How to Winterize Your Solar Pool Heating System (And Operate It Safely During Freezing Conditions)

If you own a solar pool heating system, protecting it during freezing temperatures is critical to maintaining performance and avoiding costly repairs. While Florida winters are generally mild, cold snaps and overnight freezes do happen, especially in North and Central Florida.

At Mirasol Solar, we design solar pool heating systems to handle seasonal changes — but knowing how to properly winterize or operate your system during freezing conditions can extend its lifespan and keep your investment protected.

This guide explains exactly what to do, whether you’re shutting your pool down for winter or running it year-round.

Do Solar Pool Heaters Need to Be Winterized?

In most cases, no special winterization is required — as long as your solar collectors and piping are installed correctly.

A properly designed system:

• Drains completely each time the pump shuts off

• Uses gravity drainage to prevent standing water

• Includes appropriate valves and controls

However, during unusual or severe freezing conditions, additional precautions should be taken to protect:

• Solar collectors

• End caps

• Pipe fittings

• Valves and controls

Winterizing Solar Pool Heating Systems (When a Freeze Is Imminent)

If freezing weather is expected and your pool will be shut down, follow one of the two procedures below.

Option 1: Drain the System Completely (Most Common)

This method protects the system by removing water entirely from the collectors and piping.

Steps:

1. Turn off the pool’s circulating system and allow the solar collectors and piping to fully drain.

2. Isolate the collectors using:

   • A gate or ball valve in the collector feed line

   • A check valve in the collector return line

3. Switch the solar control to the bypass position.

4. Turn the pool filtration system back on.

5. Once freezing conditions have passed:

   • Open isolation valves

   • Switch the solar control back to AUTO

✅ Best for pools that will not be used during winter.

Option 2: Circulate Water Through the Collectors

In certain system configurations, keeping water moving may be safer than draining.

Use this option only if:

• Collectors are below pool water level

• Collectors lie flat on a roof or patio cover

• Piping does not allow gravity drainage

Steps:

1. Switch the solar control to COLL so water circulates continuously through the collectors.

2. Regularly check the system to ensure all piping and collectors are fully drained when circulation stops.

⚠️ This method requires close monitoring and is not ideal for prolonged freezes.

Operating Your Solar Pool Heater During Freezing Conditions

Some pool owners operate their pools year-round, even when light freezes occur. If your system includes an isolation valve in the collector feed line and a check valve in the return line, follow these steps:

Safe Operation During Freezing Weather

1. Turn off the circulating system and allow at least 30 minutes for collectors and piping to drain.

   • If gravity drainage isn’t possible, the system must be manually drained.

2. Close the isolation valve in the collector feed line.

3. Switch the solar control panel to POOL or OFF.

4. Turn the filtration system back on to protect it from freezing.

5. Once freezing conditions have passed:

   • Open the isolation valve

   • Return the control panel to AUTO

What If Your System Cannot Be Drained?

If your system:

• Does not have isolation valves

• Cannot be manually drained

It is recommended to continuously circulate pool water through the solar heating system whenever outdoor temperatures reach 42°F or lower.

⚠️ This is not recommended when temperatures are expected to drop significantly below freezing, as prolonged exposure may still cause damage.

Common Winter Solar Pool Heating Mistakes to Avoid

• ❌ Leaving water trapped in collectors during a freeze

• ❌ Switching controls without confirming drainage

• ❌ Assuming Florida winters can’t cause freeze damage

• ❌ Ignoring valve configuration and drainage design

Why Proper Installation Matters

The easiest way to avoid winter issues is proper system design and installation from the start. Mirasol Solar systems are engineered to:

• Drain fully and reliably

• Handle Florida’s variable winter conditions

• Protect collectors, piping, and controls

If you’re unsure how your system is configured, a professional inspection can prevent expensive damage.

Need Help With Your Solar Pool Heating System?

If you’re not sure whether your solar pool heater is winter-ready — or if you’d like a system designed to handle freezing conditions automatically — our team can help.

Contact Mirasol Solar for:

• Solar pool heating inspections

• System upgrades and controls

• New solar pool heating installations

• Long-term maintenance support

👉 Solar energy at its best — all year long.