Freeze Prevention for a Hot Tub

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mkgrady

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Massachusetts
Is there a way to keep a hot tub from freezing during a power outage utilizing a portable generator? I'm looking at powering a home with a 7.5KW portable during any power outages. It will all be done to code with an interlock, inlet, signage, inspection and all the rest. I have done several of these already.

Of course the HT needs a 50 to 60 amp circuit to fully function so the generator will not be large enough for that. I would expect it to be able to run just the pump and not the heat but i don't even know if that is an option on a hot tub. If not, are there other ways of keeping the thing from freezing. I'm picturing running a cord from a GFCI receptacle and plugging in some kind of submersible heater that might draw only a few amps.
 
How long a power outage are you planning for? If it's well insulated, it'll take quite a long time to cool off.

Does the generator have a water-cooled engine? Install a liquid-to-liquid heat exchanger and use the engine's waste heat.

With or without freeze protection, it will require some sort of interlock to prevent the hot-tub heater from turning on while the house is generator powered. Maybe the interlock can also switch the hot tub over to a small (1 kW?) auxiliary heater and a second thermostat, set to about 5°C.

A thermostat and solenoid valve could be configured to drain the hot tub before it freezes.

This can't be the first time this has come up. Does the manufacturer have a recommendation?
 
A quick Google search should reveal how to keep hot tubs from freezing in the winter. Some have built-in sensors that turn on the pump near freezing temperatures, winterization is one way, draining is yet another. One website recommended 100 W shop light installed under the skirting, skirting should be intact, cover should be on.

Waste heat from the generator would be a Nifty set up for sure, however it's probably a plumbing Nightmare, and I have never seen a 7 kilowatt liquid-cooled generator
 
drcampbell said:
How long a power outage are you planning for? If it's well insulated, it'll take quite a long time to cool off.


Does the generator have a water-cooled engine? Install a liquid-to-liquid heat exchanger and use the engine's waste heat.

With or without freeze protection, it will require some sort of interlock to prevent the hot-tub heater from turning on while the house is generator powered. Maybe the interlock can also switch the hot tub over to a small (1 kW?) auxiliary heater and a second thermostat, set to about 5°C.

A thermostat and solenoid valve could be configured to drain the hot tub before it freezes.

This can't be the first time this has come up. Does the manufacturer have a recommendation?
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We have had power outage of a week in my area the last couple of winters. Not near the main lines but at the end of branches. That where this guy is located.

Air cooled generator.
The interlock I plan will just prevent the service main breaker from being on while the generator is powering the panel
Draining does work but not practical if they want to use the tub during the winter. You just don't know when the power will go down.
 
JFletcher said:
A quick Google search should reveal how to keep hot tubs from freezing in the winter. Some have built-in sensors that turn on the pump near freezing temperatures, winterization is one way, draining is yet another. One website recommended 100 W shop light installed under the skirting, skirting should be intact, cover should be on.

Waste heat from the generator would be a Nifty set up for sure, however it's probably a plumbing Nightmare, and I have never seen a 7 kilowatt liquid-cooled generator
Click to expand...

I like the light bulb idea. I'm surprised the manufacturer would think it would supply enough heat though. I guessed the heat would have to be submerged. I was thinking something like heat tape for pipes only submersible
 
mkgrady said:
I like the light bulb idea. I'm surprised the manufacturer would think it would supply enough heat though. I guessed the heat would have to be submerged. I was thinking something like heat tape for pipes only submersible
Click to expand...

As long as you keep a pump running with all Jets open, you should not have a problem with freezing, unless it is a sustained negative degree Fahrenheit cold. Many Spas already come with this feature included. If the spa you are installing already has automatic freeze protection, no further actions are needed.

Eta: if you are planning on losing power for a week in sub-freezing temperatures, the homeowner should either freeze protect his spa or drain it.
 
JFletcher said:
As long as you keep a pump running with all Jets open, you should not have a problem with freezing, unless it is a sustained negative degree Fahrenheit cold. Many Spas already come with this feature included. If the spa you are installing already has automatic freeze protection, no further actions are needed.

Eta: if you are planning on losing power for a week in sub-freezing temperatures, the homeowner should either freeze protect his spa or drain it.
Click to expand...

The automatic freeze protection feature sounds great if it has it. Is it common in hot tubs? Is there a mode of operation that tells the equipment to not heat but to also not freeze? Obviously if the unit is powered it will keep heating the water without this feature and then of course there goes the generator output breaker. I'll have to look at the manual for that hot tub model. Of course I don't know what it is without returning to the site. Not going back unless they say yes to the quote.
 
does it need to be automated?
most modern day manufactured hot tubs have a low temp threshold that will kick on the heater, but on a generator that is not sized to handle the tub then that might be too much for the gen.

even draining a tub and then allowing it to freeze can cause major damage.

perhaps best to protect the hot tub by sizing the gen to include the power needs of the tub.

w/o powering the tub directly from gen you need at least a submersible heater hooked to gen power. If the tub has insulted cover then perhaps a 100watt heater would keep it from freezing, all depends on how cold things get.
 
