Hot tub insulation improvement

oil pan 4 · 08-25-16, 01:17 PM

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.

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.

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.

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.

Daox · 08-26-16, 09:21 AM

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

ecomodded · 08-26-16, 09:30 AM

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

oil pan 4 · 08-26-16, 03:47 PM

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.

oil pan 4 · 05-03-17, 04:29 PM

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.

ecomodded · 07-06-17, 07:19 PM

I was thinking insulating the base would give good gains

oil pan 4 · 07-07-17, 09:07 AM

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.

oil pan 4 · 05-13-18, 07:19 PM

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.

Daox · 05-15-18, 09:21 AM

How thick did that get you?

oil pan 4 · 05-15-18, 09:30 AM

1 to inches on the bottom and sides.

08-25-16, 01:17 PM	#1
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	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. 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. 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. 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. Attached Thumbnails

08-26-16, 09:21 AM	#2
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Sounds like a good plan. What is the plan with insulating the tub itself? __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

08-26-16, 09:30 AM	#3
ecomodded Supreme EcoRenovator Join Date: Sep 2012 Location: Vancouver Island,Canada. Posts: 1,037 Thanks: 116 Thanked 100 Times in 87 Posts	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 __________________ To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

07-06-17, 07:19 PM	#6
ecomodded Supreme EcoRenovator Join Date: Sep 2012 Location: Vancouver Island,Canada. Posts: 1,037 Thanks: 116 Thanked 100 Times in 87 Posts	I was thinking insulating the base would give good gains __________________ To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

05-15-18, 09:21 AM	#9
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	How thick did that get you? __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

08-26-16, 03:47 PM	#4
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	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.

05-03-17, 04:29 PM	#5
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	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.

07-07-17, 09:07 AM	#7
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	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.

05-13-18, 07:19 PM	#8
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	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.

05-15-18, 09:30 AM	#10
oil pan 4 Land owner Join Date: Nov 2012 Location: NM Posts: 1,026 Thanks: 12 Thanked 127 Times in 107 Posts	1 to inches on the bottom and sides.