Overfiring a Garn

[Rick Stanley]

I was just reading about that somewhere in here but can't seem to find it now. Heaterman, you were talking about a dairy farmer and his antics. Anyway, what happens if you do push it to the boiling point by accident, does water actually boil out through the manway on top soaking the insulation and everything else or does it all just pour from the overflow tube in front?

 

[TCaldwell]

Rick, most of my burns end with a water temp of 190 to 210degf, the first time around you will get a good combo of water and steam from the front overflow tube, after that some steam and condensation drops.

 

[heaterman]

IIRC there was a fair amount of steam escaping from the lid and gouts of water and steam were shooting from the overflow tube.

Even under normal operating conditions you want to make sure the gasket is good in the manhole cover. If you do get some vapor escaping there, it can get down into the insulation especially if the Garn is in a "box" stuffed with loose fill or batts.

 

[Rick Stanley]

Ok, good. Thank you guys. Guess there's not a real danger of water overflowing the manhole. I had water come from the overflow pipe in front on the first fire, like you said Tom. I've been burning every day or so for a week, even though not much demand yet and it's not fully insulated yet, just to get a feel how much wood will do what. Nothing has overflowed and I'm not seeing steam anywhere. But I've only had it up to 190 or so, so far. I've been burning split red oak that's been under cover for a year. It's only 24" so it doesn't come close to filling the length of the fire box, but if I fill it half way to the top, like the manual recomends, it will raise the temp close to 30*. Seems pretty good, for what's not much more than an arm-full of wood.
Of course I've done everything wrong, like using the garn to keep the oil boiler hot all of the time and flowing the water through the oil boiler from bottom to top and trying to supply dhw in this way, (only as a starting point for first season). So I'm sure when it gets cold outside, I'm gonna want to run the garn as hot as I can.

 

[Jim K in PA]

You're doing fine Rick. I chuckled at your description of "doing everything wrong". Yep, I did the EXACT same things last year in my first season of burning. Before starting this season I got all my near-furnace piping redone so I can bypass the oil furnace completely. I upgraded to a properly sized flat plate HX (went from 20 to 50). I also moved my circ to the supply side, and doubled my zoning options on the manifolds. It was a lot of work, but well worth it.

Oh - in the spring I added a 50 gal electric DHW tank to eliminate the need for the boiler coil. One of my "extra" zones will be to feed the home made copper pipe sidearm to heat the DHW with the GARN instead of PP&L.

The improvement in efficiency has been tremendous. Well worth the effort to completely bypass the oil furnace. And with the flip of two ball valve levers and a switch, I can use the oil furnace as backup.

The efficiency of the GARN in terms of turning wood into heat never ceases to amaze me. I have been burning mostly pine, and mostly punky old pine at that. I get 24-36 hours worth of heat from a 2-3 hour burn.