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Water Pressure Gauge (W.G.) Standards for Square & Rectangular HVAC Ducting

Although our name suggests that we specialize in spiral round and flat oval duct, we are ready to build rectangular duct for your projects both large and small.

2″ W.G.3” W.G.4” W.G.6” W.G.10” W.G.

SPOT Rectangular Duct Standards

2” W.G. Positive or Negative

	Duct Dimension	Joint Connection	Max Length	Metal Gauge	Reinforcing Size and Longitudinal Spacing
Width Depth	0” – 12” 0” – 30”	Flat “S” Slip Drive Slip	59”	26	Transverse Connection 59” O.C.
Width Depth	13” – 20” 0” – 30”	1” Standard “S” Slip Drive Slip	59”	26	Transverse Connection 59” O.C.
Width Depth	21” – 26” 0” – 30”	1 5/8” Standard “S” Slip Drive Slip	59”	26	Transverse Connection 59” O.C.
Width Depth	27” – 36” 0” – 30”	1 5/8” Standard “S” Slip Drive Slip	59”	24	Transverse Connection 59” O.C.
Width Depth	37” – 42” 0” – 30”	1 5/8” Standard “S” Slip Drive Slip	59”	24	Transverse Connection 59” O.C. 1 ½” x 1” x 18 ga. @ 48”
Width Depth	43” – 48” 0” – 30”	1 5/8” Standard “S” Slip Drive Slip	59”	24	Transverse Connection 59” O.C. 1 ½” x 1” x 18 ga. @ 36”
Width Depth	49” – 54” 0” – 30”	1 5/8” Standard “S” Slip Drive Slip	59”	24	Transverse Connection 59” O.C. 1 ½” x 1” x 18 ga. @ 30”
Width Depth	55” – 60” 0” – 30”	TDF Flange TDF Flange	56”	22	Transverse Connection 56” O.C. 1 ½” x 1” x 16 ga. @ 36”
Width Depth	61” – 84” 0” – 30”	TDF Flange TDF Flange	56”	20	Transverse Connection 56” O.C. 2” x 1 ⅛” x 12 ga. @ 48”
Width Depth	85” – 96” 0” – 30”	TDF Flange TDF Flange	56”	18	Transverse Connection 56” O.C. 2” x 1 ⅛” x 12 ga. @ 36”

Reference: 2020 SMACNA for +/- 2” W.G.
All duct to be fabricated from G90 galvanized sheets.
All duct to be stiffened with machine-formed beads at 12” O.C.
All reinforcing to be galvanized.
All reinforcing to be secured to duct with screws at 8” O.C.
All drives over 18” to be reinforced by others.
Longitudinal seams to be snap-lock through 22 gauge and Pittsburgh for over 22 gauge.
* Reinforce all TDF Flange 55” and over with tie rod maximum 48” O.C. at each end except
where heavier gauge is used in lieu of gauge specified for that size.

3” W.G. Positive or Negative

	Duct Dimension	Joint Connection	Max Length	Metal Gauge	Reinforcing Size and Longitudinal Spacing
Width Depth	0” – 26”	TDF Flange	56”	24	Transverse Connection 56” O.C.
Width Depth	27” – 30”	TDF Flange	56”	24	Transverse Connection 56” O.C. 1 ½” x 1” x 18 ga. “Z” Maximum 48” from Connection
Width Depth	31” – 36”	TDF Flange	56”	22	Transverse Connection 56” O.C. 1 ½” x 1” x 18 ga. “Z” Maximum 48” from Connection
Width Depth	37” – 42”	TDF Flange	56”	22	Transverse Connection 56” O.C. 1 ½” x 1” x 18 ga. “Z” Maximum 36” from Connection
Width Depth	43” – 48”	*TDF Flange	56”	22	Transverse Connection 59” O.C. 1 ½” x 1” x 16 ga. “Z” Maximum 36” from Connection
Width Depth	49” – 54”	*TDF Flange	56”	22	Transverse Connection 59” O.C. 1 ½” x 1” x 16 ga. “Z” Maximum 30” from Connection
Width Depth	55” – 72”	*TDF Flange	56”	20	Transverse Connection 59” O.C. 2” x 1 1/8” x 12 ga. “Z” Maximum 36” from Connection
Width Depth	73” – 84”	TDF Flange TDF Flange	56”	20	Transverse Connection 56” O.C. 2” x 1 1/8” x 12 ga. “Z” Maximum 24” from Connection
Width Depth	85” – 96”	TDF Flange TDF Flange	56”	18	Transverse Connection 56” O.C. 2” x 1 1/8” x 12 ga. “Z” Maximum 24” from Connection
Width Depth	97” – 108”	TDF Flange TDF Flange	56”	18	Transverse Connection 56” O.C. 3” x 1 1/8” x 12 ga. “Z” Maximum 24” from Connection OR 3” x 1 1/8” x 10 ga. “Z” Maximum 30” from Connection
Width Depth	109” – 120”	TDF Flange TDF Flange	56”	18	Transverse Connection 56” O.C. 3” x 1 1/8” x 12 ga. “Z” Maximum 24” from Connection OR 3” x 1 1/8” x 10 ga. “Z” Maximum 30” from Connection

