OWB design. More water? Less water?

[AIM]

I built the one I am using now.. They are quite a bit of fun to build and the fact that I have welded for years helped a lot.

But if you don't know how to weld when you start, you will by the end.

 

[leon]

water stoves

But to the OP's point if you don't have a need why then heat thousands of gallons of water....
You are going to have heat loss regardless.

I can see if you're heating a shop.... Just having a hard time seeing the efficiency in heating
massive volumes of water when all a guy might need is a 200 gal capacity

Thermal mass is thermal mass, The more thermal mass like water or firebrick
the warmer the thermal mass and the less fuel burned.

The russian and finnish fireplaces prove my point.

The thing is you can have a very small wild fire emmiting almost zero smoke
because the fire box being half filled with fire brick is absorbing and radiating
heat and keeping the fire hot and burning any smoke particles that would escape
through the chimney.

The water load is yet another thermal mass that is radiating heat into the home or
work shop and returning with the cooler water that is going to be reheated.


If you have a fire box of a certain size that is half filled with fire brick and you are
burning a hot fire you are consuming the same amount of fuel for a large reservoir/heat
mass as you are a small one so the economics are built in there for a bigger thermal mass to begin with.


The more water the better for heating and as I mentioned previously the properly
insulated water jacket and pex tubing using the $13.00 per foot tubing which loses
one per cent per hundred feet allows that much more heat to enter the structure.

Your heating lets say 4,000 gallons with a small wild fire in the firebox which has fire brick
as half its volume ans well as firebricked sides to hold heat that radiates into the water
chamber that is above or behind the firebox like a locomotive where heat is rising and
being fed oxygen in the combustion air intake as well as using a small induced draft fan
to aid in pulling/the heat energy through the tube heat exchangers.

After a while your water is up to temperature and then the fire box can be filled with a load of
coal or wood to maintain the thermal energy that is stored in the boilers water jacket with
much less effort as the fire brick is storing and radiating heat continually and if the fire goes
out the 4,000 gallons in storage can last a day or two or three if you let the fire go out.

If you installed a bottom feed coal stoker retort to make heat in this boiler it is the same
method used in the more modern steam locolotives and rotary snow blowers used in rail service
in the lat 19th and begining of the 20th century the bottom feed coal stokers with the combustion
air blown through the coal delivery tube are still available as i understand it and I may simply decide
to do it this way with my old boiler if I still have it or I may modify a Harman wood and coal boiler
with one and have a sheet metal ash bin made for it.


if you all collectively put more firebrick in the water stoves you use you would burn less wood and make
less smoke for sure.

 

[Stihl310]

I understand the thermal mass part.... But I can't get past wanting to build a 4000 gal burner to heat a 2000 sq/ft house.. Yeah you'd have all the mass youd ever want, but you wouldnt even be touching it...

When I build my next one I may bump it to 200 gallons and go to a gasified design, but any bigger than that is really useless to me, that and it would be cost prohibitive....

I may take your advice though and install some firebrick next year.... I can see how that would be beneficial...

I have been able to get my smoke problems more under control by tinkering with the temp differential... I lucked out when I built mine and everything worked right the first time.... LOL

 

[dave_dj1]

One thing I see that some of you are missing is with the large mass of heated storage water is, you wouldn't need to burn 24/7. Maybe you would only have to fire once a week. Google Garn.

 

[THE PLUMMER]

To the OP, it would be a waste to heat double the H2O. Bigger isn't always better, and in hydronics its usually 1 of if not the biggest waste of energy. If having more standby water was a big benefit, then you'd see alot more storage standby buffer tanks. We use them only in special applications, like industrial, schools, hospitals and with specific design controls to make proper use of them. And these are tanks which loose less than 12 degrees in a 24 hr standby. So very efficient and expensive. If you could replicate this then what you would do is go with a very small OWB which heated the standby tank and then it would deliver to the zones. Sizing your standby water for a few very cold days is a waste. And sizing an entire boiler that way is even worse. Longer smaller burn times is the most efficient. Most I come across goto high fire for less than 10 minutes, on off on off is the worst thing for efficient burning. But hey anyone can install one of those OWB. I would look closely at the specs of a manufactured OWB in your size class. Buffer tanks can always be added if growth is in the future, but you can never reduce the size of an oversized OWB nor can you increase its efficiency.

