# Convertng hot tub to use wood boiler heat



## mpilihp (Feb 23, 2010)

Hello I have a 70K btu convential wood boiler and works well but for a few cold weeks a year it struggles to heat the house during the couple weeks of -15 or so degree weather but for the rest of the year it easily heats the house and DHW and spends alot of time idling.

With that we got a hot tub this summer and learned how much one REALLY costs to run.  On a good month its only $40, but we are seeing it cost 50-60 a month alot, OUCH!

So im thinking it would be worth while to utilize the heat from the wood boiler, Ive read several threads on how others have done it but because I do not have storage nor a wood boiler with alot of extra capacity (IE cant heat quickly) I am looking to do it differently.

If you look at the plumbing part of the diagram you can see what I mean.  My plan is to use an indirect DHW tank but plumb it the opposite of normal.  IE  The tank part will be filled with heating system water and the coil will have hot tub water flowing through it.







Reasons for doing this:

 - My wood boiler is small and doesn't have alot of capacity, IE when it is providing heat it only does so for a short cycle, then stops and reheats itself.  Having a 'BUFFER' tank would allow to store some heat when its avail from the wood boiler even if the hot tub isn't calling for heat.

 - Setting the plumbing up so the hot tub water flows in the HX coil gets rid of the water level issue, and reduces the MASS of hot tub water to heat up.

  - Used Indirect DHW tanks are cheap, about the same or possibly less than a HX setup.

I would also plumb in a connection from my DHW tank to allow topping off and filling the hot tub with hot water through the connection coming into the house, no more using a hose in the winter outside.

With that said Id like to hear folks pros and cons comments.

How it works electrically:

1 - Normal Electric Heat operation.  In Normal operation without heat from the wood boiler setup.  There is an added relay 'Hot Tub Call for Heat' Relay that will be activated by the 120v connection from the hot tub control box that would normally go to the 120v heating element.
When that signal is applied the Hot Tub Call for heat Relay activates.  Since this is normal heating without wood boiler assistance, the "Hot Tub Tank Top Aqustat"  would be OFF and the NC contact would be closed.  This along with the Hot Tub Call for Heat NO Contact2 closed would send 24v to the Hot tub Elect Heat relay and send 120v to the electric heat element.  Plumbing wise IM not sure how the water will flow at the hot tub but I would like to have a path where I could close off the tank heating system at the hot tub to allow complete normal running for maint or a failure.

2 - Heating the Hot tub tank - This is pretty standard, the internal aqustat on the tank is set to 150deg, when temp inside tank is less than 150deg it will close.  As long as A wood boiler is running (WB On contact closed) and B my main heat zone isnt calling for heat; Zn1 NC contact is CLOSED and then 24v AC will be applied to the relay to turn on the circ to heat the tank.

3 - Heating the Hot tub - When the water in the tank is at min 110 deg, the aqustat on the top will activate and the NO contact will close.  Then when the hot tub calls for heat, the 'Hot Tub Call for Heat' relay needs to also activate and close the NO contact 1 which will activate the relay to run the circ to pump water from the hot tub through the coil in the tank through the 3-way valve to a max temp of say 130 deg.


Some questions I have about this setup:

 - The circ that is pumping the hot tub water, can I use a normal taco 007 pump or should I use one of the special ones for domestic water?  I dont want to introduce contaminates into the hot tub possibly from the standard pump.

 - The heating pipes going out of the house to the hot tub, I am thinking of using a pre-fab insulated dual pex setup, is this OK to use?  How safe will this be to keep it from freezing when it gets down to -15 or colder outside?


 Another Idea I have and would like to implement but probably in the future is to set it up so that the hot tub's built in temp control is set to a lower temp say 85 deg and only controls the electric heat element.
 Then have another temp sensor, say a thermistor that would have a digital 'Aqustat' with normally open and closed contacts.  This would be used to control heating to the preferred temp say 102 deg via the wood boiler setup.   This would allow letting the hot tub electric element only heat to a lower temp to SAVE money and I can build a fire to heat it when we want to use the hot tub..   Its use has dropped off to once or twice a week now.

My concerns here would be What to use for the temp sensor and the "Digital Aqustat"  Is there such a thing?  Also, now with the huge difference in heating temps, how would I protect the insulated pipes going in and out of the house from freezing if we were away for a long period and no wood boiler heating going on...


----------



## Gooserider (Feb 23, 2010)

mpilihp said:
			
		

> Hello I have a 70K btu convential wood boiler and works well but for a few cold weeks a year it struggles to heat the house during the couple weeks of -15 or so degree weather but for the rest of the year it easily heats the house and DHW and spends alot of time idling.


