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[Scott7m]

Ok..  first of all, water capacity aint where efficiency comes from,  ive ran gassers that held as little as 30 gallons and stoves that held near 300 gallon, the low water capacity stove was more efficient but it had nothing to do with water capacity

If your wanting to burn chunks and odds and ends, a gasification furnace is NOT for you.  The wood needs to be fairly uniform and similar in size and pretty uniform to prevent briding in the firebox, if it bridges, it will either go out or perform in a very poor manner. 

If your wanting to burn stuff like that I would get a stove with a large firebox for sure, no indoor units I know of are capable of burning end cuts, big knots, etc.  There all designed for cordwood thats pretty uniform.

There is a lot to know in making a decision on one of these, but try not to get caught up in numbers when ur looking, the btu ratings arent accurate and are a maximum guess, companies with a lot of water will say its the best, companies with small water cap will say its the best, with every difference some company and someone is gonna tell you its better regardless if they have a clue or not

[Sprinter]

Looking at the indoor gaser they look small to me . Water tanks are like 75 gallons compared to the outdoor with 300 gallons. Sorry if these seem dumb but this is my first time buying one. The firebox also looks small  and don't look like long burn times before feeding the fire again.
 I sell firewood also so would  be burning all the chunks and odd pieces leftover as well as pine and oak would all be seasoned. Would like to be able to throw larger size pieces in to reduce splitting them down to 6" rounds. 
For size of the stove right now we have a 1500 sq ranch with a full basement and cathedral ceilings ,skylights and lots of window. 3 car garage ,hot water heater and a hot tub.Plans are to convert the excisting garage into living space install baseboard.  Add on a 3 car garage
heat the floor and a 1200 sf addition .So the house will be double in a few years .
 Open to all ideas if a outdoor gasser will out perform the indooren not having it inside will be a option.  If the indoor gasser can take larger wood and last 12 hrs  and not have to fill it every 6 to 8 hrs that would work.

The only thing indoor that might even be considered are older Tarm MB series , like 20-30 years old. Or similar natural draft units. However only Tarm would be the one to look at since they are bullet proof. (Storage required for 12hr burn) 30 year old Tarms are still fetching $500-$2800 and selling. With any gasser , wood consistency is very important, but the non gassers have a proven track record of working with less than perfect wood. I think you should be able to put any boiler in an outbuilding as long as it's not living space and within reason.
Now your 12 hour burn time will almost definately require storage unless your buying a unit that is twice the size you need. Still with a lot of capacity. Like Scott said, size of the boiler doesn't mean much, but in order to achieve long tending times of 12 hours will need X# of gallons with enough BTU to last your 12 hours.
It's impossible to do without high mass on a design day.
You need your heat loss for design day.
Btu/hr x 12 hours = X required BTU
Now Y gallons of 180 water = Xrbtu
And what boiler will supply Y gallons over 12hrs
Then Z lbs of >20%MC wood x boiler efficiency % = rough estimate of how much wood you will need to go thru ever 12 hour cycle.

You have a tuff order to fill for your specifics. None of which can be done cheap with new equipment. This is why the simplest designs are also the most cost effective up front. I think your wood quality being a big part of the problem, as no one would recommend burning junk or wet wood. It doesn't make anything look or work well.

[Scott7m]

I dont agree you need x number of gallons at all, my 30 gallon boiler had no extra storage either?

If its transferring it to the water efficiently.  When it comes to how long its gonnna last its a better question to see how much wood will it hold vs how many gallons of water does it hold, I look at it as if were burning wood not water, water is our medium of heat storage and transfer

Martyinmi used one of the small empyre pro 100 they used to make, held 30 gallons.  He liked it but it simply wouldnt hold enough wood, the firebox was only 5 cubic feet.    Hes now using a p and m optimizer 250 and it holds a lot more wood and water too. 

But when we are talking about burning knots, limb wood etc, just mark gasifier off of your list.  The 325g u originally mentioned will work well for that.

Sprinter, with all seriousness, I knoe euro models with storage can burn more efficiently with storage, but how or why would number of galllons be needed to be known if the gallons in the outdoor boiler type are continually reheated, are most of the systems you use batch burn??

