Evap ratings

[Dennis H.]

How do the manufactures come up with their figures for the number of taps for a giving size of evap.

I see one make of evap say 50-100 taps another 50-150 taps for the same size.

What is the number of gals/tap that they use when they list the capacity for an evap.

[maple flats]

Sometimes I think they optimistically guess. Same sizes can have different ratings depending on flue type and I think even sides of pan height. Most often they use the optimum rate for that rig. To get it everything must be perfect, fuel (wood perfectly dry and properly split), fueled at optimum interval, burner adjusted properly, on wood- do not have door open too long, pan sap depth on low side. Things like this boost the rate and they do it all to state rate. Then I think they use for taps rating something like a 8 or 10 hr boil/day with 1 gal/tap/day sap flow (but they might use higher flow)

[Brent]

In it's simplest form, the rating is just a factor of how much total surface area of the pans, is exposed to the fire.

The area of the syrup pan is easy. They're flat bottomed.

On my Phaneuf evaporator 2' x 6' the syrup pan is 24" x 24" = 576 square inches

The flue pan needs to be calculaed. On mine the flat parts of the pan are 24" x 48" = 1156 sq in.
There are 10 flues, each 7 1/2" deep. So there are 20 sides to the flues that comes out to 20 x 7.5 x 48 = 7200 sq in. for a total of 9276.

As noted above there are lots of other factors, but surface area is the biggest factor. If a flue pan only has 7 flues, you can see the area will go down dramatically. One maker has introduced a flue pan the effectively is raised and dropped in one. If the flues are 12 inches deep the math comes out to 20 x 12 x 48 = 11520. That's 60% more area in the flue pan to transfer heat and a substantial increase the the gallons per hour.

Air flow, insulation, steel thickness (heat conductivity) all add in to complicate the issue.