 Sounds like a reasonable setup to get more heat out of at least during the shoulder seasons.



> With that we got a hot tub this summer and learned how much one REALLY costs to run.  On a good month its only $40, but we are seeing it cost 50-60 a month alot, OUCH!


 Yup, welcome to utility bill growth...



> So im thinking it would be worth while to utilize the heat from the wood boiler, Ive read several threads on how others have done it but because I do not have storage nor a wood boiler with alot of extra capacity (IE cant heat quickly) I am looking to do it differently.


 Good idea, and no harm in being different if done intelligently...



> If you look at the plumbing part of the diagram you can see what I mean.  My plan is to use an indirect DHW tank but plumb it the opposite of normal.  IE  The tank part will be filled with heating system water and the coil will have hot tub water flowing through it.


 OK, should be no problem on that part - you might need to increase the size of your system expansion tank to compensate for the increase in system volume, but that isn't a big deal, just something to keep in mind...



> - My wood boiler is small and doesn't have alot of capacity, IE when it is providing heat it only does so for a short cycle, then stops and reheats itself.  Having a 'BUFFER' tank would allow to store some heat when its avail from the wood boiler even if the hot tub isn't calling for heat.


 That makes sense,  I would try to set up the controls to ONLY feed water to the buffer tank if the other loads are satisfied, as you don't want to freeze the rest of the house to warm the tub.  Might also be worth trying to up the max temp on the buffer tank - the more BTU's you can store in it the better when they are available, just don't over cool the boiler to get them.




> Some questions I have about this setup:
> 
> - The circ that is pumping the hot tub water, can I use a normal taco 007 pump or should I use one of the special ones for domestic water?  I dont want to introduce contaminates into the hot tub possibly from the standard pump.


 Nope, way to much 02 in hot tub water, it's even more corrosive than domestic water, not to mention the chemistry - definitely go with a stainless body pump.  BTW, I don't see how the pump provides water circulation when running on electric heat - shouldn't it be over near the electric heater element, between it and that bypass pipe?  (Might also be worth looking at using the existing tub pump for circulating the water?)



> - The heating pipes going out of the house to the hot tub, I am thinking of using a pre-fab insulated dual pex setup, is this OK to use?  How safe will this be to keep it from freezing when it gets down to -15 or colder outside?


 Not sure...  I know PEX has several chemical sensitivity issues, and I'm not sure if it will stand up to hot tub water chemistry...  I've actually gotten curious and have just posted the question on a swimming pool forum that I am also active on...  That aside, while PEX is supposed to be better at withstanding freezing than most other piping types, it should NOT be allowed to freeze if at all possible.  IMHO the pre-insulated PEX variants are overpriced and don't do that well.  Many of our users report better results and a lower cost / foot to do the sprayfoam in the ditch method...



> Another Idea I have and would like to implement but probably in the future is to set it up so that the hot tub's built in temp control is set to a lower temp say 85 deg and only controls the electric heat element.
> Then have another temp sensor, say a thermistor that would have a digital 'Aqustat' with normally open and closed contacts.  This would be used to control heating to the preferred temp say 102 deg via the wood boiler setup.   This would allow letting the hot tub electric element only heat to a lower temp to SAVE money and I can build a fire to heat it when we want to use the hot tub..   Its use has dropped off to once or twice a week now.


 Doable, the only question would be how much "rise time" there would be to get the tub from "idle"  to full heat - if it's to long, that would deter the use, which is not the idea...



> My concerns here would be What to use for the temp sensor and the "Digital Aqustat"  Is there such a thing?  Also, now with the huge difference in heating temps, how would I protect the insulated pipes going in and out of the house from freezing if we were away for a long period and no wood boiler heating going on...


For freeze protection, I'd just try to work some way to use the electric element as a "last ditch" protection for the entire system - i.e. set the electric element to come on at 45°F and turn the circ on to flow through the entire system....  

As to the monitoring and control circuitry, these days that's not a problem as there are all sorts of digital monitoring and control setups out there which would let you program whatever strategy you want...

Gooserider


----------



## mpilihp (Feb 23, 2010)

Hi thanks for the comments, im now thinking the whole idea is a bad one because of the corrosive nature of chlorinated water.  This water would be running through the HX coil inside a indirect DHW tank.  Im not sure what they are made of but would have to make sure it was stainless.  Ill shoot for a stainless pump if I do go forward with it.  See my responses to your ideas below.




