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
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
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.
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
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
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.