Box Stove to Base Heater Conversion Adventure

 
franco b
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Post by franco b » Sun. Aug. 10, 2014 11:43 am

KingCoal wrote:this description of the "heat" dropping as it gets further from the fire pot is echoed by many members here in other threads as well. I have always thought that it represented the desired effect, that of the stove progressively giving off the heat in the exhaust path till by the time the gas enters the chimney thimble there is so little left that you can hold your hand on the stove pipe for as long as you want.

am I incorrect about this ?
I think you are correct and don't see how it could be otherwise. These stoves were developed because it was desirable to raise efficiency while retaining a compact package. Once the heating unit was moved to the basement and central heat became popular, the need for compactness was no longer there. It was easy to add heat exchange above the fire.

Unfortunately the lessons learned in the best parlor stoves were forgotten and most furnaces and boilers were lacking in true air tightness making holding a small fire all but impossible. Lots of deaths in an effort to hold a small fire from check dampers built into the top of the stove. Fire pot design went straight downhill adding to the problem. Combustion chambers were air or even water cooled. Instead of keeping heat in for efficient combustion, heat was removed. Ash sifters became popular to save all the unburned coal. Kerosene heaters were used in the shoulder months to avoid the abortion in the basement. Oil heat went through its own trials until the lessons learned of proper air distribution and combustion chamber design common at the beginning of the century and before were relearned.


 
KingCoal
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Hand Fed Coal Stove: 1 comforter stove works all iron coal box stove, seventies.
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Coal Size/Type: Nut Anth.
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Post by KingCoal » Sun. Aug. 10, 2014 6:19 pm

yes, there WAS a diff. post in this location before but, I did some more " cyferin' " and came up with a better plan for the stove to chimney thimble connection.

won't go into it now, i'll include it in the pics later.

thanks,
steve
Last edited by KingCoal on Mon. Aug. 11, 2014 2:23 pm, edited 1 time in total.

 
steamshovel
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Post by steamshovel » Mon. Aug. 11, 2014 8:33 am

it sounds like you have a good handle on that, and are willing to experiment, you will learn a lot from that build. one thing I learned about burning wood and coal stoves- there are two components of overall efficiency:
•combustion - how completely the coal burns
•heat transfer - how much of the energy released is transferred to the space to be heated.
the good older stoves, and the new higher end, thickwall steel and cast stoves with the $2k+ price tag, have good combustion efficiency, so that part of overall efficiency is covered.
the cheap made in China $300-$500 Harbor Freight and Tractor Supply stoves, generally do not. these stoves are the ones that give all new stoves a bad name. with coal stoves, you generally get what you paid for.

most coal stoves, old and new, don't have heat exchangers as such, but rather use the entire stove body and flue pipe as the heat transfer surface. This is because the heat output of the stove is variable, regulated by the combustion air control.

here's something to think about- at its lowest burn rate, an excessive amount of heat transfer surface would cause the exhaust to be too cool to provide good draft. this is why the draft falls off initially, when a baseburner or baseheater is switched from direct to indirect mode. another reason is, 90 degree turns, and downward runs of exhaust flue, restrict and slow down draft.

it becomes a give-take situation, the designer tries to come out ahead in the end. give up some draft with turns and bends and more radiating surface at first, to end up ahead in the end, after the stove temp/draft rises and stabilizes. it takes more draft opening, fuel, and BTU's to heat the extra radiating area.

most well designed coal stoves, new and old, operate within the same band of overall efficiency (combustion and heat transfer) - about 70 percent plus or minus 10 percent. The lowest firing rate that maintains good combustion produces the highest overall efficiency, the slower gas flow rate through the system allows more time for heat transfer.
this is pretty easy to measure, with 2 magnetic thermometers, one on the face of stove at firebox, the other at the stovepipe exit on the stove. the 2nd thermometer located 10 feet away on the wall flue pipe, is not a good measure of the stove efficiency, that's measuring the entire installation and chimney. checking efficiency that way, is misleading. any extra radiated heat on the stovepipe run from the stove to the wall is a bonus, any stove gets that, regardless of how good it is.
the real measurements have to be taken on the firebox and stovepipe exit on the stove itself, and the 2 compared.
I've done that on a few stoves and found 60-70% is easy to get- and with good draft, best coal, and proper setting up around 78%-82% on the coldest days. the high end number does not last, because when the stove is raked and refueled, all the numbers drop down again, until it slowly builds up to max efficiency again. add a manometer and you will visibly see the draft go down, and the temps go down, in real time.

