I have a Softub and live off the grid with solar power, so I try to conserve power as much as possible. To heat my tub, rather than using electricity, I use my Paloma (a device that uses propane to heat water on the fly, and can get it VERY hot). I do this by emptying out about 15 gallons of water per day from the tub and replacing it with super-hot water from the paloma. So I only use electricity to power the jets when I am in the tub - not to heat it. It works great, but it means having to do this daily and having to waste 15 gallons of water every day. (Not to mention having to have an ugly hose run across my yard all the time)

I have a better idea, and I would love to hear your thoughts. I want to move my paloma, with it's own propane tank, to the tub. The part I can't figure out is this - I want to set it up on a thermostat, and have the paloma get it's water right from the tub(instead of the tap) - to take already hot water(say 100 degrees) and make it even hotter,(say 104 degrees) in essence. So when the tub got down to 100 degrees, the paloma would automatically turn on and heat the whole tub up to 104 degrees.

Is this possible? Are there any devices out there that would facilitate this?

Thanks for all your responses!
Jason

I work at a wholesale supply house that carries a brand of "on demand" water heaters. Don't do it, these heaters are designed to heat COLD water, not designed to act as a "boiler" type heater. Basically they just have too much flame power to do what you want to do and would overheat and shut down a lot. Some brands of these heater do have an optional thermostat but again these are intended to heat COLD water. There are brands of propane hot tub heaters out there if you have the money.
Have you considered a wood fired heater?

This can be done with a bit of thought.

A couple of things need to be known/understood though.

1. Does your propane heater heat just a 'tank'? Or does it require a flow of water through it.

2. What turns on the propane heater? Is this something you gotta stick a match under to get it going?

For starters, you'll need to get a low wattage circulation pump (since you're looking to save energy) and this one comes to mind:
http://spapartsnet.com/Spa-Pumps/Circul ... 2_0_1.html

33 watts max.
But depending upon your circulation requirements for the heater it may not be enough flow.

You'll need a thermostat that can turn the circulation pump on and off (and contained within a weatherproof box)

http://spapartsnet.com/Electric-Heaters ... 8_0_1.html

and possibly a safety thermal cut-out to prevent your tub from melting down due to unforseen overheating condition:
http://spapartsnet.com/Electric-Heaters ... 2_0_1.html

The rest is dependent upon the needs of the heater, for which you'll need to elaborate a bit.

The paloma requires water to be flowing through it. It keeps a pilot lite going so you don't need to light a match each time.

Easy enough... so it's basically a millivolt on demand system that has it's own internal temp thermostat then (designed as a regular gas hot water heater I'm guessing?).

I have no idea on the mechs of this unit obviously.

And if this is the case, well I'm about with jhknight then - but for different reasons. Yes they're designed to heat cold water, however - they're not heating up to the normal hot water requirements of a household, we're talking 104 typical max for a spa versus 160-180 F for household... the typical design would actually have a lower stress over it's lifetime; Bring in the rest of the gang here...

The water flow from a circulation pump would be enough, however, the adverse chemistry durability requirements that the water jacket would have to endure would exceed it's capability.

Within a year, you'd have a leaking heater due to corrosive effects of the spa water.

It's either that or you'll have to maintain 4.0 water chemistry 24/7, which is not easily done and more of a pain than it is worth. Most spa equipment designed can withstand minor variations and forgetfulness, but not standard hot water heaters like the paloma as I'm understanding it is.

They expect ph neutral, and no induced chemistry from anywhere - and the less mineral or other added content, the better. Fresh water, fresh water, fresh water - not the nasty crud that exists over time with a hot tub.

This is where in the previous life of many older designed spa systems, they utilized heat exchanger type design - where the spa water would be heated by an existing heater like a paloma (providing 160-180f water to the house), but the natural water tank would be surrounded by coils with the spa water in them - NOT heated directly by a gas/propane heater, rather heated indirectly by the tank water itself.

It doesn't always suit the need, but it can work... it's just a lot more costly to get it set up to begin with.

Just like anything that's 'free energy'.... the cost is always in the initial investment which may exceed ones expectations quickly.

Now that I've said all that crap...

I think you may have hit upon a unique idea though... one you'll have to work on yourself.

You empty 15 gallons of water out of the tub -
Refill with 15 gallons of hot new water.

15 gallons is NOT a lot of water. It's miniscule.

Everytime you do this, you've basically cleared 15 gallons of crappy water out of the tub & introduced 15 gallons of clean stuff.

Done repeatedly, you'd be able to maintain quite a clean spa over time, (with religion).

Less chemicals, less everything... Perhaps a time delay valve set up would be more preferential than your original thinking. Use some lawn water 24volt valves used with lawn watering systems (don't know how they'll perform with really hot water though)...

hmmm.

Could be an interesting concept to explore.

My water is rainwater, with a pretty acidic PH.
And I do not use any chemicals. (this would defeat the purpose of having a nice healing soak!)
Just a little food grade hydrogen peroxide.


Now I am even more confused!

You actually ever measured the PH?

eg.. had a standing rain capture basin and done a ph check?

It's one thing to think it, and another to actually do it.


Confusion on this subject can be easily targeted and resolved.

1. It's not a good idea to run spa water that is frequently used thru a water heater that is designed for neutral ph and expecting nice clean water all the time through it.

2. If you ignore the above, you'll end up with holes in your heater tank.

This paloma heater thing, I have no idea about, other than what you and another have said here.

What else are you using it for now? (Besides supplying 15 gallons or whatever every now and then for spa heating purposes?)

It supplies hot water to my house when the solar water heater isnt hot enough.. like if it's been cloudy for a few days...