Building my own OWB - the lowdown

[trialanderror]

ALLLL RIGHT.


need to heat ~8000 sq ft. 3 buildings, 4 zones. one building might need 3 zones, the 2nd zone coming from heating the floor if i pour the floor with the plumbing in it.anyways...

first some values to work with
7.48 gallons in 1 cbft of displacement
Doing some quick math.

the cl5036 is using 31 cubic ft of firebox to heat 196 gallons of water, which is 26 cbft.
nice. except we don't know what size the waterjacket is. the wj needs to hold the water, plus the firebox. call 31 and 26 60 for easy math....

hmm, the 6048's fb is, 60 cbft. interesting. now the 7260, the fb is roughly 100 cbft. heating 764 gallons.

Doing some more quick math, back to the 5036, they're heating 196 gallon with 31 cbft of firebox. So, 196/31 is ~ 6.32. using 1 cbft of firebox to heat 6.3gallons of water. the 6048 is 6.33, and the 7260 is 7.64. the bigger one theyre trying to heat more water with the same firebox displacement.

SOO, i figured of making a 6x5x4 fb, which is ~ 120 cbft. and there's 102 Cbft in 764 gallons of water. so i need ~ 222 cbft of water jacket. A 7x6.5x5 works out to 225.

Doing some more scribbling and math. I figured i'd make my firebox and wj out 3/8" thick mild steel. Probably overkill, but, if i'm going to spend my time, may as well make it thicker. If we all follow the warranty rules, your stuff always breaks just after the warranty expries.

Once again, some more math work. 4x8 is 32sqft. i need 322sq ft. so figure 10 or 11 sheets. I can get 2nd's for $250 a sheet. Figure $3000 in steel. I have loads of tin skirting to put around it and make a roof so it doesn't look all ghetto style.

$3000 in wj and fb
$200 in sprayfoam?
$1072 for each run of 100'Ft 1" pex runs (insulation and sleeve, supply and return)
$500 in copper plumping (may be off here, havn't done any plumbing measuring yet)
$200 for an aquatstat from honeywell. (which makes the boiler automatic and efficient, so what if it's not fancy push button digital,and run 2 thermostats for failsafe from boilover...)

few dollars for some fiberglass rope for a airtight door seal.
few dollars for a heavy solenoid to flip the damper.
i have loads of tiny squirrel cage fans for a damper blower.
i have loads of 20x20 heat exchangers for the buildings. Enough to setup ontop of each furnace, then have 10 setup in series in each house to have radiant heat if desired.
dad has collected x35 1" ball valves in the past, all new... plenty to do a 4zone system. and setup for add-on/repairs without dumping the system.
i've collected 4 circulation pumps from where i work.
we have 9 rolls of mig wire someone gave us, they're 60lbs rolls.
If it gets fancy, may need zoning valves, or some temp reguatlors for something.
few dollars for probably 5 temp gauges.
some other odds and ends.
Besides that, am i missing anything? math not right? i think i'm in the ball park figure.
for digging the trenches, my shovel has hoses
figure i'd have it started in april and done and installed somewhere in october. working few hours everyweeknight, then working on weekends.

i guess 1.25" pex is needed for like 300'+ runs.
and a tech i talked to at centralboiler said only bury the centralpex 6-8" deep. sounds a bit shallow IMO. i was thinking at least 24" with like 8-12" of sand packed around it. i'll be working in a low water table maybe 20Ft above any standing ponds in the area.

One question though, the boiler is going to be above one house, and below another house. In theory couldn't i put the vent in the plumbing at the highest house? or just add a long pipe on the top of the boiler itself so it's higher then any point in the system? same solution right?.


Or i guess spend $16,000 on the 7260, and still need to buy more for the system.

In my opinion, even with the time and work involved, it's worth the savings, and in the end, 1 fire instead of 5, and the hazard is outside.

 

[blakey]

Sounds like all you're missing is a crapload of wood, that beast will be hungry!

 

[cleanburn]

You could make a smaller or larger waterjacket. The only major thing you need to figure out is how large your firebox needs to be for your heatload. Figure out how many BTUs you need then figure there are about 5000BTUs in a pound of wood, then figure out how many pounds of wood you need then you can figure out how big your firebox should be. The water capacity can vary and it will depend on how many BTUs you want to store in that water jacket, if you store more your stove will cycle less....You can figure out how many BTUs you want to store in your water too then figure out how many gallons you want.

 

[trialanderror]

good pointer on the BTU cleanburn.

would a smaller wj and storage tanks in the house of each zone be the same as no storagetanks and a large wj?

i figure i could use the tanks in the garage, and they'll heat the garage.
2birds 1 stone?

or keep the wj the same size, and still use large storage tanks?

if you say water holds BTU potential, and it's safe to have a smaller wj and have the furnace cycle more, then who says i couldn't use this tiny 120 gallon boiler i got for free, and just have monster insulated water tanks in the garage's of the zones?

