As temperatures drop, commercial swimming pools undergo major shifts in water balance, energy demands, and equipment stress. Even indoor pools feel the impact of colder weather — from changes in chemical consumption to fluctuations in air handling performance for indoor pools.
This paper outlines how winter conditions affect water chemistry, LSI balance, chemical usage, heaters, HVAC systems, and overall facility operations, along with actionable ways to protect your investment throughout the season.
- Water Chemistry & Chemical Usage in Colder Weather
Chlorine Demand Decreases — But Monitoring Must Increase
Cold water slows down chlorine’s oxidation rate, and reduced bather loads lower demand even further. On the surface, it seems like winter reduces chemical use — but drifting setpoints, poor circulation, and staff holidays can cause rapid imbalance if testing frequency drops.
What to emphasize:
- ORP readings generally stabilize in cooler water, but are more sensitive to disturbances.
- Overfeeding is common when operators forget to adjust chemical pumps for reduced demand.
- Lower water temps slow down chemical reactions — meaning corrections take longer.
pH Behavior in Colder Weather
- Colder temperatures increase CO₂ solubility, causing pH to naturally drop over time.
- Acid feed systems often need reduced output in winter.
- Aeration (via HVAC or agitation) will have a weaker pH-rising effect in cold water.
Alkalinity & Calcium Hardness Stability
- Alkalinity and CH are more stable in cold water, but precipitation risks increase (see LSI section).
- If operators raise CH in winter to “fix” LSI, it can cause springtime scaling once water warms.
CYA (outdoors only) Stays More Stable
- No sunlight = no UV degradation.
- Operators should monitor CYA carefully if using stabilized chlorine indoors, as levels tend to rise unnoticed during winter.
- Langelier Saturation Index (LSI) in Winter
LSI is heavily influenced by temperature — cold water is aggressive, warm water is scale-forming.
Why winter is the highest-risk season for corrosive water
- As water temperature decreases, LSI drops significantly.
- Corrosive water pulls calcium from plaster, dissolves metals, and shortens equipment life.
Common winter LSI problems:
- Low LSI from cold temps + reduced CH + falling pH.
- Etching, grout degradation, and surface roughness.
- Copper leaching from heaters and heat exchangers.
Ways to protect LSI during cold months:
- Slightly raise pH and alkalinity targets.
- (Example: pH target 7.6–7.8 instead of 7.4–7.6)
- Maintain CH toward the upper recommended range.
- Ensure heaters maintain stable temps (rapid temperature swings damage LSI balance).
- Avoid raising CH excessively — temperature will rise again in spring and cause scale.
- Increased Use of Heaters: What Operators Must Know
Colder seasons significantly increase heater demand as pools try to maintain consistent water temperatures.
Impacts of colder weather on heater usage:
- Higher natural gas or electrical consumption.
- Longer run times, leading to faster wear.
- Greater risk of condensation inside heat exchangers (a major contributor to corrosion).
- More strain on older or dirty heat exchangers.
Best practices for winter heater protection:
- Keep strainers, filters, and heater bypasses clean to maintain proper flow rates.
- Prevent low-flow conditions — low flow + cold temps destroys heat exchangers.
- Maintain chemical balance to avoid heater corrosion (low LSI is a top culprit).
- Keep equipment rooms above freezing with space heaters or insulation.
- Indoor HVAC Systems & Winter Air Balance
Indoor commercial pools rely heavily on HVAC systems that manage temperature, humidity, and air distribution — and winter challenges them more than any other season.
What winter does to indoor pool HVAC:
- Outdoor air is dry → HVAC must work harder to maintain humidity.
- Cold, dry air increases evaporation when bather loads rise.
- Improper air balance leads to condensation on windows, ceilings, and ductwork.
- Increased air turnover can pull more chloramine-rich air across the pool surface.
Signs your HVAC system is struggling:
- Persistent condensation, especially during early mornings or cold snaps.
