Cooling Tower Winterization: A Shutdown Checklist for Ontario Facilities

Cooling towers that will not operate through an Ontario winter need more than a simple switch-off. Water left in basins, exposed piping, pump casings, sensor wells or low points can freeze and damage components. Deposits left on heat-transfer and water-distribution surfaces can harden during the off-season. Stagnant, inadequately treated water can also create corrosion and biological-growth risks.

A rushed shutdown may turn spring startup into an avoidable repair project. A documented cooling tower winterization plan gives the facility team time to clean the system, verify that it drains, inspect mechanical equipment, manage water treatment and identify repairs before freezing conditions arrive.

The correct procedure depends on the type of equipment, piping arrangement, local climate exposure, water-management program and whether any part of the cooling system must remain available. Open cooling towers, closed-circuit fluid coolers and evaporative condensers do not all have the same shutdown requirements. Always follow the equipment manufacturer's instructions, site-specific safety procedures and the facility's water-treatment program.

This checklist provides a practical framework for commercial, institutional, industrial and multi-unit residential facilities across Ontario.
 

Why Cooling Tower Winterization Matters

Cooling towers operate by exposing water to air so heat can be rejected from a condenser-water or process-cooling system. That design also creates several winter risks when equipment becomes idle.
 

Freeze damage

Water expands as it freezes. Even a small trapped volume can crack a valve body, damage a pump casing, split exposed piping or deform a sensor assembly. Visible basins are only part of the risk. Water may remain in equalizer lines, makeup assemblies, strainers, bypasses, low points and poorly pitched piping.
 

Corrosion and deposits

Scale, sediment and biological material that remain in the tower can dry onto surfaces during a long shutdown. Residual moisture and untreated pockets can contribute to corrosion. Cleaning before lay-up gives the spring startup team a better baseline and makes structural or coating damage easier to see.
 

Biological growth and Legionella risk

Cooling towers can aerosolize water during operation. Sediment, biofilm, water age, temperature and disinfectant residual are important factors in controlling Legionella. The U.S. Centers for Disease Control and Prevention cooling tower guidance recommends that startup, idling and shutdown procedures be incorporated into the water-management program.

Ontario also identifies cooling towers as a potential workplace source of Legionella exposure. The province's Legionella prevention guidance emphasizes the employer's responsibility to take reasonable precautions to protect workers from infectious hazards.
 

Spring startup delays

Shutdown is an opportunity to identify worn belts, deteriorated fill, blocked nozzles, leaking valves, failed heaters and control problems. Finding these issues in the fall allows parts and repairs to be planned before cooling demand returns.

For facilities with water-cooled chillers, a tower problem can limit the entire plant. Ambient Mechanical's commercial chiller system services include cooling towers, pumps, piping and related plant equipment.
 

Choose the Correct Winter Operating Mode

Before isolating anything, determine how the cooling system will operate during the winter. There are three broad modes.
 

Seasonal dry shutdown

A dry shutdown is generally used when the tower will not be needed for an extended period. The tower, associated piping and other identified components are drained, cleaned and left in the condition specified by the manufacturer and water-management plan.

ASHRAE's water-treatment guidance for extended shutdowns describes dry lay-up as the normal approach when a system is expected to remain out of service for an extended seasonal period. It stresses draining the complete system, including piping, heat exchangers, filters and dead legs, rather than draining only the visible basin.
 

Short wet standby

A system may be shut down briefly while water remains in place. This is not the same as a seasonal dry shutdown. Treatment, monitoring and scheduled circulation may still be required to control stagnation and biological growth.

The CDC distinguishes short wet standby from extended shutdown and recommends maintaining the water-treatment program and circulating treated water on a defined schedule. The facility's water-management team should establish the specific procedure and control limits.
 

Year-round winter operation

Some facilities require year-round process cooling, data-centre cooling, medical-equipment cooling or waterside economizer operation. These towers need an engineered winter operating sequence rather than a complete shutdown.