If it doesn't perform, at least the firehazard will be outside. On top of that, no matter what boiler i use, the same PEX and the same plumbing needs to be done in the houses.

with 1 gallon of water weighing 8.3334 lbs....
so take the reciprocal? 0.1199 gallons in 1 pound?
for 1" pex. pi*.25x12 = 9.42 Cubic inches of water in 12 inches of 1" pex?
with 232 cubic inches in 1 gallon of water.
according to these figures it takes 180BTU to raise water from freezing to boiling.... 1 BTU to raise 1 lb of water 1degree. I was told central pex looses 5-10 degrees for every 100F. So, 400' of pex, means 40 degree loss all the itme. so i'm always needed to waste 40BTU's of wood to maintain 180F water? sound right?

 

[MNfarmer]

I priced a CB with the thermo pex and they told me 1 degree heat loss per 100 ft. 5-10 seems REALLY high to me:jawdrop:

 

[trialanderror]

I priced a CB with the thermo pex and they told me 1 degree heat loss per 100 ft. 5-10 seems REALLY high to me:jawdrop:

centralpex, not thermopex

 

[DLav]

ALLLL RIGHT.






$1072 for each run of 100'Ft 1" pex runs (insulation and sleeve, supply and return)

$500 in copper plumping (may be off here, havn't done any plumbing measuring yet)

i guess 1.25" pex is needed for like 300'+ runs.
and a tech i talked to at centralboiler said only bury the centralpex 6-8" deep. sounds a bit shallow IMO. i was thinking at least 24" with like 8-12" of sand packed around it.

In my opinion, even with the time and work involved, it's worth the savings

Hey Trial,

I'm pretty new to the OWB game, but I can tell you a little bit that I learned so far. I priced every type of underground pipe there is, and obviously you get what you pay for. When I here ppl saying the snow is melting over the trench where they buried their pipe it makes me wonder how much heat loss does it take to warm the trench enough to melt the snow?? That sounds crazy to me, I'd be sick if I looked out and saw that happening. They must have used low-grade pipe. I bought mine from Foam Plus in Bitely MI. I see your in Mich, so if its not too far from you, you might want to check it out. Their online price with shipping is higher, but if you pick it up yourself, its very reasonable. I paid $623 for 336 feet of the foam, that is only the insulation, you'll need PVC and PEX besides. Foam Plus also had the best price I saw on PEX, unfortunately I had already purchased my PEX at another place. Also when you pick it up, the foam is in 8 foot pieces instead of 4 foot when they ship it. I bought 6" PVC sch 40 SDR from a wholesaler in Potterville, (Stremler Tile) the green SDR was 2 something a foot, the SDR has bell ends so you don't need fittings, just lots of glue and primer. The PEX in Lansing was about $1 a foot, for 1", but I could have done better at Foam Plus. I did need some 45 degree elbows. Altogether I ended up with about $6 per foot into my underground pipe. When I first installed it, I didn't have the entire trench backfilled when I started using the boiler and it snowed. Snow layed right on the PVC and didn't melt, I don't know what the R-value is, but it has to be pretty high. I have 2 runs about 100 foot, and 1 run about 130'. I put mine down deep 5 - 6 foot, I don't really have a water problem and my dad has a backhoe, so it only cost me my time and some fuel. I was mostly working with the frost/heave theory, I didn't want to buy sand and I didn't want the frost pushing a rock into the pipe. Plus I like playing with a backhoe and I got a little carried away.

Copper has gone way down right now. I did all my inside work in copper. I didn't install temp guages when I put it in and I'm kicking myself for it, I'm going to put some in after I shut it down in the spring, right now I'm using a piece of junk IR thermometer from Harbor Freight.

Good luck with your project, hope you post some pics of it.

 

[trialanderror]

H2O oasis wants 1.49 for centralpex pipe. $6.somecents for 8ft insulation, and 80 cents for the sleeve...


snow on the pvc and didn't melt? no insulation was on it or anything? i may be confused? Too bad you didn't have temp gauges. you could measure your loss if you closed everything off :S

I suppose ifyou live by you pay what you get, maybe i would be better off and buying the ultimate therompex? like people have mentioned, that's rated for 1 degree drop every 100'...

we have lots of sand. I asked my dad one time how many yards of sand he's dug up and sold. he went thru the books one day and lost count after 800,000...

