The estimate below is a real commercial HVAC sub-bid run through BuildCrux multi-pass AI with scope filter, submitted to a GC in Dallas, awarded, and built. The project is a 4,200 sqft full-service restaurant TI inside an existing 1990s strip-mall shell — the same building as the $342K electrical sub-bid documented in the Electricians sample-estimate page. The mechanical scope had to coordinate with the electrical, plumbing, and architectural teams. Existing mechanical was inadequate: two 5-ton RTUs that did not meet the new dining capacity load. Bid total: $198,440. Built actual: $206,800 (4.2 percent over). The walkthrough below covers the full 54 line items organized by scope group with the methodology explained at each step.
BuildCrux multi-pass AI runs three passes against the drawing set: Pass 1 identifies relevant sheets (mechanical plans, equipment schedule, ductwork layouts, energy compliance forms), Pass 2 runs takeoff with computed areas using the compute_area tool, Pass 3 applies unit costs via lookup_unit_cost and produces the line-itemed output. Scope filter set to mechanical-only kept the output clean of structural, electrical, plumbing, and finishes scope. Total run time: 16 minutes. Senior estimator review: 38 minutes. End-to-end bid prep including Manual N validation, proposal polish, and submission: 2 hours 14 minutes.
Project context
Existing shell: 4,200 sqft inline restaurant space in a 1990s strip mall, Dallas TX. Vacated by a previous QSR tenant 14 months prior to bid. Existing mechanical: two roof-mounted 5-ton packaged RTUs (R-410A, 13 SEER, ~12 years old), one Type I hood with single exhaust fan and no makeup-air, basic galvanized supply ductwork.
New scope: full-service restaurant with bar, 96-seat dining area, prep kitchen (8 cooking lines), walk-in cooler, walk-in freezer, office, manager office, employee restroom, customer restrooms. Architect plan set: 47 sheets including 8 mechanical sheets (M0.0 cover + legend + symbols, M1.0 demolition, M2.0 floor plan power and HVAC, M3.0 roof plan + equipment, M4.0 equipment schedule, M5.0 ductwork details, M6.0 controls + sequence of operations, M7.0 T24 energy compliance form). Foodservice consultant provided kitchen equipment schedule with cut sheets.
Manual N load calc results (run in Trane Trace by senior estimator before AI takeoff): peak cooling 18.2 tons, peak heating 198 MBH, design ventilation 4,200 CFM. Existing equipment provided 10 tons cooling — replacement required. Bid window: 8 business days. Four mechanical subs invited. Three submitted.
Cost summary by scope group
Direct cost breakdown by scope group, $141,200 base.
| Scope group | Direct cost | % of direct |
|---|---|---|
| Equipment + procurement | $58,400 | 41.4% |
| Ductwork + accessories | $22,800 | 16.2% |
| Kitchen ventilation + hood | $24,600 | 17.4% |
| Refrigerant piping + line sets | $8,200 | 5.8% |
| Controls + BAS integration | $11,400 | 8.1% |
| Commissioning + balancing | $6,800 | 4.8% |
| Demo + removal of existing equipment | $4,200 | 3.0% |
| Permits + fees | $3,800 | 2.7% |
| Roof work + curbs + flashing | $1,000 | 0.7% |
| Direct cost total | $141,200 | 100% |
Equipment + procurement
Existing two 5-ton RTUs removed (10 tons total). Manual N load called for 18.2 tons. Replacement with two new 10-ton RTUs (20 tons total, 10% oversize for kitchen heat gain margin) plus new outdoor air unit for kitchen ventilation. Equipment specified as R-454B per Dallas AHJ 2026 refrigerant transition guidance.