Reference: 2020 SMACNA for +/- 3” W.G.
All duct to be fabricated from G90 galvanized sheets.
All duct to be stiffened with machine-formed beads at 12” O.C.
All reinforcing to be galvanized.
All reinforcing to be secured to duct with screws at 8” O.C.
Longitudinal seams to be Pittsburgh.
* Reinforce all TDF Flange 43” and over with tie rod maximum 48” O.C. at each end except where heavier gauge is used in lieu of gauge specified for that size.

4” W.G. Positive or Negative

	Duct Dimension	Joint Connection	Max Length	Metal Gauge	Reinforcing Size and Longitudinal Spacing
Width Depth	0” – 22”	TDF Flange	56”	24	Transverse Connection 56” O.C.
Width Depth	23” – 26”	TDF Flange	56”	24	Transverse Connection 56” O.C. 1 ½” x 1” x 18 ga. “Z” Maximum 48” from Connection
Width Depth	27” – 30”	TDF Flange	56”	24	Transverse Connection 56” O.C. 1 ½” x 1” x 18 ga. “Z” Maximum 36” from Connection
Width Depth	31” – 36”	TDF Flange	56”	22	Transverse Connection 56” O.C. 1 ½” x 1” x 18 ga. “Z” Maximum 36” from Connection
Width Depth	37” – 42”	*TDF Flange	56”	22	Transverse Connection 56” O.C. 1 ½” x 1” x 16 ga. “Z” Maximum 36” from Connection
Width Depth	43” – 60”	*TDF Flange	56”	20	Transverse Connection 56” O.C. 2” x 1 1/8” x 12 ga. “Z” Maximum 36” from Connection
Width Depth	61” – 72”	*TDF Flange	56”	20	Transverse Connection 56” O.C. 2” x 1 1/8” x 12 ga. “Z” Maximum 30” from Connection
Width Depth	73” – 84”	TDF Flange TDF Flange	56”	18	Transverse Connection 56” O.C. 2” x 1 1/8” x 12 ga. “Z” Maximum 30” from Connection
Width Depth	85” – 96”	TDF Flange TDF Flange	56”	18	Transverse Connection 56” O.C. 3” x 1 1/8” x 12 ga. “Z” Maximum 30” from Connection
Width Depth	97” – 120”	TDF Flange TDF Flange	56”	18	Transverse Connection 56” O.C. 3” x 1 1/8” x 10 ga. “Z” Maximum 30” from Connection

Reference: 2020 SMACNA for +/- 4” W.G.
All duct to be fabricated from G90 galvanized sheets.
All duct to be stiffened with machine-formed beads at 12” O.C.
All reinforcing to be galvanized.
All reinforcing to be secured to duct with screws at 8” O.C.
Longitudinal seams to be Pittsburgh.
* Reinforce all TDF Flange 37” and over with tie rod maximum 48” O.C. at each end except where heavier gauge is used in lieu of gauge specified for that size.
Where reinforcing is required ONLY on two sides, a frame will be provided.

6” W.G. Positive or Negative

	Duct Dimension	Joint Connection	Max Length	Metal Gauge	Reinforcing Size and Longitudinal Spacing
Width Depth	0” – 12”	TDF Flange	56”	24	Transverse Connection 56” O.C.
Width Depth	13” – 24”	TDF Flange	56”	22	Transverse Connection 56” O.C.
Width Depth	25” – 30”	TDF Flange	56”	22	Transverse Connection 56” O.C. 1 ½” x 1” x 18 ga. “Z” Maximum 36” from Connection
Width Depth	31” – 36”	*TDF Flange	56”	22	Transverse Connection 56” O.C. 1 ½” x 1” x 16 ga. “Z” Maximum 30” from Connection
Width Depth	37” – 42”	*TDF Flange	56”	20	Transverse Connection 56” O.C. 2” x 1 1/8” x 12 ga. “Z” Maximum 30” from Connection
Width Depth	43” – 60”	*TDF Flange	56”	20	Transverse Connection 56” O.C. 2” x 1 1/8” x 12 ga. “Z” Maximum 30” from Connection
Width Depth	61” – 72”	*TDF Flange	56”	18	Transverse Connection 56” O.C. 2” x 1 1/8” x 12 ga. “Z” Maximum 30” from Connection
Width Depth	73” – 84”	TDF Flange TDF Flange	56”	18	Transverse Connection 56” O.C. 3” x 1 1/8” x 12 ga. “Z” Maximum 24” from Connection OR 3” x 1 1/8” x 10 ga. “Z” Maximum 30” from Connection
Width Depth	85” – 108”	TDF Flange TDF Flange	56”	18	Transverse Connection 56” O.C. 3” x 1 1/8” x 10 ga. “Z” Maximum 24” from Connection

