Winter Storm Prep for Commercial HVAC: Freeze Protection First

With a significant winter storm expected to impact Kentucky this weekend, bringing very cold air, accumulating snow, and travel/power-disruption risk, now is the time to shift your building from “efficient winter operation” into storm survivability mode.

This article is written for maintenance technicians, facility engineers, and BAS/controls folks who need a practical, technical checklist to prevent the big losses: cracked coils, burst piping, flooded mechanical rooms, nuisance trips, and long recovery times. Frozen coil failures are often triggered by controls or airflow issues (economizer stuck open, stratified mixed air, power loss, failed circulation), not just “it got cold.”

Note about our role: We’re sharing this as a readiness guide. Our company does not perform maintenance, but if you need OEM parts during/after the storm, contact our Parts Department—we can help you source the right components fast.

The big idea: Freeze protection is a chain (and chains fail at the weakest link)

Freeze protection isn’t one device—it’s a sequence that depends on sensors → logic → actuators → safeties working together. If one link lies (bad sensor), sticks (damper), or never gets tested (freezestat), the coil is the one that “pays.”

Your storm-prep goal: make the building boring. Stable mixed air temps, confirmed heating response, proven safeties, and a plan for power events.

24–48 hours before: BAS “storm mode” checks (high ROI, low wrench time)

A. Trend the right points (even 12 hours of data helps)

Trend these at 5–10 minute intervals so you can see problems before a trip or freeze event:

• OAT, RAT, MAT (mixed air), SAT

• OA damper command/feedback (if available)

• Heating valve command and discharge temp response

• Fan status/VFD speed

• Freeze alarm/freezestat status

• Boiler S/R temps, pump status (if hydronic)

  
  

Why MAT matters: many coil freezes begin with stratification (a cold “river” of OA washing part of the coil face), so the average temp looks okay until one section hits freezing.

B. Economizer sanity check (most common “oops” in extreme cold)

Economizers are a frequent culprit when sensors drift or dampers stick, pulling in excessive cold OA.

Do this quick functional check:

• Verify OA dampers move freely and return to minimum position when they should.

• Confirm “free cooling” is not active in conditions where it shouldn’t be (bad OAT/enthalpy reading can lie).

• If you have high-limit shutoff logic, confirm it aligns with your climate/sequence requirements.

Storm mindset: when it’s brutally cold, you’re not optimizing for savings—you’re optimizing for coil and pipe survival.

C. Scheduling and setbacks: don’t let the building “coast cold”

If the storm brings single-digit lows and teens for highs, deep night setbacks can create long recovery ramps that stress heat capacity and expose perimeter zones.

Consider temporarily:

• Raising unoccupied heat setpoints in perimeter/high-loss zones

• Avoiding aggressive morning warm-up sequences that open OA too early

• Keeping critical circulation running where freeze risk exists

Freezestats: verify the last line of defense (and why placement matters)

A freezestat is the standard low-limit device used to protect water coils; when air at the coil drops near freezing, it changes state and triggers protective action.

Key technical details that techs should verify:

• Setpoint: many applications commonly use a ~37°F freezestat setpoint as a typical value (sequence-specific).

• Coverage: capillary-style freezestats use a long cap tube (often 10–20 ft) that must be serpentined across the leaving-air side of the coil so it can sense the coldest section.

• Why leaving-air side: placement on the entering-air side can create nuisance trips because OA stratification can chill the sensor while the coil isn’t actually at risk.

Functional test mindset: A freezestat that hasn’t been tested might as well not exist. When it trips, you typically want a sequence like: close OA dampers, open heat fully, prove flow, and/or stop supply fan (depending on design).

Field reality: If you’re fighting nuisance trips, don’t “jump out” safeties, diagnose stratification, bad sensors, damper leakage, or coil flow issues.

Hydronic coils (preheat/reheat): flow is life

Hydronic coils freeze when flow stops, valves fail, pumps don’t run, or glycol protection is inadequate.

A. Confirm circulation and valve authority

Before the storm:

• Verify pump status (BAS proof, differential pressure if available) and exercise standby pumps.

• Stroke control valves and confirm the coil actually warms when commanded.

• Check strainers if you can—restricted flow equals reduced freeze margin.

