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Spray foam to insulate under my hot tub

Does Home Depot sell a kit that I can use to insulate under my hot tub?   

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Posted 2013-11-07T12:37:13+0000  by Chuck2013 Chuck2013

Hello Chuck 2013,


Insulating under your hot tub is about as simple as the spray foam you mention in your header: Great Stuff.


There are several varieties of Great Stuff and many are listed as "insulating" on the label.


Ask your Building Materials Associate for a recommendation that meets local codes for use around plumbing and electrical.


This product is tack free in 5-10 minutes.

Posted 2013-11-07T14:02:36+0000  by Pat_HD_ATL

Great Stuff gives off flammable vapors as it is applied and cures.  While not a huge source of ignition, it would probably be a good idea to shut off power to your hot tub during application and until the product is cured.


Wear old clothes and disposable gloves.  Once dried, the foam does not come off easily.

Posted 2013-11-07T14:55:20+0000  by Adam444

I saw cans of Great Stuff online but they said for filling cracks and such.  What should I use for filling a large volume?

Posted 2013-11-07T17:39:01+0000  by Chuck2013

I work on these things for a living and cannot recommend you use poly-foam to insulate your tub.


Start by comparing the cost of poly foam to sheet insulation and regular old fiberglass pink stuff. I think you'll find poly foam is substantially more expensive in the quantity needed to properly insulate a hot tub.


Next, consider what you'll do if there is ever a leak inside the cabinet. Some tubs are built with a fairly thin layer of insulation sprayed on the shell and all the plumbing. You still have to scrape the insulation off to find and fix a leak but it's usually not that big a deal.


Other tubs have the whole cabinet back-filled with foam so there are no open voids. If there is a leak in a full-foam tub, you can plan on hours of labor digging in the insulation just to find it. Small leaks can be impossible to locate in heavily foamed tubs.


If you insulate with sheet or roll insulation, you can just pull the stuff out to work on the tub.


No matter what you use, be sure you don't block ventilation to the equipment especially the pumps. If you seal the thing up air-tight, the motors will generate so much heat they'll trigger thermal cutoffs and most likley shut down.


Rodents love poly foam. On a cold, dark night a hot tub is a warm, inviting, safe place to hide for mice and rats. Once they're in the foam insulation, they can easily tunnel through the entire tub turining it into a rodent condo. The telltale sign will be foam 'popcorn' all over the inside of the tub and, of course, the foul funk that comes from rodent poo and urine saturating the foam insulation. If I could include attachments I would send you pictures of this nasty filth. I have to clean out one or two a month on average.


A few years ago, I worked on a tub on a golf course. Golfers on the fairway complained about rats around a residen'ts hot tub and deck. The tub was so completely infested and so badly contaminated by rodent droppings the health departmetn got involved and the tub had to be disposed of as Hazmat.


There is also a small chance of accidentally smoking your tub. The foam is formed by an exothermic chemical reaction when the A/B mix hits the air. If you spray too much foam into a confined space, it will generate a lot of heat and, in extreme cases,  can catch the tub on fire. If all that plastic starts to burn, all you can do is stand back and wait for the fire department and hope they are equipped with foam. If you hang out around a hot tub factory long enough, you'll probably see a smokin hot tub on it's way out the back door because somebody go tthe poly foam mix wrong or shot too much foam into a small space. It can also bust open the cabinet if it expands too much.


The industrial insulation kits usually contain some form of isocyanate which requires proper ventilation or a 'positive pressure self-contained breathing aparatus' (like what firefighters wear when the go into a burning bulding). People who insulate tubs at the factory usually wear pressurized suits. Anyone remember Union Carbide in Bopahl, India? An accidental release of methyl isocyanate killed thousands. Just sayin: the stuff is somewhat hazardous.


You can also accidntally crush pipe. Many newer tubs have switche from 3/4" Schedule 40 PVC pipe that is glued to fittings to 3/4" clear Vinly pipe that uses barb and clamp connections. If too much foam is applied, it can expand and crush or collapse the more flexible vinyl pipe. It was sometimes a problem when manufacturers first switched to the more flexible vinyl plumbing.


Even within the industry, there is debate over how much foam is really necessary in a tub and whether the added material expense of full-foam tubs produces any real energy savings.


As far as efficiency, the best thing you can do for the tub is buy a good quality spa cover made with closed-cell polystyrene that is at least 3" thick. If your current cover is water logged it has very little insulation value. The water in the cover will actually absorb water from the tub. You are effectively also heating the water in a waterlogged cover which will cost more in electricity.


If your looking to reduce your heating costs, most tubs operate in what is commonly called 'standard mode' which works like an airconditioner or heater in the house. Set the temperature and it maintains all day. The tub is always hot but is always heating and uses the most amount of electricity possible.


Many tubs will also have an 'economy mode' which only heats during programmed filtration cycles. This can save up to 50% over standard mode and is very useful if you use the tub at around the same time every day or only on weekends. Many older tubs will have a mechanical timer so you can set heating times manually.


See your owner's manual or contact the manufacturer for details on economy mode.

Posted 2013-11-08T16:01:51+0000  by HotTubTips
Meant to say: A water logged hot tub cover will absorb "heat' from the tub thus increasing your heating cost because you are also heating the water in the cover all day..
Posted 2013-11-08T16:06:14+0000  by HotTubTips

Thanks for the practical advice.  It's an old tub and I sure don't want to put much money into it, so I think I'll just go get some fiberglass batt insulation and have at it.  Any suggestions for that approach would be welcome.


Posted 2013-11-08T16:52:54+0000  by Chuck2013

Just be sure to leave adequate ventilation for the pump(s).


Don't pack insulation anywhere near the electric motors. Don't seal up any ventilation holes on that side of the tub.

Posted 2013-11-08T23:39:24+0000  by HotTubTips

OK, thanks.  A few years ago I did burn out both pumps due to a prior insulation attempt so I know what you mean.   Right now I have the insulation no closer than 4-5 inches from the pump motors. There are no ventilation holes, maybe I should put a few in?   I'll probably pull out some of the insulation nearest the motors in the summer.

Posted 2013-11-08T23:49:25+0000  by Chuck2013
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