Reference: 2020 SMACNA for +/- 6” W.G.
All duct to be fabricated from G90 galvanized sheets.
All duct to be stiffened with machine-formed beads at 12” O.C.
All reinforcing to be galvanized.
All reinforcing to be secured to duct with screws at 8” O.C.
Longitudinal seams to be Pittsburgh.
* Reinforce all TDF Flange 31” and over with tie rod maximum 48” O.C. at each end except where heavier gauge is used in lieu of gauge specified for that size.
Where reinforcing is required ONLY on two sides, a frame will be provided.

10” W.G. Positive or Negative

	Duct Dimension	Joint Connection	Max Length	Metal Gauge	Reinforcing Size and Longitudinal Spacing
Width Depth	0” – 8”	TDF Flange	56”	24	Transverse Connection 56” O.C.
Width Depth	9” – 12”	TDF Flange	56”	24	Transverse Connection 56” O.C. 1” x 1” x 18 ga. “Z” Maximum 48” from Connection
Width Depth	13” – 18”	TDF Flange	56”	24	Transverse Connection 56” O.C. 1 ½” x 1” x 18 ga. “Z” Maximum 36” from Connection
Width Depth	19” – 22”	TDF Flange	56”	24	Transverse Connection 56” O.C. 1 ½” x 1” x 18 ga. “Z” Maximum 36” from Connection
Width Depth	23” – 26”	*TDF Flange	56”	24	Transverse Connection 56” O.C. 1 ½” x 1” x 16 ga. “Z” Maximum 36” from Connection
Width Depth	27” – 36”	*TDF Flange	56”	24	Transverse Connection 56” O.C. 2” x 1 1/8” x 12 ga. “Z” Maximum 36” from Connection
Width Depth	37” – 42”	*TDF Flange	56”	24	Transverse Connection 56” O.C. 2” x 1 1/8” x 12 ga. “Z” Maximum 30” from Connection
Width Depth	43” – 48”	*TDF Flange	56”	22	Transverse Connection 56” O.C. 2” x 1 1/8” x 12 ga. “Z” Maximum 30” from Connection
Width Depth	49” – 54”	*TDF Flange	56”	20	Transverse Connection 56” O.C. 2” x 1 1/8” x 10 ga. “Z” Maximum 30” from Connection
Width Depth	55” – 60”	*TDF Flange	56”	18	Transverse Connection 56” O.C. 3” x 1 1/8” x 12 ga. “Z” Maximum 30” from Connection
Width Depth	61” – 72”	*TDF Flange	56”	18	Transverse Connection 56” O.C. 3” x 1 1/8” x 10 ga. “Z” Maximum 30” from Connection
Width Depth	73” – 84”	*Ward J	60”	16	Transverse Connection 60” O.C. 3” x 1 1/8” x 10 ga. “Z” Maximum 30” from Connection
Width Depth	85” – 120”	*Ward J	60”	16	Transverse Connection 60” O.C. **3” x 1 1/8” x 10 ga. “Z” Maximum 24” from Connection

Reference: 2020 SMACNA for +/- 10” W.G.
All duct to be fabricated from G90 galvanized sheets.
All duct to be stiffened with machine-formed beads at 12” O.C.
All reinforcing to be galvanized.
All reinforcing to be secured to duct with screws at 8” O.C.
Longitudinal seams to be Pittsburgh.
*Reinforce all Ward J and TDF Flange 23” and over with tie rod 48” maximum at each end except where heavier gauge is used in lieu of gauge specified for that size.
**Reinforce Z-bar 85” and over with tie rod at 48” mazimum.

Water Pressure Gauge (W.G.) Standards for Square & Rectangular HVAC Ducting

SPOT Rectangular Duct Standards

2” W.G. Positive or Negative

3” W.G. Positive or Negative

4” W.G. Positive or Negative

6” W.G. Positive or Negative

10” W.G. Positive or Negative

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