The sequence may involve:

• Capacity control and fan-speed management

• Minimum leaving-water temperatures

• Cell staging

• Basin heaters or a remote indoor sump

• Heat tracing and insulation

• Minimum flow through coils or heat exchangers

• Dry-mode operation on suitable closed-circuit equipment

• Low-temperature, vibration and loss-of-flow alarms

• Regular inspection for ice accumulation

ASHRAE's cooling tower guidance notes that winter operation requires appropriate capacity control and frequent visual inspection. Equipment manufacturers should be consulted for the approved sequence and operating limits.

If the existing design cannot reliably protect the equipment, Ambient Mechanical's HVAC retrofit and system design team can assess remote sumps, piping changes, controls, heat tracing and other improvements.
 

Cooling Tower Winterization Checklist

The following checklist should be adapted to the specific tower and facility. Assign responsibilities before work begins and record the completion of each task.
 

1. Review Documents, History and Responsibilities

Begin with the information that defines the system.

• Obtain the current operation and maintenance manual for each tower, fluid cooler or evaporative condenser.

• Review mechanical drawings, piping diagrams and control sequences.

• Check previous shutdown and spring startup records.

• Review service reports, water-treatment logs and unresolved deficiencies.

• Confirm the winter operating mode for every tower cell.

• Identify the facility representative, HVAC contractor and water-treatment provider responsible for each step.

• Confirm any warranty requirements before maintenance or chemical treatment.

The manufacturer's procedure takes priority over a generic checklist. For example, EVAPCO's cooling tower operation and maintenance instructions include seasonal shutdown tasks for the basin, strainers, makeup piping, bearings and long-term motor storage.
 

2. Map Every Component That Can Retain Water

Do not treat the tower basin as the whole system. Walk the complete condenser-water or process-water circuit and identify:

• Tower cells and equalizer lines

• Hot-water and cold-water basins

• Supply and return headers

• Condenser-water pumps and strainers

• Bypass piping

• Makeup, overflow and drain piping

• Water-level control assemblies

• Sensor wells and sample lines

• Side-stream filtration equipment

• Plate heat exchangers and economizer components

• Remote sumps

• Standby equipment and dead legs

• Outdoor hose connections or chemical-feed lines

Mark low points and confirm that the drawings match the field installation. Renovations and repairs may have created new trapped sections that do not appear on the original plans.
 

3. Plan Safe Isolation and Access

Cooling tower work can involve rotating fans, pumps, electrical energy, elevated access, chemicals, wet surfaces and biological exposure. Use the facility's hazard assessment and equipment-specific procedures.

Before inspection or cleaning, control all hazardous energy sources. The Canadian Centre for Occupational Health and Safety lockout guidance explains that push buttons and selector switches are not energy-isolating devices. Isolation must address the actual electrical, mechanical, hydraulic and other stored-energy sources.

The shutdown plan should address:

• Lockout and tagout of fans, pumps and other equipment

• Verification that isolation is effective

• Protection against automatic BAS commands

• Safe access to tower interiors and elevated areas

• Chemical handling and required personal protective equipment

• Respiratory or biological-exposure controls identified by the risk assessment

• Communication with affected operators and occupants

Only trained and authorized personnel should perform work requiring hazardous-energy control.
 

4. Coordinate Cleaning and Water Treatment

Cleaning, disinfection and chemical lay-up should be coordinated with the facility's water-treatment professional. Avoid improvising chemical concentrations or combining products.

The plan should define:

• The required pre-shutdown treatment

• Whether offline cleaning and disinfection are due

• Required contact times and monitoring

• How standby cells and low-flow branches will be included

• The permitted discharge route for treated water

• Final corrosion-control or dry-lay-up steps

• Records and test results that must be retained

Cooling tower water may contain biocides, corrosion inhibitors, scale-control products and concentrated minerals. Do not assume it can be released to a roof drain, storm sewer or the ground. Confirm the applicable municipal sewer bylaw, environmental approvals, product requirements and site procedures before draining.

CDC guidance recommends cleaning and disinfecting cooling towers as directed by the manufacturer during commissioning, startup, idling and shutdown, with offline cleaning and disinfection at least annually. The facility's site-specific water-management program should establish the actual schedule and response procedures.
 

