# How to heat hot tub with boiler water



## Northwoodsman (Aug 26, 2008)

I am currently undergoing the installation of an EKO40  with 1,000 gallon storage (pressurized).

I have a Jacuzi hot tub with 350 gallons of water and am not quite sure how to hook this up to my exisiting hot tub (HX size, electrical connections, plumbing etc).

I currently use the 240 V, 5,500 Watt tube type heater that came with the hot tub and assume that there is a way to integrate the HX into this system while still using the temperature control of the hot tub itself to turn my circ motor on/off to maintain a 104 F max temp. (I am very comfortable working on the electrical system/circuit board on the hot tub).

Also, could it be installed so that I have the electric heater on the tub as a back-up (set to a lower temperature so as not to come on except when the water temp from the boiler gets to low).

Finally, since my hot tub is located approx. 10-15' from my storage tanks would it be practical to use a homemade copper tube HX installed inside my tanks (I realize I have to cut an opening in the tanks and then seal it very good to prevent leaking when under pressure-max 30 PSI) vs. purchasing a seperate plate type HX. I was also thinking about doing the same type HX installation in the tanks for solar collectors which I plan to install next year.

Can anyone help me with the proper sizing of the homemade HX that would be required for the hot tub and future solar collectors (I don't have an exact size/# of solar collectors I plan to use but the basic calculation(s) would be very helpful and greatly appreciated).

Thanks !


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## Nofossil (Aug 26, 2008)

I heat my hot tub as a zone on my system. I built a HX using a 30" length of 6" diameter PVC. Inside, I have 16' of 1/2" copper - 8 24" pieces running back and forth, lengthwise. Lots of street elbows. The boiler water is in the copper, and the hot tub water is in the PVC shell. My hot tub has a little circulator that runs all the time, so water is always circulating through the HX.

I just disconnected the hot tub heater and wired a relay with a 240vac coil in its place. The relay contacts act as a thermostat for the hot tub zone.


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## DenaliChuck (Aug 26, 2008)

I've got a Snorkel tub (basically a wood barrel) and was planning on running boiler water through a copper coil hx in the bottom of the tub (behind the fence that the wood stove sits behind).

This would put the hot boiler water next to the coolest water in the hot tub and maybe set up gravity mixing in the tub.


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## Redox (Aug 26, 2008)

nofo, are you having any problem with the copper staining the tub?  I have thought about doing this, but was going to use a SS or cupronickel HX out of erosion concerns.  Copper doesn't usually like pool chemicals, I've found...

Chris


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## Nofossil (Aug 26, 2008)

Redox said:
			
		

> nofo, are you having any problem with the copper staining the tub?  I have thought about doing this, but was going to use a SS or cupronickel HX out of erosion concerns.  Copper doesn't usually like pool chemicals, I've found...
> 
> Chris



Zero problems so far. Of course, I've only been doing it since November 2002. Time will tell. I use bromine rather than chlorine in my hot tub. Don't know if that makes a difference.


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## Bad Wolf (Aug 26, 2008)

I haven't gotten to that stage yet but its on my list. What I was thinking of doing is to install a "T" in the 2" line that goes to the existing heater.  Run a 3/4" PEX line from the "T" to a pump, throw several loops of PEX in my heat storage tank and return to the 2" line on the other side of the heater a foot or two before it returns to the tub to allow for mixing. Then I was going to disconnect the 240 volt heater and run one leg of that (120) to the pump.  This way when the tub calls for heat it will turn on the small pump instead of the heater. There is also a circulating pump that normally comes on with the heater.  Since my storage tank will be at 170 I'm thinking that the trick will be to keep the water from picking up too much heat before it returns to the tub.  After all the tub is only at 104. I can probably adjust the number of coils of PEX to get the temp rise I need.  When the tub comes up to temp it will shut off. According to the fellow at the spa store I should install a spring loaded check valve to keep it from circulating when the jets are on. 

I _think _this will work. I'll post my results when I get it installed.

Greg H


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## 2.beans (Aug 26, 2008)

i heat my 250 gallon tub with a HX and hooked up as a zone off from my house primary loop. i use a ranco contoller to turn  on my taco switching relay. the ranco has its own temp sensor that i added to the tub and can set the tub temp with a differential of one degree. the electric element temp is set 20 degrees lower just for a back up. i cut the main water line to the electric heater and installed a plastic 2" flow check and plumbed my wood boiler HX lines on each side of the flow check. so when the tub calls for heat the water circulates thru the the tub not just across the electric element.i ran pex into my house to the HX which is in my basement. my tub pump comes on every half hour to check temp so when it does it forces water thru the heat exchanger thus preventing any chance of a freeze up. i also tried using a regular circ on the hot tub side but that didnt pan out and i had to change it to a bronze one.


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## 2.beans (Aug 26, 2008)

oh ya i also have a mixing valve on the hot tub side of my HX so it doesnt overshoot.


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## jbphan8 (Nov 23, 2008)

Hello all.  new to this site as of today and have spent much of my day researching.  Amazed by the collective knowledge and willingness to share/help.  I am in my third heating season with my Central Boiler OWB and love it.  Wish I had done it long ago.  Anyway, I am wanting to connect my hot tub to my system and further help on the utility bills.  I find  this particular thread interesting and helpful but please tell me what HX satnds for.  I'm sure it is something that I will say "well, duh" once I see it but I can;t for the life of me come up with it right now.  Thakns in advance.


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## jbphan8 (Nov 23, 2008)

Sorry for the typos.  Guess I should have proof read before submitting it!


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## Willman (Nov 23, 2008)

> please tell me what HX satnds for


Heat exchanger


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## Willman (Nov 23, 2008)

> Sorry for the typos.  Guess I should have proof read before submitting it!


Try firefox with spell check. No more typos
Will


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## jbphan8 (Nov 23, 2008)

Well, duh.  Thanks for the help.


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