> If you look at the plumbing part of the diagram you can see what I mean.  My plan is to use an indirect DHW tank but plumb it the opposite of normal.  IE  The tank part will be filled with heating system water and the coil will have hot tub water flowing through it.
> 
> OK, should be no problem on that part - you might need to increase the size of your system expansion tank to compensate for the increase in system volume, but that isn't a big deal, just something to keep in mind



Im planning on adding an expansion tank with the indirect tank.



> - My wood boiler is small and doesn't have alot of capacity, IE when it is providing heat it only does so for a short cycle, then stops and reheats itself.  Having a 'BUFFER' tank would allow to store some heat when its avail from the wood boiler even if the hot tub isn't calling for heat.
> 
> That makes sense,  I would try to set up the controls to ONLY feed water to the buffer tank if the other loads are satisfied, as you don't want to freeze the rest of the house to warm the tub.  Might also be worth trying to up the max temp on the buffer tank - the more BTU's you can store in it the better when they are available, just don't over cool the boiler to get them.



Thats the plan, if you look at the low volt control diagram there is a relay for my heat zone in line with the relay that controls the pump to heat the tank.  Also, not shown is I have a hybrid heat system (I call it that to make it sound like I did it on purpose)  Anyhow when I added my wood boiler into the heating system with the existing heating system was set  up it caused GHOST flowing through my zones.  So for my heat zones I added zone valves to stop the ghost flowing, but I let it ghost flow through my indirect DHW tank and would allow the same.  So that way  when the system is idling it is also maxing out the temp of water in the tank, works great, we always have hot water.




> Some questions I have about this setup:
> - The circ that is pumping the hot tub water, can I use a normal taco 007 pump or should I use one of the special ones for domestic water?  I dont want to introduce contaminates into the hot tub possibly from the standard pump.
> 
> Nope, way to much 02 in hot tub water, it's even more corrosive than domestic water, not to mention the chemistry - definitely go with a stainless body pump.  BTW, I don't see how the pump provides water circulation when running on electric heat - shouldn't it be over near the electric heater element, between it and that bypass pipe?  (Might also be worth looking at using the existing tub pump for circulating the water?)



My hot tub has one electric heat element and one pump.  If/when the hot tub would call for heat and the tank water isnt hot enough to heat, then the electric heat element and hot tub pump will come on as normal and heat.  The plumbing plan is to have the loop to the tank be in parallel to the normal flow of water to the hot tub pump so when just the hot tub pump is running it functions as normal.   Maybe some water would also circulate through the tank but Im hoping not.    Then when the tank is hot enough to heat, im hoping that the circ I show in the diagram for the tank on the hot tub side will also run along with the hot tubs pump and will pull some water through the tank setup heating it.



> - The heating pipes going out of the house to the hot tub, I am thinking of using a pre-fab insulated dual pex setup, is this OK to use?  How safe will this be to keep it from freezing when it gets down to -15 or colder outside?
> 
> Not sure...  I know PEX has several chemical sensitivity issues, and I'm not sure if it will stand up to hot tub water chemistry...  I've actually gotten curious and have just posted the question on a swimming pool forum that I am also active on...  That aside, while PEX is supposed to be better at withstanding freezing than most other piping types, it should NOT be allowed to freeze if at all possible.  IMHO the pre-insulated PEX variants are overpriced and don't do that well.  Many of our users report better results and a lower cost / foot to do the sprayfoam in the ditch method...



OK Ill look into fabing something myself, but my hot tub is only 1 ft from the house, will have to run lenghtwise about 5 ft before entering the house (going to initially at least have piping run through an unused dog door.



> Another Idea I have and would like to implement but probably in the future is to set it up so that the hot tub's built in temp control is set to a lower temp say 85 deg and only controls the electric heat element.
> Then have another temp sensor, say a thermistor that would have a digital 'Aqustat' with normally open and closed contacts.  This would be used to control heating to the preferred temp say 102 deg via the wood boiler setup.
> 
> Doable, the only question would be how much "rise time" there would be to get the tub from "idle"  to full heat - if it's to long, that would deter the use, which is not the idea.



Id have to play with it, but even if I can keep the hot tub heat to 90 deg on the elect and heat it up in say 4 hrs to 102 deg on the wood boiler that would be fine.  



> My concerns here would be What to use for the temp sensor and the "Digital Aqustat"  Is there such a thing?  Also, now with the huge difference in heating temps, how would I protect the insulated pipes going in and out of the house from freezing if we were away for a long period and no wood boiler heating going on.
> 
> For freeze protection, I'd just try to work some way to use the electric element as a "last ditch" protection for the entire system - i.e. set the electric element to come on at 45°F and turn the circ on to flow through the entire system.



