building a garn,what would you change?

[Wade]

I'm starting this years project of a 3000 gallon garn like boiler. I'm using my tank from my homegrown "Galeforce gasification furnace". The gasification furnace worked very well and heated the water with out any difficulty, BUT and there is always a but, the wood the furnace liked is very specific and time consuming. Has to be bone dry, right size, stacked in the fire box just right and so on. I think there are a lot of gasifier users out there heating larger buildings and there houses that are thinking the same. Don't get me wrong they produce a lot of heat from a little wood. But if you need mucho a lot of heat, you need a lot of bone dry, well prepared wood and that is time consuming. For the people using a gasifier to heat their well insulated house and go through 3-4 cords a season, it is more of a hobby. If your heating a 2400 sq ft house and a 5000 sq ft shop with its doors always open for some reason, it becomes a full time job making every piece this big and this way and that and so on!
Now back to the style of the garn boiler. After reading this and other forums it seems to be the best of both worlds, BUT is there anything different you garn owners would want to change or add? I'm thinking of a larger firebox, just for my purposes. Any other thoughts would be appreciated. I'd rather get it right the first time.
Thanks

 

[Jim K in PA]

Honestly? If I were looking at your demand, I would get two WHS1500s and run them in series, or a single WHS3200. The 3200 has a BIG fire box.

Not sure what you are trying to say with respect to the wood. Every wood gasification furnace needs dry wood to be efficient, no matter the brand or design. The GARN is not fussy about wood layout, and the round fire box avoids the "bridging" that can happen in some situtations. Large rounds and even large splits (half rounds) can reduce the burn rate, and reduce efficiency. You want an mass/surface area ratio that allows for vigorous combustion without flashover (puffing). That will vary with the wood, moisture content, and the furnace. Ihave burned up to 8" splits in the GARN, but it prefers 3-4" splits.

I did not build mine, so cannot offer input as far as fabrication. But, one of the things I would want is an extension on the return fitting in the tank to reduce the likelihood of short circuiting flow. As far as details, I would add another bung for a sight glass on the front wall.

Other than that, I think my WHS2000 does its job quite well.

 

[Wade]

Thanks Jim K! Good idea to keep input and output a fair distance from one another. What would the sight glass be used for? Water level, or do you mean a sight glass into the firebox? Thanks

 

[foxt]

Wow, build you own? Cool to have the skills to undertake something like that. I'm more of a carpenter/woodworker, probably a bad idea to put one of these together in the woodshop ...

Ditto on an extension on the return fitting - the supply/return are about 3-4' away from each other at the rear of the tank, and when you aren't plumbed p/s with continuous circ you don't get enough mix in the tank under some conditions and front temps can be as much as 10-15 degrees higher than rear temps. While I was at it, I'd add a fitting on the back of the tank itself so I could easily place a temp probe for supply temp from the tank near the supply fitting

Another thing I would look at would be a safe means to close the flue after the burn is complete to minimize standby loss out the flue.

Last thing I would change would be to lower the drain fitting so that it was absolutely at the bottom of the tank. I had to add treatment for hard water from the chemical company that Dectra hooks you up with to monitor water quality/corrosion. From what they tell me, due to the way their stuff works, I should find sludge start to develop on the bottom of the tank, and they observed that the drain (at least on a WHS2000) is not really well located to help suck that out so I will need to fiddle with it, or leave the sludge there until I drain the tank.

Having said all that, and with only half a season experience with it, it is really an elegant design and aside from the minor stuff, it's just about perfect for what I need.

Tom

 

[Wade]

Thanks foxt, I'm a cabinetmaker by trade also, working with metal is something to do to get away from the wood on the weekends. I'm definately going to incorporate a a system that closes the fresh air intake and the flue after the burn, I had the same problem with heat loss in my old stove, and the heat loss is quite substantial. Thanks again guys, I will begin to post pictures of my project as it gets underway, good or bad, any feed back always makes for a better outcome.

 

[Sting]

wash out ports at each corner in each direction

 

[Jim K in PA]

Thanks Jim K! Good idea to keep input and output a fair distance from one another. What would th sight glass be used for? Water level, or do you mean a sight glass into the firebox? Thanks

Sight glass for the water level. My hatch access is difficult to get to, so checking water level it a PITA. Not that it changes much, I just like to keep an eye on things.

Tom Caldwell installed some turbulators in his GARN to extract even more heat in the last pass of he HX. However, they do create substantial restistance to flow, so consider that in the size of the fan motor and fan design.

 

[slowzuki]

I think it would be fun to build a garn like boiler too, but the price of steel lately would keep be away, well, that and my AC buzz box doesn't like making air or gas tight welds! No couldn't be my amateur welding ticket, definitely need a DC or a tig to fix the problem!

 

[Como]

When I made enquiries I was told best to get 2x2000's. Cheaper than one 3200.

My inclanation is to go for 1 2000, and use other sources for the time we need additional supply.

