Winterizing Your In‑Ground Pool: A Step‑by‑Step Guide

By Nortech Services

1. Why Winterizing Is Essential

In frost‑prone regions, water expands as it freezes, exerting up to 5,000 psi of pressure on pool walls, plumbing, and equipment. If left unchecked, this can cause:

Cracked or burst pool shells (concrete, gunite, vinyl).
Burst pipes, pump housings, and heater manifolds.
Damaged skimmers, returns, and automatic cleaners.
Expensive repairs that can run into the thousands.

A proper winterization routine removes water from vulnerable components, adds antifreeze where needed, and protects the surface with a quality cover. Follow this detailed, season‑by‑season checklist to keep your pool safe through the cold months.

2. Tools & Materials You’ll Need

Item	Why It’s Needed
Sub‑mersible pump (2‑gallon or larger)	To remove water from the plumbing lines and the pool itself.
Wet‑dry vacuum (shop‑vac)	To suck out water from the skimmer, pump, and filter housings.
PVC pipe cutter or hacksaw	For trimming any excess pipe if needed (rare).
Pipe wrench & adjustable pliers	To disconnect and tighten fittings.
Silicone or rubber pipe caps	To seal open pipe ends after draining.
Pool antifreeze (propylene glycol‑based, non‑toxic)	Prevents any remaining water in the lines from freezing.
Cover pump (optional but highly recommended)	Keeps the cover taut, preventing water ponding and ice formation.
Winter pool cover (solid or reinforced mesh)	Provides a barrier against debris, UV, and temperature fluctuations.
Cover straps or buckles	Secure the cover against wind uplift.
Chemicals – pH adjuster, algaecide, chlorine tablets	Stabilize water chemistry before shutdown.
Safety gear – gloves, goggles, waterproof boots	Protect yourself from chemicals and sharp edges.
Thermometer	Verify water temperature before adding antifreeze.

3. Step‑by‑Step Winterization Process

Step 1 – Balance the Water Chemistry

Test the water (pH, alkalinity, calcium hardness).
Adjust pH to 7.2‑7.6 and alkalinity to 80‑120 ppm.
**Raise the chlorine to 1‑3 ppm (or use a chlorine tablet).
**Add a stabilizer (cyanuric acid) to 30‑50 ppm if you have a chlorine system.
Shock the pool with a non‑chlorine shock (potassium monopersulfate) to eliminate organics.

Why? Proper chemistry reduces the chance of algae growth over winter and prevents corrosion of metal components.

Step 2 – Lower the Water Level

Turn off the pump and filter.
Use a sub‑mersible pump to drain the water to below the skimmer (about 4‑6 in. below the skimmer opening).
Leave about 4‑6 in. of water in the main basin to cushion the shell and keep the liner supported.

Tip: If you have a vinyl liner, keep a few inches of water to prevent the liner from drying out and shrinking.

Step 3 – Drain the Plumbing

Open all return jet valves and spillway/overflow to allow water to flow out.
Remove the pump lid and unscrew the pump union (the large nut connecting the pump to the suction line).
Place a bucket under the union, then open the union to let water drain from the pump housing.
Use a wet‑dry vacuum to suck out any remaining water from the pump, filter, and heater.
Blow out the lines (optional) with compressed air (≈ 30 psi) to ensure all water is expelled.

Step 4 – Add Antifreeze

Check that all water is removed (no standing water in the pump, filter, or heater).
Pour pool‑grade antifreeze into the skimmer and return lines until you see it reach the end of each line (approximately 1‑2 qt. per line, depending on length).
Run the pump for a few seconds (if the pump is still operable) to circulate the antifreeze through the system, ensuring it reaches the farthest points.

Important: Use propylene glycol‑based antifreeze (non‑toxic, approved for pools). Never use automotive ethylene glycol—it’s poisonous to humans and wildlife.

Step 5 – Secure the Equipment

Cap all open pipe ends with silicone or rubber pipe caps.
Tighten all unions and valve stems to prevent water ingress.
Cover the pump and heater with a plastic sheet or tarpaulin to keep debris out.

