A lot can be said these days regarding the ability of a spa to retain
heat. However, in the portable spa market, these days, it is virtually a
From Coleman®, to Sof-Tub® to even the inexpensive Jacuzzi® brand
spas at Home Depot. There's hardly a portable spa manufactured out there that won't retain heat
extremely well. So, in most cases these days, it's definitely nothing to lose sleep over.
There are three different ways that heat is transferred:
- Conduction. One surface touching another.
- Convection. the natural flow of heat through air movement, and the
rising effects of it.
- Radiation. can be easily
understood as being the radiation as felt by the sun, or from a stove burner.
The most commonly used insulation material is an expanding poly-foam, which
is usually yellow to tan in color, and is used by almost every spa manufacturer. It primarily
stops the flow of heat by the prevention of convection. Without the foam, the heat would
transfer from the inside of the shell to the outside (by conduction), and radiate outward, and be
carried away by air convection. Note that all 3 factors come into play here.... but by
spraying the foam in the cabinet, the chance for convection is nil.
Some spa manufacturers utilize full foam insulation. That is, foam that fills
the spa skirt 100 percent. This is one of the most effective means of controlling temperature
loss, and has been in use for many years by most nationwide manufacturers.
Many other spas (and if you shop around, you'll probably realize this yourself),
are constructed with a thick fiberglass shell, with an acrylic type of sheet on top of the
shell. The thicknesses of these shells will vary anywhere from 1/8" to as much as
3/4" in some areas. These shells are generally more expensive to manufacture, and are
usually made in a facility that is dedicated to this purpose....then shipped to the spa
builder/manufacturer for drilling, plumbing, skirting, etc.
Usually what you will find with a spa built in this fashion, is that all exposed
surfaces of the spa shell, plumbing, jets, and manifolds, will be sprayed with foam, in some areas
thicker than others. Additionally, the foam is used to keep these components "in
place," preventing the movement of the plumbed parts, and subsequent leak problems from occuring.
Recently, I have begun to see spas built with a new type of insulation scheme,
which is rather remarkable. It uses a laminated metallic foil/air bubble seal material on the
inside of the skirt, and at the same time uses poly-foam on the spa shell and plumbing. The
effectiveness of this is insulation is extremely good, as the metallic foil contains the radiation
of heat from the spa. Actually, the foil material reflects the infrared component of heat
back into the spa itself, literally creating its own convection oven effect inside the skirt.
The result? Extremely effective recycling of heat from components such as the pump motor and
spa control system, which is normally lost through equipment ventilation.
What should you buy, then?
As I've said in the buyers guides,
buy what you like! All well-made spas will exhibit superb thermal efficiency
Personally, I prefer the feel of the thin shell material used by
Dimension One, Hot Springs, and others, but I also like the ease of service of a full thickness
fiberglass shell with limited foam... and the superb thermal characteristics of the reflective foil
material on a spa skirt... HA! It's a tough choice! But ALWAYS remember:
Buy what you like folks! They're ALL pretty good!