Hot Tub Insulation Systems By The Numbers

Hot Tub Insulation Systems By The Numbers

Hot Tub Insulation Systems By The Numbers


imagesI know a lot about hot tubs, and insulation systems, and R-values, and Thermal loss, and Reflective heat barriers, and Convection loss, and Conduction loss, and Thermal mass. and even I get confused when watching the videos about different hot tub insulation systems! I mean holy jumpin, R values, Open Celled Foam, Closed Cell Foam, Thermal drift, Diminishing Returns, Motor heat reclamation… it can get very confusing even for an expert! Especially when most of the talk is wishy washy non-tech talk! It’s all about buzz words and intentionally confusing the issues.


Now deep down My usually very reliable logic side says the more insulation there is in the system the more efficient that system is going to be, after all, let’s face it, it costs twice as much to do a full foam insulation system on a hot tub than it does to do the best perimeter systems and the base R-value is two, three, or even four times higher on the full foam spas! But, is it as Arctic Spas says in their video that the extra foam in a full foam spa is past the point of diminishing return and a waste of money and just for show?


So I went back to my tech background and decided to do it by the numbers. Science and numbers don’t lie and I really was curious as to when do we reach a point that a system has enough insulation in it? At what point is adding extra insulation into the Spa become meaningless? The law of diminishing returns says that eventually, the insulation value would be high enough that the extra insulation would be a waste of time and money but were hot tubs at that point? or was it a real meaningful difference?arctic-insualtion


To make this realistic I did two things. First I chose what I think are the best examples of each type of insulation system.


So I used Arctic Spas, to represent the Perimeter insulation systems because they use a Closed cell high-density foam approximately 3” thick as opposed to the cheaper systems using mylar, attic insulation, and styrofoam board. Arctic Spa is arguably the best Perimeter insulation system out there.


full-foamThen I choose Master Spas for the full foam system because they use the Icynene open celled foam so they can put 3x more insulation in and still get easy access to plumbing, again they are arguably the best full foam system out there.


I ignored the floor of the hot tub because both of the hot tubs I modeled use high-density foam under the floor, and I ignored the cover because any spa can have any cover and both are available with a 6” FRP covers. I also ignored the Heat reclaiming systems from the motor waste heat because even though the Master uses an active system and is slightly more efficient the Arctic uses a passive system and is a close second. Both spas are pretty good at reusing the waste heat from the motors so that’s not going to be an effector on the running costs and I really wanted to know just how the insulation by the numbers alone without all the bullshit.


So… First off I’m not going to go into How R values work and how these formulas were derived, they are accepted calculations from approved rating agencies and accepted in building standards, In other words the science is sound, there is no arguing that this is the right way to calculate heat loss in a system and if you are an anorak and really want to go to the deep end of the pool follow the links at the bottom of the article.


So here is the comparison by the numbers.


Arctic claims to use 3” of high-density foam and we will take them at their word. High-density Closed cell foam is right around  R-5/inch to R-7/inch when newly sprayed so we will go with an average value of R18 for the system.r-value


Master Spas uses a half inch of closed cell foam on the shell and an average of 8” of open celled foam in the cavity between the spa and the skirt so the R-value of the high density is about 3 and the open celled at R-3.6/inch to R-4.5/inch per inch is another R-32 so let’s round down to R35 for the whole system.


Now Arctic spa claims in their video that the extra R value is meaningless as it is past the point of diminishing returns but what do the numbers say?


We will assume four sides of a 2m wide spa 1m deep or 8m2 of surface area.


We will run two sets of numbers one to assume winter running conditions of 40 °C  (104°F) inside the spa and -10 °C (14 °F) outside. And one to assume spring or fall conditions of 40 °C (104°F) inside the tub and 10 °C (50 °F) degrees outside

heat transferThe energy required to keep up with the heat loss in a system is calculated as follows…


(The surface area of the sides)  X (Temperature difference °C) / (RSI (r value factor for metric)) = Energy required to keep up with the heat loss in watts.

Perimeter Insulation ~ R18 (RSI-3.17)

***Assumes brand new closed cell foam this will diminish over time see below***


@ -10C  8m2 X 50 / 3.17 =  126 Watts

@+10C  8m2 X 30 / 3.17 =  76 Watts

Full Foam Insulation ~ R 35 (RSI-6.16)

@ -10C  8m2 X 50 / 6.16 =  65 Watts

@+10C  8m2 X 30 / 6.16 =  39 Watts


The perimeter insulation system needs almost twice as much energy and therefore costs twice as much to replace the heat lost through the lower R-value insulation system!


