Building my own OWB - the lowdown

[Stihl310]

hehe, my mom gets pissed when i hang dollar bills in the vents and sees them flapping around....

my dad as a few drums laying around. he acutally just called me and gave me the sizes. all are radius then lenght
3'2x5'1
3' 5'7
4' 6'1
5'2 6'2
4' 5'7

then we have some monster 7' by 22' or something. huge. fuel tank from a gas station.

you think around is going to be effecient? or don't care long as it's not propane being burned?

for my door we came across this safe. it's huge. the door weighs 500lbs, and it's only 25x28. it's almost 10" thick at the center.. not cast iron, but it shouldn't warp..... but not sure how to cut holes in it for the draft. torch isn't gonig to do it. it would take days to drill.....

Couldn't you put the blower below the door??? Assuming your leaving room in the bottom for ash buildup, I'm sure you could fab up somekind of smaller area in the inside to allow for air to flow in and at the same time keep the ashes out of the way...

I would say that round should be the most efficient, however I'm no expert on the whole thing, round just eliminates fab cost and welding, also reducing total pieces of steel needing to be sheared... just easier overall to build,

 

[trialanderror]

/me ponders

yeah, i suppose i could make it somewhere instead of in the door.

. But we have them drums laying around, and dad has been bugging me to try and make something out of that before wipping out big dollar and buying 4x8 sheets....which i won't argue. I'm sure you've seen the high tech ripple top and water baffle idea from central boiler. Maybe it's not THAT better, they just print it everywhere to make you believe.


But in the end it doesn't matter what kind of boiler is used. i still need to have highly insulated water lines installed, eletricity ran to the boiler, etc etc.

i suppose if it doesn't perform to par, just remove and replace. I suppose if i need to stoke more then 30lbs of wood every 12 hrs it'd be no concern. no firehazard in the house, and only 1 fire to deal with would be better then nothing.


are you considering using storage tanks? or just have the majority of water in the boiler itself?

i thought about having a tank for each zone, the zone with the most sq to heat, haveing the larger tank.

 

[DLav]

the foam won't bend very good? must be like styrofoam or something like that? bends and bends, then snaps?

i don't need to make sharp jags. I think the worse would be to the house, ~80ft straight climb it's a sharp climb, maybe for 20ft with 6ft climb.. then levels off and another 10ft to the footings....

not sure how i want to do this. the one house has no basement. so, dunno if i should 90 out of the ground, then int othe wall, or keep going through the footings and punch a hole in the foundation? I suppose the 90 out and 90 over int othe wall wouldn't matter, just insulate it like a mofo....

Yep, polystyrene is similiar to styrofoam, you can bend it a little ways, but go to far and it snaps. Once its inside the PVC it won't break, and you can put elbows in it, you just have to miter the joint or shoot the elbow full of crazy foam as your putting it together.

My shop has a heated floor, so coming up through that wasn't an option for me. I had to come out of the ground outside then go through the wall. Went good, built a frame around it and put steel siding on it to match the shop. Insulated like a mofo... no probs.


Stihl 025
Stihl MS280
Stihl MS290
One really dumb dog

 

[Marklambert61]

PVC pipe

Yep, polystyrene is similiar to styrofoam, you can bend it a little ways, but go to far and it snaps. Once its inside the PVC it won't break, and you can put elbows in it, you just have to miter the joint or shoot the elbow full of crazy foam as your putting it together.

My shop has a heated floor, so coming up through that wasn't an option for me. I had to come out of the ground outside then go through the wall. Went good, built a frame around it and put steel siding on it to match the shop. Insulated like a mofo... no probs.


Stihl 025
Stihl MS280
Stihl MS290
One really dumb dog

Be very careful about using PVC it not rated for the needed temps...

CPVC might be an option for you but standard sch 40 PVC wont cut it.

Mark

 

[KsWoodsMan]

TrialandError, are you going to try to build something that has a secondary burn chamber for better efficiency ? or going with a straightforward firebox inside the water jacket ?

The difference might be as much as 1/3 less fuel used during the course of a heating season. 20 cords used for heating instead of 30 cords. Another benefit is reduced smoke output and cleaner emissions.

The most efficient wood burners I have seen have a downdraft design , secondary burn chamber and complete burning with over 80% efficiency.

 

[trialanderror]

i planned on copying centralboilers firebox design. maybe fab up something a bit different where the smoke has to travel against more water jacket as well.

