A common question for hot tub owners to ask is, “Does my hot tub cover waste more energy than it saves?”
This is very common because often during winter if you live in a locale where it snows, you will notice that the water inside your hot tub cools off.
You may notice that snow that collects on the top of your hot tub cover does not melt. This does not mean that your spa is so well insulated that none of the heat is leaving through the spa cover.
You may also notice that the water in you tub is cooling. This may lead to confusion, because if no heat is leaving your hot tub (which you assume because the snow does not melt), then why is the hot tub water cooling down.
This all goes back to the topic of insulation. Your cover may not be up to snuff in this category. Hot tub covers have a foam core generally covered in some type of nylon. The foam core of your cover is what insulates heat.
The way it works is there are air particles trapped between tiny foam balls that are bound together. The air that is trapped inside the foam stays the same temperature because it is trapped and does not move.
If you have a weak hot tub cover, the insulation may not be up to par. The reason your hot tub is cooling off is because water inside the tub evaporates and condenses on the bottom side of the Hot Tub cover. This water cools and falls back into the hot tub, cooling it off considerably.