 

[cleanburn]

good pointer on the BTU cleanburn.

would a smaller wj and storage tanks in the house of each zone be the same as no storagetanks and a large wj?

i figure i could use the tanks in the garage, and they'll heat the garage.
2birds 1 stone?

or keep the wj the same size, and still use large storage tanks?

if you say water holds BTU potential, and it's safe to have a smaller wj and have the furnace cycle more, then who says i couldn't use this tiny 120 gallon boiler i got for free, and just have monster insulated water tanks in the garage's of the zones?

If it doesn't perform, at least the firehazard will be outside. On top of that, no matter what boiler i use, the same PEX and the same plumbing needs to be done in the houses.

with 1 gallon of water weighing 8.3334 lbs....
so take the reciprocal? 0.1199 gallons in 1 pound?
for 1" pex. pi*.25x12 = 9.42 Cubic inches of water in 12 inches of 1" pex?
with 232 cubic inches in 1 gallon of water.
according to these figures it takes 180BTU to raise water from freezing to boiling.... 1 BTU to raise 1 lb of water 1degree. I was told central pex looses 5-10 degrees for every 100F. So, 400' of pex, means 40 degree loss all the itme. so i'm always needed to waste 40BTU's of wood to maintain 180F water? sound right?

I'd be surprised if you actually lose that much heat per foot for pex....:jawdrop:

But yeah it would be the same thing for storage tanks, but also remember your waterjacket would be outside there in the cold, where maybe the heatloss from your pex would be made up since your tanks would be in your garage or somewhere warm....depends on how good your housing around your stove is too....

 

[cleanburn]

I'd be surprised if you actually lose that much heat per foot for pex....:jawdrop:

But yeah it would be the same thing for storage tanks, but also remember your waterjacket would be outside there in the cold, where maybe the heatloss from your pex would be made up since your tanks would be in your garage or somewhere warm....depends on how good your housing around your stove is too....

Oh and you have to move that water from your stove through your pex anyways, right?

 

[cleanburn]

Oh and if you put your aquastat on your storage tanks instead of on your waterjacket you could reduce your stove from cycling more too Just think of your storage tanks as a remote waterjacket and put your aquastats there, then once your heat is all stored and happy at 185F (or whatever you want your water at) then your stove shuts off and not before

 

[DLav]

H2O oasis wants 1.49 for centralpex pipe. $6.somecents for 8ft insulation, and 80 cents for the sleeve...


snow on the pvc and didn't melt? no insulation was on it or anything? i may be confused? Too bad you didn't have temp gauges. you could measure your loss if you closed everything off :S

I suppose ifyou live by you pay what you get, maybe i would be better off and buying the ultimate therompex? like people have mentioned, that's rated for 1 degree drop every 100'...

we have lots of sand. I asked my dad one time how many yards of sand he's dug up and sold. he went thru the books one day and lost count after 800,000...

My PEX is surrounded by polystyrene insulation which is encased in PVC. There was 180 degree water flowing through the PEX with 3 inches of snow laying on top of the PVC and it didn't melt, it was like that for days, it was still that way when I backfilled it. You said you were expecting to spend $1072 for 100' section, I have about $600 in a 100' section. I had to spend some time putting it together, where the commercially made stuff is ready to install when you get it. My dad is installing an OWB and has his pipe in the ground, he paid about $12 a foot for it. I ordered a better IR, when he gets his up and running I'm going to compare the temp drops between his setup and mine. Then I'll know for sure how it compares. I'm not trying to sell you this stuff, just letting you know an option.

 

[trialanderror]

cleanburn

good idea with putting the aquastats inside the building at the storage tanks. I might acutally do that. I suppose as long as the pumps move the water quick enough, i shouldn't have a boil problem at the burner itself. Honestly i would install 2, a lowtemp one inside set at 170-180, and then a 2nd one for a shutoff max of 195-200F for failsafe boilover. Something i would like to see on a system that costs thousands......
I also plan on going berserk with sprayfoam on the boilers waterjacket

Dlav, i dunno if i can use pvc pipe, my ground is quite uneven. maybe i could get by, but i doubt it. i gotta dodge obstacles and such. I might need to stick with pex surrounded with flexible insulation and flexible sleeve.... Maybe if i can buy the 1" central pex for $1/foot from that place in bitley, not much, but something to save money.

 

[DLav]

cleanburn

good idea with putting the aquastats inside the building at the storage tanks. I might acutally do that. I suppose as long as the pumps move the water quick enough, i shouldn't have a boil problem at the burner itself. Honestly i would install 2, a lowtemp one inside set at 170-180, and then a 2nd one for a shutoff max of 195-200F for failsafe.
I also plan on going berserk with sprayfoam on the boilers waterjacket

Dlav, i dunno if i can use pvc pipe, my ground is quite uneven. maybe i could get by, but i doubt it. i gotta dodge obstacles and such. I might need to stick with pex surrounded with flexible insulation and flexible sleeve.... Maybe if i can buy the 1" central pex for $1/foot from that place in bitley, not much, but something to save money.

