Tony, I'm reading on the cast iron next to where your plate is.
Waulie, I have double wall ICC pipe, have a magnetic thermometer on the exterior of the pipe next to the internal probe, and it is consistently reading almost exactly 1/3 of the flue probe. Both probe and magnetic thermometer are 14 inches above the stove. While the pipe is hot, I can touch my hand to it for an instant without getting burned. I have just moved the magnetic thermometer to the rear of the pipe, at 14 inches. If you are right, Waulie, the temp should drop, because there is far less heat radiated off the top of the stove to the back than to the front.
Right now I am burning a load that is two splits: sugar maple, 1/2 of an 11 inch round, 18 inches long, and 1/2 of an 8 inch beech round, 18 inches long. Put them in the stove at 8:10 or so. It is now 11:06, cast iron top reading 350, flue 550, air completely closed, blue flames. Constant flames, but wispy. Not putting a ton of heat in the room. Really cold out. Just checked, and in the shelter of the house it is 6degrees F out. Crazy draft. If I open the air at all, the pipe whistles.
11:20, cast iron 350, probe 550, magnetic thermometer 170. It's down maybe 10 degrees in the back. So there is perhaps a slight effect on the magnetic thermometer in the front. Doesn't surprise me too much because it is reading surface temps...its gauge is external. The probe is reading internal temps, and I would not expect it to be influenced by the exterior temp...wouldn't make much sense to design it that way. I'll run the magnetic thermometer in the back for a while.
11:30: 350, 560, 170. I really do think my flue is pretty hot and that a lot of heat is going up the chimney.
Have a new cat. installed it Sunday night, 1 week ago. Before that, external magnetic thermometer was reading between 150 and 200, usually lit off at 150, went up to 200, then back down to about 140 - 160. Which I would translate to 420 to 480 degrees. Now at 170, I'd translate to 510. But that is 170 0n the back of the flue, and I was reading temps on the front of the flue previously. AM going to move magnetic thermometer back to front and see if it goes back up...And after I read that, I am going to move the magnetic thermometer a few feet up the flue. If you are right, there should be a dramatic drop in the temperature of the magnetic thermometer. I'd expect a much bigger drop in air than in internal flue temp as one moves away from the stove top.
OK. Magnetic thermometer on the front is reading 190 now. The other magnetic thermometer I put another 14 inches higher on the flue. It is also reading 190. It was 350 when I put it here a few minutes ago, the reading of the cast stovetop. So it may still be dropping.
HOWEVER
lightbulbs went off
. I have had the stovetop soapstone in the raised position for cooking since yesterday. Just closed the center top and the internal probe went down IMMEDIATELY and is now reading 445, the magnetic thermometer next to it is reading 185, and the one higher up is reading 150.
100 degrees cooler on the probe, with the soapstone down! So, you are obviously right Waulie. The stove top does dramatically influence the reading on the probe thermometer. I have no idea how much of the temp now being read is the result of exterior heat. Guess I'll do some experimenting, moving the magnetic flue thermometer to the back, and to different heights on the back, of the flue.
But, thanks all. I feel much more comfortable about the flue temps now, and will open the air a bit and see what happens. Maybe I don't need a damper after all.....
Waulie, it was a quick burn, but I was using smallish rounds. 52 pounds of wood, but the firebox was not full by any means. I took a picture, and may post it....This present fire is two large splits, as noted above. Much less wood than the small rounds, but I bet it burns longer. I am now four hours into the burn.
Chipsoflying, Woodstock was definitely talking about internal flue temps. The cast on my stove by the exit plate reads about 450 for hours when I have active secondaries going also.
What has been really bugging me is that the Flue temps are supposed to go down as the stovetop temps and cat temps go up...and mine was not. It was going up a lot after the cat was engaged, and staying up. BUT...it was the cast iron cooktop. And I'm an idiot, because I had left the top up in between cooking on purpose because I think it radiates more heat into the room and it is cold out...Didn't put two and two together.
Again, thanks all, for your time and thoughts.
To close, it is midnight, the probe has gone back up to 500, the magnetic thermometer next to it 190, and the one 14 inches higher 150.
About to open the air. Just crack it open. Will post again in a bit, or tomorrow, re what happens.