when the draft falls off, the firepot temp goes down, stovepipe exit stays relatively high in relation to the firepot, and efficiency goes DOWN. it starts putting less heat into the room, and more % up the chimney, even though it's burning slower and conserving fuel. you'd have to see it to believe it, but it's happened numerous times while I was watching it, so it's a definite.

The stove operator has a lot of control over the net efficiency it delivers. you're in control of it with the draft settings.
another sidenote, wood stoves always have a lower % efficiency, they naturally put more heat up the flue, just by nature of the fuel. they heat well, but waste more heat.

 
KingCoal
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Location: Elkhart county, IN.
Hand Fed Coal Stove: 1 comforter stove works all iron coal box stove, seventies.
Baseburners & Antiques: 2014 DTS C17 Base Burner, GW #6, GW 113 formerly Sir Williams, maybe others at Pauliewog’s I’ve forgotten about
Coal Size/Type: Nut Anth.
Other Heating: none

Post by KingCoal » Mon. Aug. 11, 2014 2:37 pm

Combustion chambers were air or even water cooled. Instead of keeping heat in for efficient combustion, heat was removed. [/quote] franco b

this is a very important statement and the gist of reasoning behind this whole project.

in original form, the DSM circulator cools not only the combustion chamber and side walls but the firepot too with the placement and operation of the circulator tubes, compromising both combustion and heat transfer.

i feel these tubes could have been handled another way for better performance but, that would take a more extensive retro fit than i'm prepared to pursue.

 
franco b
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Coal Size/Type: nut and pea

Post by franco b » Mon. Aug. 11, 2014 5:00 pm

KingCoal wrote:in original form, the DSM circulator cools not only the combustion chamber and side walls but the firepot too with the placement and operation of the circulator tubes, compromising both combustion and heat transfer.
Just so we are on the same page, I tend to use the terms fire pot and combustion chamber interchangeably as the place where the coal sits and burns. It's a holdover from my oil burner days. William has sometimes referred to that space just above the fire pot as the combustion chamber as you have also, so there is a little confusion on my part. I do mean the fire pot itself when referring to the combustion chamber. I tend to assign not much importance to that space above, which might very well be wrong. Obviously keeping as much heat as possible just above the fire pot will aid in burning gasses. A baffle just above the fire pot will reflect heat back into it with good results. My main concern though is keeping heat in the fire pot which is why I think those designs that circulate flue gas down around the fire pot best. I suspect you are going that route too.

 
KingCoal
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Location: Elkhart county, IN.
Hand Fed Coal Stove: 1 comforter stove works all iron coal box stove, seventies.
Baseburners & Antiques: 2014 DTS C17 Base Burner, GW #6, GW 113 formerly Sir Williams, maybe others at Pauliewog’s I’ve forgotten about
Coal Size/Type: Nut Anth.
Other Heating: none

Post by KingCoal » Mon. Aug. 11, 2014 6:12 pm

yes, as you say, I consider the area about the fire pot itself the combustion chamber.

from looking at many patent drawings and seeing them labeled that way and viewing the ratios of volume related to them I've come to think of them as differing zones much like a base chamber is from any area in the upper stove, each having a specific primary design purpose and vital relationship to the rest.

in order to get a direct / indirect exhaust path damper into my design I will have to modify the placement of the original over fire baffle but, I will be retaining it so I continue to have that advantage along with the rest i'm trying to employ.

thanks,
steve

 
KingCoal
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Location: Elkhart county, IN.
Hand Fed Coal Stove: 1 comforter stove works all iron coal box stove, seventies.
Baseburners & Antiques: 2014 DTS C17 Base Burner, GW #6, GW 113 formerly Sir Williams, maybe others at Pauliewog’s I’ve forgotten about
Coal Size/Type: Nut Anth.
Other Heating: none

Post by KingCoal » Wed. Aug. 13, 2014 1:14 pm

some how my local dealer that sold me my stove last yr. don't seem to want to call me back (since Monday ) to verify an order for the front load door glass and 6" exit collar.

on the other hand, when I just called DSM about those items I was greeted very cordially, my order confirmed and told they would get it on the after noon UPS truck today.

tonight is another work session so more later.


