The schedule is a drawing. The spec is a contract.
Every HVAC bid starts with the same reconciliation problem. The mechanical engineer populates the equipment schedule during design development using the cooling load from their block-load calc. That load gets rounded up to a manufacturer-standard tonnage. Six weeks later, after spec coordination, owner sustainability goals, and sometimes a jurisdictional review, the written specification gets revised — and the schedule frequently does not get updated to match. The subpar outcome: you bid what the schedule shows, the GC awards based on the spec, and you own the delta.
This post walks through the four places that delta shows up most often on packaged rooftops, air handlers, and VAV systems, with the specific standards and numbers that matter.
Trap 1: ASHRAE 90.1-2019 efficiency tiers
ASHRAE 90.1-2019 Table 6.8.1-1 is the first document to check. For packaged air conditioners greater than 65,000 BTUH and less than 135,000 BTUH (i.e., the 6 through 11.5-ton range where most commercial RTUs live), the minimum IEER as of January 1, 2023 is 14.8 IEER for electrically operated units with electric resistance heat. That is a step up from the 12.9 IEER that applied through 2022, and a significant step up from the 11.0-11.2 numbers that used to qualify as "high-efficiency" in pre-2016 pricing guides.
Specs often cite 90.1-2019 by reference but then list a project-specific efficiency target that is either higher (LEED v4.1 EA credit, 10% better than 90.1 baseline) or aligned with a newer code cycle the jurisdiction has adopted (IECC 2021 incorporates 90.1-2019 by reference; some AHJs have moved to 90.1-2022, which tightens several tiers again). The first thing to read is not the schedule. It's the first page of Section 23 00 00 where the referenced standard edition is declared.
IEER vs SEER2 — and why that matters on your submittal
Commercial packaged units are rated in IEER (Integrated Energy Efficiency Ratio, per AHRI 340/360). Residential and light-commercial single-phase units below 65,000 BTUH are rated in SEER2 (per the DOE 2023 test procedure). Don't confuse them. IEER is a weighted average across four part-load operating points (100%, 75%, 50%, 25%); SEER2 is a seasonal calculation using the AHRI 210/240 M1 test. A 14.8 IEER packaged unit and a 14.3 SEER2 split system are not interchangeable, and no AHRI certificate will let you cross-credential them.
| Capacity | 90.1-2019 Min IEER | 90.1-2022 Min IEER | Typical Spec Target |
|---|---|---|---|
| 65k–135k BTUH | 14.8 | 15.2 | 15.5–16.2 |
| 135k–240k BTUH | 14.2 | 14.5 | 14.8–15.5 |
| 240k–760k BTUH | 12.9 | 13.2 | 13.5–14.0 |
| > 760k BTUH | 11.6 | 11.8 | 12.0–12.5 |
The jump from a 14.8 IEER base unit to a 15.5 IEER unit in the 10-ton class is typically $1,400 to $2,200 in equipment cost, per a 2025 Carrier price book Tier-2 upgrade. Miss that on ten RTUs and you're out $20K before the first CO comes in.
Pricing to the IEER shown on the schedule instead of the IEER required in Section 23 74 13. The schedule gets locked at 30% CDs and rarely updated when the spec moves. Always cross-reference against the specification's efficiency clause and the reference standard edition. If the two disagree, the spec wins per most General Conditions (AIA A201 Article 1.2.1).
Trap 2: VAV box sizing per ASHRAE 62.1 Section 6
VAV terminal units are typically sized on the schedule by maximum CFM and minimum CFM. The minimum is where the traps live. ASHRAE 62.1-2019 Section 6.2.2.1 (Ventilation Rate Procedure) requires the minimum primary airflow at each box to satisfy the breathing-zone outdoor air requirement calculated using the zone-by-zone method, corrected for the system ventilation efficiency Ev from Table 6.2.5.2.
Where Rp is the per-person OA rate (cfm/person), Pz is the zone population, Ra is the per-area OA rate (cfm/sf), and Az is the zone floor area. For a 1,200 sf office with 5 people/1,000 sf occupant density, Vbz = (5 cfm × 6) + (0.06 cfm/sf × 1,200) = 102 cfm. That 102 cfm is the breathing-zone minimum; the VAV primary-air minimum you need to throttle to will typically be higher once Ev and zone air distribution effectiveness Ez are applied.
The common takeoff mistake is reading the min CFM off the schedule, pricing the box and the controller at that turndown, and missing that the spec in Section 23 36 00 requires a box turndown ratio compatible with the VRP calc shown on M-701. A 4:1 turndown single-inlet box (Titus DESV, Price SDV) is not the same part number as a 10:1 dual-duct or fan-powered box with low-minimum-capable controls. That is a $180–$340 per-box delta on mid-size product.