- Strong chloramine odors in the facility.
- Cold “draft” zones around the pool deck.
- Equipment room temperatures below what controllers and pumps require.
Winter HVAC best practices:
- Ensure the system is maintaining the recommended 2°F rule:
Air temperature 2°F warmer than water temperature
- Keep mechanical spaces warm enough for controllers and chemical pumps (≥72°F).
- Inspect Seresco, CaptiveAire, and other dehumidifiers for clogged filters or frozen coils.
- Modify fresh-air settings as needed — some systems require seasonal adjustments.
- Protecting Pool Equipment in Cold Weather if Shutting Down Pools.
If in a temperature-controlled room (preferred for commercial pools):
- Keep controllers energized if possible; if not, unplug and isolate them.
- Ensure probes remain wet at all times — water in probe housings evaporates faster in winter.
- Add water periodically to avoid probe tip damage.
- Remove or protect all tubing that might freeze or crack.
If not in a temperature-controlled room:
- Always remove controllers from walls and store indoors.
- Remove supply/return lines and tubing.
- Keep probes in probe housings with water OR store in a salt-water solution.
- Always keep probes wet — dry probes are permanently damaged.
- Clean and dry filter baskets, flow cells, and sample lines.
Stenner Pumps
- Remove pump tubes; clean, rinse, dry, and store indoors.
- Remove suction and discharge lines if exposed to freezing conditions.
- Clean and store injectors.
- Store entire pump and parts in a climate-controlled area.
Cal Hypo Feeders (Pulsar, etc.)
- Shut off water supply at the venturi.
- Clean venturi, check valves, tubing, and hopper components.
- Prevent water from sitting in booster pumps or venturi — standing water freezes and splits housings.
- Store hopper, tubing, and components indoors.
- Preventing Winter Pool Problems when closing pool but water stays in pool
Keep the Pool Running
- Ensure circulation pumps maintain continuous flow.
- Prevent ice formation in gutters, surge tanks, or autofill lines.
- Lower chemical setpoints slightly for lower bather loads — but do not stop testing.
Pool Water Still Requires Regular Testing
Winter does not remove your regulatory requirement for:
- Free chlorine
- Combined chlorine
- pH
- Alkalinity
- Calcium hardness
- Temperature
- ORP/pH controller functionality (if installed)
Operational risks in cold weather:
- Pump seal failures from cold brittle rubber.
- Cracked PVC when temperatures drop below ~32°F.
- Frozen backwash lines or vacuum lines.
- Scaling in heaters from poor LSI management.
- Winter Storage Tips for Commercial Pool Chemicals
Safe winter chemical storage:
- Store in original containers in dry, ventilated areas.
- Never store oxidizers and acids together (risk of chlorine gas).
- Avoid stacking containers — winter humidity can weaken packaging.
- Don’t store liquids above powders or solids.
- Keep away from flammables (paint, fertilizers, gasoline, grease).
- MOST chemicals tolerate cold, but potency decreases if they freeze, especially:
- Sodium hypochlorite (liquid chlorine)
- CO₂ regulators
- pH adjusters
- Enzymes
Cold weather doesn’t have to mean costly repairs, damaged equipment, or inconsistent water quality. When operators stay ahead of LSI changes, adjust chemical output appropriately, safeguard controllers and feeders, and maintain reliable temperature and air control, winter operations remain smooth and predictable. By preparing your pool now, you safeguard your guests, your team, and your investment well into the spring.
Here is our knowledge base links that we have around winterizing your equipment:
https://helpcenter.vivoaquatics.com/knowledge/how-to-winterize-your-controller
https://helpcenter.vivoaquatics.com/knowledge/how-to-winterize-cal-hypo-feeder
https://helpcenter.vivoaquatics.com/knowledge/how-to-store-a-ppm-sensor
https://helpcenter.vivoaquatics.com/knowledge/how-to-winterize-your-stenner-pump