Hot tub insulation improvement
 

I got this little gallon hot tub for my wife.
It holds around 280 gallons of water and has a 1,000 watt heater and it sits outside.
I figure if it gets cold enough and the heater runs all the time that could increase the power bill by up to $75 a month. That is really bad.
Then I remembered I own a FlirI7 thermal camera this should be easy.

This picture is the cover to the hot tub. You see the one line of heat escaping, that is where the cover folds. As you can see about 99% of the rest of the covers surface area is doing a very good job.
http://ecorenovator.org/forum/attach...1&d=1472144988

This is not a very good image of the side. As you can see some heat is getting away. It was 64'F that night.
http://ecorenovator.org/forum/attach...1&d=1472144988

The most obvious place for improvement. The filter housing. Just wrapping some insulation around it should take care of it. The water in the hot tub is 99'F that housing is pretty close to 99'F.
http://ecorenovator.org/forum/attach...1&d=1472144988
The filtering assembly will likely get a foam box built around it.

Turning the hot tubs temperature way down then back up to save power really is not an option right now. I figure with the 1,000w heater it will only be able to raise the temperature 3'F every 2 hours assuming no losses, so I got an 240 volt powered industrial grade 500w fish tank heater to help. It looks dangerous and is not GFI protected so it wont be on while anyone is in the tub.
The fish tank heater and the built in heater could bring the temperature up 2'F every hour.
If it works well I may order another one or 2.
I think what I can do on her last night off turn the temperature down, so the heater maintains a much lower temperature the 3 nights she works then turn it back up the morning she starts her 3 days off.
With the outside temperature being between 65 and 70 at night the tub can lose up to 5'F per hour while the cover is off. Only opening half the cover cuts losses to between 1'F to 2'F per hour.

Sounds like a good plan. What is the plan with insulating the tub itself?

I'd probably add a rigid foam skirt with a ceder surround or whatever.
For an similar effect as the slow cooker Pot cozy.

My insulated bathtub is keeping the water hot/warm for 2.5 hrs at a time

The vertical sections are insulated by about a half inch of wood and about an inch of Styrofoam. I do not know what the cover has inside it, but it appears to be working very well.

Opened it up this year but before I put the liner on the in the frame I took a bunch of 1/4 inch thick high density floor under layment cut it to fit my hot tub corners and layed it down layer by layer until it was at least an inch thick. Then put 1 layer around the inside.
So now instead of just sitting in the ground it's sitting on an inch of Styrofoam.
The flir is showing less heat loss, I just need to wait for another 64°F night to check it's heat loss again. For consistency and to make a good comparison.

I was thinking insulating the base would give good gains

You see the ring of heat around the base in the original post pic, it's not there anymore.
That's the main difference.
Next I'm going to spray foam the inside walls, I could add 1 to 2 inches of foam, there is an air gap where the liner doesn't even touch the side most of the way down the sides.

I sprayed about $200 worth of 2 canister AB foam in the hot tub this year, it can still go on a little thicker in a few spots.

How thick did that get you?

1 to inches on the bottom and sides.

Are you going to post after IR pictures.

Yeah if I can get another night close to 64°F

This is a fantastic application for a heat pump. you need a lot of 'low grade' heat delivered at around 110ºF. your 1kW heater delivers about 3300 BTU/hr. a typical 500-600W heat pump/window shaker will deliver 7-8000BTU/hr. that's 240% the heat delivered for 60% the operating cost, not including the fact that when you reach your setpoint it'll shut off.

judging by your note above, you pay approxmately $0.10/kwh. 24hrs*31days*1kw*$0.10/kwh=$74.4 for 1kw electric heater
delivered BTU/month = 2,455,200
BTU/dollar = 33,000

24hrs*31days*0.5kw*$0.10/kwh=$37.2 for 500w heat pump
delivered btu/month = 5,952,000
BTU/dollar = 160,000

I thought about using my heat pump water heater but I have no idea if it's insides can take bromide levels like found in a hot tub.

the general wisdom seems to be to use a secondary exchanger, or a titanium hx for direct contact. otherwise how long they last probably depends on the metal and pool chemistry.

When you work on the filter see if you can add a section on the return where you could add a heat exchange.

About 7 years ago we installed a hillbilly hot tub a 6' diameter galvanized stock tank.
we wrapped the wall with about 1" of flexible foam insulation and placed the tub on 2" of styrofoam wrapped in a tarp. We started out with a propane hot water tank with snap switches running the circulation pump. we tried a babington burner using used veggie oil, and later added a barrel stove, put in a liner & insulated the space between and made a heat exchanger out of 1 1/2" galvanized pipe in the firebox for the last 4 years we now heat the tub with wood. The stove is lower than the tub, so thermosyphons and needs no pump. We do not like chemicals so had to change the water at least once a week in warm weather. Two years ago we build a sand filter in a 50 gallon barrel and use a float switch and a shurflow 12V pump powered by a solar panel. Now we have crystal clear sweet smelling water and seldom change the water When we first fill the tank after our Mexican winter we first pour a gallon of bleach into the filter then fill the system through the filter, the bleach is very diluted and after running through the heater loses its chlorine smell. The firewood we burn is obtained from a local mill which puts its unused log offcuts in a pile and allows locals to take.
I think we have a pretty good system, tho we will have to buy a new stock tank for next summer.
Cheers, this is my first post for a few years as we are super busy building a house.
Just poured the master bed rm floor over radiant pipes today.

You missed the boat by about 4 and a half years.

Yeah, did not notice the date until after I wrote it............ better late than never.

It's rain water collection now, since the pump died.