Testing, Adjusting & Balancing (TAB) is the field discipline that turns a designed HVAC system into a measured, documented reality — setting every fan, terminal box, diffuser, and exhaust grille so each space achieves its intended airflow, pressure relationship, and temperature. In a healthcare facility, TAB is not a comfort exercise; it is the act that proves the building can hold the pressure cascades and air-change rates on which infection control, life safety, and clinical operation depend.

TAB sits at the front of the HVAC commissioning and activation sequence. It establishes the measured baseline that commissioning then verifies under integrated and emergency conditions, and that room-by-room certification later confirms before a space opens to patients. This article covers the TAB discipline itself — what is measured, how, to what tolerances, by whom, and how the results are documented and verified. The downstream commissioning, room certification, and activation handover steps are the subject of the companion Article and are referenced here only at the seams.

What TAB Is and Why It Is Decisive in Healthcare

TAB is the systematic measurement and final adjustment of a mechanical system so that the as-built airflows, water flows, and pressures match the design intent within stated tolerances. The classic definition breaks into three verbs:

• Testing — quantitative measurement of system performance: airflow (CFM) at fans, ducts, terminals, diffusers, and grilles; static pressures; water flow (GPM) through coils and equipment; temperatures; rotational speeds; and electrical draw.
• Adjusting — varying dampers, valves, fan speeds (sheaves or VFD setpoints), and terminal-box settings to bring measured values into agreement with design.
• Balancing — proportioning flow among parallel paths so that every branch and outlet receives its designed share, and the system as a whole is in equilibrium.

In commercial buildings, TAB is largely about energy use and occupant comfort. In a hospital it carries a clinical and regulatory weight that no other building type imposes:

• Pressure relationships are a containment control. Airborne infection isolation (AII) rooms must hold negative pressure relative to the corridor; protective environment (PE) rooms and operating rooms must hold positive pressure. Getting the directional airflow right — and proving it — is a TAB deliverable, not an afterthought.
• Air-change rates are minimums set by code. ASHRAE Standard 170, adopted through the FGI Guidelines, prescribes total and outdoor air changes per hour (ACH) for each space type. TAB confirms those minimums are met everywhere, simultaneously.
• Offsets between supply and exhaust are deliberate. The negative or positive pressure in a space comes from an engineered imbalance between air supplied and air removed. TAB sets and documents that offset; a balanced (zero-offset) room would fail.
• Regulators and accreditors expect the proof. TJC, DNV, CMS surveyors, and the AHJ routinely ask to see ventilation documentation. The TAB report — together with the room certification records that build on it — is the primary evidence that the environment performs as designed.

The Governing Standards Landscape

TAB in a U.S. healthcare facility answers to two overlapping bodies of rule: the standards that define what the system must achieve, and the standards that define how TAB itself is performed and documented.

What the system must achieve (design targets):

• ASHRAE Standard 170, Ventilation of Health Care Facilities — the source document for space-by-space ventilation: pressure relationship (positive / negative / no requirement), minimum total ACH, minimum outdoor ACH, filtration efficiency, design temperature and humidity, and whether all room air is exhausted. ASHRAE 170 is incorporated by reference into the FGI Guidelines and adopted by most AHJs.
• FGI Guidelines for Design and Construction of Hospitals / of Outpatient Facilities / of Residential Health, Care, and Support Facilities — the design standard that pulls in ASHRAE 170 and adds programmatic and commissioning requirements. The edition in force is set by the AHJ and the project's permit.
• ASHRAE Standard 90.1 (energy) and ASHRAE Standard 55 (thermal comfort) — secondary targets that the balance must respect without compromising the 170 minimums.
• NFPA 99 (Health Care Facilities Code) and NFPA 101 (Life Safety Code) — relevant where ventilation intersects smoke control, hazardous-area exhaust, and life-safety zoning.
• USP General Chapters 797 and 800 — drive the pressure cascades and ACH for sterile and hazardous-drug compounding pharmacies; TAB of those suites is verified against USP, not just ASHRAE 170.