So this clearly is a significant amount of energy difference required to keep up with the heat loss but what does it mean in dollars and cents? The perimeter system uses almost twice as much energy to keep up with heat loss as the Full foam system. 

What about the R-value over time?…


Open celled foams do not diminish over time, so the value it has 10 years down the road is 99% of the original value  


thermal driftThe closed cell foams on the perimeter systems use gasses other than air in the cells, known as “captive blowing agents,” these gasses increase the thermal resistance of the foam. However, the gasses leak out of the cells over time and are replaced by air thereby decreasing the R-value. This phenomenon is known as “thermal drift” and applies to all closed cell foams and is covered by ASTM C 1303 in the USA and CAN/ULC-S770 standards in Canada which calculate the loss of R-value over time. A foam starting at R7 will within a few months drop to R6 and CAN/ULC-S770 certification says that this foam should be considered around 5.5 to account for thermal drift over a 5 year period. So the truth is that while the closed cell foams are rated from R-5/inch to R-7/inch at the time of blowing they really should be rated between R-3.5/inch to R-5.5/inch to account for lost R-value over time! So while the pitch is that the hhigh-densityfoams are higher R-value within a 5 year period they are the same as open celled foam and after that are less!


Re-calculating the numbers to account for the loss in R-value over 5 years to give you a real picture of the average R value makes a massive difference.

Perimeter Insulation ~ R13.5 (RSI-2.83)

***Assumes R-value loss through thermal drift as outlined in Underwriters Laboratory of Canada standard CAN/ULC-S770***


@ -10C  8m2 X 50 / 2.83 =  141.34 Watts

@+10C  8m2 X 30 / 2.83 =  84.81 Watts

thermal spa

So when we take all the factors into account the reality is the full foam spa should perform more than twice as well as the best perimeter systems out there. And three to four times better than the worst ones!

This really is no surprise. There are no magic bullets folks just magic spin and marketing, there is a good reason why the full foam systems cost twice as much as the perimeter systems, the numbers say they will perform more than twice as well.


I guess there is no Santa Claus 🙁


Further reading for my fellow anoraks…


How Insulation Works


Insulation values: units of measurement and relationship between parameters


The Science of Spray Foams
Accelerated Aging Test Methods for Predicting the Long-Term Thermal Resistance of Closed-Cell Foam Insulation

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  1. Reply
    Sarah September 11, 2017 at 6:26 am

    I was looking at the Artesian Antigua from Factory Hot Tubs in Oakville.
    From the website, I thought that Artesian hot tubs have full foam insulation. The lady at the store said that it’s foam insulation(I believe she said 3″) is only around the shell, and then they have a reflective barrier. I’m confused…help please.

    • Reply
      admin September 11, 2017 at 2:08 pm

      hmmm it might be that they have changed to a cheaper insulation, I will look into it but if they have they are off my prefered brand… reflective foils are cheap junk…

      • Reply
        Jo September 11, 2017 at 3:02 pm

        I am completely embarrassed. I went to Factory Hot Tubs in Oakville yesterday an under high pressure sales, put a $5000 down payment on an Antigua. I kept saying I wanted to sleep on it but within an hour, he brought the price down from $18,000 to $13,000. How could one refuse. He said it was the last day of their Truckload sale, which included a ton of freebies (I can email you a screenshot of their “Sale” ad)., 1 of which is”Upgraded Glacier Insulation $499 value”. I now realize I’ve been duped. From their website, it says it fully foam insulated. Now that I think back, the service manager mentioned it was 3″ foam insulation on the shell,with a radiant barrier, as well as another radiant barrier inside the skirt. I have serious buyers remorse and don’t know what is the truth now, and what to do.

        • admin September 11, 2017 at 8:19 pm

          It could be worse, you did get the pro sales guy that created urgency and closed the deal but the Artesians are not a nightmare and you ended up a little high in price but not the end of the world… could be worse dude…

          There may be a law in Ontario about a cool down period applicable to truckload or other sales but if it was done on their premise it might not apply.

  2. Reply
    Twan June 15, 2017 at 11:33 am

    Hi Chris, this is a great website with a lot of useful information. I’m from the Netherlands and I have some question related to insulation.
    Last year I owned a locally build Perimeter insulated spa called Silverspas (former USA Heaven spas). It’s a great build tub, hand rolled fiberglas tub, full of waterway parts, extremely powerful, only using one 2,5ph pump, strong 110 watts filtration and very energy efficient. They are using multilayers of insolation, not comparable with Arctic. Down side was the old tub design which didn’t suits my wives body very well, so we made use of their 90 days refund policy.
    We ended up with the second on our list the new Caldera Utophia Tahitian. Same footprint, but a much roomier tub. Same jet power but with two pumps. Insulation and energy consumption wish, not near as efficient as the Silverspas, especially in colder weather conditions.
    Question, what is your experience with the fibercor insulation compare to full foam insulation material? R-value?
    Is it normal that the outside where the edge of the tub ends and the cabinet starts cabinet feels warm? sounds to me like bad insulation, maybe due to the limited space between cabinet and tub.
    Second subject is filtration, now a days, hot tub companies are moving to those small 40 watts filtration pumps to save energy, these pumps are just strong enough to keep the water moving during heating and there filtration capacity is at best just enough. What is your experience? Maybe a nice subject to be discussed next time.
    Thanks in advance,