Running out of text, my fear here is when on elect only I dont think any water will flow through the pipes to the tank.  Even if elect is on same temp it would only circ within the hot tub im thinking...[/quote]

OK thanks

~ Phil


----------



## Nofossil (Feb 23, 2010)

Laing makes a small circulator with a stainless and ceramic impeller/housing and a plastic body. I have one in my hot tub and it's designed to run 24/7. Works fine for circulating water through my HX.


----------



## timberr (Feb 23, 2010)

mpilihp,

I have my hot tub running of my wood boiler with storage. From my experience I think you are making this more complicated then needed. I use a HX for heating the tub. I have a Johnson Control set up that maintains a set heat with a 2* dif. When the hot tub (+/- 175 gal) is just maintaining itself it cycles on for a couple of minutes every 30 min on average. The biggest load is when the water is changed (heat from 50 to 104), not sure how often you need to do this but at that point you are going to want the full BTU load, but you can chose when to do this. I would think with the indirect hot water heater depending on the size you may have a 20-40 gal. buffer of hotter water but that won't last long if you are using it. Once that water has cooled you effectively have increase the total amount of water and BTU's you need to produce. Not sure how long you use your tub or if it is inside or out. Min is outside and we were in it of 90 min. this weekend and we were all very happy with temp.

Good luck


----------



## mpilihp (Feb 23, 2010)

Thanks for the suggestions, nofo ill look into the Laing circ.

timberr I may be making it more complicated but my thought/fear is the hot tub calling for heat when the wood boiler isnt circulating or is circulating to heat the house....  I realize that when we are in it the heat loss is enormous and the temp will drop, it drops now even when running the elec element.  So my main concern is when we are not using it.  IE it cycles on and off to keep it heated several times an hour.  If my wood boiler isnt circulating when it calls for heat then the elec element will come on anyhow IE no savings, and its way more hit or miss like that.  Where as if I have a buffer tank it can get heated when the wood boiler is running and has excess capacity (IE not heating the house) and then when the hot tub calls for heat the hot water is there.


----------



## webie (Feb 23, 2010)

Just an idea here .Why dont you just set this up like priority zoneing ,only useing your whole house as the priority ,Then if there is extra heat it can go to the hot tub , and then do an over ride switch for the times you are useing the hot tub so at that time it will heat on demand . I think if you do this you could skip the extra storage water heater and pump . I think all you would need would be a zone valve and a hx for the hottub . 
 My thought here is if you have such a high heat demand in your home hardly any will ever go to the hot tub till the house requires less heat  . Which is what I am thinking you are trying to achieve?


----------



## timberr (Feb 23, 2010)

Yes I understand why you are doing it. I guess what I really should have said is, you may go through a lot of work and still not be happy.  I have 500 gal. of storage and a 60 gal. Superstore for DHW. I am always amazed how much and how my storage temp can drop after a couple of showers.

Good luck with the Hot Tub, they sure are nice this time of the year!


----------



## mpilihp (Feb 23, 2010)

nofossil said:
			
		

> Laing makes a small circulator with a stainless and ceramic impeller/housing and a plastic body. I have one in my hot tub and it's designed to run 24/7. Works fine for circulating water through my HX.



Hi Nofo, In reading your post on your hot tub setup, it sounds like you just took the elec element out of the plumbing and where it was hooked up to the loop going to your HX and the Laing pump in that loop correct?

If so is this line also in line with the  hot tub pump?   IE if its in series does it PUSH through the Laing pump when its running and vis a versa does the Laing push through the regular pump?

If its not in series, how is is what Ill call the heat loop plumbed in the system.  IE so that when the main pump runs it doesnt cause a back flow through the HX loop.  IE if your HX loop were in parallel to the main pump.

Thanks

~ Phil


----------



## mpilihp (Feb 23, 2010)

timberr said:
			
		

> Yes I understand why you are doing it. I guess what I really should have said is, you may go through a lot of work and still not be happy.  I have 500 gal. of storage and a 60 gal. Superstore for DHW. I am always amazed how much and how my storage temp can drop after a couple of showers.
> 
> Good luck with the Hot Tub, they sure are nice this time of the year!



Im going to look into doing it via an HX and see how it works, Pretty much all will be the same except for the HX vs the indirect tank.  I understand that the chemestry is different with the hot tub water but when I was looking for an indirect DHW tank I looked at two 80 gal ones that a guy  had hooked up to his hot tub to allow Quick heating it to temp.  Granted from the sound of it maybe they are toast and wouldnt last long, now glad I didnt buy one of them.

