
Thats all I'm saying, I have it figured out, but the rest a secret!

[Ronmar]

I find when I build things I usually get it right on the second or third try...  So at $3K a pop, you might be better off buying the $5K unit initially and developing your own design after studying what works on that one and more importantly what dosn't over a few years of operation.

The most unique design I have seen is a downdraft or blowdown design that actually has the firebox outlet straight down into a secondary chamber.  All teh ash/embers go thru this orifice and are completely consumed.  This design of course uses forced air to accomplish the almost blastfurnace like effect(internal video looks like a blowtorch into the second chamber).  IMO, it is the most efficient and most complete combustion of the wood product before attempting to extract the heat.  It is also my opinion that wood should be burnt using forced air.  If you do not fully breakdown the wood during combustion, you better make this thing easy to clean as you will be doing a lot of that... 

As always, good luck.

[SteveU.]

Google this and copy make for the most durable, highest efficiency:
www.garn.com
For me I'll accept a bit'o loss in efficiency from ~90% down to only 72%, forgo the motors, catalysts and an electricity dependency and stick with a glass fronted, burn any kind of wood, four burn zone QuadraFire. Good for warming the heart and soul, and old arthritic bones. Our oldest dog and cat heartily agree.
Regards
Steve Unruh

[WStayton]

mobile_bob:

  About the welded-up water-tight stuff:

  I kinda have a bad taste in my mouth about any sort of welded up firebox - all generated by experiences in my misspent youth.  My Dad, who was a pretty-fair farmer-Jack-of-all-trades-welder (think upside down inside of a combine while looking in a mirror!) built a stove/furnace for our then new house.  It was an add-on to the commercial hotwater-boiler/baseboard-heat that he originally installed in the house when he built it in about 1955 - so the technology was not astounding!  Anyhow, he built a 4 x 6' x 6' box out of steel plate in which the bottom 4' x 6' was the fire-box/ash-pit and the top 2' x 6' was a water tight tank that sat there and heated the water that it contained and any time the circulators came on for the hot water boiler, circulated that 24 cu ft of hot water into the system.  It DID cut down the fuel flow to the main furnace by something like 1/4 to 1/3, but it was the ORIGINAL PITA to keep from leaking - he bought Barz-Leak by the case!  <grin>  The system was just a box with a few supports/partitions inside, made of hot rolled steel plate and arc welded together and is was slightly pressurized, 3 psi, if I remember right.  Anyway, the other seams on the unit were also continually cracking open and leaking slight smoke leaks and it was a continuing hassle to try to keep it tight.

  Being an Engineer (which will get you a cup of coffee . .  .sometimes) I figured there must be a better way!  Hence my plan for angle-iron on all intersections with furnace sealing cement.  Furnace cement has held old cast iron coal furnaces together in a more-or-less non-leaking form for about a 100 years, and I figured it was a good time not to re-invent the wheel!!!  But, you ain't never going to make a water tight joint with screws, angle iron and stove cement, so I just wrote the whole water-tight compartment idea off.

  I did think about something like a big-diameter thick-walled tube (24" - 30"?) stuck through the firebox and capped and used as the heat transfer "medium", but I figured that the surface to volume was so terrible that it would have to be about 40' long to have enough heat transfer to solve the problem effectively.  Round tubing IS attractive from the standpoint of leak tightness IF you can cap it off tightly/correctly.  A threaded "pipe cap" in 24" diameter IS available, but I don't want to think about the dies to cut the threads in the ends of the tubing!  <grin> And, most lathes have a little trouble with chucking in a piece of pipe 40' long and 30" around!!!  <smile>


About the catalysts:

   I didn't view the catalytic converters as a central-necessary part of the unit, but rather, something that I could add on and, at least appear to do something socially responsible - they don't cost a lot and on a one-try basis, I think they are worth the small effort to accomodate them, and, maybe, break-even on a cost/benefit basis.  Check back after initial fire-up, I MAY have a much different opionion of their value or lack thereof!  <grin>

SteveU.

  I thought about just ignoring the idea of having a hot water heater in the system and just using what I got from the diesel and solar-collectors but it SEEMED like a waste to have the thermal storage boxes/tanks and baseboard heating equipment and not use it to distribute all of the required domestic heat - except for the glass front in the main living area, but that is for "effect" as much as heat!

