Insulate hot tub for -40 in AK

[jpowell1979]

Ok, I got a steal on a used 7-person hot tub. I'm installing it outdoors in Fairbanks, Alaska so we can watch the northern lights is comfort. Temperatures routinely go south of -40 in December and January. I'm looking for ideas on how to best increase the insulation to keep the heating costs down. Looking inside it has a good couple of inches of spray urethane insulation already but some of the pipes are on the outside of the insulation.

My plan is to take 1 or 2 layers of 2" rigid insulation and attach it all around the cabinet with screws and washers. I was then going to attach furring strips and get some cedar T/G to basically match how the existing cabinet looks. On the top I was gong to nail on a 2x4, attach a strip of cement board and run bullnose tile all around the edge of the 4" that the insulation will stick out.

Anyone have a better idea?

 

[SolarAndWood]

Don't install it within sight of your electric meter. Even with a tub/cover designed for Northern climates, we rarely saw any snow on the cover unless it was in the middle of a squall. The snow would be 4 or 5 feet high on the deck and the cover was alway perfectly clear. When are the northern lights out? Maybe drain it for the coldest months? Even if it is close to the door, I can't imagine that it will get used when it is -40 out.

 

[zzr7ky]

Hi -

I use 2 covers at the same time. That helps here in )F weather.

Mike P

 

[jpowell1979]

A local retailer makes 6" insulated covers that are R-30 and they really cut the costs down.

I don't think that it will get much use below -20, but up to that is great fun. At this latitude the northern lights are out pretty much all winter and draining would be more hassle than anything.

My ultimate goal will be to get another heat exchanger and run this tub off my wood boiler. No sense is paying for what could be free.

 

[Corey]

You will want good perimeter insulation for sure. Also consider shooting some expanding foam in the space between the rigid foam on the skirt and the hot tub itself. The thicker the cover, the better, but you will loose a lot of heat to evaporation/condensation, so you may also want to look into a floating blanket to put on the actual surface of the water...again, the thicker, the better, plus, you can peel off the blanket for only the water you want to use and not have the whole surface exposed to the cold. I've considered putting a layer of ping-pong balls in my tub to cut down on heat loss, but don't know how it would work long term.

 

[gpcollen1]

If you are going to build out the platform for tile and insulation, maybe try installing a hinged cover with 6" or so of insulation.

 

[EatenByLimestone]

Can you install it inside?



Matt

 

[billb3]

Can't you watch the Northern Lights with your clothes on ?

 

[Flatbedford]

Maybe put it in a greenhouse?

 

[jpowell1979]

Well I visited the local hot tub retailers in town who specialize in outdoor tubs for our climate. They insulate the cabinet and floor with 2-4" of urethane spray foam and claim you can go for a weeks without power at -20 with no freeze up. They also sell the 6" insulated covers. Here is their website if you are interested. (broken link removed to http://www.arcticspas.com/index.php/en/show_content/2/38/)

Since the shell is already spay foamed a couple of inches I will add the 2" insulation underneath and all around the perimeter. I will try and get the foil lined type to reflect the radiant heat back towards the tub. Combined with the existing insulation I should have close to R-30. With all this I can't imagine the idle heat loss to be very much. Putting the tub indoors is not really an option for me.

 

[woodsman23]

Get a couple fat chicks and leave em in there.

 

[fespo]

I have mine outside and I added reflect x (sp) on the inside shell, then another layer of reflect x on the outside shell, then 4in Styrofoam. On the top cover I made a big blanket of the refect x to cover over the sides and it works great . I did get this stuff for FREE from my old job. It was left in the warehouse and I was told to clean it up. So i did clean up 8 rolls of 12' x 60' into the back of my truck. Boy do I miss that old job for the free stuff companies would leave behind. Just a waste

 

[Highbeam]

I have an 8' tub in WA. The snow accumulates on the standard 2-3" cover just as quickly as it does on the picnic table beside it. I also use a floating blue bubble sheet of plastic to help keep the water and chemicals in the tub.

My tub (a phoenix spa) came with the same 2" or so of spray foam on the shell as you describe. It also has a one inch layer of foil faced insulation board at the cabinet walls probably more for sound than insulation value.

