DIY Hot Tub Insulation

DIY Hot tub Insulation

DIY Hot Tub Insulation is essential to keeping those running costs down on your tub. As we see fossil fuel prices increasing all over the Word, more now than ever the insulation on your tub is really important. On this blog, and my YouTube Channel, there are many videos on Air Source Heat Pumps as a good way of keeping running costs down – however, DIY Hot Tub Insulation is key too.

In this article we will example the options available.

What about TubBlox Insulated Concrete Forms?

TubBlox Kits from are Insulated Concrete Forms or ICF Blocks. These Insulated Concrete Forms as the name suggests comes ready-made with the insulation.

The way that the TubBlox work is that you put them together rather like “lego for adults”. They are lightweight so perfect for the individual DIYer building their own insulated DIY Hot Tub.

DIY Hot Tub Insulation
DIY Hot Tub Insulation

Once you have the structure ready, you then pour in the concrete. The concrete gives the TubBlox their strength and the expanded polystyrene that are used in their construction gives them their insulation or R-value credentials.

This is a great way to build an Insulated DIY Hot Tub. You can read more about TubBlox Kits here

DIY Hot Tub Insulation for Block Built Hot Tubs

If you have read other articles on my site, you will know that I actually made my hot tub out of block. What I didn’t do however, was insulate it. Yes, you read that correct – I did not put any insulation in it.

The thing was, that when I built my hot tub – I didn’t really know what I was doing. As I have said many times over, this journey to helping over 600 DIYers like you means I am very well qualified to help – I made all the mistakes.

On, so how do we insulate a hot tub that is built of blocks?

Really, there are two ways for insulating block built tubs. If you are building a double skinned cavity, then inside, with the plumbing and the rebar, you can add some of the PIR boards – they come from various manufactures like Celotex – they all do the same job.

These foil backed boards can then fit inside of the cavity, adding insulation to your DIY Hot Tub then you will fill the cavity with concrete.

If you are doing a single skin of block, then you have two options. You can either put the PIR boards onto the structure before you fit the plumbing, or you can add the plumbing, then add the Pic boards around the plumbing. There is no right or wrong way of doing this.

Just be mindful that you are creating a dry warm place which will be very attractive to any rodents that you might have in your back yard – I must say I’ve picked a few out that have passed on from my control room over the years!

DIY Hot Tub Insulation
DIY Hot Tub Insulation

DIY Hot Tub Insulation for Poured Concrete Forms

Adding insulation to your DIY Hot Tub formed of poured concrete is actually quite straight forward.

In terms of the base itself, this one is always open to debate. Personally, I prefer not to insulate the base itself as I am always a little concerned about the structural integrity. However, if the insulation is placed underneath the crushed aggregate and then the concrete pad is poured on top, arguably, the structural integrity would be just fine.

However, for me the question is always whether this approach is actually worth it when most heat is lost vertically. I leave you to decide this one on your own.

Adding insulation into your poured concrete form walls just means leaving a little extra space. If you plan on having the plumbing inside your walls, they are going to be 10” at a minimum thick to accommodate the Gunite bodies.

This is fine and you can use PIR board around the plumbing before you pour. Make sure your rebar structure is good and that there is concrete on either side of the PIR for structural integrity and you will be just fine.

DIY Hot Tub Insulation for Stock Tank Hot Tubs & Pools

Stock Tank Hot Tubs if you are not familiar with these are the DIY Hot Tubs that are made from the steel animal feeders. They can also be plastic, but generally, these are the galvanised steel tanks.

Very popular and very trendy, these kinds of DIY Hot Tubs present a slightly different challenge when it comes to insulation. Firstly, there are different challenges if they are in ground or above ground.

Above ground, quite often, the jets do not go all the way around to give a more rustic look. Therefore, it would be pretty much impossible to create an insulated tank that looked good as there was be exposed insulation. However, if these are surrounded in part by a deck for example, spray foam as well as the wool loft insulation is always popular. Again, especially with the wool this makes a good nest for rodents so make sure it is well sealed.

The spray foam you can pick up in any good hardware store. This is pretty much the method of insulation that is used on regular plastic shell tubs underneath in the cabinet. Foam is sprayed in.

If your stock tank is in ground, again the spray foam is an option as too is scored PIR board so that you can actually make it bend around the tank. Wool in ground tends to absorb water and once it is damp it loses its insulation properties. Therefore, I would not recommend this kind on insulation if your DIY stock tank hot tub is going in ground.

In Conclusion

There are a number of ways that you can insulate your DIY Hot Tub. The method that you choose will largely be dictated by either the type of hot tub you are building, or the materials that you are using.

What is however clear, is that if you don’t insulate you hot tub, then your running costs are going to increase!

Happy “insulated” Hot Tubbin’

Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

Thanks - Andi


Hi, Andi here. I own and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Today, I've helped over 1000 DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi

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