B. Glycol: measure it—don’t assume it

If any loop relies on glycol, verify concentration and freeze point. Glycol protection can degrade via leaks, dilution, or poor practices over time, increasing risk during severe cold.

C. 100% OA / DOAS units: elevated risk

Units using 100% outside air are inherently more freeze-prone; design guidance highlights the importance of glycol concentration, drainability, and reliable circulation during cold weather.

Packaged RTUs: gas heat, electric heat, and heat pumps (the “solid mix” reality)

Since sites may be a mix of unit types, use a unit-category approach:

A. Gas heat RTUs

• Confirm combustion air intake and exhaust terminations are clear of snow/ice drift zones; blocked openings can create unsafe combustion conditions and shutdowns.

• Verify high-limit trips aren’t being triggered by low airflow (filters, belts, economizer issues).

Codes and guidance emphasize that combustion air must be provided appropriately and that requirements defer to fuel gas codes/manufacturer instructions for gas appliances.

B. Electric heat RTUs

• Verify staging, contactors, and safeties; electric heat can carry the building when other heat sources are constrained, but only if all stages are available.

C. Heat pumps (and defrost realities)

• Confirm defrost is functional and that auxiliary heat is available and properly staged; ice buildup plus low airflow can cause lockouts and comfort loss.

Outdoor air intakes, louvers, and snow ingestion

Wind-driven snow can enter outdoor air intakes and wet filters/plenums; repeated snow ingestion can lead to water damage, microbial growth risk, and corrosion.

If your intakes are prone to snow:

• Inspect intake locations for drift patterns and obstructions

• Ensure drains are clear where meltwater could accumulate

• Consider longer-term improvements (louver selection, placement, or snow-resistant designs)

Condensate drains, traps, and “small stuff” that causes big failures

Even in winter, you can still get condensate from humidification, defrost cycles, or internal loads. Frozen drains can shut units down or create overflow events.

Quick checks:

• Traps intact and primed (where applicable)

• Drain lines pitched and protected from freezing

• Heat trace energized where installed (verify power and control)

Power outage planning: what happens when everything goes dark?

Power failure is explicitly called out as a cause of coil freezing because pumps and AHUs stop and coils are exposed to cold air or stagnant fluid.

Before the storm:

• Know what is on generator/UPS: boiler controls, pumps, BAS head-end, network switches, key AHUs/RTUs.

• Ensure your “return from outage” sequence doesn’t slam OA open or start in an unsafe state.

During the storm: “watch these 5 things” (remote or on-site)

Whether you’re on-site or watching BAS alarms, prioritize:

1. MAT dropping fast (economizer or damper leak)

2. Heating at 100% with no SAT rise (no flow, air-bound, strainer, valve issue)

3. Freeze-stat trips (prove response matches sequence)

4. Perimeter zone temps falling (setbacks too deep, airflow imbalance, heat shortfall)

5. Combustion air/exhaust blockage on gas equipment (snow/ice drift risk)

After the storm: restart safely (don’t turn a near-miss into a failure)

As temps rise and access returns:

• Visually inspect RTU/AHU intakes and exhausts for ice blockage before ramping up.

• Bring OA ventilation back gradually if your sequences allow—avoid shocking coils with cold air.

• Look for leaks at coils, valves, and piping; coil failures can flood when thawed and pressurized.

• Review trends to identify what almost failed (the best “free” commissioning you’ll get).

Print-and-go checklist (condensed)

24–48 hours before

•  Trend OAT/RAT/MAT/SAT + heating commands + damper position

•  Verify economizer/OA dampers return to minimum and sensors read plausibly

•  Prove freezestat function + correct placement/coverage

•  Confirm hydronic flow: pumps, valves, strainers; verify glycol where used

•  Check combustion air/exhaust terminations for drift exposure (gas units)

Day of storm

•  Storm mode: OA minimum, avoid economizer cooling, soften setbacks

•  Watch MAT, freeze alarms, perimeter temps, boiler/plant lockouts

After storm

•  Clear ice/snow from intakes/exhaust; inspect for leaks and coil damage

•  Restore OA and schedules gradually; review BAS trend data

Parts Support

If you’re impacted by this storm and need OEM parts—actuators, sensors, freezestats, damper components, valves, ignition parts, VFD items, and more—contact our Parts Department. We can help you identify the correct part and source it quickly so you can get your system stabilized and back online.