 

[trialanderror]

Yep, polystyrene is similiar to styrofoam, you can bend it a little ways, but go to far and it snaps. Once its inside the PVC it won't break, and you can put elbows in it, you just have to miter the joint or shoot the elbow full of crazy foam as your putting it together.

My shop has a heated floor, so coming up through that wasn't an option for me. I had to come out of the ground outside then go through the wall. Went good, built a frame around it and put steel siding on it to match the shop. Insulated like a mofo... no probs.
/QUOTE]



called foamplus. 75cents for 1" pex. made by some company called DT Global or GlobalDT something like that. 2 kinds of foam, they're 1/2's. One is round is 1.75/ft and square is $2/ft . he said you can bury the foam right in the ground.

he couldn't give me any specs of the globaldt pex pipe...

H2O oasis wanted like 1'50 per ft for the pex. That is centralpex brandname.. But they did sell the outer sleeve for 80 cents a foot. so i might buy the pex and foam from foamplus, then the outersleeve from h2o to put around the insulation for extra protection.


next up is see if anyone knows the temp drop per X distance....gonna do some googling myself.

 

[cleanburn]

TrialandError, are you going to try to build something that has a secondary burn chamber for better efficiency ? or going with a straightforward firebox inside the water jacket ?

The difference might be as much as 1/3 less fuel used during the course of a heating season. 20 cords used for heating instead of 30 cords. Another benefit is reduced smoke output and cleaner emissions.

The most efficient wood burners I have seen have a downdraft design , secondary burn chamber and complete burning with over 80% efficiency.

Sorry but I disagree. Don't believe the BS on 80% efficiency if you do the math on the EPA website for the Central E Classic it is actually 65% efficient. Which is still pretty good compared to the older models, but if you just divide the # they have for lbs/million BTU input by the # they have for lbs/million BTU output that is 0.2/0.31 = 64.5% efficiency. The efficiency posted on the website there is based on a BS calculation if you ask me. If you do the math like I shown to compare all models its better.....There are a few other stoves on the website that have around 60% efficiency that are NOT downdrafts and far less complex designs.

http://www.epa.gov/woodheaters/models.htm


Anyways....some other stuff you guys should think about are primary and secondary air for good clean combustion, your heat exchanger design that will increase your efficiency, your fan size (you don't want too small of a fan on your big firebox...or it won't burn clean and won't heat up fast), if you do pump water from your stove to a storage tank, make sure you get a big enough pump, yes put a high limit aquastat on your stove....

 

[KsWoodsMan]

A quick look at the link provided didnt show the one listed I had in mind.


I don't see how a downdraft design makes it more complicated. If you are relying on natural draft it is barely different from that of a catalytic converter stove. Light the fire, let it warm up then manually switch over for more complete burn.

When cutting storing and loading 30 - 40 cords of wood for a less efficient boiler he might appreciate using less wood and filling it less often. Feeding that much wood into a boiler during the heating season sounds like a PT job. Cutting that much wood the rest of the year sounds like another one.

Maybe the Tarms downdraft design isn't 80% efficient overall. I bet it is much closer to 80% than 63%. It sure beats 20% - 35% like a firebox surrounded by a cold water jacket and open at the top would be.

At the very least I would build it with an insulated firebox and a baffle that runs from the back to the front. Open at the front of the fire box for the smoke to exit to the stack in the rear. At this opening I would introduce heated secondary air for better burn. This will insure the hot smoke/gasses comes in contact for a maximum distance with the water jacket in its way out after it has had all oppurtunity to burn in the combustion chamber.

Just asking a nickels worth of questions and letting him decide what he is comfortable building/feeding.

 

[trialanderror]

We do have a small boiler right now. it's a Steel king 4800b boiler. it's quite small. i'd say a 2x3x2 firebox. water capacity i'd say around 100gallon at the most. it's got a draft blower on it as well.

I think i'm going to give it a shot next winter. at the worse, i won't be burning propane, even if it doesn't burn wood nearly as effecient. In the mean time, money saved not burning propane, save up and buy a better boiler.

I i know i can use it for 1 house if i setup storage tanks and use high GPM pumps. I'd say somewhere in the 30gpm range. combine that with loads of insulation and lots of water to hold alot of BTU, should get by..... get it rip roarin and get the water up to temp, then make sure it's stoked to the max to keep a good bed of coals smoldering at all times....

the guy that gave it to us was heating an old farm house, 3 story, no insulation, and there's no sprayfoam aroudn the water box of the boiler! and his pipes were above ground and not insulated (wtf?!)