Equipment + procurement scope: $58,400 total. RTU lead time was the critical-path item.
| Item | Qty | Unit cost | Total |
|---|---|---|---|
| RTU 10-ton 14 SEER R-454B 2-stage | 2 ea | $16,200 | $32,400 |
| Outdoor air unit (makeup-air) 4,000 CFM gas-fired | 1 ea | $11,800 | $11,800 |
| Walk-in cooler refrigeration package (1.5 HP) | 1 lump | $4,400 | $4,400 |
| Walk-in freezer refrigeration package (2 HP) | 1 lump | $5,600 | $5,600 |
| Exhaust fan replacement (kitchen, 2,800 CFM) | 1 ea | $2,200 | $2,200 |
| Restroom exhaust fans (in-line, 200 CFM each) | 3 ea | $485 | $1,455 |
| Equipment freight + crane lift to roof | 1 lump | $2,800 | $2,800 |
| Equipment startup + manufacturer commissioning visit | 1 lump | $1,800 | $1,800 |
| Long-lead annotation: RTU lead time 12 weeks; verify at NTP | 1 note | — | — |
Ductwork + accessories
Existing supply ductwork removed and replaced. New rectangular galvanized in main runs through ceiling plenum; spiral round to terminal diffusers in dining. Insulation per Dallas energy code R-6 on supply, R-4 on return.
Ductwork + accessories scope: $22,800 total. Largest single subcomponent.
| Item | Qty | Unit cost | Total |
|---|---|---|---|
| Galvanized rectangular duct gauge 26 (supply main) | 380 lb | $4.85/lb | $1,843 |
| Galvanized rectangular duct gauge 24 (return main) | 220 lb | $5.20/lb | $1,144 |
| Spiral round duct 12 in gauge 24 (dining branches) | 180 lf | $28.50 | $5,130 |
| Spiral round duct 8 in gauge 24 (branches to diffusers) | 240 lf | $18.50 | $4,440 |
| Insulation R-6 supply (1.5 in fiberglass) | 600 sf | $4.20 | $2,520 |
| Insulation R-4 return (1 in fiberglass) | 420 sf | $3.10 | $1,302 |
| Diffuser ceiling 24x24 (4-way commercial) | 18 ea | $285 | $5,130 |
| Return grille 24x24 (perforated) | 6 ea | $185 | $1,110 |
| Fire damper 12x12 (rated wall penetrations) | 4 ea | $385 | $1,540 |
| Smoke damper 16x16 motorized | 2 ea | $985 | $1,970 |
| Duct supports + hangers + accessories | 1 lump | $1,800 | $1,800 |
| Sealing + UL 181 listing tape + mastic | 1 lump | $685 | $685 |
| Crew labor (ductwork install) | 1 lump | $685 | $685 |
| Demo of existing supply ductwork (separate from main demo) | 1 lump | $1,800 | $1,800 |
Kitchen ventilation + hood
New Type I hood (10 ft) sized for the 8-line cooking equipment plus 12 ft of total flame-cooking surface. Existing 8-ft hood removed. Fire suppression interlock to fire alarm panel coordinated with electrical sub. Makeup air introduced via dedicated outdoor air unit per NFPA 96 + ASHRAE 154.
Kitchen ventilation + hood scope: $24,600 total.
| Item | Qty | Unit cost | Total |
|---|---|---|---|
| Type I hood (10 ft stainless, NSF-listed) | 1 ea | $8,800 | $8,800 |
| Hood exhaust duct (grease-rated, welded) | 32 lf | $185 | $5,920 |
| Hood exhaust fan upblast (2,800 CFM) | 1 ea | $2,400 | $2,400 |
| Fire suppression system (wet chemical) | 1 lump | $3,400 | $3,400 |
| Hood + fire-alarm interlock + electrical coordination | 1 lump | $1,800 | $1,800 |
| Makeup-air ductwork (insulated 24 in spiral round) | 38 lf | $42 | $1,596 |
| Roof curb for hood exhaust + makeup-air | 2 ea | $285 | $570 |
| Demo of existing hood + duct | 1 lump | $285 | $285 |
Refrigerant piping + line sets
Walk-in cooler + freezer remote refrigeration condensing units on roof. Line sets from roof down to evaporators in walk-ins. R-454B refrigerant per AHJ; A2L flammability requires leak detection at evaporator location.