~ Phil


----------



## Gooserider (Feb 25, 2010)

For what it's worth department, I found a couple of references in Watts manuals for PEX that said not to use it in swimming pools, and to avoid high concentrations of chlorine - so I would say that while PEX is OK to use on the boiler side of an HX, it would NOT work for the pool side...  Which gives more support to the approach I've seen most people doing of installing a sidearm in the tub plumbing, and running boiler water to it...

Gooserider


----------



## Nofossil (Feb 25, 2010)

mpilihp said:
			
		

> Hi Nofo, In reading your post on your hot tub setup, it sounds like you just took the elec element out of the plumbing and where it was hooked up to the loop going to your HX and the Laing pump in that loop correct?
> 
> If so is this line also in line with the  hot tub pump?   IE if its in series does it PUSH through the Laing pump when its running and vis a versa does the Laing push through the regular pump?
> 
> ...



In mine it's a separate loop for the Laing that circulates water through a filter and the heating element. I just re-plumbed it to go through my HX rather than the electric element. For several years, I had them plumbed is series so that I could use the electric element if needed. I never used it and eventually bypassed it.


----------



## mpilihp (Feb 27, 2010)

Ok im on board with doing the seutp without the indirect hot water tank and use a Plate HX.  My question is what size should I use?

My Boiler is 70K output and the hot tub is a small 3-4 person, I dont know the gallon size but Ive been told it was 5-600 gallons.  It has a single 120v electric heating element and runs on a standard 120 20amp circuit but takes forever to heat it.

So I see the Plate HXs are sold by the # of plates but what size should I get?   Want to be able to transfer as much heat is avail when the boiler is running as I do not have any storage.   I could afford up to the 40 plate but if I dont need it that large Id just soon get the smaller one.

Thanks for your help, much appreciated.

~ Phil


----------



## webie (Feb 27, 2010)

Ok if you are planning on going with a HX I would probably get something like this instead .
http://cgi.ebay.com/OUTDOOR-WOOD-FU...emQQptZLH_DefaultDomain_0?hash=item27af285c8d
 Not to doubt you but I have a 7 person hot tub and it is 8 by 8 and holds 500 gals , also my heating element is 220 and it only heats at about 5-6 degrees an hour so it is also slow . I am thinking if you are into a 3-4 person tub you may be down around that 400 gal range but then again  I have been knowen to be wrong before


----------



## webie (Feb 27, 2010)

This looks like the same thing only half the price .
http://www.outdoorfurnacesupply.com/series-85000-pool-heat-exchanger-p-183.html


----------



## mpilihp (Feb 27, 2010)

Hi thanks, I honestly have no idea how many gallons are in my tub, just going by the person that sold it to me, bought it used.  So if yours is 500 mine im sure is less, so ill go with 400.

I was thinking of something like this for the HX, more in my budget:

http://cgi.ebay.com/Plate-heat-exch...emQQptZLH_DefaultDomain_0?hash=item19ba33f98e

THere are 30 and 40 plate ones for alittle more, sometimes I can find them used for less.

The concern about chemical makeup in hot tubs and copper causing issues, I see several on here have made HXs out of copper pipe, anyone having issues with that?  

~ Phil


----------



## webie (Feb 27, 2010)

Hey how about this one .
http://cgi.ebay.com/20-Plate-Copper...emQQptZLH_DefaultDomain_0?hash=item518f3960a9
 I read on , I am not sure you can use this on the hot tub , I would contact the guy selling these first to be sure , Certainly the price would be right .


----------



## webie (Feb 27, 2010)

There are a couple of guys on here that have built there own exchnagers useing 4 inch PVC and then a run of copper pipe inside and they seam to be working . Hot tub water actually is pretty mild , we all sit in it just not sure what long term effect is on copper but for the couple of bucks it takes to build one heck I will give it a try .
check out this thread that is where the picture is from .
https://www.hearth.com/econtent/index.php/forums/viewthread/50202/


----------



## mpilihp (Feb 27, 2010)

Yes Ive seen those, there are basically two sizes, 7.5x3" and 12x5" or 12x3"   and then the number of plates.  Not many of them talk about actual btu transfer through them, dont know if Id be ok with the smaller size or if I need the larger one, I think this is a good deal, its a 12" long x 4"  but only 20 plates, its $140

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110498150798&ssPageName=STRK:MEWAX:IT

~ Phil


----------



## Gooserider (Feb 28, 2010)

I would suggest a sidearm style HX rather than a plate unit...  Usually the sidearms are less money or can be home built, and IMHO they are more fault tolerant in terms of not being affected by things like any debris in the water that could clog a plate unit (and junk WILL get past the filter, I don't care how good it is...)