 

[Wade]

The one thing I don't like about the final pass of the GARN is that it is so high up on the unit. Even if all the heat is taken off, that final pass is in a fairly hot layer of water and picks up heat again on the way out. We had it that way on our stove and the air temp was always the temp of the water at the top of the tank. If the final pass was at the bottom of the tank would that not be better? Coolest water at the bottom of the tank right? I cant remember who was educating us on here about heat transfer, but he said that the hottest air or water (what have you) should enter the heat exchanger closest to where the hottest water being heated is exiting.So straight out of the firebox, couple passes in the upper level of the tank and as the gasses cool, drop down in the tank and exit at the bottom when all heat is removed. I hope everyone understands what I'm trying to explain and any thoughts on it would be appreciated. Thanks And for the price slowzuki, I'm planning on doing this for 1000-1500 dollars, way less than a GARN 3200, and the watertight welds got me thinking to take my time, unless they invent a wood fire to burn underwater! Thanks again.

 

[fabguy01]

Thanks Jim K! Good idea to keep input and output a fair distance from one another. What would th sight glass be used for? Water level, or do you mean a sight glass into the firebox? Thanks

Sight glass for the water level. My hatch access is difficult to get to, so checking water level it a PITA. Not that it changes much, I just like to keep an eye on things.

Tom Caldwell installed some turbulators in his GARN to extract even more heat in the last pass of he HX. However, they do create substantial restistance to flow, so consider that in the size of the fan motor and fan design.

What is a Turbulator? Thanks nate

 

[heaterman]

Wow, build you own? Cool to have the skills to undertake something like that. I'm more of a carpenter/woodworker, probably a bad idea to put one of these together in the woodshop ...

Ditto on an extension on the return fitting - the supply/return are about 3-4' away from each other at the rear of the tank, and when you aren't plumbed p/s with continuous circ you don't get enough mix in the tank under some conditions and front temps can be as much as 10-15 degrees higher than rear temps. While I was at it, I'd add a fitting on the back of the tank itself so I could easily place a temp probe for supply temp from the tank near the supply fitting

Another thing I would look at would be a safe means to close the flue after the burn is complete to minimize standby loss out the flue.

Last thing I would change would be to lower the drain fitting so that it was absolutely at the bottom of the tank. I had to add treatment for hard water from the chemical company that Dectra hooks you up with to monitor water quality/corrosion. From what they tell me, due to the way their stuff works, I should find sludge start to develop on the bottom of the tank, and they observed that the drain (at least on a WHS2000) is not really well located to help suck that out so I will need to fiddle with it, or leave the sludge there until I drain the tank.

Having said all that, and with only half a season experience with it, it is really an elegant design and aside from the minor stuff, it's just about perfect for what I need.

Tom

The drain is elevated to keep it from plugging with sludge. In addition a little sludge is not going to hurt at the bottom of a Garn due to the epoxy coating on the bottom of the tank. it's there to accommodate what you are referring to.

 

[Sting]

What is a Turbulator? Thanks nate

(broken link removed)

 

[Wade]

The way I'm going to try to recover more heat is to have the return water which is very cold after it goes through the concrete floor,enter in a tube that is surrounding the final pass tube of the exhaust. If there is any heat left in the flue gases it has a better chance to be taken off. The tube will have a slight decline so any condensation will run out of the pipe. I'm thinking this might work but if I have over looked something please speak up.

 

[heaterman]

The way I'm going to try to recover more heat is to have the return water which is very cold after it goes through the concrete floor,enter in a tube that is surrounding the final pass tube of the exhaust. If there is any heat left in the flue gases it has a better chance to be taken off. The tube will have a slight decline so any condensation will run out of the pipe. I'm thinking this might work but if I have over looked something please speak up.

If you're going to develop condensation in any of the flues it would be advisable to make those sections out of stainless. Condensate from wood fired equipment is very corrosive. Doesn't really matter if you drain the condensate out of the tubes, it's still forming and running off the walls destroying metal as it goes.

 

[brad068]

Wade I like your title. I myself built a garn style.

https://www.hearth.com/talk/threads/11262/

https://www.hearth.com/talk/threads/35906/

The stock setting is pretty hard to beat. I did alot of experimenting and the unit is just about perfect stock.

I broke up the last pass to try and extract more heat and in the end I think that I am getting to much heat out. At a full burn my final pass right out of the boiler is @240*F and it blows white clouds of steam. Looks like my shed is on fire some days.

My tank is a 1500 gal Dari-cool bulk tank. The drain is right on the bottom and with the smooth stainless, it looks almost like the day I built it when I washed it out. I made an adapter on the drain to except 1.5" pipe thread so I just hook up a 1.5" hose and drain and then rinse.

My flue pipes are sch 40 a106 pipe. This is probably and overkill but thats the way I build things.

Good luck and keep pics.

 

[Wade]

Garnification that is truly one great piece of work. If mine looks like a fraction of your set up I will be happy. Those pictures were great and your comment about doing experiments to improve the design sound like what we have been trying. I guess I will keep it almost basic but incorporate some ideas from this forum. Nice to see people out there not afraid to put the checkbook away and tackle a project themselves.

