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Insulating an outdoor hot tub


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I have a Blue Ridge Spa by Jacuzzi, circa 2000 or 2001. It came with the house when I bought it about 15 years ago.

It was originally on a cement slab to the side of the deck, and since then I rebuilt the deck to recess it.


It originally had a 2x4 border (with 1" of it showing), and underneath that was a thin frame (maybe 1/4") to make it pretty. Inside of that frame was a piece of Styrofoam, maybe 1/2" thick. Over the years, though, that 2x4 had almost entirely rotted away, and half of the frame was rotted and falling apart. So for the last several weeks I've busted out the old border, ripped out the thin frame, and replaced the border with a 2x6... the photo below shows the new border, and I left 5" out so it could be used to sit wine glasses on.

Underneath the deck, though, is where I have a question.

The front of the hot tub (where you see the orange tag in right side of the photo) has been more or less exposed for the last 10 years, when I began replacing pumps and other hardware. The contractor put 2x6 rafters in front of the screws that held the frame in place so I had to break the frame off to get to the heat pump, and after that I just leaned it back in place. It never had Styrofoam or anything, so the only insulation was the foam that's adhered to the acrylic shell. The front is easy-access to the main circuit board, heat pump, and circulation pump.

To the back-right is the jet pump.

Back-middle, there's some sort of PVC junction that appears to be attached to the thin frame. That's the only part I couldn't get out, when I pulled on the frame all of this PVC started to come with it.

On the left, there's nothing but tubes.

I don't want to leave all of this exposed, so I was planning to staple a sheet of plastic to the bottom of the deck and let it drape down. Maybe lay 2x4s around the cement slab underneath, then staple the plastic to that, too... then it would be nice and stable, but easily moved when I need access.

Question 1: is that OK to do, or would it cause condensation inside that might be a problem for the pumps and circuit board?

Question 2: I'm in zone 7A, so sub-freezing temperatures aren't uncommon during the winter. Would you recommend any type of additional insulation around the shell? I thought about regular pink home insulation, tucked in between the pumps and the shell, but I wanted to run it by you guys and gals first.

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6 hours ago, csdude55 said:

the photo below shows the new border, and I left 5" out so it could be used to sit wine glasses on

 

 

I thought about regular pink home insulation, tucked in between the pumps and the shell, but I wanted to run it by you guys and gals first.

 

 

The "shelf" for wine glasses is especially important !!!!

My 32-year-old CalSpa has the expanding foam type insulation.  Of course this makes it quite tough to access any plumbing on the non-equipment side to find/fix any repairs.  So fine if nothing ever needs service.  I like the pink fiberglass insulation idea myself; this is what a contractor used for us when he installed a bathtub into our remodeled bathroom, at our suggestion.

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I'd never heard of Rock Wool, so I had to Google it. There are a LOT of things called Rock Wool! LOL  Some are for planting sprouts, some for sound deadening, some that looks like the right thing for $20, and some that looks like the right thing for $600... it's hard to wade through it all.

Is this what you're talking about?

https://www.amazon.com/ROXUL-Mineral-Temperature-Insulation-Density/dp/B07JHWZGDW/

I was originally thinking about 2 of these, which is R-19 and 6" thick:

https://www.amazon.com/Owens-Corning-E61-Fiberglass-Touch-Insulation/dp/B0044G35XU

The Roxul in the first link would be 1/2 the price (very appealing!), but it's also 1/3rd the thickness so I'm going to guess that it's more equivalent to R-3 (I read that the R value doesn't really apply)? But Google does make it sound better for outdoor applications, and I hate to spend $200 on the pink stuff then have to replace it in a few years.

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The photos don't really show what you are dealing with down below. Is there a cabinet around the spa or is it just exposed?

Depends how you want to insulate. Below you can make up yourself with contractor bags tightly taped wit tuck tape. Then you can place bags where you need them.

sunrise spas hottub

 

Or if you want you can use flexible foil backed rolls and wrap the entire perimeter http://buyinsulationproducts.com/roxul-enerwrap-80-flexible-blanket.html

Or just pack the rockwool inside and enclose the cabinet. Just don't get to close to pumps. They need space to breath

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Under the deck is totally exposed. There was originally a thin wooden cabinet frame that was mostly cosmetic, but it had rotted away and I had to rip out what was remaining. So now the pumps, motors, and tubes are totally open air.

The pumps and motors are a foot or two away from the shell, so I think it would be easy to tuck insulation in between the motors and tubes as long as it's pliable like the pink stuff. Unless you think I should tuck it between the tubes and the shell?

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1 hour ago, csdude55 said:

Under the deck is totally exposed. There was originally a thin wooden cabinet frame that was mostly cosmetic, but it had rotted away and I had to rip out what was remaining. So now the pumps, motors, and tubes are totally open air.

The pumps and motors are a foot or two away from the shell, so I think it would be easy to tuck insulation in between the motors and tubes as long as it's pliable like the pink stuff. Unless you think I should tuck it between the tubes and the shell?

make sure you leave room for the pumps to breath  they do need air circulation     I used roxul to replace the spray foam that was dug out of my tub  works great and cheap  I did NOT bag mine as i was filling odd shaped voids. In  your case I would bag it  you will need to build a cabinet around it too  again leave vents on pump side

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Well, lots of ideas, but I don't like any of them.

Spray foam is pricey and shrinks over time. Fiberglass and rockwool soak up and hold water, but I guess bagging it would help. Foil bubble wrap is almost useless. And then, whichever you choose, you have to build a cabinet (under your deck) to hold it in.

I would build a "cabinet" out of insulation board, attaching directly to the frame with screws so you can easily remove it if needed. It sounds like your pumps can remain outside of this enclosure.

https://www.lowes.com/pd/Common-1-in-x-4-ft-x-8-ft-Actual-0-9375-in-x-3-875-ft-x-7-875-ft-R-Expanded-Polystyrene-Foam-Board-Insulation/3365576

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I won't deny, $12 for a 4x8 sheet fits the budget a whole lot better! I could buy 4 sheets for $50 and make the cabinet 4" thick, having an R value of 17-20.

For the sake of my electric bill, though, I'm kinda tempted to do both... bag up rockwool and pack it in, then build a cabinet around the outside for both protection and additional insulation. During the winter my electric bill hits $300 USD, so if I can knock $50 off of that then it would be worth the investment.

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Regarding Rockwool / Roxul, can you tell me the difference between these two?

https://www.amazon.com/ROXUL-Mineral-Temperature-Insulation-Density/dp/B07JHWZGDW/

https://www.lowes.com/pd/ROCKWOOL-COMFORTBATT-R-30-Stone-Wool-Batt-Insulation-with-Sound-Barrier-15-25-in-W-x-47-in-L/3610406

All of the results at Lowes are ROCKWOOL COMFORTBATT, and talk about sound deadening. But it's R-30, versus the cheaper ROXUL from Amazon only being R-8. But I've read that R-ratings on this are irrelevant since they repel water, so I'm getting confused.

Which would you recommend to go inside of a cabinet built with the insulation board that @RDspaguy recommended?

Also, is the purpose of wrapping it in plastic to keep water out? With it being water-repelling I wouldn't think that step would be necessary.

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