I think if you looked through the tub / pool setups that people have done here, most (if not all) have used sidearm type HX's 

From what I've seen a lot of the sidearms also have the advantage that they can simply be spliced into the same pool plumbing that the electric heater uses, and thus take advantage of the existing tub pump, etc. for the tub-side plumbing.  Since they have just about zero head resistance, this works well.  OTOH, a plate unit might cause problems because most of the plate HX's have high internal head resistance.

Gooserider


----------



## mpilihp (Feb 28, 2010)

Hmmm So Plate HX units can clog?  Couldnt I reverse the flow and FLUSH it out with  high pressure every so often??

Well the home made HXs ive seen involve copper which some have said can be a problem with hot tub water chemistry.  THe ones available for sale are expensive and have large port sizes.   Making one will cost something, and would involve copper, I can get a Vaughn type indirect tank for $100, Ive bought 3 tanks so far for about $100 each and the copper coils in these are easily replaced from the top of the tank.  The other thing is if for whatever reason the coil in it went bad from the look of it I could cut the coil out and put in a home made copper HX as others have done in PVC.  Then this way Id get the benefit of having a buffer tank of hot water for when the hot tub would call for it.

So, im wishy washy on what way to go. 

~ Phil


----------



## mpilihp (Feb 28, 2010)

Ok its a nice day so I figured Id open up the hot tub maint panel and see how I might be able to connect up my lines to heat the hot tub via the wood boiler.  What I found kinda shocked me, the only power line leaving the control panel is to the pump, nothing else.  Look close at the pump, on the body of the pump there is this curved white plastic thing with two braided clear lines connected to it (can only see one connection)  One of the clear braided lines goes to the base of the pump on the left side by the big pipe ive labeled INPUT.  The second clear braided line goes to the pump housing as well by the red pipe which is on the OUTPUT side of the pump.  (both other ends of the braided lines on the pump body are on the back side so you cant see them)

I think this hot tub is ONLY heated by the excess heat the pump generates and no electric element!  No wonder the pump runs all the time and for a long time, it has to get the pump body heated up before it generates heat I think.





So I have two options I think, the first is to disconnect one of the clear braided lines on the pump body heater and splice in my HX heating loop inline with the pump body heater.  Issue with this is I dont know if the pump is NOT running if water will flow through my wood boiler HX heat loop (note there will be a laing plastic pump in the wood boiler hx heat loop)  The connections are on the other side of the pump body are are right on the pump, not on the pipes going to it......





My second option is to use the drain connection on the PUMP FEED pipe and have that go to my heat loop and connect the return from my heat loop into the plastic pipe for the Jets on the output side.  Potential issue with this is when the hot tubs pump runs will its high pressure pump water backwards in my heat loop back to its input or will the running Laing pump prevent the backwards flow?  Or would just putting a one way valve in the heat loop prevent this?





Which of these two options do you think is the best one?  THE first option would be the easiest for me and least disruptive to the hot tub incase we decided to sell it.   

Also, does anyone think I shoudl also put in an actual electric heating element instead of the plastic pump body suto hx thing?    Id think an actual elec element would be more efficent than this for when we are not running the wood boiler.

Thanks

~ Phil


----------



## Gooserider (Feb 28, 2010)

mpilihp said:
			
		

> Hmmm So Plate HX units can clog?  Couldnt I reverse the flow and FLUSH it out with  high pressure every so often??


You could, but often it can be tricky to reverse the flow, since most pumps will only work in one direction, which means you'd need a second pump and / or some tricky plumbing...  Seems easier to me not to have the problem in the first place...

[/quote]Well the home made HXs ive seen involve copper which some have said can be a problem with hot tub water chemistry.  THe ones available for sale are expensive and have large port sizes.   Making one will cost something, and would involve copper, I can get a Vaughn type indirect tank for $100, Ive bought 3 tanks so far for about $100 each and the copper coils in these are easily replaced from the top of the tank.  The other thing is if for whatever reason the coil in it went bad from the look of it I could cut the coil out and put in a home made copper HX as others have done in PVC.  Then this way Id get the benefit of having a buffer tank of hot water for when the hot tub would call for it.

So, im wishy washy on what way to go. 

~ Phil[/quote] Welding stainless is not an easy DIY project for most, I agree, so most of the home-built units will be made with copper just because it's fairly easy to sweat it together...  I've also heard mixed reviews on copper and tub chemistry, but according to the folks over on Troublefreepools.com (where I get really good advice on the care and feeding of our pool) a lot of commercial pool heaters actually have copper HX's, and don't give problems IF you keep your water chemistry properly adjusted...