5. Clean the Basin and Water-Distribution Components

Remove leaves, dirt, sludge and other debris from accessible areas. Depending on the equipment and approved procedure, inspect and clean:

• Hot-water and cold-water basins

• Suction strainers

• Spray nozzles and distribution headers

• Fill media

• Drift eliminators

• Equalizer lines

• Side-stream filters

• Accessible heat exchangers

• Remote sumps

Cleaning methods must suit the tower materials and coatings. Aggressive pressure washing, scraping or incompatible chemicals can damage fill, galvanized surfaces, protective coatings and seals.

Record unusual scale, corrosion, sludge or biological material. These findings can indicate a water-treatment, filtration, airflow or operating problem that should be corrected before the next season.
 

6. Inspect Mechanical and Structural Components

Use the off-season inspection to identify work that can be completed before spring.

Inspect, as applicable:

• Fan blades, hubs and shafts

• Belts, sheaves and alignment

• Gear drives and oil condition

• Bearings and lubrication points

• Motors and motor mounts

• Guards and access panels

• Vibration switches

• Louvers, fill supports and drift eliminators

• Basin surfaces, seams and coatings

• Ladders, platforms, railings and access doors

• Fasteners, seals and flexible connectors

Do not automatically lubricate or change oil without checking the manufacturer's requirements. Some bearings and gear drives have specific products, quantities and long-term storage instructions.

Create a deficiency list that identifies priority, parts, responsible party and target completion date. Photographs can make the spring handoff much clearer.
 

7. Drain the System Completely Where Dry Lay-Up Is Required

Open the specified drains and verify that water actually leaves the system. An open valve does not prove that a blocked drain, unpitched pipe or isolated section is empty.

Pay particular attention to:

• Basin corners and sumps

• Pump casings and strainers

• Equalizer lines

• Makeup assemblies

• Exposed valve bodies

• Bypass lines

• Low points in outdoor piping

• Instrument tubing and sensor wells

• Standby cells and isolated branches

Where the design permits, compressed air may help remove water from low points. Use it only when the manufacturer and engineered procedure allow it. Excessive pressure can damage equipment or create a projectile hazard.

Leave drains in the position specified by the manufacturer and clearly document all valves that must be returned to service before startup. Some manufacturers recommend leaving basin drains open during seasonal lay-up to prevent rain or snowmelt accumulation.
 

8. Verify the Remote Sump and Drain-Back Arrangement

A remote sump located inside a heated space can provide effective freeze protection when the outdoor tower and piping drain back correctly. It does not work merely because a tank exists.

Confirm that:

• Piping slopes toward the sump

• Drain-back paths are unobstructed

• Check valves and isolation valves are in their required positions

• The sump has enough working volume

• The indoor space remains heated

• Level controls and alarms function

• The tower basin does not retain water after pump shutdown

Baltimore Aircoil describes a heated indoor remote sump as a preferred basin-freeze-protection approach for suitable systems. Final operation must follow the tower and system design.
 

9. Protect Any Components That Must Remain Wet

If any part of the system retains water, define how each exposed component is protected. Possible measures include heat tracing, insulation, basin heaters, indoor remote sumps, circulation or an engineered antifreeze solution in a compatible closed loop.

Important limitations include:

• A basin heater protects water in the basin around the heater. It does not automatically protect remote piping, pumps, makeup lines or valves.

• Heat tracing must be installed, controlled and maintained for the actual design conditions.

• Insulation slows heat loss but does not create heat.

• Antifreeze is generally associated with compatible closed-circuit portions, not something to add casually to an open condenser-water system.

• Immersion heaters should not be energized in a drained basin unless the equipment is specifically designed and controlled for that condition.

For closed-circuit fluid coolers, coil freeze protection deserves particular attention. ASHRAE notes that exposed piping may require heat tracing and insulation and that water-filled coils may need emergency draining or supplemental heat where antifreeze is not used.
 

10. Inspect Freeze-Protection Controls and Electrical Systems

Test protection devices before cold weather rather than waiting for the first freeze.

