Self-Cleaning Hot Tubs - Energy Efficiency Part 1 - Full Foam
Posted by Greg Butler on Mon, Apr 12, 2010 @ 11:21 AM
If you are doing your homework and researching a hot tub, you realize that in its most simply form, a free-standing / portable hot tub can be described as a "bowl-in-a-box". When we look at a hot tub this way, we will realize for the purposes of keeping our bowl of water warm without significantly increasing our power bill each month, there truely are only so many ways to insulate the bowl, the box or the space between the two. I will address each in turn:
1. Full Foam
One way is to use what is commonly referred to as "full foam". In this case, the cavity between the bowl and the box is sprayed completely full of foam. This is an effective way to insulate a hot tub. Many manufacturers choose this route because it is easy, cheap and effective. More importantly for these manufacturers, it is very easy for sales staff to communicate and subsequently for customers to understand.
However, it should be noted, that it is NOT the foam that does the majority insulating - it is the space or air trapped in the little bubbles or pockets in the foam that does most of the insulating. Just like your fiberglass pink insulation in your house, the fiberglass batting does not insulate, but the air trapped within. This is why your contractor will fit this snuggly between the walls in your home, but they will not pack it tightly in there.
As mentioned, this is an effective way to insulate a hot tub, but there are limitations to this type of insulation:
The notion that MORE INSULATION MEANS BETTER energy efficiency is COMPLETELY FALSE. The idea is not to get more insulation - if it were, we would build bigger boxes. The idea is for your hot tub to be more energy efficient. To use the home analogy, if more foam was better, the exterior walls in our homes would be several feet thick instead of simply 6 inches. Therefore, we must agree, that stopping the cold and keeping the heat requires just a certain amount of insulation, and more is not always better.
The second limitation of this type of insulation is THE TYPE OF FOAM USED. There is open-cell foam and there is closed-cell foam. Quite simply, the open cell foam soaks up water - the closed cell does not. If you install a hot tub with open cell foam in a damp, rainy environment where fog and drizzle are common - the foam will soak up water and will decrease the overall energy efficiency of the hot tub over time.
The third limitation of the full-foam method is that of rodents and animals that would be attracted to heat and that can burrow. This is not a big issue in Newfoundland, but in provinces where field mice and snakes are prevelant, these full foam cabinets attract so many rodents that service techicians commonly kick the hot tub prior to servicing to drive animals out!
With servicing in mind, the fourth and most important limitation of full foam hot tubs is servicing. This is primarily reason why most hot tub manufacturers which no longer implement this method insulation have ceased the practice. In the event that there is a leak in your hot tub - this does happen - servicing a full-foam hot tub is a nightmare! The process is as follows:
1. Tip the hot tub on its side
2. Begin a "dig-out" - us a hand shovel or spoon type of instrument to begin digging the mushy wet open cell foam out of the space between the "bowl and the box".
3. Stop digging when there is no more "mush"
4. Because your hot tub is empty, you should guess where the leak came from (you may have several pipes, unions, fittings, suctions now available.
5. If it is obvious (a line slipped off a jet body for example). Re-clamp, re-glue the fitting.
6. Re-spray the entire hot tub with a field kit of insulating foam
7. Tip hot tub back in place, refill and restart.
Some manufacturers will tell you that they put the equipment on the outside of their hot tub to facilitate servicing and to allow you to put more foam inside. Never is there a mention of the type of foam, the fact that more is not better, and there is never any explanation of how one fixes a leak in one of these hot tubs.
In summary,
1. Dead Air Spaces in the insulation do the the insulating - not the foam itself
2. More is not better
3. Open Cell foam will soak up water decreasing the energy efficieny of your hot tub
4. Rodents commonly burrow into hot tubs using this sort of insulation
5. Servicing requires a "dig-out"