I have never done business with them, but if you wanted a stainless HX, one of our banner sponsors sells this HX http://www.outdoorfurnacesupply.com/series-155000-pool-heat-exchanger-p-184.html which is on the big side, but at $299 it seems pretty reasonable...  Yes, it does have big ports on it, but that is no big deal, just means you'd need some reducer fittings.  

Gooserider


----------



## mpilihp (Feb 28, 2010)

Hi what I ment about reversing the flow to flush it out is when I drain the tub to clean and replace the water I could hook a hose to it and blast water through the HX and clean it  out.

Im trying to do this on the low budget, Im thinking a small HX to start with will work as after looking at how the existing heating of the water works is pretty feable.  (see other post I did about how to hook up to the hot tub)

~ Phil


----------



## rowerwet (Mar 1, 2010)

to heat the water during the summer, why not use your current hot water heater, run a loop from the inlet and outlet pipes of the hot water heater to a HX on the tub with a pump to circulate, it is most likely more efficient for heating water than an electric element.


----------



## Gooserider (Mar 1, 2010)

mpilihp said:
			
		

> Hi what I ment about reversing the flow to flush it out is when I drain the tub to clean and replace the water I could hook a hose to it and blast water through the HX and clean it  out.


Might work, I wouldn't put bets on it, as from what I've heard, the crud can take just as much water going backwards to get it out, as it took to get it in there in the first place.



> Im trying to do this on the low budget, Im thinking a small HX to start with will work as after looking at how the existing heating of the water works is pretty feable.  (see other post I did about how to hook up to the hot tub)
> 
> ~ Phil



As I said, your call, but I still think you'd be better off w/ a sidearm - but I guess worst case if the FP doesn't work is that you'd need to replace it later...

Gooserider


----------



## Gooserider (Mar 1, 2010)

I decided that it would be better to have one thread for this project rather than a bunch of different ones, so I have merged the three threads into one - it looks like it might have mixed up the continuity a bit, but it keeps all the discussion of the project in one place, and makes it easier to keep track of...

Gooserider


----------



## Gooserider (Mar 1, 2010)

mpilihp said:
			
		

> Ok its a nice day so I figured Id open up the hot tub maint panel and see how I might be able to connect up my lines to heat the hot tub via the wood boiler.  What I found kinda shocked me, the only power line leaving the control panel is to the pump, nothing else.  Look close at the pump, on the body of the pump there is this curved white plastic thing with two braided clear lines connected to it (can only see one connection)  One of the clear braided lines goes to the base of the pump on the left side by the big pipe ive labeled INPUT.  The second clear braided line goes to the pump housing as well by the red pipe which is on the OUTPUT side of the pump.  (both other ends of the braided lines on the pump body are on the back side so you cant see them)
> 
> I think this hot tub is ONLY heated by the excess heat the pump generates and no electric element!  No wonder the pump runs all the time and for a long time, it has to get the pump body heated up before it generates heat I think.


 Sounds like it might be the case, I have heard of tub setups that essentially use the motor heat to warm the tub.  Essentially that plastic thing is a water jacket, a small amount of the pumps output water is diverted from the output, sent through that water jacket and back to the input side.  The claim is that by getting rid of the separate heating element they save energy, as the pump should be running a good bit of the time anyway to keep the water mixed.  However with this kind of setup, you might be limited in how much energy you save by going to wood since you will need to circulate the water anyway.  Essentially right now the tub company would tell you that you are getting the tub heat for "Free" as there is no separate heating element, and you need to run the circulation pump anyway...

It MIGHT be possible to put in a second smaller pump that just circulated the water in the tub and HX and spent fewer Watts in moving the water around, but if doing that then you'd want to get a very low flow resistance HX so as to allow the smallest tubside pump possible.



> So I have two options I think, the first is to disconnect one of the clear braided lines on the pump body heater and splice in my HX heating loop inline with the pump body heater.  Issue with this is I dont know if the pump is NOT running if water will flow through my wood boiler HX heat loop (note there will be a laing plastic pump in the wood boiler hx heat loop)  The connections are on the other side of the pump body are are right on the pump, not on the pipes going to it......


That would sort of work, but you'd have very limited flow, due to both the small line size and the restriction of the plastic HX...  It would also only work if the main pump was running, which kind of defeats the purpose of doing the boiler connection.

