There’s no question that energy efficiency has become more important than ever. So every option should be explored.

And when it comes to pools and spas, that means looking at heat — specifically how to retain it.

But there isn’t one magic bullet — several components go into those kinds of savings. Covers and energy-efficient forms of heating do the heavy lifting, but there is another method that makes sense in some situations — insulating inground pools and spas. Here, professionals discuss its value.

Part of the equation

When used alone, insulation can reduce energy usage by about 5 percent. But when included as part of a comprehensive energy-saving strategy — starting with a cover — insulation helps the dollars add up.

However, it makes more sense in some applications than others. For example, a vessel that needs to consistently remain at a higher or lower temperature could benefit.

“When you have an inground spa, you’re putting it up to 102 degrees, and the heat’s just radiating out of it,” says Barry Justus, president of Poolscape Inc. in Burlington, Ontario, Canada, and the builder of Canada’s Greenest Pool.

Spas are especially good candidates for insulation when they are in cold climates, or are placed in a raised setting without buffering by the ground.

Pools less frequently need insulating, but there are some exceptions, such as therapy pools that must consistently remain at a high temperature, or vessels heated with a solar system.

“When you’re dealing with solar, you’re dealing with a very low rate of climb,” says Mike Giovanone, owner of Concord Pools in Latham, N.Y., a Pool & Spa News Top Builder. “So solar needs all the help it can get containing heat, where if you have natural gas and you want to punch the pool up 10 degrees, you’re going to do that, whether the walls are insulated or not.”

Insulation also can help with some indoor pools and spas, particularly those that are placed near an external wall, and which are more prone to heat loss.

“The heat will go out through the soil and then go up,” says Neil Anderson, president of Lodi, Calif.-based Neil O. Anderson and Associates. “If the pool or spa is near an external wall, then it’s going to enter the colder ground outside.”

Conversely, builders should not add insulation when installing a vessel in a high water table, since the light material could make the concrete shell more prone to pop.

Application methods

The two most common methods for insulating inground pools and spas utilize a spray-on material or panels.

The first involves a sprayed-on polyurethane, similar to the expansive foam found around portable hot tub shells.

It’s fairly easy to install: After excavation and plumbing, spray enough foam throughout the hole to line it. Builders who cast shells in place can go back and spray behind the walls after pulling the forms.

Some builders subcontract this work out to a home-insulation installer — an option worth considering because the substance is quite toxic. When installing it themselves, crews should be suited up for protection.

In terms of thickness, Anderson has found 3 inches to be the point after which owners will experience diminishing returns on the polyurethane product he’s studied. The material Giovanone uses stops improving proportionally after 4-to-6-inch thicknesses, while Justus’ caps off at 2 inches. It’s a good idea to check with the manufacturer or  vendor to determine the most effective thickness.

The second method involves panels of extruded polystyrene. The dense material doesn’t allow water to permeate and won’t crush, says Gene Brown, president of Valley Pool & Spa in Kelowna, British Columbia, Canada. Both he and Justus work with Styrofoam brand SM panels, made for inground applications. Brown works with panels measuring 2-by-8 feet, and has found that a 1-1/2-inch thickness to be ideal, although they do come in thicker sizes.

The panels, which can be purchased at many building supply stores, are easier to install than the spray-on method, so the labor can normally be performed by in-house crews.

Understandably, this option won’t work well around curves, so the panels make the most sense on rectangular and geometric shapes. Justus also likes to use them when  the insulation must be exposed in an underground bunker.

When dealing with this product, builders should prepare the excavation so that it’s as flat and smooth as possible. “SM is fairly brittle — it won’t flex,” Brown says. “So everything needs to be straight, and all the ground prep underneath has to be very good in order to hold it in place, so it doesn’t break.”

When installing the panels, place them so they butt up against each other, then adhere them in some way. Brown tapes panels together to form as much of a seal as possible, while Justus’ crews put glue on the back to tack the panels down to the concrete. Some panels are available notched around the edges so they can interlock in place and eliminate escape routes for the heat.

Regardless of the method, builders may want to over-excavate the pool and backfill with sand. This protects the insulation and shell from ground water, which will conduct heat away from the pool or spa faster than dry earth.

When installing the insulation itself, the most crucial part is to insulate the top 3 feet, because there’s a direct escape route for the heat at that level. However, Anderson suggests taking it through the entire dig for added protection. For best results, continue to apply the material 3 to 4 feet back under the deck to prevent heat from escaping out of the flatwork.