We have written before on how to size a solar pool heating system. We even have a solar pool heating sizing calculator. However, we still get lots of questions asking why are solar pool heaters sized based on surface area rather than the volume of water.

Size is Related to Surface Area

Most people think that the pool volume is the most important factor. After all, more water should mean more heating, right? Initially, more solar panels will heat a given pool faster. A larger pool will take longer to heat up.

So why is surface area used instead of volume?

Once the pool is heated up during the day, heat is lost overnight, and that’s the amount of heat needed the next day. Most heat is lost at the surface of the pool to evaporation and radiation. In fact, over 80% of the heat loss can occur at the surface. That’s why covering a pool is so helpful in maximizing temperature.

As a result, we mostly concern ourselves with the surface area, not the depth.

The vast majority of residential pools in Florida have a pretty standard average depth. Some pools have large beach walk-ins. Clients often think that this reduces the average depth and volume, so fewer solar panels are needed. That is not the case, unless the shallow are makes up a large percentage of the pool.

A solar pool heater simply replaces heat lost to the ground and sky.

If your pool is particularly deep, or you want to minimize recovery time after poor weather, you can certainly oversize a system. However, you may be spending money unnecessarily. Most people are happy with a solar pool heater that recovers overnight heat loss each day. A solar heated pool is always warmer then an unheated pool!

How Many Solar Panels Do I Need

There are lots of factors that go into sizing a system. It’s part science, part art and experience. Most importantly is establishing expectations with our clients. If we do that, we can use the tools we have to size a system effectively based on a list of factors.

The most important factor, or at least the starting point for sizing your solar pool heater, will be the pool surface area. We can obtain that with aerial measurements (using special tools and proprietary methods), and often via the property appraiser’s website.

Let us help you size your solar pool heater based on your pool size and roof orientation! Contact us today.