 

[AIM]

I'm not sold yet on the oodles of water idea. If I was building around a 120 cu ft firebox then as has been said the gallons would be high simply by design. (huge firebox is gonna need huge water jacket)

I want to build one approximately 30 cubic ft. Why 30? Well my current one is about 6 cu ft if I did my math right. (24" round X 40" deep)
During a really cold snap I have to load 4 times a day. I figure that 4-5 times bigger equals a load once a day. It likely doesn't work exactly this way but it's gotta be better.
Do I build a 300 gallon jacket or a 600 gallon jacket around a 30 cu ft box?

I have another thought but I gotta get to work. I'll post tonight.

 

[NRwooduser]

More water!!!

I modified a taylor and have about 800 gallons of water. I have fired a water stove for 20 years.A simple carolina water stove first, now a modified taylor. pros that I have learned cause of the more water.

Don't add water like I did with the 400 gallon carolina. I hardly ever have to add water.
Smaller fire box = good long smolder free burning. Happy neighbors.
It doesn't sit there and smoke up the neighborhood.
Very little creosote. Easy cleaning.
Don't have to go out and fire late at night. Fire go's out that's fine, fire in the morning.
Fire in the summer and heat DW easy.
Seems like it's easier on the wood when It doesn't just set there and smolder away.

I wished I had made it hold more water, maybe 1500 gallons.

 

[leon]

OWB design

I'm not sold yet on the oodles of water idea.

If I was building around a 120 cu ft firebox then
as has been said the gallons would be high simply
by design. (huge firebox is gonna need huge water jacket)

I want to build one approximately 30 cubic ft. Why 30?
Well my current one is about 6 cu ft if I did my math
right. (24" round X 40" deep)

During a really cold snap I have to load 4 times a day.

I figure that 4-5 times bigger equals a load once a day.

It likely doesn't work exactly this way but it's gotta be better.

Do I build a 300 gallon jacket or a 600 gallon jacket around a 30 cu ft box?

I have another thought but I gotta get to work. I'll post tonight.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++===



WHY on earth would you want to build a boiler fire chamber that is one

and one seventh cubic yards in capacity???????


Do not forget that the firebox itself will shed heat out the stack when it cools down

even further unless you intend on filling it half full of fire brick for thermal mass and

to keep the fire hotter at all times??????????


A fire box that large with or without a fan for forced draft with out a

firebrick liner and filling the firebox half full of fire brick as well

and in no way improves one combustion efficiency if the fire box

box is stuffed with wood and only allows the fire to smolder and

not obtain adequate temperatures to offer proper combustion.

 

[leon]

Owb

I modified a taylor and have about 800 gallons of water. I have fired a water stove for 20 years.A simple carolina water stove first, now a modified taylor. pros that I have learned cause of the more water.

Don't add water like I did with the 400 gallon carolina. I hardly ever have to add water.
Smaller fire box = good long smolder free burning. Happy neighbors.
It doesn't sit there and smoke up the neighborhood.
Very little creosote. Easy cleaning.
Don't have to go out and fire late at night. Fire go's out that's fine, fire in the morning.
Fire in the summer and heat DW easy.
Seems like it's easier on the wood when It doesn't just set there and smolder away.

I wished I had made it hold more water, maybe 1500 gallons.

Thank you NRwooduser for proving what I have stated time and time again.

 

[leon]

Owb

To the OP, it would be a waste to heat double the H2O. Bigger isn't always better, and in hydronics its usually 1 of if not the biggest waste of energy. If having more standby water was a big benefit, then you'd see alot more storage standby buffer tanks. We use them only in special applications, like industrial, schools, hospitals and with specific design controls to make proper use of them. And these are tanks which loose less than 12 degrees in a 24 hr standby. So very efficient and expensive. If you could replicate this then what you would do is go with a very small OWB which heated the standby tank and then it would deliver to the zones. Sizing your standby water for a few very cold days is a waste. And sizing an entire boiler that way is even worse. Longer smaller burn times is the most efficient. Most I come across goto high fire for less than 10 minutes, on off on off is the worst thing for efficient burning. But hey anyone can install one of those OWB. I would look closely at the specs of a manufactured OWB in your size class. Buffer tanks can always be added if growth is in the future, but you can never reduce the size of an oversized OWB nor can you increase its efficiency.

I sincerely disagree with you about improving a water stoves efficiency
specifically using my boiler as an example as it is half filled with firebrick.