 
KingCoal
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Location: Elkhart county, IN.
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Baseburners & Antiques: 2014 DTS C17 Base Burner, GW #6, GW 113 formerly Sir Williams, maybe others at Pauliewog’s I’ve forgotten about
Coal Size/Type: Nut Anth.
Other Heating: none

Post by KingCoal » Wed. Aug. 13, 2014 9:01 pm

well, we stood up all the walls of the base chamber and tacked everything together and to the base plate.

i got a couple of pics but, when I had my son install a new OS in the computer I didn't realize I had to reinstall my photo shop so I can attach them.

i'll have to do that asap.

thanks,
steve

 
KingCoal
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Location: Elkhart county, IN.
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Coal Size/Type: Nut Anth.
Other Heating: none

Post by KingCoal » Thu. Aug. 14, 2014 7:03 pm

geeeeeeez, working with pics is alot harder now. i'll have to study up on how my system is working so I can remember how I got these pics up loaded.

any way, this is the base chamber. the length of the tube on the outside was run wild on purpose so that the exit collar that will come out the top can be aligned with a "T" in the upper original collar. I twill then be trimmed back and welded shut.

internal dimensions are 4.5 x 19 x 21.5. the tube is 4 x 8. the chamber will be bolted to the bottom of original ash pit floor with a flat rope gasket.

the welding is going on the rest of this week while I get pics of the inside of the stove, then the mods to it.

thanks,
steve

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KingCoal
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Coal Size/Type: Nut Anth.
Other Heating: none

Post by KingCoal » Fri. Aug. 15, 2014 6:11 am

hmmmm, 20+ views and 1/2 that many magnifications of the pics since I last posted and no comments.

that could go a couple of ways. nothing very unusual or of direct concern with the perceived form and functionality OR so out of line as to deter further interest or involvement :shock:

making the final decisions on the scope and focus of the nec. mods to the stove and going ahead, hope it works :lol:

 
steamshovel
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Post by steamshovel » Fri. Aug. 15, 2014 6:41 am

I got sidetracked, getting ready for winter, fixing 2 gas tanks in power equipment that had leaks, so haven't been following the thread.
that box design looks good to me. this is not rocket science, we're basically talking about a glorified exhaust pipe/radiator. there's nothing mysterious about burning coal or wood, and plumbing the smoke out of the stove and home. people have been doing it for 100's of years, in the case of wood, 1000's of years.
sometimes there is a tendency to over-complicate this kind of thing.
with the strong draft your chimney has, it is going to work.
that looks similar to other pics I've seen on this site, of the baseburner passages in old stoves. sort of like a 2 into 1 split flow setup in the base. I say give it a whirl, let 'er rip ! :D
it's going to throw heat with a firepot that big, even if there was only a straight pipe up with an mpd.
that box will give the extra radiating surface. it won't radiate as well as cast iron, but still very good.
great work, you're a good welder and fabricator.
you could sell that mod to people with box stoves and make some $$ on the side maybe
presto- instant baseburner. see, nothing so difficult about that ! :)
there are a few different types of coal stove people. the purists who prefer the old antiques and nothing else.
and the operators and tradesmen that like the old stoves, but are open to new ideas and burning the new stoves as well, stoves with hoppers and electric fans in them.
the purists tend to get really quiet, when someone with hands on skills steps in, who can actually build a stove from scratch. there's quite a few hands-off guys who don't do anything but fire the stove, and have others build, restore, repair it.
let's be frank, a good welder can build a stove himself with steel plate, from scratch. make it thick enough, it will last 200 years, using modern alloy steels.
IMHO, awesome, fire it up !
who knows, maybe you'll have your own stove business someday ! 8-)

 
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blrman07
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Post by blrman07 » Fri. Aug. 15, 2014 7:25 am

KingCoal wrote:thanks SS i'll try to do those concerns justice.

