Above ground pool in winter?

[jfriesner]

Am I nuts?
Here is what I've got brewing in my head.
Pour a 8"x6" footer, with rebar, a bit bigger then the pool.
Level good clean sand in the bottom of it 2" short of the top. Then build a 50" treated stud wall the size of the pool liner plus 2" all the way around and attach to footers with 1/2" all thread stubs out of concrete. Wall would go flush with inside of footer. Now add 2" F150 4x8 foam panels to the bottom and sides. I like to cut everything 1/4" short and use pray foam cans to perfectly lock everything together. I can get an intex 12x24 pool liner for $350.

Then place the liner inside and attach to top of wall via screws and fender washers, there wont be any weight pulling down its only to hold in place until filled. Then i would insulate the stud wall with fiberglass and wrap it with plastic vapor barrier. Put some type of barn wood siding on it.

On top of the wall I would put a 1x10 cedar board all the way around and calk the underside of it where it meets the liner just to keep water from splashing into the small crack and down the wall.

Then I would build a lid made out of cedar 2x4 screwed and glued with a slight hump in it to shed water to the sides. The lid would have 2" foam in between all the structural boards. Put a rubber gasket where the lid meets the 1x10 rim so it makes a good seal. Lid would then be roofed with I'm thinking cedar shakes. Attach it with heavy duty hinges on one side and use a winch to lift/lower the lid.
Lastly on one end of the pool I would build a well insulated cabinet to house all the plumbing/electrical.

Now I realize this will take quite a bit of energy to heat 8,000gal up to 95F. But once its there I only need to replace what escapes. I'm thinking by building a giant thermos like this it wont actually lose much. Now I want to be able to use this when its -25F out. I know crazy right. But I am crazy. My hot tub project went so well i'm wanting to expand.

I would heat it with a tubular pool exchanger, thermostat, zone valve type set up.

Thoughts? I think I can do this build for under $1500.

 

[moresnow]

Sounds like fun. Your wood heated hot tub in this weather reminds me of the Norwester Lodge up on the Gunflint. -40F outside. Hot tub was maybe 100' from the room door? Hair would be froze solid by the time you got back to the room. Brrrrrr. Good snow/riding years up there back then. Feeling to old to brave the cold anymore!

 

[jfriesner]

Went out and cut some firewood and had an idea to simplify and cheapen the heating element of this project. Instead of buying a large enough stainless pool exchanger and pump I could just run 1/2" pex on top of the 2" foam in the bottom. Then put 3/4" foam between the runs and lay the liner on top of that. Then I can run it with just a pump, thermostat, and a cheaper plate exchanger since I wont be running pool water through it.

 

[cantoo]

How much heat do you expect to lose when you have it open and using it? Build what you are planning and then put something like this over it. I paid $500 for this size.

 

[jfriesner]

How much heat do you expect to lose when you have it open and using it? Build what you are planning and then put something like this over it. I paid $500 for this size.
View attachment 623742

Wife would not approve of anything tent style. We've had them in the past and she is not a fan. I am not a fan of how much moister they lock in and start to mold. I feel like having a lid that closes close to the water level will help keep heat in and also minimize space for any bacteria/mold to grow.

Calculating heat loss when the lid is up is hard. The pool size will be 12x24 and 52" deep making it just over 8kgal. My hot tub is 1200gal and even when its -20 out with the lid completely off, jets running, and bubbles going for about 15min, it only loses about 1degree an hour. It wont loose anything if the heater is running but i killed power to it just to test how quickly it lost heat. I was amazed at how long it took to finally register 1 degree loss. There are so many variables to account for with heat loss like wind, air temp, humidity, etc... But I figure it i try and plan on designing it to withstand -30 and not require a massive heat load on my heatmor then I should be ok. If not I'll just have to dump 8kgal of hot water on the ground and use it seasonally.

I do know that even on the coldest of days while swimming you will not ever notice it cooling off with that large of a body of water. It will take hours to knock it down enough to notice. My kids will use it probably a couple hours every other day or so. The rest of the time is just maintaining that large body of water at a reasonable temp. I'm thinking of running 500' coil of 1/2" pex under the pool hooked up to a 400,000BTU 30plate exchanger. That should easily be able to replace any heat loss.

Key is going to be to minimize the heat loss while not in use. With my plan I don't think its going to lose much at all. My 1200gal hot tub right now has a 27year old cover on that is warped and falling apart and has 1"+ gaps all over the place and loses heat like crazy. My OWB has no problem keeping it hot and I have not noticed much of an increase in wood consumption after adding it.

 

[greenskeeper]

sounds ambitious, but I doubt you'd be able to get the temperature up to comfortably swim outside in the winter.

just basic math, even if the insulated pool was equal to the hot tub in terms of heat loss, you'd need a OWB 6.6 times larger than what you've got for the hot tub, and the pool is going to have exponentially larger surface area exposed.

An in-ground pool might have a chance, but probably not.

 

[jfriesner]

sounds ambitious, but I doubt you'd be able to get the temperature up to comfortably swim outside in the winter.

just basic math, even if the insulated pool was equal to the hot tub in terms of heat loss, you'd need a OWB 6.6 times larger than what you've got for the hot tub, and the pool is going to have exponentially larger surface area exposed.

An in-ground pool might have a chance, but probably not.