My firebrick gets heated up and stays hot and returns heat back to the
combustion process reducing the amountof smoke and wasted energy
out the stack. I wish I had done this 28 years ago.


An idling water stove or smoldering wood stove are no ones friends especially if
you have neighbors nearby and the wind is not moving.

Aa small intense fire is ideal for water mass and fire brick mass for heat storage.
Even though you are shedding heat to an extent but the reduced amount of wood
smoke wasting and exiting the stack when you have thermal mass to absorb and
radiate heat back into the combustion chamber it is worth every penny you spend
on firebrick.

 

[AIM]

Thank you NRwooduser for proving what I have stated time and time again.

Now I haven't seen any "PROOF" from either side of this discussion. I have seen opinions and observations but no PROOF.

Let me ask you this leon. If more water is always better. Why aren't the OWB manufacturers offering up boilers with huge capacities or selling storage tanks as an option. I think a few of the hydronic companies are but by and large most do not. And why don't you have a series of storage tanks.
I have to believe that if a guy goes bigger and bigger, sooner or later you get to a size that is just TO big to be efficient for your application.

Take the school boiler for example. If you were heating ONLY a 3000 sq ft house with the same system it just wouldn't be efficient. (At least I don't think it would be)

Another design variable is how big should the water jacket be in comparison to the fire box.

 

[woodman6666]

Now I haven't seen any "PROOF" from either side of this discussion. I have seen opinions and observations but no PROOF.

Let me ask you this leon. If more water is always better. Why aren't the OWB manufacturers offering up boilers with huge capacities or selling storage tanks as an option. I think a few of the hydronic companies are but by and large most do not. And why don't you have a series of storage tanks.
I have to believe that if a guy goes bigger and bigger, sooner or later you get to a size that is just TO big to be efficient for your application.

Take the school boiler for example. If you were heating ONLY a 3000 sq ft house with the same system it just wouldn't be efficient. (At least I don't think it would be)

Another design variable is how big should the water jacket be in comparison to the fire box.

The reason that OWB manufacturers dont offer boilers with huge water capacities is because it costs more to build. More steel equals higher price tag but what your forgetting is with this volume you gain much more time between loads, but that is hard for the owb manufacturers to sell if it comes at a price $4k higher than their competitor. Bye the way I used to be a Central dealer years ago. And I had this discussion at length with them. And that is when I decided to build my first boiler. I guess the Proof you are looking for for me is the 2-3week burn times and not having to handle, cut, split any of the wood my skid puts in my boiler. Also I can burn just about anything stumps, round bales, etc. Not trying to steer you away from this again just telling you my experiences.

 

[mtfallsmikey]

The reason that OWB manufacturers dont offer boilers with huge water capacities is because it costs more to build. More steel equals higher price tag but what your forgetting is with this volume you gain much more time between loads, but that is hard for the owb manufacturers to sell if it comes at a price $4k higher than their competitor. Bye the way I used to be a Central dealer years ago. And I had this discussion at length with them. And that is when I decided to build my first boiler. I guess the Proof you are looking for for me is the 2-3week burn times and not having to handle, cut, split any of the wood my skid puts in my boiler. Also I can burn just about anything stumps, round bales, etc. Not trying to steer you away from this again just telling you my experiences.

This is the way to go if you have large buildings to heat, need massive amounts of water to satisfy load, I'm sure the heat loss is really high. I think most OWB mfrs. have pretty decent designs, maybe except for Shaver, which has been knocked pretty hard by their owners here on this site in the past. Buffer storage is a must with gasification boilers, they burn really clean, but you are escentially blast burning for short durations of time. If I could design/build my own OWB, I would be looking at how to make it recover more quickly from temperature drops, vs. the water capacity. That's for standard residential use tho...

 

[leon]

water stoves etc.

Thank you NRWooduser, Woodman6666 and Del_Corbin for verifying my
statements position and the physics of heat transference from your
personal experience.

 

[AIM]

WHY on earth would you want to build a boiler fire chamber that is one

and one seventh cubic yards in capacity???????


Do not forget that the firebox itself will shed heat out the stack when it cools down

even further unless you intend on filling it half full of fire brick for thermal mass and

to keep the fire hotter at all times??????????


A fire box that large with or without a fan for forced draft with out a

firebrick liner and filling the firebox half full of fire brick as well

and in no way improves one combustion efficiency if the fire box

box is stuffed with wood and only allows the fire to smolder and

not obtain adequate temperatures to offer proper combustion.