  The interior of the building is pretty simple:  One large kitchen-dining-living room (about 24' x 24'). a very small bath (5' x 8') and two bedrooms (10' x 12' ea) with a total of 50 lineal ft of 32" deep closets scattered around.  I suppose I could just up the size of the living area glass-front stove and depend on natural convection to keep the rest of it, more or less, comfortable.  Having said that, though, I am a fugitive from living in South Florida for about 20 years and am pretty "cold-blooded", so I do like to have the interior spaces at least CAPABLE of being any temperature I want.  Having a -20F night and needing to add four MORE quilts to the bed doesn't seem like a good time to me!  <grin>


Ronmar:

  Only three try's???  I'm disappointed!  <grin>

  I did, sort of think about what if I built the furnace/stove and it was a dismal failure with so many problems that I COULDN'T solve them and get it running satisfactorily!  Having said that, though, I am a tinker by avocation and throughly enjoy continuously tweaking and trimming and turning and adjusting to try to get it JUST-RIGHT!!!  I never did understand the folks that want to buy a "black-box" with three connections and one control (ON/OFF) and just plug it in  and go - no calibration, no tweaking, no nothing!!!  Aside from the fact that such systems are largely built from unobtainium and designed with a strong dose of heavy  duty industrial bullspit - they AIN"T NO FUN!!  <grin>

  Check back in about eight months, I'll definately be poorer and, just  maybe, wiser!!!  <grin>


SteveU

  About the "modern" whiz-bang systems that heat your house, pet your cat, sweep the floor, sew on buttons and shovel the driveway - all while being driven by a microprocessor running at 3 GIG. 

  I am a little shy of things that incorporate "too much" and EVERYTHING runs off of an electronic idiot.  Yes, when they are properly and completely calibrated and adjusted they do "EVERYTHING" but, if a mouse craps on one of the connections, the system goes DOWN and the fall back is frequently ZERO.

  Of course even a cursory examination will show my MECHANICAL engineer standing in the back ground, tapping his foot, and saying "And how does THIS work, exactly???" 

  My biggest complaint with "modern" computer controlled devices is that they seem to be largly all or nothing.  Having lived around things mechanical for sixty-odd years, it has been my experience that s#!t happens, and you should at least THINK about what you're going to do when it is the middle of night in the middle of a snow storm in the middle of January with the temperature at -30F and the whole business goes tits-up because of the proverbial mouse pee on a connection!  (Plus, it was probably tough on the mouse!  I've peed on an electric fence once! <grin>)

  In defense of high-tech high-speed micro-controlled gee-whiz, WHEN they work, they are superior to anything else on the planet - what I have a problem with is what happens when they DON'T work!

  All or nothing seems to me to be a piss-poor design philosophy for anything having less fail-safe than an anvil - but that's ME!  YMMV!

Thanx for the input guys - keep 'em coming!

Regardz,

Wayne Stayton

[vdubnut62]

Wayne......... well, I don't know where to start. I have had 30+ years experience in heating with wood.

1/2 or .500 or whatever you want to call it, WILL get hot enough to - for want of a better word- "slump" in the application that you describe.
I can supply pics of my wood fired furnace to prove it, when I don't have a fire in it. Most of my firebox is 3/16, and has been rebuilt several times
in 20 years

Give up on pipes for heat exchange, period.  Go with water cooled walls in the firebox.
Piping surrounded with cooling water is viable.
Maybe you could devise a way to place the catalysts here, in exhaust pipes surrounded by water.

Give up on building your own until you have a bunch of hands on time.

My best advice (remember it's worth just what you paid for it!) is find a used water furnace on craigslist.
There are usually a lot of them for sale in your area in the off season.
The Garn is topnotch but extremely pricey. I have their literature package here somewhere as proof.
Look for a used Tarm, they last very well and have good parts availability. These things are built in gasifiers, coal burners, and conventional types
with electric, gas and oil backup burners.

Best of luck to you in your endeavor.
Ron

[WStayton]

vdubnut62

  Being a inveterate bargain hunter, I am always looking for a cheap(er) fix . . . but, My. brother, who is in the business and is a dealer for a couple of different lines, told me that I should be VERY cautious of a used whole-house furnace because, in his experience, most of the low time ones that were for sale had been seriously overtemperatured and they were thus warped and almost impossible to seal, thereafter.  Not sure how large a sample size that is, but he has gotten "burned" on at least three units that he either bought or took in trade that I know of.  I sort of figured that if a guy who was playing with them on a day to day basis could get burned, I was almost guaranteed to have a problem. 

