I am curious as to batch burn times with the new controller. My o2 controlled garn has different burn profile, with 80lbs of dry cordwood it takes approx 1.9hr or 104 minutes equating to .76lbs wood/minute. My controller works a little differently, manually adjustable to shut the inducer off at 200degf., the water was 185degf. What btu/lb value would you use to calculate the output?
garn burn times?
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What was your maximum flue temperature during the burn Tom? I noticed yesterday when I was burning 5x12x24 slabs and about 45 minutes into the burn, I was cruising at 550* with some smoke. I put a chunk of 2x6 a few inches in front of the intake, the smoke disappeared and the temperature dropped to 450* and stayed for at least 20 minutes when I last checked. I am going to order the turbulator from Garn and see if that helps my flue temps. I cleaned my flues the first of February.
George, with my un-garn turbs at the last pass my temps are about 300degf, this is partly due to the closed loop burn, with a setpoint of 5.5% residual o2 in the fluegas. As the o2 drops the secondary burn and flue temps will rise if there is enough secondary air the burn will remain clean, if not it will smoke. you had just enough secondary air to maintain a very low o2 combustion thus smoke. When you put the 2x6 in front of the primary it redirected the airflow around the wood pile and out the secondary doing 2 things. One retarding the woodpile burn rate and simultaneously adding more secondary air, excess air and cooling the fluegas. A turb will help flue temps but if possible monthly cleanings will make a big temp difference. I use a knotted wire wheel on a drill with extensions for the straight tubes and hand brush the bends with fiberglass rods and a flue brush. this should yeild a 50deg drop alone. it takes very little flyash to insulate the hx tubes, and or if you happen to burn some wood with a high mc.
Thanks Tom, my wood is 15%MC on my moisture meter. It has been stacked for four years. I have been having a problem slowing the burn and reducing puffing or smoking. Some of my problems have been too small of splits or round wood but this worked well in out Accucraft fireplace that I used to use to heat our house before the Garn. I was worried that the large half log maple/yellow birch pieces (attached) would be too slow of a burn but the flue temperature said differently. I normally have to burn with the firebrick in place to get a clean burn.
I guess I will have to clean the flue more often and also start to increase the size of my splits or not split at all (which would really slow drying times) in hopes of slowing the burn rate and possibly eliminate the use of a firebrick. I have been satisfied with my consumption but would like to get the puffing and smoke under control.
“When you put the 2x6 in front of the primary it redirected the airflow around the wood pile and out the secondary doing 2 things. One retarding the woodpile burn rate and simultaneously adding more secondary air, excess air and cooling the flue gas.”
Isn't this a better situation than a high flue gas temperature at the fan and excess temperatures going out the chimney?
Instead of redirecting, I have to wonder if restricting the airflow at the inlet or outlet or a smaller volume fan would not help the burn with dry wood.
Do you have an opinion on the size of the load, packed density of the load, distance of the load from the primary inlet/secondary chamber? I had not thought of the flow pattern till you mentioned the flow around the 2x6, around the wood, and into the secondary.
I guess I will have to clean the flue more often and also start to increase the size of my splits or not split at all (which would really slow drying times) in hopes of slowing the burn rate and possibly eliminate the use of a firebrick. I have been satisfied with my consumption but would like to get the puffing and smoke under control.
“When you put the 2x6 in front of the primary it redirected the airflow around the wood pile and out the secondary doing 2 things. One retarding the woodpile burn rate and simultaneously adding more secondary air, excess air and cooling the flue gas.”
Isn't this a better situation than a high flue gas temperature at the fan and excess temperatures going out the chimney?
Instead of redirecting, I have to wonder if restricting the airflow at the inlet or outlet or a smaller volume fan would not help the burn with dry wood.
Do you have an opinion on the size of the load, packed density of the load, distance of the load from the primary inlet/secondary chamber? I had not thought of the flow pattern till you mentioned the flow around the 2x6, around the wood, and into the secondary.
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Hi George,
The problem with the 2x6 is that impact of the redirecting simultaneously disrupts the air flow in the primary chamber too drastically. sort of like putting the fire out and and sending all the air up the flue at the same time. since your wood is consistently dry, a known variable, maybe experiment with a 2x4, less restriction than a 2x6, just thinking but possibly a angle iron with holes drilled through it about 4 inches in front of the primary? This is what got me going down the path of o2 control, the real crux is that any fixed p/s air with a batch burn is a compromise, the best thing you can do is be very conscious of wood species, size and mc, having said that all wood piles eventually dry out. look at the grandpa,s garn garn graphs for open loop and that,s what is happening in your firebox, give me a call if you want, I am home all day.
