Most pool owners think of heating as something you add: a heat pump, a bank of solar panels, a gas heater. But before you add heat, it’s worth stopping the heat you already have from escaping. That’s what a solar blanket does, and it’s why we recommend one for almost every pool we see.

Your pool is a solar collector whether you like it or not. On a clear Highveld or Cape day, the water soaks up most of the sunlight that lands on it. The problem is what happens next. As soon as the sun drops, that heat starts leaving the water, and by morning most of it is gone. You start every day from scratch.

A solar blanket breaks that cycle. It lets the sun’s energy in during the day and then puts a lid on the pool at night, so the heat you gained stays in the water. Do that for a few days in a row and the temperature climbs, with no heater and no running cost.

Where your pool’s heat actually goes

Water loses heat in three ways: through the walls and floor, into the air by radiation and convection, and by evaporation. Of the three, evaporation is by far the biggest. Every litre of water that evaporates off the surface takes a large amount of energy with it, which is exactly the same effect that cools you down when you climb out of the pool and the wind hits you.

Those figures explain why a thin sheet of plastic can make such a difference. The blanket sits directly on the water, so there’s no air gap for moisture to escape into. Shut off the evaporation and you’ve shut off the biggest leak in the system.

How much warmer will my pool get?

With no heater at all, a well-fitted solar blanket used every night will typically lift your pool by 6°C or more compared with the same pool left open. In sheltered, sunny conditions the gain can reach 10°C. That’s the difference between a pool you look at in October and a pool you swim in.

Two things to be clear about. First, it’s cumulative. The blanket doesn’t heat the water the way a heater does; it stops the water cooling down, so each day builds on the one before. Give it three to five sunny days before you judge it. Second, the blanket has to be on the pool to work. A blanket rolled up at the side of the pool overnight is doing nothing, which is why we’ll come back to the roll-up station later.

A heater adds heat. A blanket stops you losing it. Do both and you get the warmest pool for the least money.

Already have a heat pump or solar panels? You need this even more

It sounds backwards, but the owners who benefit most from a solar blanket are the ones who’ve already invested in heating. Here’s why.

A heat pump is efficient, but every degree it adds during the day leaks away overnight if the pool is uncovered. So tomorrow it has to replace that heat all over again, and you’re paying for electricity to heat the same water twice. Put a blanket on the pool at night and the heat pump only has to top up the small amount that’s lost, which means fewer running hours, a lower electricity bill, and a unit that reaches your target temperature much faster in spring.

The same logic applies to solar panels. Panels collect free heat, but they can only collect it while the sun is up. Without a blanket, the gains from a good day are largely gone by morning. With one, you keep what the panels earned. Many pool owners find that a blanket plus panels gets them into comfortable swimming temperatures without ever needing powered heating.

• Heat pump runs fewer hours It maintains temperature instead of rebuilding it every day
• Solar panel gains are kept, not lost Overnight losses drop sharply, so each day starts warmer
• Faster start to the season Reach your target temperature in days rather than weeks
• Smaller heating system does the job Less heat loss means you don’t have to oversize the heater

The savings that aren’t about heat

Less chlorine

Sunlight is chlorine’s enemy. The UV in direct sun breaks down free chlorine in the water quickly, which is why an uncovered pool in summer can burn through its chlorine in a single afternoon. A solar blanket shades the water from UV while it’s on, and it stops chlorine evaporating off the surface along with the water. The US Department of Energy puts the chemical saving from covering a pool at 35–60%. Fewer top-ups, fewer trips to the shop, and more stable water.

Less water

An uncovered pool can lose several centimetres of water a week to evaporation in hot, windy weather. Every centimetre is water you pay to replace and then pay again to balance and treat. Cut evaporation by around 95% and you’ll notice how rarely you reach for the hosepipe.

Fewer leaves, less cleaning

Leaves, dust, insects and pollen land on the blanket instead of in the water. Hose them off before you roll it back, and your pool stays cleaner, your filter runs longer between backwashes, and your pool cleaner has less to do. If you’ve got trees near the pool, this alone can justify the purchase.

What makes a good solar blanket

Not all bubble covers are equal. There are three things that determine how well a blanket performs and how long it lasts.

Thickness. Blanket thickness is measured in microns (a micron is a thousandth of a millimetre). Thin, entry-level covers are often around 300–400 micron and tend to go brittle and shed bubbles after a season or two in strong African sun. A 500 micron blanket, half a millimetre thick, holds more air, insulates better and stands up to UV and chlorine far longer.

Lamination. A double-laminated blanket is made of two layers bonded together rather than one. That bonding makes the bubbles far less likely to delaminate or split, which is the usual way cheaper covers fail.

Bubble design. The bubbles are the insulation. A multi-bubble layout, where each cell is divided rather than a single large dome, traps more air and keeps its shape under weight and heat better than a basic single bubble.

Fitting your blanket

Installation is simple, but one step catches people out: give the blanket a day on the water before you cut it.

1. Bubble side down

   The bubbles go into the water and the smooth side faces the sky. The bubbles do the insulating; the smooth top sheds leaves and water.

2. Float it and leave it for 24 hours

   Lay the blanket on the pool, roughly in position, and let it relax and flatten in the sun for a day. It will settle and spread slightly, and cutting before that means cutting it short.

3. Trim to the pool’s edge

   Using sharp scissors or a utility knife, trim along the inside edge of the coping so the blanket sits just inside the pool. Cut around steps, ladders and the weir mouth. Don’t leave an overlap onto the paving; it lifts in the wind and doesn’t help.

4. Use it every night

   The blanket is doing its most important work between sunset and sunrise. Make putting it on part of the evening routine and the results follow.

Why a roll-up station turns a good idea into a habit

Here’s the honest truth about solar blankets: the ones that work are the ones that get used. A blanket that’s awkward to take off and put back on gets left off, and a blanket that’s left off does nothing.

Dragging a wet 500 micron blanket off a 4m x 8m pool by hand is a two-person job, and it ends with the blanket in a heap on the paving. Heaped like that in full sun, with no water to cool it, it overheats and ages fast. A roll-up station fixes both problems at once. One person winds the blanket onto the tube in under a minute, and the rolled blanket sits off the ground, out of the way and ready to pull back over the water in the evening.

One sizing tip: the tube needs to be longer than your pool is wide, since the blanket rolls onto it edge to edge. If your pool is 3.5m wide, you want the 4.0m station. Measure the width before you order.

Getting the longest life from your blanket

• Keep it on the water or on the reel Never leave it folded or heaped on paving in the sun
• Take it off when you shock the pool Very high chlorine levels attack the plastic; wait until levels are back to normal
• Rinse it off now and then A quick hose-down removes dust and chemical residue
• Cover the rolled blanket if it’s stored for long A light reflective sheet over the reel protects it when it’s off the pool for weeks
• Watch for standing water on top A little is normal; a sagging puddle usually means the blanket is slightly too big

Frequently asked questions