So i think if i insulate everytying, it should do quite well.

but either way, i still need the pex and heat exchangers installed in the houses.

 

[cleanburn]

A quick look at the link provided didnt show the one listed I had in mind.


I don't see how a downdraft design makes it more complicated. If you are relying on natural draft it is barely different from that of a catalytic converter stove. Light the fire, let it warm up then manually switch over for more complete burn.

When cutting storing and loading 30 - 40 cords of wood for a less efficient boiler he might appreciate using less wood and filling it less often. Feeding that much wood into a boiler during the heating season sounds like a PT job. Cutting that much wood the rest of the year sounds like another one.

Maybe the Tarms downdraft design isn't 80% efficient overall. I bet it is much closer to 80% than 63%. It sure beats 20% - 35% like a firebox surrounded by a cold water jacket and open at the top would be.

At the very least I would build it with an insulated firebox and a baffle that runs from the back to the front. Open at the front of the fire box for the smoke to exit to the stack in the rear. At this opening I would introduce heated secondary air for better burn. This will insure the hot smoke/gasses comes in contact for a maximum distance with the water jacket in its way out after it has had all oppurtunity to burn in the combustion chamber.

Just asking a nickels worth of questions and letting him decide what he is comfortable building/feeding.

I have seen many downdrafts and they have been around for a long time. There aren't too many that are actually being made anymore compared to the others. There also aren't too many that are on the EPA website for cleaner burning stoves and Tarm's isn't there.... Downdrafts do require smaller pieces of wood, you can't throw in unsplit 14 inch rounds in them and expect them to burn clean or efficient.

You can not get over 70-75% efficient with a OWB unless you are prepared to start condensing and reusing that condensation in your stack. Pellet burners can get above that efficiency because the pellets are MUCH drier than normal cordwood. I'm talking overall efficiency, not combustion efficiency. Combustion efficiency doesn't mean much to anyone.

I'm just saying that you can make an efficient stove even if its not downdraft.

 

[blakey]

/me ponders



i suppose if it doesn't perform to par, just remove and replace. I suppose if i need to stoke more then 30lbs of wood every 12 hrs it'd be no concern. no firehazard in the house, and only 1 fire to deal with would be better then nothing.

It could be 10 times that much wood in the cold weather to heat all you want to heat. I know how much I use, It would be quite a job to come up with 2 or 3 times as much wood. Looks like a great project, I admire anyone who can fabricate something like that.

 

[trialanderror]

One of my friends bought a 120gallon burner too small for his setup. He installed a massive 700gallon storage system. Even when it fire goes out he can still have up to 36-48 hours of heat to pull off the water.


took a while to get warm. but once it's kept warm, no different then keeping 120gallons warm. only differences would be longer heat up and longer cool down.

i do understand, in the examples, using a 250,000 BTU unit....
200gallon burner to heat 4000sq ft.
200tgallon burner to heat 4000sqft with say, the 700gallon storage. Heating the same sq footage, just the longer heat up, and longer cool down. both the same scenario.

using 200gallon to heat 10,000sq ft. won't work.
using 200gallon to heat 10,000sq ft with 700gallon storage, won't work.

 

[DLav]

Trial
I wish I knew about that sleeve when I was putting mine in. 80 cents a foot beats 2+ a foot that I paid for the SDR. You should come out pretty good on the cost of your pipe. One tip, when your putting it together, do it in warm weather, that PEX is pretty stubborn when its cold out, it doesn't like to straighten out, keeps curling back up. I don't know the exact temp drop yet, like I said, I neglected to put in temp gauges when I installed mine. I might just shut it down and install them, if I do, I'll get you the exact temp loss on that style pipe.

 

[DLav]

Be very careful about using PVC it not rated for the needed temps...

CPVC might be an option for you but standard sch 40 PVC wont cut it.

Mark

I didn't use PVC for the water line, I used it for the sleeve around the insulation that contains the PEX.

 

[KsWoodsMan]

I have seen many downdrafts and they have been around for a long time. There aren't too many that are actually being made anymore compared to the others. There also aren't too many that are on the EPA website for cleaner burning stoves and Tarm's isn't there.... Downdrafts do require smaller pieces of wood, you can't throw in unsplit 14 inch rounds in them and expect them to burn clean or efficient.

You can not get over 70-75% efficient with a OWB unless you are prepared to start condensing and reusing that condensation in your stack. Pellet burners can get above that efficiency because the pellets are MUCH drier than normal cordwood. I'm talking overall efficiency, not combustion efficiency. Combustion efficiency doesn't mean much to anyone.

