Maple Setup and Guidelines

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How does vacuum and atmospheric pressure affect the sap run? Examples of Tree Pressures and sap flow:

  • 12-18 psi = Fair sap run
  • 19-24 psi = Good sap run
  • 25+ psi = Great sap run
  • 15” of Hg of vacuum = 5 psi change in pressure. 20” of Hg of vacuum = 10 psi change in pressure.
  • Vacuum systems turn a fair sap run into a great sap run and can increase sap yield by 50 to 100%.
  • A vacuum system must be capable of producing a vacuum of 15” of mercury at the far end of the lateral tubing for it to be considered economical.
  • A vacuum pump’s capacity is measured by how much air it can move in a certain amount of time – cubic feet per minute (CFM). For every 100 taps in tubing system, a pump with 1 to 1 ½ CFM is needed. If 500 taps are on vacuum, a pump with a capacity of 5 to 7.5 CFM is needed.

Designing a Tubing System – the goal is to get vacuum at the tap hole. Long spans of tubing will cover a lot of area but will have lower vacuum capabilities. Short spans will cover less area but will increase your vacuum capabilities. Sugarbushes must have a compromise between the two.


  • 100 to 150 feet apart (up to 250 feet apart without vacuum) and less than 1000 feet (variation will occur with tap density & sugarbush dimensions). 150’ x 1000’ will cover 3.5 acres.
  • Vacuum system mainlines should maintain a constant slope of 2 to 4% - a portion of the mainline under vacuum with a slope as small as ½ percent will work, but this portion must be as short as possible to maintain efficiency.
  • Non-vacuum mainlines can follow steeper slopes and drainages.
  • Downstream Mainline diameter should be increased when two upstream mainlines merge – usually a 1” to 1½“ increase

A well thought out vacuum tubing setup allows:

  • Maximum vacuum at the tap hole.
  • Leaks to be found faster.
  • A single leak to have less impact on the overall tubing system.
  • Faster tapping and cleaning tubing.

Mainline Sizing

<5% Slope

5 to 10 % Slope

>10% Slope

¾” Mainline Diameter

<400 Taps

300 to 500 Taps

300 to 600 Taps

1” Mainline Diameter

<700 Taps

400 to 900 Taps

600 to 1100 Taps

1¼” Mainline Diameter

<1100 Taps

900 to 1400 Taps

900 to 1800 Taps

1½” Mainline Diameter

<1600 Taps

1200 to 2000 Taps

1200 to 2600 Taps

5/16” Lateral Lines – keep lines steep, tight and as straight as possible

  • With vacuum – 1 to 8 taps per lateral line.
  • Without vacuum – 10 to 15 taps per lateral line. Natural vacuums can be created.
  • Do not “vent” lines, instead keep them straight and tight to prevent air locks.

Tapping Guidelines

  • Tap only trees 12 inches diameter at breast height (DBH) and larger.
  • 1 tap hole in trees 12 to 18 inches DBH.
  • 2 tap holes in trees greater than 18 inches DBH.
  • Place no more than 2 tap holes per tree. The more holes, broken branches, scars, etc., the less pressure can build up in the tree.
  • Drill tap holes at a slight upward angle to prevent sap pooling. Drill “check-valve” spouts at a flat angle.
  • Use the smaller-diameter “health spouts” (5/16- or 19/64-inch spouts). Health spouts are preferred, but the 7/16 inch spouts are still acceptable and common when using buckets to collect sap.
  • Drive spouts with care to avoid splitting the bark and wood.
  • For 7/16 inch spouts, place the tap hole no more than 2 1/2 inches deep and for the smaller-diameter spouts, no more than 1 1/2 inches deep.
  • Tap only white, clean wood. To avoid areas of discoloration and decay, don't place new tap holes within 6 inches horizontally and at least 2 feet directly above or below old tap holes.
  • Make sure “drops” (tubing attached directly to the spout) are long enough (18” to 36”) so tap holes can be placed on all sides of the tree.
  • Don't retap existing holes in any given year to expose new wood, or drill new holes to prolong the sap run.
  • Don't use a tap-hole sanitizing agent.
  • Remove spouts from tap holes immediately after the season. Sizing the Evaporator

Evaporator Size











Evaporation Gal/hour











An example in sizing an evaporator by tap number:

  • A good sap run will yield about 1 gallon of sap per tap
  • 750 taps x 1 gal/tap = 750 gallons
  • Time available each run to boil sap = 8 hours (you determine this number)
  • Evaporating capacity needed = 750 gallon / 8 hours = 93.75 gal/hr
  • A 3’x12’ evaporator (estimated evaporation of 100 gal/hr) would be needed

A reverse osmosis machine can remove 50 to 75% of the water from raw sap. Instead of boiling 750 gallons on a 3’x12’ evaporator for 8 hours, a producer would only need to boil:

  • 188 (75% reduction of water by RO) to 375 (50% reduction of water by RO) gallons in 8 hours (an evaporation capacity of 24 to 47 gal/hr, on a 2’x6’ to 30”x8’ evaporator)
  • or boil on the 3’x12’ evaporator for only 2 hours (75% reduction of water by RO) to 4 hours (50% reduction of water by RO), instead of 8 hours (without RO)
  • or boil on the 3’x12’ evaporator for 8 hours with 1500 taps (50% reduction of water by RO) to 3000 taps (75% reduction of water by RO), instead of 750 taps (without RO)

Fuelwood – About 20 gallons of syrup can be produced from 1 cord of wood, or 1 cord of wood for every 80 to 100 taps.

Download the Fact Sheet


Extension State Specialist, Forest Resources
Full State Specialist/Professor, Natural Resources
Phone: (603) 862-4861
Office: UNH Cooperative Extension, Taylor Hall, Durham, NH 03824