Wind shift shut me down

[maple marc]

Today I experienced something new: in the middle of a good afternoon of boiling on my 2x4, suddenly my boil dropped, my stack temperature plummeted, and when I opened the door to fire I got a terrible back draft. I actually first thought that something was blocking my SS 10" stack. In two seasons of operation I have felt that this rig has too much draft on 9' of stack--I usually have to close the draft door and block the crack with fire bricks to prevent the stack base from glowing red. After choking on smoke and CO today, I realized that the wind had come up from the SE, apparently creating a down draft as it came over the roof peak. My stack is along the wall of our corn crib, away from the roof peak. It's height is 1' lower than the roof peak.

I quickly called around and scrounged a 4' section of stack to add to the top. This didn't help. It's interesting that in two years of boiling, this is the first time the wind has come out of this direction. I also realized that the height of the stack is much more important than the diameter. If I had to build my stack over again, I would go with 6" or 8" and add at least 6' in height. I might also add a damper.

Anyone experiment with those revolving stack hats?

Any thoughts would be appreciated.

Marc

[Pete33Vt]

I too had a really tough time this week with boil. It was on thrusday(20) Boil was ok in the morning then bang everything went flat. No matter what I did could not get it going. Almost shut her down. But struggled through the day. Burnt alot of wood and finally got everything cleaned up. Ended up with 9 1/2 gals. Got home and thought about it have a feeling it had to due with spring begining. I hope things straighten out. As to your ? could have something to due with that also. Since it hasn't happened in two years. Mabye the weather was just right for that to happen. Hope you get it figured out.

[Russell Lampron]

Marc,

I think that your stack diameter is too big for a 2x4 evaporator. I have an 8" stack on my 2x6. You also want your stack 2' or more higher than the peak of the nearest roof. I don't know if you would have had the same problem with a smaller and taller stack but I think you will solve your other problem if you change it.

[Hop Kiln Road]

Strange, couldn't get our evaporator to operate normally either yesterday...Most of the day was in the mid 20's and high winds and it wouldn't boil. Bruce

[tapper]

Over the years of making syrup I experience 1 or 2 days a season like this and Thursday was one of those days. Soaking wet wood didnt help me much but, I was able to maintain 1200 degree stack temp and the boil rate was still low by 20 gph for the day.

[argohauler]

I know my evaporator doesn't like low pressure days. On Wednesday this week it was raining and it just wouldn't boil the way it should. Thursday and yesterday were high pressure and it boiled fine.

I've been told by some "maple experts" that you should have your smoke stack at least twice as long as your evaporator for it to draw properly.

[Brent]

I think what you guys are experiencing is that the change in wind direction is producing lower pressure IN the sugar shack. Most of our buildings for boiling are not sealed at all, and if there is a lot more cracks on the downwind side you will get negative pressure inside. Put a door or window on each side and open the one on the windward side. It can be like adding a blower.

Height of the stack above the roof is important, but enough height will only get you out of the high back pressure caused by the roof. If the building is negative pressure, you're still going to get back draft.

Some days in our house on the hill I need to open the door on the windward side to avoid blasts of smoke when I fire the woodstove that heats the house.
And this house is pretty airtight.

[Dennis H.]

From reading and studing residential building codes, what I have found about chimmneys is that they should extend at least 2' higher than any portion of a building/roof within 10' but should not be less than 3' above the highest point where the chimney passes through the roof.
I added a pic to help and explain.
So depending on the pitch of your roof and how close to the ridge your flue is will dictate how high your flue should be.

Hope this helps.

[Brent]

Talking to an old timer around here he says neglecting this, the clearance from the stack top to the roof, is one of the greatest causes of home and sugar shack fires. You gotta get it up there for safety and to get out of the roof induced high pressure when the wind is on it.

[HHM-07]

i have a 2x4 rig with an 8" stack 6 foot above the roof peak , boiled Friday and it seemed to go normal (good) my thoughts are a 10" stack is too large for your 2x4 they have a small firebox

[Brent]

I agree HH even 8" is plenty. The Leader Half Pint only has 6" and it has the same size firebox. 10" would be overkill

[maple marc]

Thanks for the great ideas. I was totally ignorant of evaporators when I bought it last year (still don't know much), and I sort of feel I was "over-sold" on the SS 10" pipe. I was told that to get the maximum evaporation rate out of that 2x4 I would need 10". Now it appears to be actually counter-productive! 10" SS pipe is going for $90/section! I wish I had met you all last year.

I wonder how I might effectively solve my problem--short of replacing the whole base and stack with 6". Since I probably should add more height, would adding 6' of 6" pipe (adaptor required of course) work or not? What about adding a T at the top--is this ever done? It could also double as a rain cover. An extra 6' is going to make it mighty tough to reach up there with an overturned bucket. I do it now with an old 15' windsurfer mast with a coat hanger taped to it.

Many thanks again for your great ideas,
Marc

[WESTVIRGINIAMAPLER]

There are plenty of people out there looking for 10" stainless stack for replacements, so you should be able to sell it for not a lot less than what you paid for it.

I have a 2x8 and it has 10" stack just for reference.

[Harken]

I have a 10" dia. stack on my 2x4 as well. It draws like crazy..I need to keep the damper almost tight shut to keep the pan from big foam ! I don't see that as a problem.

[Mike Van]

A not so hot pic. of the 8" stack on my Leader 2x4 - http://img.photobucket.com/albums/v386/MikeVan/evaporator.jpg There's probably 7' of pipe in the barn, it goes out into a chimney with 6x10 flue tile in it, then up another 6 or 7 ft. 9 years on this setup - I run with the draft door off, no damper in the pipe. Never had the weather [wind, low pressure, etc] affect my boiling. What I've seen though is the spaces in my V-grates get plugged with coals or ash & slow me down. I made up a poker I can reach in through the draft door and clean them out - what a difference it makes -

[argohauler]

I have a 10" dia. stack on my 2x4 as well. It draws like crazy..I need to keep the damper almost tight shut to keep the pan from big foam ! I don't see that as a problem.

Don't choke it off, add some defoamer or vegetable oil and let er boil as hard as she can go.

[maple marc]

Well, I fired up again three days later with a change in the weather--nice light north wind. Oh no.....it's happening again......no draft at all....smoke coming out of all cracks in the arch.

That was it--I had to investigate the stack. The one thing I had done after my last successful boil last week: I forgot to put the bucket on top of the stack, and then we had 2.5" of rain the next day. I kept wondering if my brain fade had caused a problem. A friend went up to the roof and pushed a 15' pole down through the stack while I watched through the arch with a flashlight. The pole wasn't able to make it down to the fire bricks. After a lot of poking, he pushed through a screen--something I had forgotten about. It came with the rig--some hardware cloth at the base of the stack, I suppose to keep critters out. That screen apparently had become totally blocked with soot that the rain washed down the stack. No draft at all. We pulled the screen out, fired up and had a great boil. In fact, we are back to plenty of draft. With the draft door closed and cracks sealed, the stack temperature was hitting 1200 degrees occasionally. The flue pan was spitting a bit, making a mess of the outside walls of the pan. But we set a record for evaporation rate--about 20 gph!

Bottom line, you guys with screens at the bottom of your stack--just something to cause a problem.

Marc

[Mike Van]

Good for you Marc - Sometimes the easiest thing goes................