[martyinmi]

tomscarpt,
Google Wood Gun 140 or 180.
They are true gassers that employ a draft inducer as opposed to a fan. Almost all smoke is sucked out while the door is opened.
I've seen a 140 and it is a terrific unit. I think it holds about 10 or 11 cu.ft. of wood (the 180 is a fair amount bigger) and about 80-100 gallons of water. I think a 180 would suit you better based on your future heating needs. I don't believe that the uniformity (or lack thereof) of your wood would be a deal breaker either on the Wood Gun. I think they make even larger models too.
They are engineered to run either with or without storage, so that'll make me and Scott happy, as well as Sprinter!

The best advise I'd share with you would be to make certain that you buy a unit with a draft inducer if you plan on running it inside.
I've seen first hand what a pole barn looks like after running an outdoor unit inside and it's not pretty. So unless you are very quick at loading, you will have a smelly smoke filled work area. If that work area is attached to your home, momma will most likely be unhappy.
Check with your insurance agent also. I've never heard of anyone's rates going up because of an OWB installed outside. I've heard of MANY folks getting their policies either cancelled, or at least their rates going up significantly because of an indoor wood burning appliance.

Good Luck!
 

[Sprinter]

What I am saying is during the 12 hour cycle, X # of heated gallons need to be delivered to the house. Whether it's the same gallons recirculated or those in storage. So if its 800 gallons of 180 degree water, the boiler must be able to recirc and recover the btu delivered by 800 gallons at 180 for example.

So a boiler without storage would have to hold enough wood to last 12 hrs and be able to recover & circulate the required btu.
Obviously there are few boilers out there that will deliver 40kbtu for 12 hours by itself. But any boiler with storage and doing batch burns can be made to do so. If the main goal is 12 hour tending times, you'd have to go with an oversized unit, and if the standby losses aren't bad, then it's not much of an issue. Just the expense of the larger unit.
Advantage high mass, since the low mass models just don't have the firebox size.

[yoderheating]

 I don't understand why you would oversize a unit if you were looking for 12 hour burn times. Don't most outdoor furnace base burn times on 12 hour fills?

[tomscarpt]

Starting to get a clear picture on this.
Placing the gasser inside  is out. The wood gun looks very interesting has a nice size firebox up to 31" long  can go inside But not sure about the stainless steel part. I am comparing that to just a owb and was told to stay away from them with the stainless tanks.Anyone know the price of the wood gun's ?
If it was up to me I would just buy a owb so I could throw all the leftover wood odd pieces ect and burn it.The township approved my permit with a clause (have to sign a waiver from the dep for smoke ) They have the right to shut it down. So that's were the gasser came in to play.
I can change what wood I burn how about a piece of odd ball every few loads to get rid of that.Can aged dry pine be used have a endless supply of that ,

[hondaracer2oo4]

Tom,

   I assume the indoor gassers are similar to the outdoor ones in the fact that you need to have some pretty uniform size pieces of firewood to prevent what they call bridging. Bridging is when the logs burn and leave a gap around them  making it hard for the wood to off gas because of the air spaces between the wood. Im sure that pine would work but your burn times will be extremely short I think.

[martyinmi]

The Wood Guns primary burn chamber (the 140 and up) is big enough to where I don't think you'd have any issues with bridging.
If memory serves me correctly, It is very close in design to my P&M 250, and I have no issues with bridging at all with seasoned wood. If moisture content it a bit too high I've had uglies bridge.  I burn any and everything that I cut- crotch wood and all. I call all those uglies "unstackables". (Got that name from Dean186) The little Empyre Pro Series 100 (ProFab) I used for  one season would bridge if I used too many uglies in it.
There haven't been many issues with the Wood Gun that I'm aware of. Like any other gasser, you'll just have to burn seasoned wood, keep heat exchange areas clean, and replace wear items when necessary.
It seems like they are priced similar to P&M's offerings based on output, but I've not talked to the folks at alternateheatingsystems.com in a while, so I wouldn't bank on that statement.
The two gassers I've owned burn any species of wood just fine. I've burned pine, spruce, basswood, willow, poplar, oak, ash, maple, locust, etc. Just do your best to make sure it's relatively dry and you and the boiler will be happy.

[jrider]

I have the P&M 250 and I pretty much only burn uglies leftover from selling firewood and haven't had a bridging issue since I got the unit 3 seasons ago.