Have you ever had a bath where the heat seems to dissipate ten minutes after you get in? The same is true for hot tubs. In order to keep the heat in and your electricity bill down, the smartest thing you can do is make sure your hot tub or bath is insulated correctly. Some manufacturers may try and cut corners by just spraying one layer of foam around the hot tub without including its base. Do not buy this type of insulation. What may save you money in the short term may steal the nickels out of your pocket in the long run. It can also provide a limited noise barrier and can keep the structure solidified.
When it comes to hot tub insulation, this is a relatively inexpensive method of keeping in the heat by blanketing the hot tub shell. All the sides and undercarriage are filled with foam. The only downside to this popular method is repairs sometimes make it necessary to remove the spa insulation, in its entirety. This can damage the insulation; especially if you chose the sealed variety. To prevent this from occurring, make sure you purchase spa foam insulation that can come apart in blocks while still maintaining the seal.
The issue with the unsealed type of hot tub insulation is that radiant heat from the motor is pumped away from the tub and swapped with cool air which makes the insulation less effective than the warm barrier method of insulating.
Also, if you are buying full foam insulation ensure that you purchase a polyurethane foam that is closed-cell and therefore high density. It would also be beneficial to use this in layers. Some insulation manufacturers use open cell low density packing foam.
The mother of all hot tub insulators is the warm air barrier system, sometimes called blanket insulation, created to keep the radiant heat inside the tub and providing you with electricity cost savings in the long run. It is similar to the full foamed system because it insulates the cabinet and the back of the tub. These layers of insulation should be placed on all interior walls and along the sub-floor. The warm air barrier re-circulates the radiant heat.
The easiest way to throw your money away is not to cover your hot tub. Not covering your spa not only allows the heat to escape rapidly, but also allows debris to clog your skimmers. When uncovered, evaporation of your water occurs which makes your motor work harder and creates more wear and tear on the whole unit. To combat these issues a simple spa cover will do the trick. There are many types of hot tub covers and as usual you get what you pay for. I recommend purchasing a top of the line model in your budget for long term gain.
The last thing to remember is to check the R-Value rating on any insulation. The R-Value is very important when it comes to insulating your hot tub. The higher the R-Value, the better it insulates, saving you money in the long run. R-Value measures the thermal resistance of the material.