HVAC Estimating: Ductwork, Equipment, and Piping Quantification

HVAC is often the largest single MEP trade on a commercial project. It is also one of the easiest to get wrong. Ductwork is priced by weight but drawn by size. Equipment prices move with lead times. The scope splits between the mechanical contractor, the sheet metal sub, the controls vendor, the electrician and the test-and-balance firm are rarely spelled out as clearly as they should be.

This guide covers how commercial HVAC estimates are commonly structured, how to turn duct drawings into pounds of sheet metal, and what to check before you submit.

Division 23 Scope

In CSI MasterFormat, HVAC is Division 23 – Heating, Ventilating, and Air Conditioning (HVAC). Frequently used sections include:

• 23 05 00 – Common Work Results for HVAC (including 23 05 93 Testing, Adjusting, and Balancing)
• 23 07 00 – HVAC Insulation
• 23 09 00 – Instrumentation and Control for HVAC
• 23 11 00 – Facility Fuel Piping (including natural gas piping)
• 23 20 00 – HVAC Piping and Pumps (hydronic, steam, refrigerant)
• 23 30 00 – HVAC Air Distribution (ducts, duct accessories, fans, air terminal units, diffusers and grilles)
• 23 50 00 / 23 60 00 – Central Heating and Central Cooling Equipment (boilers, chillers, cooling towers)
• 23 70 00 – Central HVAC Equipment (air handling units, packaged outdoor units)
• 23 80 00 – Decentralized HVAC Equipment (split systems, unit heaters, fan coils)

Design is governed by the International Mechanical Code (IMC) or the local mechanical code, with ASHRAE 62.1 for ventilation and ASHRAE 90.1 for energy. Duct construction is typically specified to SMACNA’s HVAC Duct Construction Standards.

Ductwork Takeoff

Measure by size, price by weight

Duct drawings show sizes (for example 24x12 rectangular or 14” round), but sheet metal is bought, fabricated and often priced by the pound. The standard takeoff process is:

1. Measure the length of each duct size by system (supply, return, exhaust, outside air).
2. Work out the perimeter, which gives surface area per foot.
3. Assign a gauge based on the largest dimension and pressure class.
4. Convert surface area to weight using the weight per square foot for that gauge.
5. Add an allowance for seams, joints, reinforcement and waste.

Gauge selection

The gauge depends on the duct’s largest dimension, its static pressure class, and its joint and reinforcement spacing. SMACNA tables cover all of these, and the project specification can override them. For low-pressure rectangular galvanized duct, a common rule of thumb for budgeting is:

Largest duct dimension	Typical gauge (low pressure)	Galvanized weight (lb/SF)
Up to 12”	26 ga	0.906
13” – 30”	24 ga	1.156
31” – 54”	22 ga	1.406
55” – 84”	20 ga	1.656
85” and over	18 ga	2.156

Use this table for budgeting and quick checks only. Medium- and high-pressure systems, exhaust ducts (such as kitchen grease duct, which the IMC requires to be heavier), and stainless or aluminum ducts all need their own gauge selection from the spec and SMACNA.

Fittings and accessories

Count these separately:

• Elbows, transitions, offsets, takeoffs and tees. Many estimators convert these to equivalent length or weight, while others price them per piece.
• Volume dampers, fire dampers, smoke dampers and combination fire/smoke dampers. Note which ones need electrical connections.
• Access doors, turning vanes, flexible connectors, and flex duct runouts to diffusers.
• Diffusers, registers and grilles by type and size, counted from the air device schedule.
• Air terminal units (VAV boxes, fan-powered boxes) with any reheat coils. Hot water coils need piping and control valves.
• Duct insulation or liner, by square foot and thickness.

Worked Example: Converting Duct Size to Weight

Example (not a real project): A low-pressure supply main has two sizes of rectangular galvanized duct.