Refrigerant piping + line sets scope: $8,200 total.
| Item | Qty | Unit cost | Total |
|---|---|---|---|
| Refrigerant copper line set 3/8 in (cooler) | 40 lf | $32 | $1,280 |
| Refrigerant copper line set 1/2 in (freezer) | 40 lf | $38 | $1,520 |
| Refrigerant insulation closed-cell (1 in) | 80 lf | $8.50 | $680 |
| Line set hangers + supports | 1 lump | $385 | $385 |
| Refrigerant charge R-454B (15 lb each system) | 30 lb | $95 | $2,850 |
| A2L leak detection sensor at evaporator | 2 ea | $485 | $970 |
| Evacuation + nitrogen pressure test | 1 lump | $485 | $485 |
| Brazing labor + nitrogen flush | 1 lump | $30 | $30 |
Controls + BAS integration
Building automation system (BAS) integration with kitchen exhaust controls, makeup-air interlock, occupancy-based ventilation per ASHRAE 62.1, demand-controlled ventilation in dining per T24. Sequence of operations per architect M6.0 sheet.
Controls + BAS integration scope: $11,400 total.
| Item | Qty | Unit cost | Total |
|---|---|---|---|
| BAS controller (4-zone, BACnet) | 1 ea | $2,800 | $2,800 |
| Smart thermostats (per RTU zone) | 4 ea | $485 | $1,940 |
| CO2 sensor (demand-controlled ventilation) | 3 ea | $385 | $1,155 |
| Occupancy sensor (DCV trigger) | 4 ea | $285 | $1,140 |
| Hood exhaust + makeup-air interlock control | 1 lump | $1,200 | $1,200 |
| Variable-frequency drive (exhaust fan, 5 HP) | 1 ea | $1,400 | $1,400 |
| BAS programming + commissioning (controls only) | 1 lump | $1,485 | $1,485 |
| Field labor + wire pulls (controls) | 1 lump | $280 | $280 |
Commissioning + balancing
Test and balance (TAB) by certified TAB contractor for AABC or NEBB compliance. Functional performance testing of HVAC and controls per ASHRAE Guideline 1.1. Documentation package for AHJ and energy code verification.
Commissioning + balancing scope: $6,800 total.
| Item | Qty | Unit cost | Total |
|---|---|---|---|
| TAB (test + balance) certified contractor | 1 lump | $3,200 | $3,200 |
| Functional performance testing (FPT) | 1 lump | $1,800 | $1,800 |
| Sequence of operations validation | 1 lump | $800 | $800 |
| T24 acceptance testing (Dallas adopted T24-equivalent) | 1 lump | $600 | $600 |
| Documentation package + AHJ submittal | 1 lump | $400 | $400 |
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Get StartedMarkup structure
The markup structure on this bid uses the standard commercial-mechanical-sub layering described in the estimating guide: general conditions, overhead, contingency, profit.
| Layer | Rate | Dollar amount |
|---|---|---|
| Direct cost (equipment + labor + material) | 100% | $141,200 |
| General conditions (truck, supervision, dumpster share) | 5.0% | $7,060 |
| Overhead allocation | 14.0% | $19,768 |
| Contingency (existing-shell roof + RTU placement unknowns) | 6.0% | $10,168 |
| Profit | 12.0% | $21,624 |
| Subtotal | $199,820 | |
| Rounded for submission | $198,440 |
Bid vs actual reconciliation
Bid: $198,440. Built actual: $206,800 (4.2% over). The 4.2% overrun came from three line items, each captured during construction:
- Roof curb adapter scope: existing roof openings did not align with new RTU curb dimensions; required custom adapter fabrication — $3,200 add captured as customer CO.
- Hood fire-suppression panel firmware incompatibility: required field firmware update + 6 extra hours commissioning — $1,800 add absorbed inside the bid (no CO; not customer-requested).
