How to bid HVAC work as a subcontractor

Start with what you are actually bidding

Division 23 is the mechanical package, and the price of the equipment is rarely where a mechanical bid goes wrong. The boundary is. Settle it before you price a single pound of sheet metal.

Inside your own division, the usual split looks like this:

• 23 31 00 HVAC Ducts and Casings and 23 33 00 Air Duct Accessories. Sheet metal, fittings, hangers, volume dampers, duct access doors.
• 23 37 00 Air Outlets and Inlets. Diffusers, registers and grilles.
• 23 21 00 Hydronic Piping and Pumps and 23 23 00 Refrigerant Piping, plus the equipment sections: heating boilers under 23 52 00, packaged water chillers under 23 64 00, air handling units, rooftop units, split systems, fan coils and unit heaters.
• 23 07 00 HVAC Insulation. Duct and pipe insulation sits inside Division 23 but is often bought as its own subcontract. Confirm which side of that line you are on before you assume it.
• 23 09 00 Instrumentation and Control for HVAC, sometimes pulled out into Division 25 Integrated Automation instead. This is the most expensive assumption in mechanical bidding.
• 23 05 93 Testing, Adjusting and Balancing. Many owners and GCs contract the balancer directly so the balancing is independent of the installer. Read the specification, not the habit of the last job.

Controls earn the extra attention because the drawings mislead you. Control valves, control dampers and thermostats are drawn on the M sheets and listed in your equipment schedules, but the sequence of operations that actually prices the work sits in the specification. A sub reading only the drawings either sees controls as clearly theirs and prices a fraction of the real package, or assumes the controls contractor has all of it and prices none. Decide in writing whether you carry the full building automation system, the field devices only, or nothing past the equipment interface.

Then there are the edges that are not Division 23 at all but are drawn on your sheets or bolted to your equipment:

• Roof curbs and structural support. The curb may come factory-built with the rooftop unit or be field-built. Dunnage steel under the unit is a structural steel item. Flashing the curb into the roof membrane belongs to the roofer. Three trades, one penetration, and a curb nobody bought is a change order.
• Electrical connection of mechanical equipment. Line-side power, disconnects, starters and variable frequency drives. Factory-mounted or field-furnished is the question, and the equipment schedule and the electrical panel schedule frequently disagree.
• Louvers and dampers at the envelope. The louver is drawn on the architectural elevations and specified with louvers and vents in Division 08. The damper behind it is yours.
• Firestopping at duct and pipe penetrations. Sometimes carried by the GC as one firestopping contract, sometimes yours penetration by penetration. A smoke damper also brings a fire alarm interface and end-switch wiring with it, which is a third trade again.

Read the drawings for your sheets, not the whole set

• M-series sheets carry the work: floor plans, mechanical room enlarged plans, roof plan, riser diagrams, schedules and details.
• Schedules beat plans. The equipment schedule gives you tags, capacities, electrical characteristics, filter arrangement, accessories and often the basis-of-design model number. Price from the schedule, use the plan for routing and count. The same is true of the air device schedule, which tells you neck size and finish that the plan never shows.
• The reflected ceiling plan has your air devices. Diffuser counts and locations are coordinated on the architect's RCP, not the M plan, and the two do not always agree. Count off the RCP and note the discrepancy in your clarifications.
• S sheets tell you if the roof can hold your unit and whether dunnage is already drawn.
• E sheets tell you who is furnishing starters and drives.
• P sheets pick up, or do not pick up, your condensate drain and gas piping. Condensate routing is the classic orphan between the mechanical and plumbing packages.
• The specification carries the money: sequence of operations, commissioning obligations, duct pressure class, insulation thickness and jacket, submittal requirements.

Get the sheet metal quantity right

Ductwork is bid by weight, in pounds of sheet metal by gauge, not by linear feet. That single fact changes everything about how you take it off.

Here is the gotcha that separates estimators who have fabricated duct from estimators who have not: the gauge steps with the duct's largest side dimension and with the pressure class, so one continuous run can carry three different gauges. A trunk that starts wide at the air handler and reduces as it sheds branches is heavier metal at the beginning and lighter at the end. Take the whole run off at the small-end gauge and you have quietly underbid the pounds on the heaviest part of the system. See ductwork gauge for how the gauge is selected.

Three more things the obvious duct takeoff misses:

• Fittings. Elbows, transitions, offsets, taps, boots and end caps. Fittings carry more pounds per foot of run than straight duct, more fabrication labour per pound, and more drop. Count them as items, do not smear them into linear footage.
• Hangers and supports. Rod, strap, trapeze, seismic bracing where required. Real material and real labour, invisible on the plan.
• Rectangular versus round. For the same airflow these are not the same number. Round and spiral duct is fewer pounds but the fittings are usually purchased rather than shop-fabricated, which moves cost from your shop to your material line. If the drawings are single-line and the sizes are not noted, you are being asked to size the duct, and that is delegated design you should price and disclose.

Everything else has its own unit:

• Equipment by tag and count from the schedule, priced off vendor quotes, with freight, rigging and the crane pick called out. A shared crane day is a negotiation, not a given.
• Piping by linear foot per size and per material, then valves, fittings, specialties and hangers as separate counts. Hydronic piping and refrigerant piping are different trades' worth of labour per foot, so never blend them.
• Insulation by square foot of duct surface and linear foot of pipe, per thickness. Duct insulation is a surface-area takeoff, not a weight takeoff, so duct insulation needs its own pass over the drawings.
• Controls by point count, derived from the sequence of operations. One VAV box on the plan is a controller, a damper actuator, a flow sensor and a space sensor in the controls package.

What the GC checks when leveling mechanical bids

Bid leveling is the GC normalizing every bid to one common scope. Expect them to look for:

• Controls: in, out, or partial. Item by item, not as a sentence.
• Balancing: yours or theirs. And whether commissioning support hours are in your labour.
• Insulation: duct, pipe, both, or neither.
• Equipment basis of design. Which manufacturer you quoted, and whether you took a substitution.
• Roof curbs, dunnage, flashing, and who furnishes each.
• Starters, drives and disconnects.
• Firestopping, sleeves and access doors in hard ceilings.
• Long-lead equipment and your bid validity date. Large air handling units and chillers carry lead times that outlast a bid, so state how long your price holds.
• Allowances carried, and for what.
• Unit prices for adds, so changes are a lookup rather than a re-bid.

Anything you leave silent gets filled in with an assumption, and the assumption will not favour you.

Structure the proposal so it survives leveling

Five parts, in this order. The number with the scope sections it covers. Inclusions as a list of items. Exclusions as the same kind of list, which is the most valuable section in the document. Clarifications and assumptions: duct pressure class assumed, air device count taken from the RCP, controls boundary, balancing, curb and flashing responsibility, crane assumptions, submittal review duration, bid validity. Then unit prices, per pound of duct by gauge, per air device, per linear foot of pipe by size.

Where this fits

If you are running the takeoff itself, Ruh reads the drawing set, measures the ductwork and piping, and prices the measured quantities against your own price book, with every line traceable back to the sheet it came from. That traceability is what you need when a GC calls to ask why your sheet metal weight is different from the other three bidders.