My hot tub uses 49% of my electricity per month...lets fix that.

[tmprof]

So a few years ago, I bought an old broken down hot tub for $300 and restored it to working order. This took me about 2 months since all the frame wood was rotten and all of the jets were leaking. I re-sealed everything, rebuilt the 2 main motors and added an additional circulation pump for heating. I also bought a brand new control module with a 5.5 kw electric heater.

Fast forward to September 2023 and I have installed a 5kw solar system with a 30kWh battery that is working amazing. Here is the graph of my solar / consumption:



My hot tub heats 10-11 times per day using avg 6100w for 20 mins each time. This ends up being about 21.9kWh per day, 657kWh per month. This is nuts...I know people on this forum say that a hot tub really drains the power but I had no idea!

My solution was to purchase a natural gas tankless water heater off of craigslist (cost me $100) and use that in place of the electric heater currently in use:

I tested it and it seems to be heating properly up to 140 degrees.

 

[Lt.Dan]

So a few years ago, I bought an old broken down hot tub for $300 and restored it to working order. This took me about 2 months since all the frame wood was rotten and all of the jets were leaking. I re-sealed everything, rebuilt the 2 main motors and added an additional circulation pump for heating. I also bought a brand new control module with a 5.5 kw electric heater.

Fast forward to September 2023 and I have installed a 5kw solar system with a 30kWh battery that is working amazing. Here is the graph of my solar / consumption:

View attachment 182668

My hot tub heats 10-11 times per day using avg 6100w for 20 mins each time. This ends up being about 21.9kWh per day, 657kWh per month. This is nuts...I know people on this forum say that a hot tub really drains the power but I had no idea!

I have the same problem, but mine is only 120v ? I rarely use it though, so it's rarely on. But it takes a full day to get hot

 

[peakbagger]

All You've Ever Wanted to Know About Wood Fired Hot Tubs

A deep dive on owning, maintaining, and enjoying all the benefits of a traditional wood fired hot tub or cedar soaking tub at home

www.fieldmag.com

 

[tmprof]

So here is my plan:


I'm going to add a section of plumbing that inserts the NG heater into the hot tub existing plumbing.

 

[peakbagger]

All You've Ever Wanted to Know About Wood Fired Hot Tubs

A deep dive on owning, maintaining, and enjoying all the benefits of a traditional wood fired hot tub or cedar soaking tub at home

www.fieldmag.com

Do you have a floating insulated cover?. That can help. If the tub is not insulated underneath and is just raw fiberglass that is also a heat loss.

 

[tmprof]

I have 2 concerns with this.
1. Will the circulation pump put too much pressure through the NG water heater
2. Will the current hot tub controller freak out since the water will be heated more than the existing 5.5kw heater

To prevent this, I added a bypass valve between the hot and cold hoses so I can mix some of the cold water with the heated water. This will reduce the water flow going to the NG heater and also let me control the temperature of the hot water going back into the hot tub by mixing some of the colder water in with it.

 

[tmprof]

Here is the plumbing I bought to do this:






You can see the bypass valve I added to control the flow/temp and also the cold water temp sensor to measure the incoming water temp.

 

[tmprof]

Do you have a floating insulated cover?. That can help. If the tub is not insulated underneath and is just raw fiberglass that is also a heat loss.

I have a thick cover, but not a floating one. I added a lot of insulation between the fiberglass and the wall of the hot tub. Just went to Home Depot and picked up some rolled up home insulation.

 

[teal95]

Yep, hot tub is roughly 50% of our electric also. It's my wife and daughter's toy so I just live with it.

 

[peakbagger]

FWIW, if there is any space between the liquid and the cover there is significant convective air flow that is created. I have seen but do nto know the source of floating covers that sit directly on the surface. That makes a big difference in heat transfer out of the liquid

 

[tmprof]

I'm really bummed since the next 2 weekends I'll be traveling for Holiday / family stuff. My plan is to add this the week after Christmas. One more thing I'll have to do is create a waterproof box around the NG heater since this will be outside. I'm going to be attaching it to one of the fence 4x4's that sits about 3 ft from the hot tub. Last weekend I added an additional Natural gas line with a ball valve (I love PEX) next to the hot tub. I already had a line ran for the outdoor fire pit so it was easy to just "T" off of it for the heater.

 

[tmprof]

FWIW, if there is any space between the liquid and the cover there is significant convective air flow that is created. I have seen but do nto know the source of floating covers that sit directly on the surface. That makes a big difference in heat transfer out of the liquid

Yeah, I totally agree. Also, my hot tub cover is very old that came with it when I bought it. I'm planning on purchasing a new one next year.

 

[tmprof]

Yep, hot tub is roughly 50% of our electric also. It's my wife and daughter's toy so I just live with it.

Ooooh yeah, I LOOOOVE my hot tub. My family and I get in it several times a week. There is no way I'd decide to remove it.

 

[Crowz]

Yep hot tub as I said before is Dark Lord of the Sith evil when it comes to power usage !

Your plan looks sound though

 

[teal95]

My parents had one so I've had one available for 20+ years. I think I've been in one maybe 3x of my own volition. I missed the fish gene...

 

[yodamota]

Is there any chance you can hook up a immersion heating element as a dump load when you are at float? to supplement the gas heater?
of course it would need to be protected from pesky feet.

 

[tmprof]

Is there any chance you can hook up a immersion heating element as a dump load when you are at float? to supplement the gas heater?
of course it would need to be protected from pesky feet.

That's an interesting idea! I have a very old hot tub with a large area where the filters are located. There is plenty of room to add a heating element here. I'd have to be able to control it so it doesn't overheat the tub tho.

 

[James Getman]

I turned on my new solar the first week of November and was amazed how much power the hot tub used, drained the battery in no time. Tried shutting the spa off after use in the early evening, and restating when the sun comes up in the morning. The temperature defecet would take half the day to restore. Air temperatures around freezing take the fun out of the spa, so shut it down for the season. Will see how it works out in April.

 

[yodamota]

That's an interesting idea! I have a very old hot tub with a large area where the filters are located. There is plenty of room to add a heating element here. I'd have to be able to control it so it doesn't overheat the tub tho.

well sounds like you have it made in the shade! I am curious if you would need a thermostat if the thing was only on for a few hours per day. either way I am sure you can get a thermostat to control the element.

 

[Lt.Dan]

Air temperatures around freezing take the fun out of the spa, so shut it down for the season. Will see how it works out in April

I am thinking about putting mine in a shed for this exact reason... I've seen it a few times, mini-bar, TV, etc. Makes it much easier to get out of the hot tub without freezing your balls off.