Do note that you have two or more 5-6 HP electric motors inside that cabinet that need air to prevent overheating so you can't just fill the bloody thing with foam. Also consider that you will need access to these motors and wiring areas under the tub so keep them clear.

Every tub that I've seen rests on little or no insulation directly on the ground membrane. Meaning that you can't insulate under the tub. But you can set the entire tub down on a layer of XPS insulation. Consider it a raised hearth.

Have you thought about burying it? To protect it from the wind and to make entry easier. If you can't protect it with earth then you can build a super cool insulated deck around it to minimize the exposed tub surface. It will make climbing in and out easier too.

Most tubs will not be able to keep up with the heat loss while opened up in low temps. Even worse if you run the blowers. My 60 amp 220 tub will slowly lose heat if ambient temps are in the teens. Your time in the tub will be limited.

I could not imagine living in a cold climate without the tub. Ours only added a slight amount to the power bill. Enjoyment is huge.

 

[firefighterjake]

. . .
I could not imagine living in a cold climate without the tub. Ours only added a slight amount to the power bill. Enjoyment is huge.

My wife and I love getting in the tub in the winter . . . for me it's a good way to unwind after a long day of sledding . . . and for her (not a lover of Maine winters) it's a way of getting outside and enjoying the fresh air. As you said, it's worth the minimal cost to us.

 

[Flatbedford]

My wife has wanted one since we bought the house six years ago. Maybe I'll use all the money I save heating with free wood to get one. :lol:

 

[Bobbin]

You haven't lived until you've had to replace a zipper in one of those insulated folding hot tub covers. The sewing is the easy part... what really sucks is getting the rigid insulation in and out of the form-fitting cover. We charge accordingly. The vinyl used to cover the insulation is probably the worst material in the world to withstand the constant folding and the manufacturers naturally NEVER reinforce the areas that bear the repeated stress...

It's just about time for some of those to roll into the shop, they usually follow right on the heels of pool covers... yippee! it's called job security.

 

[TreePapa]

My wife has wanted one since we bought the house six years ago. Maybe I'll use all the money I save heating with free wood to get one. :lol:

Check C/L ... round here, there's always several being given away if you can haul 'em away. A few are even in decent shape. One of them tubs should fit nicely on your old flatbed, you just need a few buddies to help you get in on (and off) the truck.

Peace,
- Sequoia

 

[stejus]

Two ways to look at heat loss in a hot tub.

1. Cold air penetration around the bottom and sides.
2. Heat loss from rising steam in hot tub.

I was told most heat loss is from a poor cover. Heat rises so it makes sense. If the cover sags and collects water, it may be time to replace. Most covers are designed to last 5 years. I don't see any harm with adding another layer of insulation around the perimeter during your cold months. I would not do this when temps get above freezing in fear of over heating your pumps. They generate heat when running and if they overheat, there goes your pumps.

The only exposed plumbing should be in the control panel area where the electrical and pumps are located. They make insulated blankets to fit in this area during winter months. The other internal plumbing is insulated.

I would not drain and fill very often in your climate. If you drain, you have to make darn sure you blow out the lines. If you don't, kiss the hot tub goodbye as the internal plumbing will look like shredded cheese once the cold air gets to them.

I've used my hot tub when temps were near zero. I don't think I'd want to do -40 degrees! Must be what we're used to I can't see the northern lights in my part, just the stars and few planet's visible from earth.

 

[Highbeam]

There is lots of plumbing under the tub shell that is not insulated. For instance, all of the pipes to and from the pumps and the lines from the filters. Only when these lines get near the shell do they get coated in insulation.

Newly rebuilt 6HP pumps are 200$ each in my area. I just replaced one.

We sat out in the hot tub when the air temp was in the mid teens and the wind was blowing. My oh my did we get windburned and our ears were numb. The beverages stayed cold on the tub's edge though.

 

[zzr7ky]

Hi -

When I was in Manley Hot Springs the naturally hot water tubs are inside a frame that has a couple layers of plastic and a blower motor or to keep it inflated.

I also keep 2 hot tub covers on the tub in the Winter. It helps.

Mike