  Do you think his experience is typical, or he just the victim of VERY bad luck???

  I do appreciate the comments and I have no desire to reinvent the wheel if there is no reason to do so - advice is solicited!

  Thanx for your comments,

Regardz,

Wayne Stayton

[vdubnut62]

I think your brother is either not looking in the right places or not looking for the right signs of overheating.
If a waterstove, the only way it could be destructively overheated is to boil it dry.  Or very low on water. But you should already know all this.

My whole house furnace has been overheated all it's life. The walls are warped and slumped with cracks and holes in them.
The solution is to weld new plates over the outside. The door and frame, along with the flue pipe flanges  and draft have never warped.
And, I know that it's hard to believe, the door and draft are a metal to metal airtight(for stove purposes) fits.
This is accomplished by spray painting the doors, closing them, then grinding off the high spots, highlighted by  the paint transfer.
The Mennonite that builds them throws in a sheet of burning newspaper, closes the door for 30-60 seconds or so, opens it up, and if the paper flares up then he pronounces it good enough.
Just call me Dub
Ron

[WStayton]

vdubnut62:

   In as much as I have NO reason to reinvent the wheel, if that isn't required, I guess I should go back and take a look at some of the CL stuff sitting around . . .

  Part of the problem with my brother's situation is that he has no patience to fiddle around with something - he wants to take it in, plug it in, fire it up and have it work, first time, every time.  Spend two weeks trouble shooting, fixing, overhauling - not even remotely likely!  Of course, his point of view comes from a stove/furnace retailer and if he takes in a stove and spends a couple of thousand dollars in labor on getting it up and running, he will be succesful financial failure!

  How much do you charge to consult?  <grin>

Thanx  for your input - I'm always happy to have somebody save me few thousand dollars and a couple of months of aggrevation!

Regardz,

Wayne Stayton

[SteveU.]

Hey WayneS.
On your response on #9 are you confusing me Steve Unruh with someone else?? I am a well know KISS anti-electronics on critical systems kinda guy. Doesn't matter much if this computer I type on goes down - I'll switch back to pen, paper and postage stamps; TV-video down - then I have lots of books, But 250+ days of needing mold/rot abating heating is critical for cough, cough old man lung health.
If you look at the Garn system just a few motors and timers and a couple of thermal switches- and the timers are even wind up mechanical. Totally non-electronic.
Look up my now favorite stove manufactuer www.quadrafire.com at their bulk wood stoves (grrr - not that pellet trash) - ALL mechanical and able to exceed the most stringent in the US woodstove burning emissions here in Washington state with NO Cats. Visible smoke, internal unit and stove pipe coating soots are all just lost potential heating carbons to me a woodburner. I want all of my co-bonded fuel C's and H's split apart and safely bonded to two O's for the carbons and one O for the hydrogens giving me the heat of these oxidization's.
Both of these woodheating systems use sacrificial, inexpensive replaceable internal loose fit thermal brick linings. I've learned in the last 35 years from experience this saves and shields the expensive metals. $3.00 a brick good for 5,000 to 15,000 hours of direct wood combustion exposure.
But my house is smaller and my climate while long wet and cool is less severe than yours. While you do need whole house heat distribution I can get-a-way with a single point source.
My clockwise internal house air distribution: 1906, 9 foot ceiling small living room raised up to 75-85F by our in room woodstove -> hot rising air flows through to the 9 foot high small dining room with the temp now down to 70-75F -> sinking  air then flows into the 8 foot high kitchen/hallway(central electric furnace thermostat location)/bathroom temp dropping to 65F -> air perculates into the corner bedrooms at a comfortable 55-60F then return floor crawls back into opposite end of the living room for reheating. Whole house is just a big slow speed heated cyclone.
Hmm. Does help to have a 50+ yo heat hating wife. No, dear I did not use the hated M-M-M word. She wants the cool return air end of the living room couch; me the warm air outgoing couch end.
Best of luck on your project.
Washington State Steve Unruh