stack reduction...major problem?

[MapleME]

My 24x60" I just purchased has an 8" stack. My old evap had a 6" stack, and I had hard-plumbed it through the roof....meaning, I have a permanent piece of metalbestos nailed to the roof sheathing that I connected to, with a roof jack and storm collar over that.

So besides ripping it out and replacing with 8", my option is to reduce the evap stack down to 6" just before it goes through the roof.

Am I going to kill the evap rate doing this? I don't think I have the time or energy to pull shingles, and re plumb a 8" stack.

Thoughts. Thanks

[Sunday Rock Maple]

Perhaps the surest answer would be to hook it up, add water and boil to see what your rate is --- you have to set the rig up anyways and if you are OK with the rate then no need to do the demo.

Good Luck!

[Brent]

you might try adding extra lenghts of stack above the roof line to increase the natural draft.

[Sugarmaker]

I am sure it would work with it necked down but you may not get as good of draft. I would recommend doing what you need to to go to the 8 inch. I don't think you would ever regret the work time and money to open up the roof items to accept 8 inch stack!
Regards,
Chris

[wiam]

6" equals about 27 square inches
8" equals about 50 square inches

Seems like too big of a difference to me. My 2x6 Mason has 10" stack.

[MapleME]

Wiam, elaborate on the square inches thing. your numbers show me its almost a 50% difference which I agree is huge. Just trying to determine what is exactly your SI refer to. Thanks

[Stamford sugarmaker]

Side question- how do you measure boil rate while boiling water? I never heard of this procedure and may need to do so because I am reducing my new 7" 2 X 4 stack down to 6".

thanks, Peter

[DrTimPerkins]

...how do you measure boil rate while boiling water?...
1. Start evaporator, boil water for at least an hour to achieve steady-state evaporation (even longer is better, especially if wood-fired).
2. Measure depth of water in (sap) feed tank.
3. Continue boiling for an hour
4. Measure depth of water in (sap) feed tank.
5. Subtract depth at end of hour from depth at beginning of hour = X inches of water boiled off per hour.

You can convert this to gallons if you know the size of your tank. Try to do the depth measurements on a part of the tank with straight sides, not in the curved section.

[DrTimPerkins]

6" equals about 27 square inches
8" equals about 50 square inches

The cross-sectional area of a circle can be found by using the formula:

Area = pi x r-squared

pi=3.141592653589793

r = 3 (for a 6 inch stack), so r-squared = 9

r = 4 (for a 8 inch stack), so r-squared = 16

Therefore....

a 6" stack has a cross-sectional area of 28.3 inches squared.
a 8" stack has a cross-sectional area of 50.3 inches squared.

Conclusion....you're cutting down the cross-sectional area by nearly half using a 6" versus an 8" stack. It's likely you'll have draft issues if you neck it down that much and/or not be able to achieve maximum boil rates with a 6" stack. Do it right the first time and increase your stack to the recommended diameter.

[MapleME]

Thanks, Doc. after seeing a 50% difference, seems like a NO BRAINER!!

6" metalbestos stack for sale!!!!

Want to buy- 8" metalbestos!!!

[Stamford sugarmaker]

Thanks, Doc. Same deal here- went with the 7" instead of the 6''. Got it all done today with this nice warm weather.

Peter

[spud]

This may seem like a really dumb question but i have to ask. Can a smoke stack have a 90 degree or does it have to be straight?

Spud

[backyard sugaring]

If you have to turn it use two 45's instead.Good luck Lee

[wiam]

I would go with a size larger pipe if I had to put a 90 degree bend in it.