    • Reply
      admin June 18, 2017 at 2:17 pm

      Hi Twan

      The insulation is a mess… so much misinformation out there. Look at R values… simple as that the science never lies and you can’t beat expanded foam for r-value per inch, it is also the most expensive which is always a good guide to where the truth lies 🙂
      Circulation pumps also called Hush Pumps, and silent flow pumps are sold as an advantage and often as an upgrade on Hot Tubs.

      The Pitch is that they are small efficient pumps that clean your water 24 hrs. a day and are quiet and efficient to run.

      It’s usually about a $500 upgrade and in my opinion, they are not as good a the alternative which is a high flow circ system.

      Although they use a small amount of power they run 24hrs a day whereas the high flow pump only has to run about 4 hrs a day to clean the same amount of water both systems use similar amount a power per day.
      They wear out more quickly because they run all the time.
      The tiny energy savings against the increased cost of replacement parts make them more expensive over the long run.
      They can only filter so much water a day. if you have a heavy bather load or a party or busy weekend of hot tubbing it can take them a while to recover whereas with a high flow system you can change how many hours the pump runs! So after a party you can throw it on 24 hr mode (or any other amount) and it will filter up to 6 times more water than a circ pump can over the 24hr period.
      Circ pumps are also low flow and this means you need to be very regimented with filter cleaning, if the filter gets too dirty they go into flow error easily, the hi flow systems don’t unless you are truly negligent.
      The new anti vibration mounting systems make the good hi flow 2-speed pumps almost as quiet as the Hush pumps, there is very little difference.
      I’m not a fan I think they are sold to add margin into a deal or added value perception. It’s all marketing spin.

  3. Reply
    Emilia April 14, 2017 at 6:21 am

    Great piece of information on insulation systems. Will definitely read more of your articles to gain insights on hot tubs. Thanks.

    • Reply
      admin April 18, 2017 at 1:51 pm

      Hi Emilia!

      Thanks and if you want to contribute send me your articles!

  4. Reply
    Mike February 27, 2017 at 4:07 pm

    Thanks mate! I’ll check that out

  5. Reply
    Sharon Reams January 24, 2017 at 6:30 am

    Great Post! Thanks for sharing the insulation systems properly.

  6. Reply
    Rhys January 21, 2017 at 5:12 pm

    I was looking at the MAAX brands esp. VIta Spa and it looks like they have stopped doing full foam and moved to a copper, recycled insulation, and then thinsulate insulation system. Have you seen these in action yet? I know that mylar has been shown to been a poor insulator but cooper is an almost perfect IR reflector past about 650nm. From the marketing it looks like they are trying to get away from VOCs.

    • Reply
      admin February 22, 2017 at 2:31 pm

      Hi Rhys

      They are actually trying to get away from the high cost of doing spray foam.

      Well the copper is a good radiant reflector the problem is in this application reflective heat systems just do not work that well.

      Reflective systems work well at reflecting heat away from systems and specifically with a specific air gap and in a horizontal orientation. In a vertical orientation, they cause alot fo thermals and do not have adequate thermal mass to contain heat in a system.

      They work well in warm climates for reflecting sun heat away from attics, but if you research it they do not work well in cold climates at containing heat in a system… read this”

    • Reply
      admin January 25, 2017 at 2:10 pm

      A lot of people have stopped because it is expensive.

      And a good sales person can spin any insulation system into a plus. There are great pitches out there for perimiter systems that confuse the issues and trick people with pseudo science

  7. Reply
    Mike January 21, 2017 at 3:51 pm

    Do you have any tips on mats and flooring for the tub to help with insulation or reduce heat loss from the base? I’ve been using a foam mat on top of “astroturf” which is a fake plastic grass, but I don’t think it’s the best. Can you help?

    • Reply
      admin January 25, 2017 at 2:12 pm

      Yeah the base of even the best insulated spas are the lowest insulation.

      First avoid pitting them on decks, and you can put a sheet of 2″ closed cellinsulation under the patio stone base

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