I got busy at work and had to put this conversation on hold for a while but now I'm back in the thinking stage.

I don't follow your question. Why on earth I'd wanna build a firebox 1 1/7 a cu yard?
Are you thinking bigger? or smaller?

I kind of picked that 30 cu ft out of the air. I just want something much bigger than the 6 cu ft that I have now. I don't want to get to big due to the location that it will occupy when it's done and also the simple cost of building a mammoth beast.

 

[Bricks]

I run a gasification boiler and from all I have read and been told going to large storage will not change the amount of wood one will burn but only the number of times in a given time period of firing the boiler. There again if not done properly heat loss due to storage can up the amount of wood burned.

 

[THE PLUMMER]

1. the OWB companies have spent far more (than anything this site could or will do) time and money researching and testing what sizes and capacities perform best. Steel and its cost have very little and almost zero impact on what the size is. 1 of the largest expenses is the certification process, you can't even imagine what that new phase 2 combustion cert and EPA certs cost them. They are double the price not just because of the engineering and materials in them. Capacity addresses 1 thing best, lag time, why store enuff water to heat your space 4 or 5 times over, when you might only need some of that for a cold start like at a cottage that gets weekend use. It takes longer to bring up to temp and takes more wood to maintain temp. The perfect and correct size would be 1 that calculates your burn times and btu requirements. If and only if you expanded and needed more you could always add a buffer tank to increase volume. Buffer tanks are pricey but they are more efficient than any OWB. The larger the volume of water the more output required from the fire box, this mean larger size or more efficient style burn. Otherwise the lag time to heat up the larger volume increases to much and no one wants to take 6 hours to raise the temp a couple degrees.

Your firebrick adds only a small amount of burn efficiency if any, whether it ads anything to the boilers overall efficiency is hard to say. Firebrick usually aids most in start up by more mass, it doesn't have enuff heat to raise combustion efficiency, however it can maintain a higher temp once there. Once the call for heat is done the blower shuts down any aid the brick might have done for the burn. It a good thing but there is more to burn efficiency than Firebrick.

 

[AIM]

Let's take a bit and change the question. Instead of "how much water",,,,, let's rephrase to "how much water versus firebox size?"......

Wood burns at about 900° to 1200°. If you have a water jacket the size of a warehouse and a firebox the size of a shoe box you'll never get the temp up.

(I have to think in extremes to make my mind work)

The other extreme is a water jacket a 1/2" larger than the fire box. You'll boil over constantly.

Somewhere in between is the perfect combination of water versus fire..

X cubic feet of fire box "SURFACE AREA" will heat X cubic feet of water EFFICIENTLY.

Somewhere I have read that a pound of wood will heat a pound of water at a certain % of efficiency. I can't find it now but I believe this study will help in this discussion.

 

[dave_dj1]

I'm no expert nor do I own an OWB but I think some are missing the point of having a large amount of storage. Once the large mass of water is up to temperature, you don't have to heat it from ambient temperature back to 165-180. All you are doing is making up the difference from what btu's you have extracted to heat with. If you have say 1000 gallons of water in a well insulated tank and it is at 170 degrees and you draw it down to 160 degrees you only have to heat it back up to 170. More storage will mean that you can draw off that storage for a longer period of time. If everything works as it should you shouldn't need to have a continuous burn but rather a burn when needed to raise the storage temp back up.
just my .02
dave
Again I say "google Garn".
taken from the garn website: When the GARN WHS unit drops below the operating temperature of your system, start a fire and heat the water again.

 

[NRwooduser]

Dave, your right on saying:

"If you have say 1000 gallons of water in a well insulated tank and it is at 170 degrees and you draw it down to 160 degrees you only have to heat it back up to 170. More storage will mean that you can draw off that storage for a longer period of time. If everything works as it should you shouldn't need to have a continuous burn but rather a burn when needed to raise the storage temp back up."
I always fire my stove to 195 degrees and then let it go out. Here in NC it's not as cold as it is up north. I fire it hard then let it go out at night then in the morning it's down to maybe 160 then I put some good seasoned wood in, throw alittle diesel fuel, light it up and turn on the fan and make it burn as hard as I can back up to 190. By the time it recovers to 190 there is nothing but good hot coals, no smoke.You be surprise how long a box of hot coals will keep the water up there. When you have more water storage you can play around with the firing.