Depending on the design, verify:

• Basin heater operation and low-water protection

• Heat-trace circuits and controllers

• Outdoor-air temperature sensors

• Low-temperature alarms

• Pump proof and flow switches

• Vibration switches

• Remote sump level controls

• Freeze-stat or coil-protection sequences

• BAS alarm routing and remote notifications

• Standby power assumptions where applicable

Ambient Mechanical's building automation and HVAC controls services can help verify alarm logic, trends and winter operating sequences. A heater or heat-trace cable that is energized but not producing the required heat may not generate an obvious BAS fault, so physical verification remains important.
 

11. Isolate Makeup Water and Prevent Accidental Refilling

A leaking makeup valve can slowly refill a drained basin or exposed line. Confirm positive shutoff and monitor sections where unintended water entry could cause freeze damage.

Also consider:

• Rain and snow entering open equipment

• Leaking bypass or isolation valves

• Water migrating through equalizer lines

• Condensate or other connected systems

• Automatic BAS sequences that could restart a pump

• Temporary hoses or drains left connected

Label out-of-service equipment and identify the intended valve positions on the shutdown record. Where consequences are significant, schedule periodic winter inspections.
 

12. Preserve Motors, Bearings and Drives for the Idle Period

Long-term storage requirements vary. The manufacturer may require motor-space heaters, periodic shaft rotation, gear-reducer operation or special lubrication steps.

Do not rotate equipment until hazardous energy has been isolated and the procedure confirms it is safe. Record each required off-season task in the preventive-maintenance schedule so it is not forgotten after the initial shutdown.

This is a natural fit within a broader commercial HVAC preventive-maintenance program, particularly for facilities with several towers or multiple seasonal assets.
 

13. Test the Final Shutdown Condition

After the work is complete, perform a documented walk-through with the facility representative, HVAC contractor and water-treatment provider as appropriate.

Verify that:

• Required sections are clean and dry

• Drains and valves are in documented positions

• Makeup water cannot refill drained equipment

• Required heaters and heat tracing remain active

• Equipment that must stay off is safely isolated

• Protective controls and alarms are operational

• Open deficiencies are assigned and scheduled

• The spring startup procedure is available

A second inspection after the first freezing weather can reveal trapped water, failed heat tracing, unintended refilling or alarm problems that were not visible on shutdown day.
 

14. Complete the Shutdown Record

The shutdown record should allow another qualified operator to understand exactly what was done and what remains outstanding.

Include:

• Shutdown date and weather conditions

• Tower and cell identification

• Operating mode selected

• Cleaning and treatment completed

• Water-quality readings and service reports

• Drain and valve positions

• Lockout status

• Heater and heat-trace test results

• Alarm and notification test results

• Mechanical and structural deficiencies

• Parts ordered and work scheduled

• Photographs of basin, drains and isolated valves

• Required off-season inspections

• Spring recommissioning steps

• Names of the people who completed and verified the work

Good records reduce the chance that a temporary override, closed valve or disabled alarm becomes a startup problem months later.
 

Common Cooling Tower Winterization Mistakes

Draining only the basin

Pumps, equalizer lines, makeup piping, bypasses and low points may still contain water. Trace the full system.
 

Assuming the basin heater protects everything

It does not protect remote piping or every connected component. Each water-filled section needs its own freeze-protection strategy.
 

Shutting down treatment before addressing stagnant water

Wet standby requires continued control. Extended shutdown requires an approved dry lay-up or other water-management procedure.
 

Sending treated water to the wrong drain

Confirm the approved discharge route before draining. Cooling water chemicals and concentrated solids may be restricted by municipal or environmental requirements.
 

Relying only on the BAS

A BAS can indicate commands and alarms, but it may not reveal a blocked drain, failed heater element, damaged heat trace or water trapped in a low point. Physical inspection is essential.
 

Leaving repairs until spring

Fall findings should become scheduled work orders. Waiting until cooling demand returns can create rushed repairs and longer downtime.
 

Planning for Spring Startup During the Fall Shutdown

Winterization and spring startup should be treated as two parts of the same maintenance cycle. During shutdown, document what the startup team will need to reverse, inspect and test.