The problem with the 2x6 is that impact of the redirecting simultaneously disrupts the air flow in the primary chamber too drastically. sort of like putting the fire out and and sending all the air up the flue at the same time. since your wood is consistently dry, a known variable, maybe experiment with a 2x4, less restriction than a 2x6, just thinking but possibly a angle iron with holes drilled through it about 4 inches in front of the primary? This is what got me going down the path of o2 control, the real crux is that any fixed p/s air with a batch burn is a compromise, the best thing you can do is be very conscious of wood species, size and mc, having said that all wood piles eventually dry out. look at the grandpa,s garn garn graphs for open loop and that,s what is happening in your firebox, give me a call if you want, I am home all day.
Happy Easter Tom! I was thinking of checking with you later today. I've been splitting and stacking wood, trying to take advantage of the nice cool weather (ice on the puddle this morning) before the heat and the BUGS arrive.
I have done a few burns since we talked and your advice has solved my problems. I am not using a firebrick in front of the primary supply. I have been using mixed sizes, but nothing overly large. The wood is the same moisture content. The big change is your tip to leave a air space for the secondary supply to flow to the secondary burn chamber. This morning at 5 I fired a good load, a mix of hard maple, a few punky maple pieces, and a few dry balsam rounds. This would have been a puffer for sure when I filled the chamber completely. I did not have coals so a couple of pieces of paper, a few sticks of kindling and a few maple splits started the fire. In five minutes I finished loading and shut the door. There was not excessive smoke at start up and seven minutes later I was gassifying and smoke disappeared. What a difference. Thanks a lot!
Glad to hear you're getting around the issues you were having Sawyer. TC has you on the right track for sure.
Just a couple comments after looking over the comments here. ........15%MC wood will try to "run away" in almost anything. That is borderline too dry.
A full load on a Garn is considered 1/2-2/3 of the distance to the top of the firebox. Anything over that destroys the secondary airflow pattern and combustion can "go south".
Reducing overall air flow by restricting the intake would probably accentuate your problem. You can't change the fact that a given amount of fuel is present in the firebox and it wants to burn. Reducing airflow will just lead to a dirtier burn just like you and others have already experienced when there is too much fuel load.
Think of it this way........On an older engine, pulling the choke knob reduced air flow through the carb and enriched the the fuel/air ratio. When the engine started it smoked. There was more fuel present than the reduced amount of air could burn. The same thing is happening in your Garn.
Just a couple comments after looking over the comments here. ........15%MC wood will try to "run away" in almost anything. That is borderline too dry.
A full load on a Garn is considered 1/2-2/3 of the distance to the top of the firebox. Anything over that destroys the secondary airflow pattern and combustion can "go south".
Reducing overall air flow by restricting the intake would probably accentuate your problem. You can't change the fact that a given amount of fuel is present in the firebox and it wants to burn. Reducing airflow will just lead to a dirtier burn just like you and others have already experienced when there is too much fuel load.
Think of it this way........On an older engine, pulling the choke knob reduced air flow through the carb and enriched the the fuel/air ratio. When the engine started it smoked. There was more fuel present than the reduced amount of air could burn. The same thing is happening in your Garn.
Your choke analogy is a good one Steve. I guess 15% is the demise of working on your firewood too far in advance. The wood I loaded in the shed Saturday will not be needed till the fall of 2018. At my age I like the idea of being ahead while I still have the health and energy to do the work.
I will have to live with diminished loads and consider the higher output/pound due to lower moisture. I would imagine the beetle killed pine out west must be a problem as MC must be low on the stump given some of the low relative humidity of the area.I do not remember reading the ½-2/3 full loading nor too dry in my manual. This is what is so great about those passing along their experiences on this forum. After Tom explained his experiences in our phone conversation his methodology was clear and I know how to avoid the problem. Yesterday I knowingly pushed the limits, slightly over a ¾ load which left a small area over the load and a notch on center for the secondary air. This gave a lot of fuel for the primary and excessive smoke was visible for 15 minutes before the flue cleared out.
I am splitting less to produce less surface area than I did previously, 10”-11” diameter only once. I hope this will also minimize the problem using the larger splits above a few smaller rounds in each load.
Well its time to head to town for a replacement hydraulic hose for the grapple bucket on the Bobcat…..never a convenient time.
I am splitting less to produce less surface area than I did previously, 10”-11” diameter only once.
That will certainly help because the factor at play here is the amount of fuel actually available to the flame front. Too much all at once makes smoke. Save yourself some work and use bigger pieces of that same dry wood and you'll be surprised at the difference.
That will certainly help because the factor at play here is the amount of fuel actually available to the flame front. Too much all at once makes smoke. Save yourself some work and use bigger pieces of that same dry wood and you'll be surprised at the difference.
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