Division 23 HVAC specifications tell the mechanical contractor exactly what to buy, how to install it, and how to prove it works. On a tenant improvement, these specs can run dozens of pages. For general contractors and project managers, they are also a frequent source of scope gaps, missed submittals, and closeout headaches. This guide decodes the key sections, explains what each one requires, and shows how to manage the mechanical scope from bid to closeout.
Use it as a practical reference when you read specs, write subcontracts, or review mechanical bids.
What Is Division 23?
In the U.S., most commercial specs follow MasterFormat, published by the Construction Specifications Institute. In MasterFormat, Division 23 covers heating, ventilating, and air conditioning.
Inside the division, each section has a six-digit number and a title. Some sections, for example, set general rules for all mechanical work. Others, by contrast, cover specific products like ducts, fans, or rooftop units. Together, they define the HVAC scope.
Key Division 23 HVAC Sections for TI Work
Tenant improvement specs usually include these core sections:
- 23 05 00 – Common work results for HVAC, such as hangers, sleeves, and labeling
- 23 05 93 – Testing, adjusting, and balancing
- 23 07 00 – HVAC insulation
- 23 09 00 – Instrumentation and controls
- 23 31 00 – HVAC ducts and casings
- 23 33 00 – Air duct accessories, such as dampers and access doors
- 23 34 00 – HVAC fans
- 23 37 00 – Air outlets and inlets, such as diffusers and grilles
- 23 74 00 or 23 81 00 – Packaged rooftop or unitary equipment
However, restaurants and labs may add sections for kitchen exhaust, fume hoods, or specialty systems. So always read the full table of contents.
Common Work Results
First, section 23 05 00 sets the ground rules. For example, it may cover pipe and duct supports, seismic restraints, sleeves through walls, labels on equipment and ducts, and coordination with other trades. It often references firestopping requirements at rated walls.
However, these details are easy to skim past. Yet missing a labeling or support rule can cause a failed punch walk. So review this section closely with your mechanical subcontractor.
Division 23 HVAC Ductwork Rules
Next, the duct sections set materials, metal thickness, joints, sealing, and pressure ratings. Many specs reference standards from SMACNA for duct construction and leakage.
For GCs, two items matter most here. First, sealing and leakage testing requirements, which affect labor. Second, insulation requirements, which affect material cost and ceiling space. Confirm both before pricing.
Equipment Requirements
Likewise, the equipment sections name makers, models, sizes, efficiency, and features. For rooftop units, they may specify economizers, hail guards, smoke detectors, and control interfaces. In addition, they set warranty terms.
In practice, equipment drives lead time. So push submittals early and confirm that the specified features are available from the maker. Late substitutions can stall the whole project.
Division 23 HVAC Controls Rules
Meanwhile, section 23 09 00 covers controls. It may require a full building automation system, specific protocols, sensor types, and programming. It also often calls for point-to-point checkout and owner training. As a result, the controls scope reaches all the way to the last week of the job.
Unfortunately, controls are a frequent source of delay. Parts can have long lead times, and programming happens late in the job. Therefore, involve the controls contractor early and confirm the sequence of operations.
Testing, Adjusting, and Balancing
Then section 23 05 93 asks a balancing firm to measure and adjust air and water flows. Many specs require an independent firm certified by a recognized balancing association. The final report must show measured versus design values.
So plan time for balancing after ceilings and controls are done. Learn more on our controls, testing, and balancing page.
Submittals for Division 23 HVAC
Before buying anything at all, the mechanical sub sends product data and drawings for review. A typical package includes:
- Data sheets for each unit
- Duct shop drawings
- Diffuser and grille schedules
- Fan and damper data
- Controls drawings and sequences
- Insulation data
Then review the package before sending it to the architect. Missing pieces lead to rejections and lost time.
Why GCs Should Care About Division 23 HVAC
HVAC is often one of the largest trade packages on a TI. It also touches the roof, the structure, the electrical system, and the ceiling. So gaps in the mechanical scope can ripple across the whole job. For instance, a missed curb can stall a crane day. Likewise, a missed control point can delay final inspection. A careful read of Division 23 HVAC up front prevents these surprises.
Scope Gaps to Watch
Also, some work sits between divisions. Common gaps include:
- Power wiring to rooftop units and fans (Division 26)
- Roof curbs and flashing (Division 07)
- Structural supports for heavy units (Division 05)
- Fire and smoke dampers tied to the fire alarm (Division 28)
- Condensate drains to plumbing (Division 22)
- Kitchen hoods supplied by the food service vendor (Division 11)
A scope matrix attached to each subcontract settles these questions before work starts.
Closeout Requirements
Finally, Division 23 HVAC usually calls for a full closeout package. It often includes as-built drawings, operation and maintenance manuals, warranties, the balancing report, controls documentation, and owner training records. Start collecting these early.
How to Read a Spec Section Quickly
Every spec section has three parts. Part 1 is general. It lists submittals, quality rules, and warranties. Part 2 is products. It names the brands and models. Part 3 is execution. It tells crews how to install, test, and clean.
So, to price a job, start with Part 2. To plan the schedule, read Part 1 and the test steps in Part 3. Field crews mostly need Part 3. With this simple map, a thick spec book gets much easier to use.
When Specs and Drawings Disagree
Sometimes the spec says one thing and the drawing says another. For example, the spec may call for lined duct while the plan shows wrapped duct. Do not guess. Instead, send a short question to the engineer. Most contracts say which document wins, yet a quick answer avoids a fight later. Keep a log of these questions so nothing gets lost.
Division 23 HVAC on Small Jobs
Small tenant jobs often have short specs. Some have none at all, just notes on the drawings. Even so, the same ideas apply. First, ask what equipment is approved. Next, find out who balances the system. Finally, learn what closeout papers the owner wants. Clear answers early make small jobs run just as smoothly as big ones.
Tips for General Contractors
- Read every Division 23 section, not just equipment.
- Build a scope matrix for gray areas.
- Push equipment and controls submittals early.
- Coordinate power, roofing, and structure for rooftop units.
- Schedule balancing after ceilings and controls.
- Collect closeout documents as you go.
FAQ on Division 23 HVAC
Does Division 23 HVAC include kitchen hoods?
Sometimes. Hoods may sit in Division 11 or 23. Check the spec and the equipment schedule.
Who hires the balancing contractor?
It varies. Some specs require the owner to hire an independent firm. Others make it part of the mechanical subcontract.
Work With a Division 23 Specialist
Clear specs and careful review keep HVAC on budget. Visit our Division 23 contractor page, or ask our estimators to review your spec.