"radiating area" I am adding just 5.46 sq. ft of radiant surface ( 1.037 cubic foot of enclosed volume ) to the stove. which combined with the area of the original stove still allows me to achieve the 27.7 / 1 ratio of radiant surface to grate area and providing the rest of the stove much more direct exposure to the heat generated and the exhaust path.

i don't feel i'm out of line in expecting the stove to work fine with the original size fire pot and no more coal than ever needing to be burned.

"additional exhaust travel path hinders draft" I agree

in my installation the DSM 1400 in original direct draft form ( although I did have an additional draft diverter in place all last season as well ) will produce 450* stove top temps. with the primary open 1/8" and 2 MPD's CLOSED in the smoke pipe.

i believe I have more than enough draft to cover all likely operational conditions.

thanks,
steve
In a thread dealing with a chubby stove modification I posted a while back I stated that I had read a LOT of engineering books dealing with fire pot surface to radiation surface ratio in your old stoves that survived the ages. The chubby stove modification was to put a cylinder on top of the chubby to increase the radiation surface without increasing the fire pot size. One thing that popped out in my reading regarding the old base burner stoves that have survived was a rule of thumb ratio between fire pot size and radiation surface. No matter what the configuration of the radiation surface, the stoves that survived both the efficiency and heat transfer tests had a radiation to fire pot size of 27:1. Those that got too far away from that ratio just didn't make the cut and ended up in scrap yards.

I note with a smile that you have calculated your ratio to 27.7:1 !!!

Don't forget to have a method to easily cleanout the baseburner chamber without disassembling the entire stove. The easiest way is to copy the handhole cleanout method used on boilers.

Rev. Larry
New Beginning Church
Ashland Pa.

 
KingCoal
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Coal Size/Type: Nut Anth.
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Post by KingCoal » Fri. Aug. 15, 2014 7:47 am

thanks SS much apprec'd.

i have just one more sticky wicket to deal with.

the original and new base chamber exit collar is 6" / 28.26 sq. in.

the upper chamber above the fire pot is 5719. c.i., the base chamber is 1838 c.i., it's split into 3 areas roughly 613 c.i., the transition areas that the exhaust will travel thru on the sides of the stove are about 306 c.i. each. there's a recognizable ratio pattern there.

the transition areas are 2 W x 17 L x 9 D. the upper and lower walls are 34 sq. in.

how many sq. in. of opening do I provide in that 34 sq. in. area to keep the draft and flow rate up ?

somewhere about 21 sq. in. on both sides i'm certain but I don't know if it should be very much more.
Last edited by KingCoal on Fri. Aug. 15, 2014 11:24 am, edited 1 time in total.

 
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Sunny Boy
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Post by Sunny Boy » Fri. Aug. 15, 2014 8:23 am

You've got some leeway in that the flue gases can speed up and slow down as the cross sections of the areas it travels through change.

Just think of an auto intake system. While it's a more extreme example, it shows whats possible by just using atmospheric pressure as the driving force (in carb design it's called pressure drop, not vacuum). Lets take one common example that has worked well for over 100 years - the average in-line 6 cylinder motor.

The air/fuel gets drawn through approximately a 1 inch opening (carburetor venturi) to feed about a 250 - 275 cid motor and it works fine. Ok, the pressure drop is more extreme than your stove's draft, but it gives you a better idea of how much force just using atmospheric pressure outside the stove (or motor) can exert.

The other thing is, how fast do you want those flue gases going ? Obviously, the bigger the pathway the slower the gases travel giving time to shed heat. The reverse argument is that a large cross section pathway lets heat stay in the center of the pathway, away from the walls. Maybe more study of older stove's flue gas pathway proportions will give you a ratio like you found with your firepot's 27:1 ????

Paul

 
franco b
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Coal Size/Type: nut and pea

Post by franco b » Fri. Aug. 15, 2014 10:13 am

I agree with Sunny Boy that your figure of around 21 should be no problem.


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