I burn coal mostly, sometimes wood, and have magnetic thermometers... that they're not "exact" as a probe type thermometer should not come as a shock to anyone. The thing is stuck on the outside of the metal pipe, the probe is inside the stream of gasses moving through it. As creosote builds up on the inside of the pipe it insulates the pipe and reduces the temperature on the thermometer.
I do have to question the "double it" theory however... really?
When I've got a good bed of coal purring away approaching maximum temp and can actually watch the boiler temperature needle moving upward... the mag therm on the door says 425 and the stack temp says 475... Double? Seems like all I'd be brushing out of the pipe weekly is a little dust if I was hitting those temps, and the walls of my firebox would be much cleaner than they are...
I'll buy a probe type and check it out though... interesting.
Watch out, blocking barometric dampers... my boiler's manual was specific and in numerous places advised to limit the draft on the boiler to less than .04 inches of water. Stack temps can go too high overdrafting the boiler, and it won't burn efficiently if it's trying to combust in a vacuum. Mine was puffing back at me, and was getting frequent coal gas explosions until I put the barometric damper BD, in and adjusted it to .02 inches of draft. Was also loading the thing every 3-4 hours on coal, and 2-3 hours on wood... the smoke was awful under those conditions. Stack temps on the mag therms was running 475-600 degrees... too hot. With the conditions lacking the BD, it was not a matter of "if" I was going to have a chimney fire, but "when". That is good advice, to not second guess the manufacturer of your boiler etc. My Atmos requires .1 WC draft & I have this with a strong drafting chimney, Randy
Newmac_Owner said:
Well, I took the advice of the board members. I'm impressed! I purchased a probe thermometer and the results are surprising. My magnetic Rutland thermometer reads 200 deg, and the probe reads 600 deg
![shock !!! !!!](/talk/styles/default/xenforo/smileys/shock.gif)
! So, I guess my stack temps are fine. I couldn't believe what a difference there was in temperature readings! Throw those magnetic thermometers away!!