Winterizing a NY Pool: Complete Checklist

Closing a pool in Westchester is not the same as closing a pool in Virginia. New York winters bring deep freeze-thaw cycles, multiple ice events, and long stretches of sub-20°F temperatures. Water in pipes expands when it freezes — and PVC, copper, and the gel-coat surface of a heater all crack when that happens.

Almost every "why does my pool need a $4,000 repair?" call we get in April started with a closing that skipped one step in October. Here is the complete checklist we use.

When to close

Close once daytime highs sit consistently below 65°F — usually mid-to-late October in Westchester. Closing too early (while water is still warm) gives algae a head start under the cover. Closing too late risks an early freeze before the lines are blown out.

Step 1 — Balance the water (one week before closing)

Balanced water doesn't rust your equipment or etch your plaster over the winter. Aim for:

• pH: 7.4–7.6
• Total alkalinity: 80–120 ppm
• Calcium hardness: 175–250 ppm
• Free chlorine: 1–3 ppm
• Cyanuric acid: 30–50 ppm

If you only fix one thing, fix pH. Water that sits at 6.8 for six months will pit metal and eat plaster.

Step 2 — Deep clean

• Brush every wall, step, and the tile line.
• Vacuum the entire floor — not just the visible debris.
• Empty skimmer and pump baskets.
• Backwash sand filters; clean cartridge filters with a degreaser and let them dry.

Step 3 — Shock the pool

Use a non-chlorine shock or a strong liquid chlorine dose 24–48 hours before closing. Let the pump run overnight to fully circulate it. Then test again — free chlorine should be 1–3 ppm when you close, not higher. Closing a pool with 10 ppm chlorine bleaches the cover.

Step 4 — Lower the water level

Drain the pool to roughly 4–6 inches below the skimmer opening (for a mesh cover) or 12 inches below for a solid cover. Lowering the water keeps it out of the skimmer throat, where freezing causes the most expensive cracks.

Never drain a pool completely. An empty in-ground pool can float out of the ground when groundwater rises in spring. We have seen it happen. It is catastrophic.

Step 5 — Blow out the plumbing lines

This is the step that separates DIY closings from professional ones. Every line must be cleared of water and plugged:

1. Connect a high-output blower (a shop vac is not enough for a long run).
2. Blow each skimmer line until bubbles come out of the return — about 30–60 seconds per line.
3. Insert a Gizmo (expandable plug with a spring inside) into each skimmer.
4. Blow the return lines, then plug each return.
5. Blow the main drain line and seal it at the equipment pad with a valve closed.
6. If you have a spillover spa, blow those lines too — they're often forgotten.

Any water left in a horizontal run of pipe will freeze, expand, and crack the PVC. Repair means digging up the deck. Do not skip this step or hand it to someone who isn't sure.

Step 6 — Drain the equipment

• Open the pump drain plug and remove the basket lid.
• Open the filter drain plug. For sand filters, set the multiport valve to "Winterize."
• Drain the heater completely — remove the pressure switch and any drain plugs the manufacturer specifies. A heater is a $2,500+ component; it deserves attention.
• Drain the chlorinator and remove any remaining tablets.
• Store all drain plugs in the pump basket so you can find them in spring.

Step 7 — Add winterizing chemicals

Add a winter algaecide and a winter pool floater (slow-release chlorine and stain inhibitor). Pour them in front of a return jet just before you cover so they distribute.

Step 8 — Cover

Use a mesh safety cover for in-ground pools — it sheds leaves and rain while keeping debris out. Make sure every anchor is engaged and every strap is tight. A loose cover is a hazard and lets debris in.

For solid covers, you'll need a cover pump that automatically removes accumulated rainwater. Standing water on a solid cover becomes a frozen, 1,000-pound disc by January.

Step 9 — Check on it through winter

Once a month, walk out and look. Is the cover still tight? Is there standing water? Are the straps still attached? Five minutes a month prevents 90% of mid-winter problems.

What we see when this is done wrong

• Cracked skimmer throats from water left in the line.
• Burst returns inside the pool wall — a four-figure dig-up repair.
• Heater heat exchangers split open. Always a full replacement.
• Plaster etching from unbalanced water sitting all winter.
• Cover failure due to standing water — algae bloom comes free with that.

Closing is the highest-leverage day of the year

A professional closing in Westchester costs $400–$700 depending on pool size and equipment. The repair bill for a bad closing is routinely $2,000–$5,000. If there is one service to hire out, this is the one.

Clear Pools & Hot Tubs closes hundreds of pools across Westchester every fall. We're booked weeks in advance — if you're closing this season, get on the schedule early.