2x6 In Hood Preheater

[mainebackswoodssyrup]

We just purchased a used 2x6 oil fired rig. Its a Devereaux Mystique and comes with a hood. We plan to make a copper preheater in the hood, running copper 2-3 times around the hood and then to the float box. My question is what size copper should we use? Is 1" Copper big enough like our buddys 2x6 wood fired? His rig boils 40 gph and we were told this one was doing around 70 gph with the hood and no preheater. Do we need a bigger line? 1.25" or 1.5"?

[wiam]

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

[Michael Greer]

You want that tubing IN the steam hood. Steam is the best heat transfer medium, and it's much hotter in there than any outside surface can get you. Mine is a bunch of parallel, 1/2" tubes with about an inch of space between. That tubing will have cold sap in it (at first) and as a result will sweat in the steam. That condensation will fall back into the flue pan below and un-do what you've just done so it will have to have a tray under it to catch the drips. There will be a lot and it will have to be piped out of the hood, where you can drop it toward the floor drain, or like in my case, pipe it over to the sink where you will enjoy a continuous stream of scalding hot distilled water. Very handy for cleaning and rinsing things.

[mainebackswoodssyrup]

Awesome, thanks guys. I hadn't thought about the condensation on the pipes but makes sense. We have hot water from the spigot anyway so we'll have to figure out what to do with that I guess.

[Sugarmaker]

Couple things: 3/4 thin wall copper should be good. If he is doing 40 GPH with a preheater, and you have been told yours will do 70 why would you need to add a perheater? 70 gph on that size rig is awesome. I only got about 80 -90 gph on the old 3 x 10 rig. I would run the heck out of it as is!
Regards,
Chris

[maple flats]

I made my preheater using 4 manifolds and made it in two tiers. The manifolds (off Ebay) are copper, have a 1" header and 6 outlets out the side of 1/2" each. The first one takes in the cold sap, then in my case the 6 -1/2" tubes I soldered in go 52" to the far end of my hood to another header. There I put an elbow on and a vent pointed up on one end of the header and the end opposite where the cold entered at the other manifold, I have a street elbow pointing up and then a vent Tee which gives me a place to vent air if needed and points the next header parallel to #2 header. Then 6 more tubes 52" long get back to straight above the #1 header, and a length of copper gets it out of the hood. Both the cold sap in and hot sap out pass thru holes I Greenlee punched in the hood. From #1 to #2 the tubing rises about 2" then the elbow and vert tee climb about 2 more inches then from #3 to #4 headers it rises another 2", so my hot sap comes out about 6" higher than my cold sap went in. Once out the 1" line turns 90 degrees to a 1" tee. The center leg of that points down to the flue box inlet and the straight leg has a female adapter bushed to put a thermometer in to read the sap temperature. On the cold sap in leg as it passes over the float box I have a Tee, with a drain valve pointed down. When finished for the day, I open that valve to drain the heater and it falls into the float box. On my 3x5 flue pan, I get temperatures of 160-175 once fully boiling, until the auto draw opens. Then the temp drops to about 100F. When the draw closes the temperature climbs back to the 160-175F. To get those you need a damper on the steam stack, close the damper until at full boil you just start to see a little steam leakage thru any leaks in the hood, then lock it there. My damper has a position lock on it.. With a shorter flue pan you might even want to build a 4 tier heater. Just go up from #4 to #5 and so forth. Each time you go from one end to the other use the opposite corner to run the flow, that way the unit should keep the flows essentially equal in each tube. You could also get away with just a 1" rise from #1 to #2 and so forth to keep the whole unit flowing and still fit in the hood. Two essential points, you must have a funnel under the steam stack to channel the condensate to the hood drain or the tray you use to run the pre-heater condensate to the hood drain. If you don't the drips falling back into the flue pan need to be boiled away again.
While I built mine with 3 vents, 2 off header #2, and one at the outlet of the hot sap line from the hood. As it turned out my head tank is high enough that gravity moves the sap and I have never needed to open any of the vents, my head tank bottom fitting is 16" above the outlet for hot sap from the hood. If I were to build another one I think I would use a 1.25 header with 6 outlets of 3/4". My guess is that that would move the sap thru slower to got more heat before getting to the float box. In use I get a solid stream flow out of the hood drain and it fills a 5 gal pail in about 90 minutes. I then dump it to drain and repeat.

[mainebackswoodssyrup]

Great info, thanks again.

Sugarmaker........you sound like my partner! I'm one of those go big or go home kind of guys. I also was told 70 GPH. That number sounded high to me, maybe others would have a better idea of what it will get? I'm hoping for at least 60 GPH and more is better so bring on the preheater!