The foam they sell in Bitely is pretty rigid, works well in PVC, but won't bend very far without breaking, you can make gentle sweeps, like you could with PVC, but for sharp bends you need to miter it and and use a 221/2 or a 45 degree elbow, they don't recommend bending PEX at a 90. If you have a lot of obstacles to work around it probably wouldn't be the best stuff for you to use. I had relatively straight trenches. Good luck with it though, sounds like you have quite a project ahead of you.

 

[MNfarmer]

centralpex, not thermopex

Sorry about that trial.. I misread your post!! Good luck with your boiler!

 

[Stihl310]

Whether you realize it or not, you just opened my eyes to something I didn't even think of... the cubic foot to gallon relationship... when I calculated this on my current design it was 12.5... which means I was heating 12.5 gallons of water for every cubic foot of firebox... I redesigned it, going from a 3' long firebox to 4', and from a 26" diameter to 28"... this brought me to 7.87, which I feel should do me well...

Thanks for posting this, great info..

 

[trialanderror]

oh yeah? you made yoru own burner? specs man! specs! don't leave us hangin'!!!


but then again that goes back to what cleanburn mentioned. small amount of water around the firebox. less water heats quicker, and if it's always in circulation, it should be good. i'm thinking of using storage tanks in the building to having lots of BTU potential at any given time. even if i pull alot of BTU's from the water with fans, there would be such quanitiy of it it would take alot to chill. which in return wouldn't call for draft nearly as much...

Assuming everything is insulated to the max. Which is what i'm trying to figure out right now. hate to dig up 100' twice....

/me eyeballs a old 5000gallon drum in his backyard.....

 

[Stihl310]

oh yeah? you made yoru own burner? specs man! specs! don't leave us hangin'!!!

Haven't built it yet,still in AutoCAD :

As of now the design is an inner circular firebox of 28"dia. with an outer water jacket or 40", this gives me a 6" chamber all the way around... Length will be 4' with the firebox inset from the back 2" to allow water around all surfaces except where the door is... the door I'm still hung up on, not sure whether or not to go water filled or just insulated. As of now I have had it quoted to build, and believe it or not it is cheaper for me to hire a machine shop to build it rather than buying the material and building it myself... Although my welding skills are sufficient to do the welding I feel that I'd be better of just letting them build the main part of the boiler just to ensure good welds and professional fabrication... the door and the rest of the enclosure will be built by me..

The firebox, according to calcualtion will hold 139 gallons of water, with a 16.9 cubic foot firebox. I'll be installing a blower with a solenoid controlled damper all of cours hooked into a therm. I'm using pex line to run the supply to my house, then finishing off the remainder of the run to my furnace with copper... I'm excited about getting it built, I hate this propane heat, it never feels warm, and the bill isn't any fun to pay either...........

Before anyone says it's too small, I'll only be heating a 1700 sq/ft house, with no plans of adding on... I do have plans of eventually building a shop, but I'm going to heat it with it's own dedicated wood burner inside

 

[trialanderror]

The foam they sell in Bitely is pretty rigid, works well in PVC, but won't bend very far without breaking, you can make gentle sweeps, like you could with PVC, but for sharp bends you need to miter it and and use a 221/2 or a 45 degree elbow, they don't recommend bending PEX at a 90. If you have a lot of obstacles to work around it probably wouldn't be the best stuff for you to use. I had relatively straight trenches. Good luck with it though, sounds like you have quite a project ahead of you.

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....

 

[trialanderror]

Haven't built it yet,still in AutoCAD :

As of now the design is an inner circular firebox of 28"dia. with an outer water jacket or 40", this gives me a 6" chamber all the way around... Length will be 4' with the firebox inset from the back 2" to allow water around all surfaces except where the door is... the door I'm still hung up on, not sure whether or not to go water filled or just insulated. As of now I have had it quoted to build, and believe it or not it is cheaper for me to hire a machine shop to build it rather than buying the material and building it myself... Although my welding skills are sufficient to do the welding I feel that I'd be better of just letting them build the main part of the boiler just to ensure good welds and professional fabrication... the door and the rest of the enclosure will be built by me..

The firebox, according to calcualtion will hold 139 gallons of water, with a 16.9 cubic foot firebox. I'll be installing a blower with a solenoid controlled damper all of cours hooked into a therm. I'm using pex line to run the supply to my house, then finishing off the remainder of the run to my furnace with copper... I'm excited about getting it built, I hate this propane heat, it never feels warm, and the bill isn't any fun to pay either...........

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 easily 300lbs, 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.....