Section A: 24” x 12”, 120 LF, 24 ga (largest dimension 24”)

• Perimeter: 2 x (24 + 12) = 72 in = 6.0 ft
• Surface area: 6.0 ft x 120 LF = 720 SF
• Weight: 720 SF x 1.156 lb/SF = 832.3 lb

Section B: 36” x 18”, 60 LF, 22 ga (largest dimension 36”)

• Perimeter: 2 x (36 + 18) = 108 in = 9.0 ft
• Surface area: 9.0 ft x 60 LF = 540 SF
• Weight: 540 SF x 1.406 lb/SF = 759.2 lb

Subtotal: 832.3 + 759.2 = 1,591.5 lb

Allowance for seams, joints, reinforcement and waste (assumed 20%; many shops use a range of roughly 15-25%): 1,591.5 x 1.20 = 1,909.8 lb, so use about 1,910 lb.

Labor (illustrative): If your historical installation rate for this size range is 3.0 hours per 100 lb, then 1,910 / 100 x 3.0 = 57.3 field hours, before adjustments for height, congestion or phasing. Shop fabrication hours are separate if you fabricate in-house.

A quick sanity check on airflow is also useful. Cooling equipment is commonly selected at roughly 350-450 CFM per ton. A 10-ton rooftop unit at about 400 CFM/ton moves around 4,000 CFM. If the schedule shows something very different, confirm whether it is a dedicated outdoor air unit or a special application before you price it.

Equipment

Get written quotes for major equipment (RTUs, AHUs, chillers, boilers, cooling towers, VRF systems, exhaust fans). Record the quote date and lead time. When you review quotes, check:

• Capacity, voltage and phase against the equipment schedule
• Included options: economizers, VFDs, hail guards, factory controls, disconnects, curbs
• Freight, rigging or crane, startup and warranty
• Whether controls are factory-mounted or supplied by the controls contractor

Keep prices out of rules of thumb. Equipment pricing depends on the manufacturer, options and market conditions, so a vendor quote should always win over a per-ton guess.

Piping and Controls

Hydronic piping (chilled water, heating hot water, condenser water), steam and refrigerant piping are taken off by material, size and joining method: welded, grooved, press or brazed. Count valves, strainers, specialties and insulation separately. Controls (23 09 00) are often a separate subcontract. Confirm whether the quote includes control wiring and low-voltage conduit, or whether that falls to Division 26.

Labor

Mechanical contractors commonly start from published labor units, such as the MCAA labor estimating manuals or the libraries in mechanical estimating software, and then calibrate them with their own job-cost history. Sheet metal labor is usually tracked per pound or per fitting. Piping labor is tracked per foot and per joint. Adjust for working height, congested ceilings, phasing in occupied buildings, and roof access for rooftop equipment. Build crew rates from local burdened wages. See our labor burden guide.

HVAC Estimating Checklist

• Reconcile the equipment schedule with the plans and specifications
• Take off ductwork by system and size, then convert to weight by gauge
• Confirm the pressure class and any spec gauge requirements that override the rule of thumb
• Count dampers and identify which ones need power or fire alarm interface
• Count air devices from the schedule and check them against the plans
• Separate hydronic, refrigerant and condensate piping
• Confirm scope for controls, test-and-balance, fire/smoke damper wiring and equipment starters
• Include rigging, cranes, roof curbs and equipment supports
• Include startup, commissioning support and closeout documents
• Record equipment quote dates and lead times

Common Mistakes

• Pricing duct by linear foot without a gauge and weight conversion. Large mains get badly underpriced.
• Using one gauge for the whole job. The largest dimension and pressure class change the gauge.
• Leaving out fittings. They can make up a large share of the sheet metal labor.
• Missing the controls and electrical interface. Who wires dampers, VAV boxes and starters?
• Forgetting test-and-balance or assuming another party covers it.
• Relying on stale equipment quotes when lead times and prices have moved.

For the broader MEP picture, see our MEP estimating guide and the complete MEP estimating guide.

How F&K Estimatings Can Help

F&K Estimatings prepares Division 23 takeoffs covering ductwork by size and weight, equipment and air device counts, piping and accessories, organized by CSI section so they’re easy to review and level. Scope gaps between mechanical, controls and electrical are flagged as RFIs rather than assumed. See our HVAC estimating services, review pricing, or contact us with your drawings.