The spring plan should include:

• Removal of lockouts under the approved procedure

• Confirmation that all drains and access panels are restored

• Valve-position verification

• Tower and basin inspection

• Water-treatment startup and cleaning or disinfection requirements

• Makeup-water and level-control testing

• Pump rotation and flow verification

• Fan, drive and vibration checks

• Alarm and BAS sequence testing

• Inspection for winter damage

• Controlled commissioning before peak load

The CDC warns that stagnant water can lose disinfectant and increase Legionella growth risk. Restarting a tower is therefore more than refilling and pressing start. Follow the water-management program and manufacturer procedure before aerosol-producing operation resumes.
 

How Ambient Mechanical Can Help

Cooling tower winterization involves mechanical equipment, water systems, electrical protection, controls and safe work procedures. Coordinating those areas before freezing weather can prevent small omissions from becoming expensive failures.

Ambient Mechanical services cooling towers, water-cooled chillers, pumps, condenser-water piping and building controls across commercial, institutional and industrial facilities. Our team can help with:

• Seasonal cooling tower shutdowns and inspections

• Chiller and condenser-water system maintenance

• Pump, valve and piping repairs

• Basin heater and freeze-protection checks

• BAS alarm and sequence verification

• Off-season equipment repairs

• Cooling tower, piping and controls retrofits

• Spring startup and recommissioning

Facility managers can also review Ambient's cooling tower project experience and broader commercial HVAC services.

If your facility needs a seasonal shutdown plan or has unresolved freeze-protection concerns, contact Ambient Mechanical before sustained freezing conditions arrive.

Frequently Asked Questions About Cooling Tower Winterization

Should every cooling tower be drained for winter?

No. The correct approach depends on whether the tower must operate, its design, piping and sump arrangement, manufacturer instructions and the facility's freeze-protection plan. A seasonal tower may use dry lay-up, while a year-round process tower requires an engineered winter operating sequence.
 

Does a basin heater winterize the entire system?

No. A correctly selected and operating heater protects the intended basin water. Exposed piping, pumps, valves, makeup assemblies and other components may require drain-back, heat tracing, insulation, circulation or separate protection.
 

What is the difference between wet standby and dry shutdown?

During wet standby, water remains in the system and treatment, monitoring and periodic circulation may still be required. During dry shutdown, the identified system components are drained and placed into a dry, offline condition under the approved procedure.
 

Should the tower be cleaned before or after draining?

The sequence should follow the water-management plan and manufacturer instructions. Cleaning and any required disinfection generally need to be coordinated while the system can safely circulate and dispose of treated water. The basin and accessible components should be left clean for the idle period.
 

Can cooling tower water be drained into a storm sewer?

Do not assume so. The water may contain treatment chemicals and concentrated solids. Confirm the permitted discharge route under the facility's approvals, local sewer bylaw, environmental requirements and product instructions.
 

How often should the tower be inspected during winter?

Frequency depends on the design and risk. Facilities should schedule checks for unintended refilling, debris, ice, heater or heat-trace failure, alarm condition and storm damage. Year-round operating towers require more frequent observation, especially during extreme cold.
 

When should winter repairs be completed?

Identify deficiencies during the fall inspection and schedule work early enough to test the system before cooling demand returns. Long-lead motors, drives, fill and controls components can make late spring repairs difficult.
 

Does cooling tower winterization eliminate Legionella risk?

No single shutdown task eliminates risk. Legionella control depends on a site-specific water-management program that addresses cleaning, disinfection, treatment, stagnation, monitoring, startup and corrective actions.
 

Protect the Cooling Plant Before Freezing Weather

Effective cooling tower winterization is a controlled change in operating state, not merely a shutdown command. The facility must choose the correct winter mode, manage water quality, isolate hazardous energy, remove water from vulnerable components, test the protection that remains active and document the final condition.

When the work is completed carefully, the benefits extend beyond freeze protection. The facility enters spring with cleaner equipment, known deficiencies, reliable records and a clearer startup plan.

For support with cooling tower maintenance, seasonal shutdowns, freeze-protection controls or condenser-water system repairs, request an assessment from Ambient Mechanical.