Have a cupola now want a steam hood but have a question

[bison1973]

Right now I have a cupola but want to add a hood for next season. My question is... can the steam stack be run up into the cupola opening and still work well as opposed to running it through the roof?

[RileySugarbush]

That's what I'm doing. As long as you have a pretty long stack, it draws the steam up without problems. I need no damper to keep my preheater working well, and don't get much leakage out of the hood. On my 2x3 flue pan I have a 6" diameter steam stack about 8' long with a 45° bend in it to shoot up into the cupola, which is offset over the syrup pan. Works great!

[maplekid]

you shouldnt have no getting steam out cuase it forms a almost like a vaccum or like draft for a fire and it will just float out of your door.if your hood has a exhaust fan then it will work better.

[Breezy Lane Sugarworks]

If you're using the hood for a pre-heater too......DON'T use an exhaust fan...it'll defeat the purpose. and if the stack is sized right for the amount of steam, then it'l make it out anyway on its own.

[Fred Henderson]

Someone please correct me if I am wrong but doesn't a natural draft on a steam hood work to lower the atmosphere pressure thereby lowering the boiling point for the sap.

[RileySugarbush]

Yes and no. The draft lowers the pressure in the hood an infinitesimal amount. (neat word, hey?) If you think about the hood with the doors open, the draft is working and and pressure in the hood is still basically the same as the rooom. Closing the doors doesn't really suck in the sides of the hood, the pressure drop is very small. There would be no noticeable depression of the boiling point. Even with an exhaust fan, I don't think you could measure the boiling point change.

[brookledge]

I have a hood with a pre-heater and I have a couple of lengths of pipe on it to get it up into the cupola. I have no hood on my syrup pan so I figured why put it through the roof.
As for the debate of whether a hood should be dampered or not, I can tell you my experience. When I got my new hood and pre heater Leader said you may want to add a damper to raise the temp of sap coming out of the preheater.
The first year I boiled with out one because no store around me had one big enough. The sap coming out averaged 185-190. I bought one on ebay and put it in for the next year and saw my average temp go up to 200-205.
I know that sap will boil at a lower temp under vacuum but it will boil hotter under pressure.
I feel that I'm better off having the sap coming in as hot as possible so that there is a constant boil at the inlet.
But it seems like this issue would be a good one to be studied by some one with a good physics background
Keith

[Fred Henderson]

OK guys who is going to do the math on this one?

[Michael Greer]

It's a good question. Obviously when the preheater is working well, and delivers sap at 200+ degrees, you'll get more of it boiling in the sap pan...BUT...If the steam damper is closed off too tightly, it seems like it's going to hamper the removal of moisture. The whole point is to get the water out right? It would take someone with more engineering math than I'm capable of, and I'd wager that the folks designing the evaporator units have done a lot of that design fork for us. It isn't always necessary to re-invent tie wheel...especially if you can steal 'em.

[Sunday Rock Maple]

We vent our hoods into it -- no issues.

[Hop Kiln Road]

This will answer the questions:

www.uvm.edu/~uvmaple/sappreheaters.pdf

Long range weather forecast here looks cold through February - give us plenty of time to tinker.

[Sugarmaker]

This will answer the questions:

www.uvm.edu/~uvmaple/sappreheaters.pdf

Long range weather forecast here looks cold through February - give us plenty of time to tinker.

Thanks for posting the link to the research. Guess I read that before. About 15% improvement with a preheater in a hood.
Regards,
Chris