 

[Wade]

Well, here is the tank that I am using, it works out to 3450 gallons, but I figure once the firebox and all are in it should be around 3000 which will give ample storage. I got the tank at my local scrap yard, he didn't want to spend the time cutting it up so he sold it for 500$. Any ideas on the easiest way to mount this,maybe in a cement cradle? Second picture is the tank compared to my old empyre 450 OWB. I bought it at the same junkyard six years ago for 250$ and used it for the last 5. Cheap heat. It had a rotted out water jacket by the door for some reason, 3 hours later it was good for 5 years. I'm using the top half of the firebox and fabbing up the bottom with the empyres outer water jacket skin.

 

[allan]

Wade

I'm building my version of the Garn out of a 3000 gallon tank that I bought off of bay for $500. I have everything drawing up and the plate steel cut out on a plasma machine. The 5-inch pipe I bought is A53 schedule 40. It is pressure rated. We use this same pipe for our steam lines at work. I used a piece of structual grade for the 6-inch pipe for the air intake. Unless you can get good pipe at the scrapeyard, I have 4K into my steel plate and pipe. All new materials and I had the steel burned using my cad files that emailed to the steel supplier. The pipe fitting are expensive, especially the Tees. I started cutting my take ends, should have all the holes cut out tomorrow. I will post some pictures when I get a chance. The only thing that I have not drawn up yet is the door. I really like the Garn door, but I will probably not do anything that fancy. I don't see the door getting hot anyway since the fire is all pulled into the secondary burn chamber.

Allan

 

[Wade]

Hey Allan, I hope your project goes as good as I hope mine does. I got 60' of 4" boiler tube from another junk yard for $2 a foot. You said you are using 5", will that perform a lot better than 4", because I couldn't find any cheap 5". All my tee's and nineties were $10-15, used as well. How are you introducing the combustion air into the firebox? One, two or multiports? As for the door, simple is good, I want a bigger door than the Garn. I'm making the firebox 36" wide, 48" tall and 60" long.

 

[brad068]

Wade

I'm building my version of the Garn out of a 3000 gallon tank that I bought off of bay for $500. I have everything drawing up and the plate steel cut out on a plasma machine. The 5-inch pipe I bought is A53 schedule 40. It is pressure rated. We use this same pipe for our steam lines at work. I used a piece of structual grade for the 6-inch pipe for the air intake. Unless you can get good pipe at the scrapeyard, I have 4K into my steel plate and pipe. All new materials and I had the steel burned using my cad files that emailed to the steel supplier. The pipe fitting are expensive, especially the Tees. I started cutting my take ends, should have all the holes cut out tomorrow. I will post some pictures when I get a chance. The only thing that I have not drawn up yet is the door. I really like the Garn door, but I will probably not do anything that fancy. I don't see the door getting hot anyway since the fire is all pulled into the secondary burn chamber.

Allan

Hey Allan,

The door does get hot about an hour into the burn. I used two tank ends one 20" and one 22" and mounted one inside the other.This leaves a perfect 1" gap for 1" rope door gasket. I also packed ceramic fiber in between and this does help to keep the door cool for about an hour or so.

Yeah, sch pipe is not cheap nowadays and the fittings.

 

[brad068]

Hey Allan, I hope your project goes as good as I hope mine does. I got 60' of 4" boiler tube from another junk yard for $2 a foot. You said you are using 5", will that perform a lot better than 4", because I couldn't find any cheap 5". All my tee's and nineties were $10-15, used as well. How are you introducing the combustion air into the firebox? One, two or multiports? As for the door, simple is good, I want a bigger door than the Garn. I'm making the firebox 36" wide, 48" tall and 60" long.

Wade, that is a big box. That is volume that could be occupied by more water than air. The new kids boiler is out of a 3000 gal tank and his box is one sheet of 4x8, .25" steel rolled and that is plenty big.

And guys, the air collar has a baffle in it so the combustion air has to go up and around the door collar which in turn preheats it and keeps the frame cooler. The air first enters the firebox on top then makes its way to the bottom entrance.

 

[jklingel]

Wade: Quite an undertaking, and good luck to you w/ it. When these types of questions pop up, I'm always curious what the original builder would do differently. Maybe if you bounce some of your ideas off Garn they can tell you why they think they won't work too well, or that they sound good and may incorporate some into new Garns. From what I hear of them, they are pretty sound folks and may well be open to fresh ideas. If you ever ask, pls let us know what transpires. thanks. j

 

[Wade]

Wade, that is a big box. That is volume that could be occupied by more water than air. The new kids boiler is out of a 3000 gal tank and his box is one sheet of 4x8, .25” steel rolled and that is plenty big.

How long of burn can you get with a box that size? I want at least a six - seven hour burn if needed. I don't want to babysit a furnace like my last gasifier.During the day when our mill-work shop is running, it takes a lot of heat, doors open,heat exchanger in spray booth. Could you please explain your air intake a little more. Does it pass right by the bottom entrance, go up around the door to the top entrance and continue on around the door to the bottom entrance.How large are your intakes for the burn chamber? Thanks again guys.

 

[heaterman]

Allan::

Did you get in on the Dirty Jobs program recently shot at the Locks?