Garn 1500 Flue Temps

[eauzonedan]

I'm on season 2 with my 1500 and am noticing what I think to be higher than previous/normal flue temps as shown by the digital Garn sensor located just past the induction fan. I've see up to 580 degrees (30+ minutes into burn with an outside temp of about 10 degrees) I am wondering what others are showing. My wood is likely a bit dryer than last year (current MC 12% to 15% (using a cheapo meter) I have added a few upgrades over the summer,since last year, as follows:

1.)Flow stabilizer added

2.)Rain cap added

3.)Temp sensor had the earlier analog size hole in the cover plate and I had to use a bushing to fit up the digital sensor. This cover plate has been updated and the sensor now sits about an inch further into the air flow since I no longer have a bushing.

4.) burn rate adjuster (aka brick) is set to low (short height) setting

5.) Oak cordwood +/- 24'' (as limited by my splitter) and approximates 3"x6" splits

I had some puffing going on and have since dropped loads to the 60# to 80# range and pack as tight as I can. My thoughts are (all the following adding up): the rain cap and stabilizer may have added a bit of air flow resistance, the deeper setting of the sensor is now hitting a hotter place in the airstream and the slightly dryer wood is burning better.........

The tubes were cleaned within the last month and a half. I'm wondering at what point I can puke something at these temps and/or if others are hitting something close to these temps. I"ve already increased the size of newer splits. I have some, but not unlimited, control on the MC by storing/drying procedure changes. I suspect the 2000 in identical conditions would read a bit lower just because the tubes are longer and more heat is stripped off before hitting the sensor...... Appreciate the input and thoughts of the Garn Guys Brain Trust out there. Dan

 

[JohnDolz]

I'm on season 2 with my 1500 and am noticing what I think to be higher than previous/normal flue temps as shown by the digital Garn sensor located just past the induction fan. I've see up to 580 degrees (30+ minutes into burn with an outside temp of about 10 degrees) I am wondering what others are showing. My wood is likely a bit dryer than last year (current MC 12% to 15% (using a cheapo meter) I have added a few upgrades over the summer,since last year, as follows:

1.)Flow stabilizer added

2.)Rain cap added

3.)Temp sensor had the earlier analog size hole in the cover plate and I had to use a bushing to fit up the digital sensor. This cover plate has been updated and the sensor now sits about an inch further into the air flow since I no longer have a bushing.

4.) burn rate adjuster (aka brick) is set to low (short height) setting

5.) Oak cordwood +/- 24'' (as limited by my splitter) and approximates 3"x6" splits

I had some puffing going on and have since dropped loads to the 60# to 80# range and pack as tight as I can. My thoughts are (all the following adding up): the rain cap and stabilizer may have added a bit of air flow resistance, the deeper setting of the sensor is now hitting a hotter place in the airstream and the slightly dryer wood is burning better.........

The tubes were cleaned within the last month and a half. I'm wondering at what point I can puke something at these temps and/or if others are hitting something close to these temps. I"ve already increased the size of newer splits. I have some, but not unlimited, control on the MC by storing/drying procedure changes. I suspect the 2000 in identical conditions would read a bit lower just because the tubes are longer and more heat is stripped off before hitting the sensor...... Appreciate the input and thoughts of the Garn Guys Brain Trust out there. Dan

Hi Dan, if you check around you will find another thread on flue temps that I started about a month or so back. People were very generous with their feedback. I switched to a bigger model boiler so it is hard for me to compare to last year but this year I have VERY dry wood and have seen some really high flue temps. I won't get into the details of my boilers easy cleaning vs. self cleaning but I can tell you that i have been able to keep the flue temps lower by cleaning the tubes more often than I did last year. IF you were asking for a piece of advice to get the tems down I would say clean he tubes (based on my experience only, I am no familiar with the Garn).

 

[mike van]

My Garn 1000 runs in the high 500's for the 1st hour, i've seen it at 615 once or twice. Dry wood too, doesn't matter if it's oak, maple, locust or the pine I burnt 2 cords of early in the season. Same temps.

 

[Karl_northwind]

You are on to something there Dan, the Flue passages in the 1500 and 1000 are shorter than the 2000, and that will not help. the other thing is the size of the splits, and the MC. I have usually seen them run with larger splits, at least the main load above the kindling.

Did the old sensor with the bushing sit near the center of the flue passage or was it towards the edge? I don't remember.

The puffing is definitely a sign that you need to increase the size of the wood/pack tighter. The chimney cap could have an impact on that, but I don't imagine you're going up there to take it off any time soon.

how did the tubes look?

karl

 

[eauzonedan]

Appreciate the info guys. Karl: always good to hear from you. We need to get together and solve a few problems over a couple home-brews.....

I broke one of my rules which says you should never change more than one variable at a time......summer lay up lends itself to doing that however. One other variable I induced (but did not mention) was the addition of a dedicated filter loop in the storage tank. When I ran it full time - it wiped out my stratification. Once I got the tank cleaned up - I switched to just cycling it with the blower and that got me back to about 50 degrees of stratification (a good thing in my case). Once the filter pumps kicks in (now only during a burn) - it kicks butt on mixing (also a good thing). The reason I mention it is that I think there are two issues with the air flow in a Garn. One being actual combustion of fuel, and the other being that the amount of air flow is a big component in stripping the heat out of the combustion gasses and transferring that heat to the storage. It looks like Martin did a balance act with the number of tubes as well as their location. Messing with that static situation by creating flows inside the tank - could also maybe contributing to my higher temps, which are monitored near the back end of what is just a big Heat Exchanger system.

My gut says the biggest component of my situation is the wood MC and stick size. I was hoping a few Garn Guys may have added any of my noted alterations - one at a time, and would have some input on their individual impact. As far as the tubes - they were clean about 6 weeks ago and I was still seeing the issue after the cleaning. Keeping track of MC, stick size as well as outdoor temp is bad enough, but adding this many variables at once.( without monitoring them one at a time) was not a very good idea on my part.

I'm in the process of finishing the skin on the Garn enclosure and will do a clean of the tubes over the next couple weeks as part of that process. The last cleaning showed less than an 1/8 inch of black soot. It was removed by a pass or two of the brush and did not appear to impact the monitored temps. I'll also try a couple loads of +/- 24% MC without the brick and see how that goes.........

Anybody got a clue as far as how hot is too hot? I just don't want to break anything. I suspect efficiency drops as the monitored flue temp goes up, but that concerns me less than doing any damage to something.

Dan

 

[eauzonedan]

oops......... Karl:
you asked about the revised sensor location. That cover plate is just round plate with a slight clip off one side to clear the blower. Both sensors locations were at the same center of the circular portion of the plate. I re-used the sensor - so that didn't change. Due to the removal of the bushing the new sensor placement is now about an inch further into the air flow. This puts the far end of the sensor a few inches (maybe 3?) beyond the back side of the plate. This location is just downstream of the fan and close to the upstream end of the new flow stabilizer, which was also an upgrade from my first season. The tubes make a 180 degree change in direction at this location as well as go thru the fan. I would guess it as being pretty turbulent as far as the air flow.
Dan