Pool Heater Winterizing: The Complete Shutdown Checklist (2026)

Quick answer

Winterizing a pool heater means fully draining the heat exchanger, header, and connected plumbing before the first hard freeze — not just turning the unit off. Per Raypak’s own winterizing documentation, the sequence is gas and power off first, then open the drain plugs, then blow the remaining water out with an air compressor or shop vac, since a heat exchanger with trapped water left inside it is the single most common cause of a cracked-exchanger repair once temperatures drop. One detail trips up a lot of owners: automotive antifreeze should never go anywhere near a pool heater — pool-industry guidance confirms it reacts dangerously with pool chlorine — and draining-and-blowing-out properly makes pool-specific antifreeze unnecessary in the heater itself anyway.

Why skipping this is the costliest mistake in this guide

Trapped water left inside a heat exchanger expands by roughly 9% as it freezes, and metal doesn’t flex to accommodate that — it cracks. Our heat exchanger guide and repair cost guide both cover that part as one of the more expensive single-part replacements this site tracks, and a freeze crack is rarely something a manufacturer’s warranty treats as a covered defect, since it’s framed as an owner-maintenance failure rather than a part failure. The fix costs far more than the ten minutes winterizing actually takes.

Gas heaters: shut off, isolate, drain, blow out

Based on Raypak’s own published winterizing steps, which generalize across gas heater brands with only minor variation:

1. Shut off gas at both the heater’s own valve and the supply line valve.
2. Cut power at the breaker — the heater’s circuit and the pump’s circuit separately if they’re on different breakers. If you run pool automation (Pentair EasyTouch, Jandy AquaLink), position any valve actuators so they won’t drain the pool itself before killing power to the automation system.
3. Close isolation valves between the heater and the rest of the equipment pad so pool water can’t just refill the heater after you drain it.
4. Open the drain plugs on the inlet-outlet header, typically 2-4 threaded plastic or metal plugs. On newer Raypak AVIA/AVIA HD units, remove the ProTek Shield anode module first — it’s bolted into the header and blocks a full drain if left in place.
5. Disconnect the unions and tilt the heater toward the plumbing if you can, so gravity pulls out what the drain plugs miss.
6. Blow out the lines with an air compressor, shop vac, or leaf blower until no more water comes out, then replace the drain plugs.

Heaters built before 1998 may still have an older copper pressure-switch tube that needs disconnecting and draining separately — anything newer than that doesn’t carry this step, per Raypak’s own documentation.

Heat pumps: a similar drain, with one extra flush step

A heat pump follows the same gas-off-doesn’t-apply version of the sequence above — cut power, close isolation valves, disconnect the inlet/outlet unions or open the drain plug, let it fully drain, then blow the lines clear. AquaCal’s own cold-weather guidance adds one heat-pump-specific step the gas-heater process doesn’t need: flushing the heat exchanger with a garden hose before the air blow-out, then clearing the water circuit with roughly 50 psi of compressed air. Reconnect the unions loosely afterward (don’t fully tighten) so the opening keeps debris and insects out of the heat pump over the off-season without trapping fresh water back inside.

Solar panels: drain or self-drain, don’t just leave them full

Solar heating panels need the gentlest version of this: either drain them completely or leave them tilted into a position where they self-drain by gravity, since standing water in a rooftop panel over winter is the same freeze-crack risk as a gas or heat-pump exchanger, just in thinner plumbing. Our solar pool heater guide covers panel sizing and types if you’re deciding what to install before worrying about how to close it down for the season.

The antifreeze question, answered straight

Pool-industry winterizing guidance is consistent on one point: automotive antifreeze should never be used on any pool equipment, including the heater, because it reacts dangerously with the chlorine already in a pool system. Pool-specific propylene-glycol antifreeze exists and is sold for exactly this use, but the same guidance calls it likely unnecessary for the heater itself once you’ve properly drained it and blown the lines clear with air — it’s really a backup for plumbing runs (like underground pipe sections) that are hard to fully clear, not a substitute for draining the heater. If you see antifreeze recommended for a pool heater specifically, confirm it’s the pool-rated kind before buying any.

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When to actually do this

There’s no fixed calendar date — watch your extended forecast instead. A hard freeze generally means a sustained overnight low at or below roughly 32°F, not a brief dip that recovers by morning. That’s a slower-moving seasonal threshold, different from the 35-38°F trigger covered in our freeze protection guide, which reacts automatically to a single cold night while the pool is still open and running. Once overnight lows start regularly flirting with freezing, winterize before the first night your forecast shows staying at or below it — don’t wait for the first freeze to actually happen before starting.

The bottom line

Winterizing is cheap insurance against the single most expensive repair this site covers: gas and power off, drain plugs open, lines blown clear with air, and — on newer Raypak units — the ProTek Shield anode pulled before the header can fully drain. Skip the automotive antifreeze entirely, and don’t assume pool-rated antifreeze replaces an actual drain-and-blow-out; it’s a backup for hard-to-reach plumbing, not the heater itself. Do the sequence once before the first hard freeze and the heater’s internal plumbing comes through winter intact, ready for spring startup instead of a cracked-exchanger repair bill.

Sources: Raypak — How to Winterize Your Pool Heater, PoolResearch — How to Winterize a Pool Heater, AquaCal — cold-weather and winterizing guidance, Leslie’s Pool — Pre-Season Checklist: Pool Heater and Heat Pump Maintenance