What Size Maple Evaporator Do I Need? Taps to Gallons per Hour
Ratings are maker claims or 2006 averages; real output depends on dry wood, firing and draft, and one maker's chart runs about 40–60% above the manual's averages. Past about 50 taps a continuous-flow hobby evaporator is the practical choice (Cornell). Evaporators and pans we looked at →
The rating tables behind this
| Pan | Surface | Rated gal/h |
|---|---|---|
| 12 × 20 in pan | 1.67 sq ft | 1 |
| 19 × 36 in pan | 4.75 sq ft | 3 |
| 2 ft × 33 in pan | 5.5 sq ft | 5 |
| 2 × 4 ft | 8 sq ft | 15 |
| 2 × 6 ft | 12 sq ft | 25 |
| 2 × 8 ft | 16 sq ft | 35 |
| 30 in × 8 ft | 20 sq ft | 50 |
| 30 in × 10 ft | 25 sq ft | 60 |
| 3 × 8 ft | 24 sq ft | 70 |
| 3 × 10 ft | 30 sq ft | 85 |
| 3 × 12 ft | 36 sq ft | 100 |
| 4 × 12 ft | 48 sq ft | 140 |
How it works
The math behind it
The Producers Manual, UNH and Cornell all size a rig the same way: gallons of sap from a big run divided by the hours you can boil. The planning figure is about 1 gallon of sap per tap per good day (Cornell gives a 0.5 to 2.5 gallon range), and the manual says to plan on no more than a 10-hour day and that a boil under about 3 hours is inefficient once setup and cleanup are counted.
Flat pans evaporate roughly ¾ to 1½ gallons of water per square foot per hour depending on the heat under them (Ohio State), so the pan surface you need is a range. Rated evaporators come from UNH's backyard table for small pans and the 2006 Producers Manual's averages of several makers' ratings for flue-pan rigs (2 × 4 ft = 15 gal/h, 2 × 6 = 25, 3 × 10 = 85); the 2022 edition dropped the table because each design has its own rate, and one maker's current chart runs about 40–60% higher.
Storage follows the 2022 manual: at least 1 gallon of sap storage per tap per day of flow for buckets, 1.5 for gravity tubing and 2 for vacuum. Firewood follows its rule of 1 cord of dry hardwood per 75–100 taps on an efficient evaporator; open-pan hobby boiling burns far more.
FAQ
Common questions
- What size evaporator do I need for 50 taps?
- At the 1 gallon-per-tap planning figure, 50 taps can bring 50 gallons on a good day. Over a 6-hour boil that is about 8 gallons of water per hour, which a 2 × 4 ft flue-pan rig (rated about 15 gal/h in the 2006 tables) covers with room to spare; on a flat pan you would want 6 to 11 square feet of surface.
- How long does it take to boil 40 gallons of sap?
- At 2% sugar, 43 gallons of sap holds about 42 gallons of water to remove. On a 1 gal/h steam-table pan that is around 40 hours; on a 2 × 4 ft evaporator rated 15 gal/h, under 3 hours.
- Are the gallons-per-hour ratings reliable?
- They are planning numbers. The Producers Manual calls its table an approximate guide, the figures are from 2006, and makers' own charts run higher. Dry wood, firing, draft and sap depth all move the real rate.
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