How do I protect a pool heater from freezing in winter?

Protect a pool heater from freezing by one of two routes: have it drained and shut down by a licensed pro for the off-season, or keep the pump circulating water through it for the whole cold spell. Never rely on the heater itself to keep the pool from freezing. Water left standing in the heat exchanger expands as it freezes and can crack it, and Raypak does not warrant its heater against freeze-ups.

Why the heater is the weak point

A heater holds water in a coil or header inside a cabinet, often with no way to see it. When the pump stops in freezing weather, that water sits still and freezes. The damage can show up in spring as a leak at the headers or exchanger. Raypak puts the warranty position bluntly: the heater is not warranted against freeze-ups.^[1]

For the same reason, the pipes and equipment around the heater need protection. Why pool pipes freeze over winter explains what happens to the pump, filter and lines.

Option one: run the pump through short cold spells

For a brief cold snap, circulation is the protection. Raypak says that heater operation can continue during short-term cold spells, and that when temperatures are between 0°F (-18°C) and 32°F (0°C), flow (continuous pump operation) must be maintained.^[1] Moving water is harder to freeze than still water.

Some limits apply:

• Do not use the heater as the freeze protection. Raypak cautions against using the heater to maintain water temperatures just above freezing or for freeze protection, and says continuous pump operation is a must and additional protection may be required.^[1]
• The pump must not stop. A tripped breaker, a time clock that cycles the pump off overnight, or a power cut leaves the heater full of still water exactly when it is coldest. Ask your pool service to set the pump to run continuously for the duration of the cold spell, and have someone check on it.
• Cold pool water is hard on a gas heater. Raypak says prolonged operation with water temperatures below 50°F (10°C) is not recommended, and that operating the heater for prolonged periods with pool water below 50°F can seriously damage the heater and is not covered by the warranty.^[1] If you do start the heater in cold water, the manual says to operate it continuously until higher temperatures are reached.^[1]
• A digital Raypak locks out in very cold water. It displays "Low Temp Lockout" when the water temperature is below 36°F (2°C).^[1]

If a hard freeze is forecast and the heater has not been winterized, the pump needs to run around the clock until it passes, and a pool business should look at the heater in spring.

Option two: shut the heater down and drain it for winter

For a heater you will not use until spring, Raypak says heaters installed outdoors in freezing climate areas may be shut down for the winter.^[1] Its winterizing procedure begins with turning off the gas valve, the manual gas valve and the electrical supply to the heater, and continues with opening the drain plug on the return header so the water runs out.^[1]

That procedure involves isolating the gas supply and removing cabinet panels, which is the work of a licensed professional here. A pool company that winterizes the pool will normally do the heater at the same visit, along with draining or blowing out the pump, filter and lines. Ask for these in the written quote:

• the heater drained and shut off at the gas and electrical supply, not just switched off at the control
• the heater drain plug or drain valve left open or removed over winter, as the heater maker directs
• a note of anything they could not drain
• the date they will come back to open the system in spring

What winterizing a pool costs in Virginia covers the price range, and whether to winterize the pool yourself or hire a pool company helps you decide how much of the job to hand over. Heater manuals differ by make and model, so the business should follow the manual for your heater rather than a general routine.

In spring

Do not simply switch the heater back on. Ask the pool company to close the drain plug and check the system for leaks while the pump circulates. If the heater went through a freeze unprotected, the damage can be hidden until water pressure reaches the exchanger. If it leaks, read whether to fix a pool heater or buy a new one, and what a technician checks when a pool heater will not fire for the start-up checks.

When to call a licensed pro

Draining and shutting down a gas heater means closing off the gas, and Virginia regulates gas work by licence. No individual may engage in work as a liquefied petroleum gas fitter or natural gas fitter provider unless licensed under the same article of the Code.^[3] The definition of a liquefied petroleum gas fitter excludes hot water heaters, boilers and central heating systems, which require a heating, ventilation and air conditioning or plumbing certification.^[2] Ask the business which DPOR licence it holds for your heater, and check the licence before you pay a deposit. DPOR advises getting at least three written bids or estimates using identical plans and specifications so you can compare prices and contractors.^[4]

Call right away if you smell gas, see ice on or water leaking from the heater after a freeze, or find the heater cabinet wet inside. Browse more pool and spa equipment answers or find pool and spa businesses.

To book winterizing or a freeze-damage check, describe the pool heater job and licensed local businesses reply.