That math would work if it took all the BTU's my stove makes to heat my hot tub. But on top of heating my home and DHW my stove barely notices the hot tubs draw. And after I replace the cover this summer the BTU demand will be reduced at least by 50%. It leaks like crazy right now.

With my design i'm basically building a giant Yeti cooler and i'm betting on the fact that it will not take much to maintain the water temp but will probably put a good load on the system when it is in use. But again its not a public pool that will be open 8hrs a day. Maybe an average of 1hr a day. Right now my hot tub is pulling roughly 6kBTUH. So even with that math my boiler could keep up with an added demand of 39kBTUH but i would go through wood like crab through a goose and loading it every 6hrs. But its not a constant load like that. There will only be a heavy load when lid is up. Once its closed heat loss should be very minimal.

 

[SeMoTony]

Wife would not approve of anything tent style. We've had them in the past and she is not a fan. I am not a fan of how much moister they lock in and start to mold. I feel like having a lid that closes close to the water level will help keep heat in and also minimize space for any bacteria/mold to grow.

Calculating heat loss when the lid is up is hard. The pool size will be 12x24 and 52" deep making it just over 8kgal. My hot tub is 1200gal and even when its -20 out with the lid completely off, jets running, and bubbles going for about 15min, it only loses about 1degree an hour. It wont loose anything if the heater is running but i killed power to it just to test how quickly it lost heat. I was amazed at how long it took to finally register 1 degree loss. There are so many variables to account for with heat loss like wind, air temp, humidity, etc... But I figure it i try and plan on designing it to withstand -30 and not require a massive heat load on my heatmor then I should be ok. If not I'll just have to dump 8kgal of hot water on the ground and use it seasonally.

I do know that even on the coldest of days while swimming you will not ever notice it cooling off with that large of a body of water. It will take hours to knock it down enough to notice. My kids will use it probably a couple hours every other day or so. The rest of the time is just maintaining that large body of water at a reasonable temp. I'm thinking of running 500' coil of 1/2" pex under the pool hooked up to a 400,000BTU 30plate exchanger. That should easily be able to replace any heat loss.

Key is going to be to minimize the heat loss while not in use. With my plan I don't think its going to lose much at all. My 1200gal hot tub right now has a 27year old cover on that is warped and falling apart and has 1"+ gaps all over the place and loses heat like crazy. My OWB has no problem keeping it hot and I have not noticed much of an increase in wood consumption after adding it.

On the heat exchange to the air via evaporation. My Dad's Dad and brothers were all thermo dynamic engineers. I grew up around all types of theories and how it relates to physical actions.
The greater the difference in temperature the faster the movement of heat into the cold side of the movement. That movement will be seen in the quantity of steam above the surface of water. I wish good fortune to you in this endeavor. If I'd actually studied the needed math my opinion wood be backed by approximations of heat loss at a given difference of temperature and the level of humidity. The lower the humidity increases the rate of heat transfer also, which is why an enclosure wood also be a help. The enclosure wood not need to be heated itself as the open pool wood warm the air while increasing the humidity inside to slow the heat transfer. I hope that bit of info on the physics that I know is an assist.
Stay safe and warm Folks

 

[unclemoustache]

Nothing ventured, nothing gained. Give it a shot. It's only money, and if it works, you'll be everyone's favorite neighbor!

Sounds like fun. Your wood heated hot tub in this weather reminds me of the Norwester Lodge up on the Gunflint. -40F outside. Hot tub was maybe 100' from the room door? Hair would be froze solid by the time you got back to the room. Brrrrrr. Good snow/riding years up there back then. Feeling to old to brave the cold anymore!

Growing up in MT, dad would play basketball on Thursday evenings with some other friends down at one of the high schools. We three brother would tag along and play on the gym equipment, shoot hoops ourselves, or whatever. We'd all shower in the locker rooms but not dry our hair. We'd then go outside and run around until our hair froze. Ears darn near froze as well, and I hate cold ears, but I wanted frozen hair more!

 

[greenskeeper]

That math would work if it took all the BTU's my stove makes to heat my hot tub. But on top of heating my home and DHW my stove barely notices the hot tubs draw. And after I replace the cover this summer the BTU demand will be reduced at least by 50%. It leaks like crazy right now.

Whatever the load it's at least 6.6 times more, probably closer to 10x due to the increased surface area exposed to heat loss.

I guess if you got it up to 95F in the fall and kept it there it might work.

 

[Woodcutteranon]

I follow this couple on Youtube who are transitioning to off-grid living. They built a wood fired hot tub and this reminded me of what you are trying to do. I know this is much smaller scale than a pool but could be thought provoking. This video below is a short look at what they accomplished but they have an entire 11 video series on their entire project.

 

[OnTheRoad]

How many cord a year do you think it would take?

 

[jfriesner]

How many cord a year do you think it would take?

Hard to know for sure. We are on track to burn 8-9cord this year from October 1 to May 1. I'm guessing its gonna take an additional 2-3cord a year to heat a pool that size. But again i only need to replace whats lost and my experience with closed cell foam is it does not loose heat very easily. My hot tub was not designed for MN winters and was shipped from California. All I did was put 1-1/2" foam panels all the way around it and spray foamed any cracks shut. It stays at 106F no matter what and does not put much of a load on our system at all.