Heavy Broken Hot Tub Covers Waste Energy. I saw this advertised on line
the other day. When I went to check out the guys website, guess what
he’s selling? Rigid foam hot tub covers that will end up heavy or broken,
usually within two years.
Instead of selling you something that won’t get heavy or broken he
keeps selling the same thing, hoping you won’t notice. If you have had
to replace a hot tub cover because it got heavy, maybe the question you
should ask before you buy the next one is, Why?
What causes the foam Hot Tub Covers to get heavy is that it traps
moisture inside. Rigid foam board is used in lots of insulation
applications. It can be used around refrigeration storage areas like in
a super market. Layers of foam board can insulate the cool storage area
while the customer area can be kept comfortably warm. But in this type
of installation the foam is not subjected to hot moist air. As long as
the foam stays dry it has a predictable insulation value. But if the
foam were to have moisture in it instead of the little air spaces it
uses to insulate, it would have no insulation value at all.
If you wanted to produce the perfect environment for a rigid foam
board to become saturated it would be to put it over a source of warm,
humid, steam. You couldn’t get water into it faster even if you tied it
to the bottom of your swimming pool. Why? Because water molecules are
bigger than steam molecules. Steam can get into smaller spaces faster
than water. And once the steam cools, it condenses back into water,
displacing air in the foam as it does.
Long before you notice the hot tub cover getting heavy, moisture has
begun to replace the air spaces in your cover. When it does, the little
insulation value that cover might have had, goes down dramatically.
From whatever it may have been when you first put it on your hot tub it has
gone down to as much insulation as a wet piece of plywood by the time
you actually notice it got heavy.
You might get fooled into thinking that it is still insulating well
because snow won’t melt off it. Unfortunately, you would be wrong. Snow
won’t melt off a frozen pond either but it doesn’t mean the ice is
insulating the water. When snow falls on a saturated foam hot tub cover, it
freezes the moisture in the cover because it is laying directly on the
cover. The water of your hot tub is never in contact with the foam since
the foam is resting way up on top of the acrylic of the hot tub, usually
about a foot above the water surface. What’s happening is the warm spa
water is evaporating into steam. That steam is rising, because that is
what heat does, until it hits the bottom of the frozen hot tub cover. Then
the steam cools and turns back into water. The water, now cooled,
falls, because that’s what cold does, back into the warm spa water,
cooling it off.
So if you wanted to invent a radiator to cool off your warm hot tub
water this would be the perfect design. Put a block of frozen foam over
the water. Load it up with snow so it will keep the spa cover frozen
and stand back and watch the power meter spin. Instead of buying
another rigid foam spa cover that will positively end up like the one
you are replacing now, shop online for one that is designed better.
Look for Hot Tub Covers that will insulate the water from the water surface, without rigid foam.