It doesn't matter what you do on the tub side however, if you are wondering about flow on the boiler side of the HX - the HX is a WALL between the two systems, and while you may throw some BTU's over the wall, the flow on one side won't have ANY influence on the flow on the other...  In terms of BTU flow when one side of the HX isn't flowing, unless you have flow from thermosiphoning, the temperature on the two sides will rapidly balance, and you would have no BTU transfer since there would be no temperature differential to drive it.



> My second option is to use the drain connection on the PUMP FEED pipe and have that go to my heat loop and connect the return from my heat loop into the plastic pipe for the Jets on the output side.  Potential issue with this is when the hot tubs pump runs will its high pressure pump water backwards in my heat loop back to its input or will the running Laing pump prevent the backwards flow?  Or would just putting a one way valve in the heat loop prevent this?


That would NOT work, or at least not when the main pump is running, as you have the two pumps "fighting" each other.  You would also get a "short circuit"  flow path through the tub pump when it wasn't running. However if you put a one way valve on EACH line, and set up your controls to only allow one of the two pumps to run at a time, then it would be OK, and essentially what I suggested a few lines up...



> Which of these two options do you think is the best one?  THE first option would be the easiest for me and least disruptive to the hot tub incase we decided to sell it.


  I would go with the second option (but using a sidearm HX as mentioned earlier)  I don't think the first option would give you enough flow to be worth while...



> Also, does anyone think I shoudl also put in an actual electric heating element instead of the plastic pump body suto hx thing?    Id think an actual elec element would be more efficent than this for when we are not running the wood boiler.


I would not mess with the pump HX.  Remember that at the same time it's heating the tub water it is cooling the pump motor...  What I don't know is how important that cooling is to the pump motors life span, and while it may not be the most efficient heater, it is "free" heat that you get whenever the main pump is running - like when you are in the tub and wanting the jets at full power...

It might make sense, but it would take some careful measurements and calculations to be sure, to put an electric element in the same loop as the boiler HX, assuming you were doing a setup like your second choice - then you could run the small pump and the element rather than the big pump...  The question though would be which approach would give you the lowest operating cost, and even if it were the small pump, would the payback be worth it?

Gooserider


----------



## mpilihp (Mar 1, 2010)

Hi thanks for the comments, alot to respond to.  

Hot water heater idea, my DHW is in an indirect HW tank and when the wood boiler isnt running its heated by oil which I am trying to eliminate burning oil as much as possible, but it does pose an interesting idea if I could limit it from using it in the summer when Im burning oil.  A project I am currently working on is hooking up my second indirect DHW tank and second 3-way valve to pre heat the DHW to give us longer times between heating it via the wood boiler during shoulder seasons.

As for the pictures and ideas on how to actually hook into the hot tub, the wood boiler heating loop will have a small low flow pump always running flowing water through the HX or Side arm.  In that loop will be a digital Ranco aqustat on the rec side of the hx coming from the hot tub.  When that temp drops below say 103 it will kick on the circulator on the heating system side of the hx IF the wood boiler is running.  The existing heating control/sensor in the hot tub will be left as is and set to a lower temp, say 101 (not sure of the values)  but the idea being if the wood boiler isnt on once it gets down to 101 then the hot tub would heat itself the way it normally does,  

Between 1st and 2nd option, I agree I dont think there would be enough flow through the plastic HX on the pump and I had not though that its probably used to cool the pump motor.  So I think I will go with option 2 with as you said with one-way valves on both of the external heat lines.

My new question is this, in the picture the piping on top of the red pump connection where I showed to insert a T, what kind of hose is that and how do you make connections to it?   It looks like they are GLUED into the T to the pump.  Im thinking on that side I would need to Cut in and glue in a T.  THe other side would be easy as I can just connect onto the drain.

~ Phil


----------



## Gooserider (Mar 1, 2010)

I could easily be very wrong, but that looks like the pictures I've seen on Troublefreepool.com of what they call "flexible PVC" hose.  Never worked with it, but my understanding is that it takes the same glue and fittings as regular PVC, and is worked the same way...   I think I see some markings on the pipe, which might give you a clue as well...

If that doesn't work, I'd take the picture over to troublefreepool, and ask them over there - they are nice folks and I'm sure they would be able to ID the pipe very easily and tell you what you'd need to work it.  They are also good folks on dealing with pool chemistry.  Since I started following their advice on taking care of our pool, I've never had my water looking so clean, and at the same time I'm spending a LOT less money, and much less effort on taking care of the pool...  I would definitely say they are a rather damp equivalent to the hearth...

Gooserider


----------



## mpilihp (Mar 1, 2010)

Hi thanks, I think I have a plan, now I need to prep my system for connecting this to it, good summer project,

~ Phil


----------