Step 6 – Install the Winter Cover

Lay the cover flat over the pool, ensuring it’s centered.
Attach the cover pump (if you have one) to remove any water that collects on top of the cover. This prevents ponding and ice formation that can lift the cover.
Secure the cover with straps, buckles, or a cover reel system. Tighten enough to prevent wind uplift but not so tight that the cover tears.

Cover Types:

Cover Type	Pros	Cons
Solid Vinyl Cover	Excellent barrier against UV, debris, and water loss; best for harsh climates.	Heavier; requires a pump to remove water.
Reinforced Mesh Cover	Lighter, easier to handle; allows rain to drain naturally.	Less protection against UV and debris; may allow some algae growth.
Automatic Cover (motorized)	One‑touch operation, tight seal, excellent protection.	Expensive (often $2,000‑$5,000); requires power source.

Step 7 – Final Checks

Verify the water temperature is below 50 °F (10 °C) before adding antifreeze—colder water reduces the amount needed.
Double‑check all caps and plugs for tightness.
Remove any pool toys, ladders, or diving boards (store them indoors).
Set a reminder to inspect the cover after heavy snowfall or strong winds.

4. Common Mistakes & How to Avoid Them

Mistake	Consequence	Prevention
Leaving water in the pump housing	Frozen water expands, cracking the pump housing.	Fully drain and vacuum the pump; use a wet‑dry vac.
Skipping antifreeze	Residual water freezes, rupturing pipes.	Add the correct amount of pool‑grade antifreeze to every line.
Cover not taut	Water ponds, freezes, and lifts the cover, exposing the pool.	Use a cover pump or tension system; check after storms.
Using automotive antifreeze	Toxic to swimmers and wildlife; can damage pool components.	Only use propylene‑glycol pool antifreeze.
Covering a pool with high water level	Hydrostatic pressure can cause the cover to pop off or the liner to bulge.	Lower water level below skimmer before covering.
Neglecting chemistry before shutdown	Algae blooms over winter, leading to a messy spring clean‑up.	Shock and balance water, add algaecide before closing.

5. Spring‑time Re‑Opening Checklist

Action	Details
Remove the cover	Use the cover pump to dry the cover, then roll it up and store it.
Inspect for damage	Look for tears, holes, or mold on the cover; replace if needed.
Reconnect plumbing	Remove caps, open unions, and ensure all valves are in the open position.
Fill the pool	Use a garden hose or water truck to bring water level back to the normal operating height (above the skimmer).
Turn on the pump & filter	Run the system for at least 24 hours to circulate water and flush out any remaining antifreeze.
Test water chemistry	Re‑balance pH, alkalinity, and chlorine; shock the pool again.
Check for leaks	Inspect pump, filter, heater, and all fittings for any drips.
Clean the surface	Remove any debris that may have settled on the water or cover.

6. Cost Overview (Typical for a 15,000‑gal In‑Ground Pool)

Item	Approx. Cost (USD)
Pool‑grade antifreeze (prop‑glycol)	$30‑$50 per 5‑gal jug (you’ll need 1‑2 jugs).
Winter cover (solid vinyl, 15‑k gal)	$300‑$600 (mid‑range).
Cover pump	$80‑$150 (optional but highly recommended).
Labor (if you hire a pro)	$200‑$400 for full winterization (draining, antifreeze, cover install).
Total DIY	$410‑$800 (materials only).
Total Professional	$610‑$1,000 (materials + labor).

Note: The cost of preventing a cracked shell or burst pipe (which can run $5,000‑$15,000 in repairs) far outweighs the modest expense of proper winterization.

7. Frequently Asked Questions (FAQ)

Question	Answer
Do I need to drain the entire pool?	No. You only need to lower the water below the skimmer and drain the plumbing. Completely draining a concrete or gunite pool can cause structural issues.
Can I use a garden hose to fill the pool in spring?	Yes, but be aware of water‑softening chemicals (if you have a softener) that can affect pool chemistry.
What if I forget to add antifreeze?	If any water remains in the lines, it can freeze and cause a burst pipe. If you discover a burst after a freeze, you’ll need to replace the damaged section.
Is a mesh cover enough for winter?	In mild climates it may suffice, but in frost‑prone areas a solid cover with a pump is recommended to prevent water accumulation and ice damage.
How often should I replace the cover?	Every 5‑7 years for solid vinyl covers, or when you notice tears, UV‑cracking, or loss of tension.