Just about all spas/hot tubs made in the last 7 or so years have electronic controls,,trying to just hook up the pump and heater would require getting into the control pak and attempting to bypass the main boarc,,,not a good idea,,heater and temp control are done electronically,,,old tubs that use air controls you might be able to do this, but there are still some electronic components that would have to be dealt with,,,,basically if you can't supply the 50 or 60 amps needed, don't mess with modifying the control pak,,,New boards and paks are not cheap!
 
mkgrady said:
The automatic freeze protection feature sounds great if it has it. Is it common in hot tubs? Is there a mode of operation that tells the equipment to not heat but to also not freeze? Obviously if the unit is powered it will keep heating the water without this feature and then of course there goes the generator output breaker. I'll have to look at the manual for that hot tub model. Of course I don't know what it is without returning to the site. Not going back unless they say yes to the quote.
Click to expand...
Freeze protection is usually programmed into the pak, but it is an option that can be turned off,,,best to find out the manufacturer and make of the pak,,just knowing the make and model of the tub will not always give you the info you need about the control pak
 
The manual with my spa specifically states that draining is not sufficient for freeze protection.
Apparently the normal drain will not empty everything. I would need to tear apart the internal piping.
 
retirede said:
The manual with my spa specifically states that draining is not sufficient for freeze protection.
Apparently the normal drain will not empty everything. I would need to tear apart the internal piping.
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Or drain what you can, add antifreeze and run the pump briefly.

Sent from my XT1585 using Tapatalk
 
Spa plumbing typically gets blown out with air,,there can be over 10 gal. of water remaining in the lines on a "drained" spa, due to the plumbing configurations, anti freeze does not provide adequate freeze protection,,,to blow out the lines, plumbing must be disconnected at all unions and each jet has to be blown out individually from the inside of the spa
 
JFletcher said:
A quick Google search should reveal how to keep hot tubs from freezing in the winter. Some have built-in sensors that turn on the pump near freezing temperatures, winterization is one way, draining is yet another. One website recommended 100 W shop light installed under the skirting, skirting should be intact, cover should be on.

Waste heat from the generator would be a Nifty set up for sure, however it's probably a plumbing Nightmare, and I have never seen a 7 kilowatt liquid-cooled generator
Click to expand...

Can you even buy a 100 watt light bulb anymore?
 
Patwano said:
... There can be over 10 gal. of water remaining in the lines on a "drained" spa, due to the plumbing configurations, anti freeze does not provide adequate freeze protection,,,to blow out the lines, plumbing must be disconnected at all unions and each jet has to be blown out individually from the inside of the spa
Click to expand...
Yikes! If you don't plan on using it all winter, that's a crapload of labor to shut it down for the season. Which part of "water runs downhill" is incomprehensible to spa designers?

tkb said:
Can you even buy a 100 watt light bulb anymore?
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You can buy a 150-watt light bulb, (and 200, 250 & 300) but why would you want to? It'll burn out in a thousand hours, (⅑ of a year) and getting its heat into the water will be indirect at best. A small strip heater would offer much better longevity & reliability, and I have my doubts that 150 watts is enough heat for Massachusetts.
 
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If you don't have a freeze protection option in controls, the thing to remember is the place(s) that are likely to freeze and cause damage is in the piping under the tub.

As mentioned just placing a 100 watt bulb inside the closure will make a huge difference. Placing an aquarium heater in the tub will do nothing for keeping the pump and piping from freezing. All the heat applied directly to the tub will rise to the top levels of the water in the tub, those bottom levels will continue to get colder.
 
is the anti freeze setup supposed to be fool proof and be left unattended if power goes out and gen kicks on?

i would not use a light bulb, they too fail often, even an odd harmonic from gen power could cause a tungsten filament to fail very quickly. use a heating matt instead.

but how does gen power get to the make-shift heating element? someone strings out some extension cord and jams a heating element behind the skirting of the tub?

would it not just be easier to size the gen to be able to power the tub heater and low-speed motor, thats usually how these tubs operate when low temp threshold protection kicks on.
 
FionaZuppa said:
is the anti freeze setup supposed to be fool proof and be left unattended if power goes out and gen kicks on?

i would not use a light bulb, they too fail often, even an odd harmonic from gen power could cause a tungsten filament to fail very quickly. use a heating matt instead.

but how does gen power get to the make-shift heating element? someone strings out some extension cord and jams a heating element behind the skirting of the tub?

would it not just be easier to size the gen to be able to power the tub heater and low-speed motor, thats usually how these tubs operate when low temp threshold protection kicks on.
Click to expand...

I've been there, power is out during cold weather, one doesn't even think of hot tub once power is out. Most outages are only a few hours at the most. it is when that unusual condition happens and it is say 10 days when that hot tub will get you. If it isn't too extremely cold it likely pulls through without freezing. By the third or fourth day I might think about the hot tub, it is then I will place something in the plumbing area to provide some heat - or maybe even drain the tub. The tub I have is a small one and just draining it does remove enough water from critical places you shouldn't need to worry about any residual water causing damage if it freezes though.
 
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