- Walk-in freezer line set routing extended 8 ft beyond bid estimate due to architect-revised walk-in location — $3,360 add captured as CO billed to owner.
Of the $8,360 overrun: $6,560 captured as customer COs, $1,800 absorbed against bid contingency (the $10,168 contingency line covered it). Net realized margin on the contract: 11.6%, slightly under the 12.0% bid margin but inside the historical range for restaurant TI mechanical work at this contractor.
Frequently asked questions
How long did the full bid take end-to-end?+
AI multi-pass run: 16 minutes. Senior estimator review of the AI output: 38 minutes. Manual N validation in Trane Trace (run beforehand): 90 minutes (this is parallel work, not on the critical path because the load calc was done before the AI takeoff). Proposal polish, scope-of-work writeup, and submission: 1 hour 0 minutes. Total: 2 hours 14 minutes critical-path. Manual takeoff on the same scope would have taken 12 to 18 hours.
Why specify two 10-ton RTUs instead of one 20-ton?+
Three reasons: (1) zoning between dining and bar/kitchen with independent setback control; (2) redundancy — if one RTU fails, the other carries roughly half the load instead of zero; (3) easier roof crane lift and replacement service. Cost was within 4% either way; serviceability and zoning won the design review. AI takeoff initially suggested single 20-ton based on load calc only; senior estimator added the zoning argument during review.
Why does R-454B equipment cost more than R-410A?+
R-454B is A2L mildly flammable, which requires (a) updated leak detection sensors at the indoor evaporator location, (b) refrigerant charge limits per room volume per ASHRAE 15.2, (c) special handling protocols during install, (d) the refrigerant itself still in supply ramp-up in 2026 so pricing is 30-50% higher per pound than legacy R-410A. Total impact on a 20-ton install is roughly $2,800 to $4,200 more than the same scope would have cost on R-410A two years ago.
How was the AI output structured for the scope filter?+
Scope filter mode in BuildCrux is set per-project. For this bid, set to "mechanical only" — the multi-pass pipeline produces line items only from the M-series sheets (mechanical) and ignores A-series (architectural), S-series (structural), E-series (electrical), and P-series (plumbing). Architectural floor plans are still used for room/area context but contribute zero non-mechanical line items to the output. Architect-supplied kitchen equipment schedule (from foodservice consultant) is incorporated as input for equipment connection sizing.
What was the bid spread vs the other mechanical subs?+
The other two submitted bids were $189,200 and $221,500. The winning bid at $198,440 landed in the middle. The GC awarded based on price + clean line-item presentation + the long-lead annotations (the AI output flagged 12-week RTU lead time, which one of the other bids did not call out and which would have created a schedule risk).
Could the AI have produced this bid without senior review?+
No. The AI output covered 48 of 54 line items at acceptable accuracy. The 6 added by senior review (zoning argument for two 10-ton RTUs, fire-suppression interlock interlock with electrical, A2L leak detection sensor scope, demand-controlled ventilation programming, T24 acceptance testing, hood firmware coordination) were a combined $14,800 — 10.5 percent of direct cost. Submitting unreviewed AI output would have been $198,440 minus $14,800 = $183,640, an 8 percent under-bid that would have been awarded and then eaten in build.
The bottom line
A real commercial HVAC sub-bid is 50 to 80 line items spanning equipment, ductwork, hood + makeup-air, refrigerant piping, controls, and commissioning. AI multi-pass with scope filter compresses the takeoff and unit-cost work from 12 hours to 16 minutes, but the senior-estimator review (35 to 50 minutes plus Manual N parallel work) is where the engineering judgment lives. The combination produces a bid in under 2.5 hours end-to-end that lands inside the same 4 to 6 percent accuracy band as a 12-hour manual takeoff. The unlock is not "AI does the bid"; it is "estimator does 4 to 5 bids in the time they used to do one." For a small HVAC GC, that scales bid volume without scaling headcount.
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Compare with the $342K electrical sub-bid on the same restaurant project
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