Preheater in hood

[Johnjenner]

So I posted earlier about making a preheater around the stack thank you very much for the answers. My thought is at this point I will make a pre-heater in the hood. Has anyone tried using copper pipe with radiator fins attached. I have a bunch of the copper pipe with fins that you would see in baseboard hot water heat. I'm wondering if that would be more effective as a pre-heater tube versus just copper pipe .

[maple flats]

That would work fine, but be sure there is no old solder in them. Heating still uses 50/50 lead solder.
That being said, most preheaters just use the plain copper tube. Design it so you can vent if necessary. You will get more surface area if you use ready made manifolds. I used 4 of these and made a 2 tier heater https://www.supplyhouse.com/Sioux-Chief-678-20644-1-Copper-Manifold-w-1-2-Sweat-Loops-6-Outlets?utm_source=bingad&utm_medium=shopping&msclkid=b0a4d90904d4128f34f083f5245ffffa
Be certain to build a drip tray for under the heater and the steam stack, or you will need to re-boil the condensate, it needs to be channeled out of the hood.
My pre-heater brings the sap from 35F up to about 170-175 but only until my auto draw opens, then it falls to about 110-120F. After the auto draw closes it climbs back to 170-175F. I draw over 6 gal finished syrup/ hr. You also want a damper in your steam stack and close the damper until you start to see steam leak out any leaks in the hood, that gives you max. heat exchange.
Several have built such pre-heaters, search on this forum, mine and others have pictures.

[Haynes Forest Products]

I did it 20 years ago and cant tell you if it was better or worse than bare copper. I didn't have anything to compare it to. The heat transfer is different when it comes to air verses liquid. Back then I was trying anything to get better evaporation rates but once again no way to compare.

This is my opinion only I think it sucked as far as the disconnect between the aluminum and the copper. Yea they are pressed on tight but over time you get a corrosion barrier that is microscopic but its there. Then you have the cleaning and fragility of the unit. I have tried about every possible way to preheat sap and the best one yet is thin wall copper with the Smoky Lake condensate tray that allows full steam contact.

[Ghs57]

You might have a hard time catching all the condensation drips with all those fins.

I have two seasons on my home built preheater. I have ten loops of 1/2 bare copper, vented at the top manifold, and it works pretty well. I couldn't find a ten outlet manifold, so I made my own out of tees. Lots of soldering, but no leaks. While its running, I can't hold onto the pipe feeding the float box. Even with a drip channel under each loop, and across each end, it's hard to catch it all. On the upside, there is a steady stream of pure hot water for cleaning up as I go.

[maple flats]

I think to get one of the manifolds for copper sweat you need to get it from Supply House or you can find them on Ebay. Just be carefull, the prices vary widely for the same thing. Back when I got my 4 manifolds I paid $18.99 each thru Ebay, but others offered the same spec manifolds for up to and even over $100 each. Those are vendors preying on buyers who think they can't get them for less, or are under the impression that a $20 one with 6 take offs is higher quality at $100 than $20. They are the same. Be careful not to get ones made for Pex, they will then cost loads to convert to copper sweat at the cost of heat exchange space.