I was looking at the Garn website (did not find it that user friendly, hard to find good pictures/info) and was wondering how the heat transfer differed from other gassifiers? From the limited pictures it would appear that there is a large water jacket around the combustion chamber. Wouldn't this reduce the efficiency and make it similar to a OWB? Or is the storage separated within the system and only a small amount of water is heated then ciculated/exchanged. It would seem to me that you'd need to keep the water temp up and not let the fire go out. Am I right in thinking this? Most of the other gassifiers I see heat small volumes of water <100gal and therefore the temp must be alot hotter or at least temps can get up to 2000F before they are squelched by the water jacket so that efficient burn rates can be achieved.
Garn questions
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Watch the garn movie at the garn web site. The garn does have a large water jacket but the difference is the fire box and secondary chamber is ceramic and that is where the wood and gas is burnt. Then the hot exhaust passes thru pipes in the water jacket lowering the exhaust down to 250* and out. The difference between the garn and most other gasification boilers is most other ones pump the heat from the heat exchangers to the storage. The garn you start a fire each time (looks very simple and fast) when you need to raise the water temp in the storage. Most other ones you can start from coals, but not always if it has been to long between fires.
leaddog
leaddog
heaterman
Minister of Fire
Garn differences..............where to start..........? It's like comparing a thoroughbred to a donkey. They both have long tails, eat hay and oats, have hooves and longish ears but the similarities end there.
A garn has a very large heat exchanger area compared to anything else I have seen. I'd have to do the math but off hand I'd guess the smallest unit would be 130 sq ft+. This is substantially more than you'll find in nearly any other gasifier of the same firing rate. Result: excellent heat transfer. The burn chamber is large. The difference between that and a typical OWB is that there's roughly 50' of 5" heat exchanger tube behind it, all of which is submerged in the water. It will drop the secondary burn temp from 1,700*+ down to about 300-350 at the exhaust. The only time you'll get condensation in the flue is when your water temp is below 120 or so. It's an issue that can be easily dealt with if it's an issue at all.
Keeping the water temp up: There is no aquastat or any other typical on/off control device for the fire. You turn on the combustion blower via the wind up timer, load your wood and walk away. The enormous storage volume will soak up all the heat without having to cycle the fire. You really can't imagine how simple it is and what that feature does for you until you've seen one operate.
There is really no need to start a fire each time. Once you learn how much time to crank on for a given burn, there will almost always be coals left after the timer shuts down the burn. With the air velocity moving through the Garn's burn chamber, it doesn't take many coals to get another load of decent wood going pronto. I've seen garn's set for over 24 hours with no fire in them and still have enough coals to self light. It's interesting to me to see some of the guys here adding timers to their boilers to keep them from "running cold" or running with no water temp left. The Garn has operated on the simple timer principle for over 30 years. Again, you have to see one of these things run to fully appreciate how simple they are and how well the concept works. Concept = burn it all, burn it hot, burn it fast, burn it clean.
A garn has a very large heat exchanger area compared to anything else I have seen. I'd have to do the math but off hand I'd guess the smallest unit would be 130 sq ft+. This is substantially more than you'll find in nearly any other gasifier of the same firing rate. Result: excellent heat transfer. The burn chamber is large. The difference between that and a typical OWB is that there's roughly 50' of 5" heat exchanger tube behind it, all of which is submerged in the water. It will drop the secondary burn temp from 1,700*+ down to about 300-350 at the exhaust. The only time you'll get condensation in the flue is when your water temp is below 120 or so. It's an issue that can be easily dealt with if it's an issue at all.
Keeping the water temp up: There is no aquastat or any other typical on/off control device for the fire. You turn on the combustion blower via the wind up timer, load your wood and walk away. The enormous storage volume will soak up all the heat without having to cycle the fire. You really can't imagine how simple it is and what that feature does for you until you've seen one operate.
There is really no need to start a fire each time. Once you learn how much time to crank on for a given burn, there will almost always be coals left after the timer shuts down the burn. With the air velocity moving through the Garn's burn chamber, it doesn't take many coals to get another load of decent wood going pronto. I've seen garn's set for over 24 hours with no fire in them and still have enough coals to self light. It's interesting to me to see some of the guys here adding timers to their boilers to keep them from "running cold" or running with no water temp left. The Garn has operated on the simple timer principle for over 30 years. Again, you have to see one of these things run to fully appreciate how simple they are and how well the concept works. Concept = burn it all, burn it hot, burn it fast, burn it clean.
Heaterman,
I agree 100% with what you stated. The simplicity and easy of use is just phenomenal. I'm wondering if you are going to install one for yourself, or maybe you already did?
I agree 100% with what you stated. The simplicity and easy of use is just phenomenal. I'm wondering if you are going to install one for yourself, or maybe you already did?
heaterman
Minister of Fire
As of right now I have no plans to install a Garn or anything else. My natural gas bills run $250-$300 in the highest months, average for the year is about $120 per. ROI would be Waaaaaaaaaaaaay out there for me. I have to say that if I put up a shop someday it will have a Garn in it. Of the dozen or so brands and types of wood heating appliances I have installed, I am truly impressed with them.
Thanks for the info. This is exactly what I wanted to know. This greatly swings my attention to a Garn seeing as how I really want ease of use. I'll have to contact Garn to see if they have anyone down this far on the prairie. I am planning on a trip up to the Green Bay area this summer, maybe I can find a forum member along the way that is running a Garn?
heaterman
Minister of Fire
Biomass:
You are certainly welcome to call me directly if you need any info on a Garn. My cell is 231-920-4808. The factory can be a bit hard to get in touch with.
You are certainly welcome to call me directly if you need any info on a Garn. My cell is 231-920-4808. The factory can be a bit hard to get in touch with.
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