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

T

tmprof

New Member
Joined
Jun 9, 2021
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70
Location
Humble, Texas
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:

1702486550711.png

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:
1702486763456.png
I tested it and it seems to be heating properly up to 140 degrees.
 
tmprof said:
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!
Click to expand...
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
 
So here is my plan:

1702488570201.png
I'm going to add a section of plumbing that inserts the NG heater into the hot tub existing plumbing.
 
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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.
 
Here is the plumbing I bought to do this:

1702487179912.png

1702487196141.png


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.
 
peakbagger said:
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.
Click to expand...
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.
 
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
 
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.
 
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peakbagger said:
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
Click to expand...
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.
 
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 said:
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.
Click to expand...
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.
 
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.
 
tmprof said:
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.
Click to expand...
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.
 
James Getman said:
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
Click to expand...
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.
 
yodamota said:
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.
Click to expand...
The NG heater turns on when it senses water flow which is already controlled by the hot tub. I'm hoping I won't need to add an external thermostat or timer.
 
A lot of those type O.D. setups are prone to freezing damage. Fyi if it applies to anyone’s location.
 
QCA spas are not made to be drained for freezing weather. High spots in the plumbing don't completely drain causing freeze damage. Pay the power company all winter or hire a tech to properly drain it every fall. I added a plug and use a shopvac the get most of the water out.
 
If your wanting to shut the hot tub down then you just put antifreeze in it. Here's a howto I found that covers it :

Before draining the hot tub, be sure to get these pieces of equipment as they will be needed:

A wet and dry vacuum cleaner to suck out as much excess water in the pipes, jets, and hot tub as possible.

A garden hose to help with draining from the hot tub’s drainage plug.

Towels to assist with absorbing the water from the bottom of the hot tub.

Propylene Glycol Antifreeze/Non-Toxic Antifreeze to keep the hot tub’s pipes from freezing during the winter. This is a very specific type of antifreeze that is sold for hot tubs. Do not use the type that you would use for your vehicle as it is toxic.

A long funnel to assist you in pouring antifreeze into the hot tub’s narrow openings.

The best propylene glycol antifreeze on Amazon is from Engine Ice.

It’s an Amazon’s Choice product, has hundreds of near 5-star reviews, comes with free Prime shipping and is at a great price (especially compared to the others on Amazon).



How to Get a Hot Tub Ready Again after Winter

This is important information to know. After all, you don’t want you, your family members or any guests soaking in antifreeze!

So first, you are going to have to remove all traces of the antifreeze from your hot tub before it is safe to use.

To do this, you need to fill the hot tub with water. Then add 2 times the amount chlorine or bromine that you would normally use to neutralize the antifreeze.

After that is done, you will need to repeat the steps above to drain the hot tub. Then refill it again before placing your clean filter cartridges into their places.
 
AmpD said:
A lot of those type O.D. setups are prone to freezing damage. Fyi if it applies to anyone’s location.
Click to expand...
I live in Houston and we don't get a lot of heavy freezes. I'm hoping that since this runs every 2 hours or so, it won't freeze maybe? Also, I'll insulate the hoses as well as keep the NG tankless heater in a waterproof enclosure
 
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