I'm just saying that you can make an efficient stove even if its not downdraft.

Not being on the list doesn't mean they dont exist. The one pictured isnt intended to be a stand alone outside boiler like the CB or a woodgun. I was thinking of total or overall efficiency also, not just combustion efficiency. 95% burn efficiency and 85% heat transfer is 80.75% overall efficieny. Their Product Data Sheet claims greater than 90% overall efficiency. 80% seems doable easily enough, with properly seasoned hardwood in the right design of stove like theirs. The manufactures still want to keep the stack temps above the condensation point for obvious reasons so the efficiency probably won't get much better.

Most gas , oil or propane furnaces since the late 70's should be able to achieve that kind of transfer efficiency. And since downdraft burners crack the tar and creosote molecules there will be very little that doesn't get burned with good mixing in a combustion chamber.

I never said that good stoves couldn't be made that aren't downdraft design. And there isn't any one right way to burn wood for heating fuel. Just that downdraft ( gassification) is the way that appeals to me and might be of interest to the OP.

By design all tar and creosote is 'cracked' to much easier to burn gasses as it passes through a glowing bed of hot charcoal in a downdraft gassifier. Those hot coals are so reactive they can break the molecular bond of water (live steam) and carbondioxide to pull away the oxygen in it to form carbon monoxide. Carbon Monoxide is combustible as is the leftover Hydrogen molecules. I dont know of any other stoves that are able to reach this kind of combustion temps to be able to fully crack all the creosote and get this high of a burn temp going on a sustaned basis.

Agreed secondary combustion is important to be able to break past the 35% to 55% efficiency range from conventional burning.

I wish the OP the best of luck and fortune in his endeavor. From the sounds of things he is going to try it a step at a time to gain knowledge and experience to see if it is doable on a bigger scale than just a single house. He will get a feel for it and while he is loading his OWB and watching how wood burns( or rather the smoke) he can be thinking about different designs to incorporate in his design.

 

[trialanderror]

Trial
I wish I knew about that sleeve when I was putting mine in. 80 cents a foot beats 2+ a foot that I paid for the SDR. You should come out pretty good on the cost of your pipe. One tip, when your putting it together, do it in warm weather, that PEX is pretty stubborn when its cold out, it doesn't like to straighten out, keeps curling back up. I don't know the exact temp drop yet, like I said, I neglected to put in temp gauges when I installed mine. I might just shut it down and install them, if I do, I'll get you the exact temp loss on that style pipe.

ball valves man! ball valves! you can never have enough to shut off a section whether desire or emergency.......


when about you think you can get back with some numbers? I might start trenching right now, and buy the material later.

 

[DLav]

ball valves man! ball valves! you can never have enough to shut off a section whether desire or emergency.......


when about you think you can get back with some numbers? I might start trenching right now, and buy the material later.

I've got the valves, I can isolate the boiler from the lines and the heat exchanger from the lines, and valves where it enters the house and I have drains at all three isolation points. The problem is where the pipe enters the basement, it comes in real low and rises to the ceiling. After draining the lines, I'm going to have water dripping from that copper pipe for a while, the few times I've sweated copper after draining the water out I had some problems. I can sweat it dry, but I have a lot of trouble when there is moisture in there. Any tips on sweating copper when there is trace amounts of water in it?

 

[Stihl310]

I've got the valves, I can isolate the boiler from the lines and the heat exchanger from the lines, and valves where it enters the house and I have drains at all three isolation points. The problem is where the pipe enters the basement, it comes in real low and rises to the ceiling. After draining the lines, I'm going to have water dripping from that copper pipe for a while, the few times I've sweated copper after draining the water out I had some problems. I can sweat it dry, but I have a lot of trouble when there is moisture in there. Any tips on sweating copper when there is trace amounts of water in it?

Stuff a piece of bread in it, the bread will soak up the water and then mix into the water once turned back on... they also make little gell caps you can stick in the lines to plug them, they eventually dissolve.

 

[trialanderror]

A concern. If i used bigger pumps for the bigger plumbing, would i make a gain?
Another concern, how many inches for so many feet of elevation would hinder pump performance? Would i need 2 pumps per zone? one to pull the water out of the boiler (push to the house), then another pump to push water into the boiler (pull from the house)?

also

1 1/4 pex? or 1"?

1" or 3/4" copper for inside the building?