Mason 2x3 - Stack Temp Questions

[ducxsterdoo]

Hi.. been searching the forum on stack temp and stacks glowing red, and not 100% sure what I should change, if anything.

Did my second boil today. I'm getting right around 7.5 GPH rate. Today I noticed that my stack temp (magnetic external thermometer) was pushing 800, and the tee out of the back of my evaporator was starting to glow red (see pic).

IMG_20200224_174530.jpg

I do have AUF and have been running it nearly at the lowest setting. If I run without the blower, the boil definitely is not as hard as when the blower is on, but it's still boiling at a decent rate.

I'm not necessarily unhappy with my current boil rate, but want to make sure I'm running as efficiently as possible and not sending too much heat up the chimney, and worst yet, causing it to overheat.

I'm burning mostly wrist sized maple and cherry, with some scraps of rough cut hemlock siding thrown in each time I fire.

Thoughts?

-craig

[Chickenman]

Mine looked like that the first 2 years boiling on it. I redid the bricks at the back of my fire box and started adding wood less often. I'm still getting 8+ gallons boil rate and with the same type of thermometer and I'm running in the 4 to 600 range now.
I could only get 1 season out of my stack as I know I was over firing the unit when my entire 10 foot stack would be cherry red and a 3 foot flame shooting out of the stack like a jet engine with an after burner.
Now, I split my wood smaller and add it less often and everything seems to be running more smoothly. I can open the door to add wood without having to turn the blower down and I'm not eating flames when I do.

[ducxsterdoo]

What did you do to change the bricks in the fire box?

[ecolbeck]

If you google “bricking mason arch maple” and look under images you will find some pictures of a wall in the middle of the arch which pushes the fire/flue gasses up against the bottom of the pan. That may help improve the heat transfer to the pan and keep your evaporation rate high while keeping flue temperatures moderated. However, with such a short arch, high flue temperatures may be hard to avoid.

[Chickenman]

What did you do to change the bricks in the fire box?

I will try to get you a pic tonight when I get home from work.

[ducxsterdoo]

This is how I bricked mine... The wall is less than 3" from the pan and I raised up the floor behind the wall.

20191027_124044.jpg

[ecolbeck]

That looks great. Perhaps you could shrink the gap to the pan down to 2" and extend the wall towards the flue exit. I think the idea is to keep flue gasses in close contact with the bottom of the pan for as long as possible. You could even extend the wall towards the firebox door. This would mean covering up some of the grating (not a problem) and would depend on the length of wood you are using. This would give even more contact time with the bottom of the pan. As mentioned before, short pans are not terribly efficient.

[eustis22]

for the cavity behind the wall, I bricked my Mason 1/2 way up the stack hole so its the same height as the wall. I have an XL so the preheater pan sits over the flame as well and my preheater achieves regular boiling too.

[Chickenman]

IMG_20200225_141101.jpg
This is mine. Little different, but it works.

[ducxsterdoo]

Thanks... Blocking the stack opening partly is interesting. That doesn't affect the draft at all?