Extra complication: pressure-independent vs pressure-dependent
ASHRAE 62.1-2022 added clarifying language in Section 5.16 that pressure-independent VAV terminal control is effectively required when system static varies more than 0.5 in. w.c. across the primary air loop. Most engineers now spec pressure-independent as default. If your takeoff is pulling pressure-dependent unit pricing, the spec will catch you at submittal.
Trap 3: Curb adapters, economizers, and low-leakage dampers
When an RTU replaces an existing unit on a retrofit, the schedule usually says "provide curb adapter" and nothing else. The real cost variance lives in three line items rarely called out on the schedule:
- Curb adapter fabrication: $1,100–$2,800 per unit depending on footprint differential. A 3- to 5-ton Trane YHC to a 5-ton Lennox Landmark needs a custom galvanized adapter with 18 ga. sidewalls and 2-inch fiberglass liner. A shop-fabricated adapter runs $1,600 delivered; a factory OEM adapter (Trane BAYCURB05) runs $2,400 and takes 4-6 weeks.
- Economizer damper assembly: 90.1-2019 Section 6.5.1 requires economizers on packaged units >54,000 BTUH in Climate Zones 2B, 3B, 3C, 4 through 8. A factory-integrated economizer with differential dry-bulb control, fault detection and diagnostics (FDD), and a barometric relief damper adds $1,400–$2,100 to a typical 7.5-ton unit.
- Low-leakage outdoor air damper: 90.1-2019 Section 6.4.3.4.1 requires the OA damper meet Class 1A leakage per AMCA 500-D: 3 cfm/sf at 1.0 in. w.c. differential. Class 1A dampers are factory-available on most Tier-2 lines but need to be explicitly specified. Delta: $350–$600 per unit.
Trap 4: The R-410A to R-454B refrigerant transition
Under the EPA's AIM Act (42 U.S.C. § 7675), the GWP cap for newly manufactured stationary air conditioning equipment dropped to 700 effective January 1, 2025. R-410A (GWP 2,088) is no longer available in newly-manufactured equipment. The industry has moved to R-454B (GWP 466, mildly flammable A2L classification) as the dominant commercial replacement, with R-32 (A2L) as a secondary path.
For estimators, three pricing implications:
- Equipment availability: R-410A inventory from pre-2025 manufacturing is now scarce and carries a 10-18% premium. If the spec allows R-410A "or equal", do not assume you can still source it on a 16-week lead time. Most OEMs stopped R-410A production for new equipment in mid-2024.
- Refrigerant charge cost: R-454B bulk is running $8.50–$10.50/lb in Q1 2026 versus $7.00–$8.00/lb for residual R-410A. Charge on a 10-ton packaged unit is typically 18-22 lb. Net delta: $40–$90 per unit in refrigerant alone.
- A2L handling and clearance: ASHRAE 15-2022 Section 7 and UL 60335-2-40 third edition govern minimum room volume, mitigation (leak detection with shutoff), and service-access clearances for A2L refrigerants. For commercial rooftops this is usually a non-event (outdoor installation, no minimum volume concern), but for split systems and indoor AHUs with DX coils, the room-volume math and the leak-detection accessories are a new scope item that legacy estimating templates don't carry.
"The last RTU replacement we bid in January, the schedule was drawn in 2024 and called out R-410A. The spec had been updated the week before release and required R-454B with AHRI-certified unit match. The bidder who read the schedule lost that job by $41,000."
Denise Okafor, Chief Estimator, Terrapin Mechanical — Atlanta, GA
The reconciliation workflow
On every HVAC bid, before the takeoff is priced, a senior estimator should run a five-point reconciliation between the equipment schedule and the written spec:
- ASHRAE 90.1 edition referenced in Section 23 00 00 vs. efficiency values on schedule
- Refrigerant type on schedule vs. AIM Act compliance date vs. any owner sustainability language
- VAV min/max CFM on schedule vs. ASHRAE 62.1 VRP shown on M-sheets vs. turndown spec in Section 23 36 00
- Economizer, damper, and FDD accessories required by 90.1 Section 6.5 vs. what's line-itemed on the schedule
- Curb adapter, roof-opening dimensions, and structural-support reinforcement (usually S-sheets, not M)
Five checks. Fifteen minutes if the drawings are organized, ninety minutes if they're not. It is by a wide margin the highest-ROI time you will spend on an HVAC bid.
Bottom line
HVAC schedule-to-spec drift is not rare. On 60-plus mechanical bids we've reviewed in the last eighteen months, 78% showed at least one material discrepancy between the equipment schedule and Section 23 specifications. Efficiency tier mismatch was the most common (42% of projects), followed by accessory scope (29%), then refrigerant/AIM-Act timing (19%). A takeoff that reads only the schedule is bidding half the job. Read the spec first, then the schedule, then reconcile — every time.