Help adding Insulation to hot tub? What type of insulation would you recommend?

[duganderson]

I'm fixing a 450 G. 2017 Dr. Wellness G15 hot tub that I'm planning to give to a friend or to sell or possibly keep for my cabin. It has only been used for two years.

The insulation on this tub seems light. (please see photos below) Would you recommend adding more insulation? If so, what type of insulation would you recommend? This tub has 97 jets and three 6 HP high quality pumps so there is a lot of plumbing on this tub?

If I did not add insulation, any guess on how expensive this tub would be to run per month? (I live in MN so winters are cold and it would be used in the winter)?

If I added more insulation, any guesstimate on how much this would help with energy costs?

Any other suggestions about reducing cost to run this tub?

Thanks!

 

[cowboycasey]

I am not sure but we have @RDspaguy who fixes tubs all the time

 

[RDspaguy]

Spray foam will never pay for itself, and has problems associated with it in spas.
On a tub like that I would get some 1" foamboard insulation and cut pieces to fit between the frame boards. This will be almost as good as spray foam with none of the drawbacks and a fraction of the cost. Your only concern is overheating the equipment, so be sure to leave any vents in the cabinet uncovered. If overheating becomes an issue you can always add some vents, but you will probably be fine up there in the frigid north.

 

[duganderson]

@RDspaguy......thank you for the response.

A few questions please......

Are you saying to just use one layer of the 1" foam board and mount it in between the frame nearest to the outside of the tub?

The tub had the tinfoil like heat reflection paper. Would you mount this on the outside of the 1" foam board OR the inside OR skip re-installing the heat reflective paper?

Would you add 1" board where possible to the bottom of the tub too?

If there is space to mount more than one 1" board in places, would you bother or do you think that one board is sufficient?

 

[A.O.]

Ahhhh... Minnesota..

 

[RDspaguy]

Are you saying to just use one layer of the 1" foam board and mount it in between the frame nearest to the outside of the tub?

Exactly.

The tub had the tinfoil like heat reflection paper.

C'mon Doug, I know you're a smart guy. How much insulation value do you think that foil wrap provides? It's little more than an air barrier. Use it or pitch it, you won't notice the difference.

Would you add 1" board where possible to the bottom of the tub too?

You can set the tub on the foamboard if you like, but unless your spa is on a raised deck you will have little heat loss from the bottom. Most of your heat loss is out of the top, which is why a good fitting cover is so important.

there is space to mount more than one 1" board in places, would you bother or do you think that one board is sufficient?

You can do a double layer if you like. They may even make the foamboard in thicker sheets, I'm not sure. But too much insulation and the pump residual heat will overheat the circuit board and crash the controls. So be careful.

 

[duganderson]

C'mon Doug, I know you're a smart guy. How much insulation value do you think that foil wrap provides? It's little more than an air barrier. Use it or pitch it, you won't notice the difference.

I appreciate the "smart guy" comment but my teen sons may disagree with you on that one

As you probably know, the silver paper is a radiant barrier, not a conductive barrier, to heat transfer. I did not think the silver paper had any chance of being helpful either, but my uncle who is a mechanical engineer was saying a radiant barrier paper can be pretty effective. My google search on radiant barriers suggested that they can save 5-10% energy saving in certain conditions. I may add it to the inside of the insulation boards just for fun in case it helps some.

Thanks again for the tips on the insulation boards. That sounds like the best solution!

 

[RDspaguy]

but my uncle who is a mechanical engineer was saying a radiant barrier paper can be pretty effective. My google search on radiant barriers suggested that they can save 5-10% energy saving in certain conditions.

Well, there you go. Not the first time I've been wrong, nor will it be the last.

but my teen sons may disagree with you on that one

Yeah, well, they know everything. Just ask them and they will tell you.

 

[Weasel2017]

I appreciate the "smart guy" comment but my teen sons may disagree with you on that one

As you probably know, the silver paper is a radiant barrier, not a conductive barrier, to heat transfer. I did not think the silver paper had any chance of being helpful either, but my uncle who is a mechanical engineer was saying a radiant barrier paper can be pretty effective. My google search on radiant barriers suggested that they can save 5-10% energy saving in certain conditions. I may add it to the inside of the insulation boards just for fun in case it helps some.

Thanks again for the tips on the insulation boards. That sounds like the best solution

Thats the problem with radiant barriers and foils, on their own they provide next to no insulation. When coupled with a heat source they perform quite well. For example, we install radiant foil under concrete slabs with in-floor heat. On their own they do nothing but once the system is up and running they do an excellent job reflecting that heat back up into the slab.

 

[dan1333]

I love this forum, I learn new stuff about my hot tub all the time as well as construction info, chemistry, and now physics!

 

[duganderson]

Well, there you go. Not the first time I've been wrong, nor will it be the last.

@RDspaguy.....I don't know about wrong....I don't know how much they really help in a spa but maybe worth putting back in if someone already has them. Also, I have learned a TON from you on this forum and thank you for all of your contributions.

duganderson said:
I appreciate the "smart guy" comment, but my teen sons may disagree with you on that one

Yeah, well, they know everything. Just ask them and they will tell you.

It's reassuring to know that it's maybe not just my kids that go through this phase.

 

[Newdude]

It's reassuring to know that it's maybe not just my kids that go through this phase

I have girls, and same. Except hissy and bitey like upset cats. But other than that, same.