There are many different techniques for insulating spas. In order to evaluate the different ways manufacturers insulate their spas it is important to first know that spas loose heat through radiation, convection, and conduction. Choosing a spa that offers the best reduction in heat loss will be the most energy efficient.
3-7% Conduction: Heat energy is transferred directly through materials in contact with each other, where a temperature difference exists. Heat transfer along a metal rod is a simple example of conduction.
Up to 45% Convection: Air, when heated, becomes less dense than the surrounding air and rises upwards. The denser and cooler air flows downwards. These air movements are known as convection currents.
50-75% Radiation: Heat energy may be radiated across the air space and then be absorbed by another body. Radiant energy from the sun is an example, where this energy may be absorbed as heat by the human body.
For maximum efficiency hot tubs should be designed to minimize each source of heat loss.
ThermoLock Insulation: Is a modern method of insulation which uses the least amount of kilowatt energy to heat the water and allows access to the spas plumbing for easy maintenance. Thermolock insulation incorporates a perimeter insulation blanket on the inside of the spa cladding which blocks conduction heat loss and in addition traps the heat generated by the pump motor. The heated air helps heat the water in the spa and reduces heat loss through convection. There are different types of insulation material used in this method of insulation (spray foam, styro-foam and high performance natural fibers). The best type of insulation is one that is mold resistant, insect resistant, can be easily removed and replaced to its original condition and comes with the best insulation warranty.
NOTE: Radiation is major source of heat loss. To prevent heat loss through radiation, the perimeter insulation must incorporate a thermal reflector (Survival Blanket) to radiate heat back into the spa plumbing and water.
Foam Fill Insulation: This is the way most spas were originally insulated. This method of insulating consists of completely filling the inside of the spa enclosure with spray foam. And directly venting out the pumps heat. This is the least energy efficient method of insulation and also the most difficult to service. The main benefit of this style of insulation is that it less expensive to build a spa this way then with Thermolock construction.
Most manufacturers have evolved to the more energy efficient Thermolock method but there are still some manufacturers that use foam fill. This method of construction consists of completely filling the inside spa enclosure with low density spray foam. This methods does not offer any reduction of heat loss through radiation or convection and is the least energy efficient method for reducing heat loss.
Another concern of foam fill, is that it is very difficult and expensive to service the plumbing. To properly service the plumbing, the spa typically needs to be returned to the factory so that they can dig out the insulation and then respray the foam back in with special equipment. If the spa is serviced on location, the service tech will have to lift the spa and dig the foam out and then use a can of spray foam which unfortunately does achieve the same quality compared to the special spray equipment used at the factory.