I just picked up an old shell that I am planning on rebuilding. I am in the spray foam business, so I have access to two pound spray foam. I was thinking of spraying about 2-3 inches to the inside of the cabinet walls, the floor of the cabinet and then the top 18 inches of the shell. My thoughts are that the heat from the pumps will then keep the space in the cabinet warm, and transfer through the shell into the water. This will also allow access to the components by simply removing access panels.

Would this be a good way to insulate, or should I spray the underside of the shell. I am located in Ontario Canada, so we get some serious winter temperatures.

Also if I insulate as outlined, would I need any ventilation for the motors. I am looking forward to your response.

Regards
Edtheinsulator

Wont the foam sprayed on the cabinet walls basically "glue" them shut?

As for gaining heat from the pumps... While this "may" be true for the time during which the pump(s) are running, in most efficient spas the pumps are NOT running for the vast majority of the time. The question becomes, will you be losing MORE heat during the time the pump is not running, than you will gain during the time it is?

Thanks for your reply Dr Spa. Good point about the spray foam on the walls, I will probably spray the wall panels before attaching them.

As far as the heat loss when the pumps are not running. There will be a good cover on the hot tub when not in use, the walls are sprayed, and the floor is sprayed, also I will be spraying under the lip of the shell and about a foot below the water line. Would this approach not minimize or virtually eliminate heat loss. My theory is that the warm water will also keep the pumps and hoses from freezing when they are not running.

The foam I am using is 2 Pound polyurethane foam. Do you have any other suggestions or thoughts on this approach.

Maintaining the pipes at 80f isn't going to do a better job at keeping them from freezing than maintaining them at 40f. Of course if there's a long, long power outage, having enough heat from the main spa water being able to keep the pipes and equipment from freezing is a good thing, but at what cost. How less efficient will the spa be overall for this insurance, that may never be needed?

While there are a number of theories on what insulation method is most effective for spas there has NEVER been a side by side comparison of the same spa insulated by different methods.

The worst thing for heat loss is "air infiltration". Think weather stripping around your door. You can put a foot of insulation on the panels, but if you have any kind of air leaks it's all pretty much worthless....

Do you sell spray foam? If so could you PM me the cost?

I'm of the opinion that what you want to do will help keep down the electric cost. As Dr Spa said trapped air will help insulate so if you can eliminate any air 'leaks' it will help without a doubt.

Spa companies that sell un-insulated tubs and claim that air is a natural insulator kill me. Why do we insulate our houses then? When I walk up to service a hot tub in the middle of winter and see steam bellowing out of the wood cabinet like the unit is on fire it always makes me laugh.

Dan the spa Man
Yes I do sell spray foam insulation but it is not in small containers. We buy it in 45 gallon drums and then manufacture the actual foam in our spray foam truck. You can buy small "froth Packs" which will run you around $500. Try fomo products, you can also go to sprayfoam.com, you will find some suppliers there.

Thanks for the info.

Well it has been over a year since I built my hot tub. I did insulate as I described in my original post. The tub has worked phenomonally well. When the tub is in use, the water temperature rises about three degrees in 15 minutes, just from the pumps running. I have checked frequently when the pumps start and the heater never comes on, unless I manually increase the temperature.

I have occassionally openened the service panels, inside the skirt is always warm. Also we had approximately 4 feet of snow last winter, there was no snow melt against the skirt. I have not seen a significant increase in my electric cost, maybe $20 a month. Furthermore, an infra red thermal scan indicated no heat loss through the panels of the skirt. Overall I am very pleased with the results.

I too live in Ontario i found that by insulating the cabinet and base with spay foam works fine(not the tub shell), I insulated the tub by using insulation pillows, if i have to change anything structurally to the tub or repair leaks its not encased in foam that has to be cut out and cleaned also i found that mice like to tunel there way into the spray foam when its sprayed to the tub (nice warm nest for them)

Good thread...

I just picked up a brand new spa and am concerned about the foam inside. It is a partial foam, tub itself and pipes.. it's not too thick not even an inch..

ED: I'm actually just outside of Ottawa so -40 degree winters are not uncommon here. I was almost tempted to go the Mike Holmes route with the spray foam..


I was at Rona and they sell bags of insulation, I forget the rating it's the pink insulation cut into 2 foot square pieces.. I am tempted to go but a few bags and stuff it in the cabinet of my tub.. It's less messy then spray foam and alot easier to work with if something lets go.