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Hot tub insulation - how much of a difference?

Hot tub insulation - how much of a difference?


Old 10-15-05, 10:04 PM
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Hot tub insulation - how much of a difference?

I'm building my own hot tub out of wood that will be roughly 450 gallons. I'm trying to decide if I want to insulate the walls and floor of the tub. There will be a foam cover for the top. How much of a difference would it make if I put 2-4" of styrofoam insulation around the walls and floor? How quickly (roughly) does a tub that size cool off normally? (say, on a 50 degree day) I've never had a hot tub before...
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Old 10-16-05, 06:02 PM
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I would say insulate it unless you have a strong aesthetic reason not to. You will spend a bit of money (on gas or electric) heating the water so you might as well keep it warm once you get it to the temp you want.
Old 10-16-05, 06:24 PM
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In the end it would probably cost about 30% more for me to insulate, and it would look better without it. I will be heating it with wood, which will only cost about $0.25 per heat up, so losing heat isn't much of a concern, but having insulation would keep it warmer until the next day if I want to heat it up again.
Old 10-18-05, 11:24 PM
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This summer I just built a wood hot tub myself. It is 6' diameter at the top, and 5'6" diameter at the bottom. I think its right around 450 gal as well. I used 1x6 cedar for the walls (now wish I had used 2x6). The wood walls of a hot tub are actually pretty good at retaining heat. All of the premade wooden hot tubs, such as rhtubs.com, only use 2x6 wood for the walls with no insulation. Most of the heat loss is through evaporation, and radiant heat through the top, not the walls. So the best way to keep the heat in is to have a perfectly cut bubble cover to eliminate evaporation, and a thick foam cover that is airtight. The bubble cover will also keep the foam from becoming waterlogged which happens after a couple of years. Small bubble covers can be purchased from rhtubs.com for less than $20.

Here's a picture of my tub before it was completly finished. I have added a top rail that hides the liner, and did some landscaping. Everything was built from scratch. I currently only am using a bubble cover for insulating until I can get a 2-3" piece of foam to make a better cover. On a 50 degree night, with 1" thick walls and a bubble cover on the surface, the tub will only loose 8 degrees overnight. This is with the fiter turned off since the plumbing isn't insulated yet (very big losses if it is going overnight).

I am using my pool's pump, filter, and 175k BTU heater to heat it, and only turn the heat on when I want to use the tub. It heats up 24 degrees/hour. Right now the water is a frigid 58 because I've been too busy to use it recently.

If you have any questions, feel free to ask me.


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