# Forum Home Renovation Heating & Cooling  Wood fired pool heater

## stan250

I would like to convert a slow combustion wood heater into a pool heater.
In the US they sell wood burning heaters which sit outdoors. I am in high risk bushfire zone with a long fire ban season so the heater will have to go indoors which isnt a bad thing in winter. These wood burning pool heaters really do work very well and I have many fallen trees on my block - more than I can ever use so this seems a suitable way to heat the water. 
Now there seems to be two problems; firstly the type of coil which can be used.
Pool water contains salt and chlorine. Salt reacts with steel (even stainless if there is minimum oxygen) and chlorine apparently reacts with copper to produce a toxic liquid. This leaves titanium or aluminium.
All of the store bought heaters with a wetback coil or box use either copper or mild steel I believe. Which means having an ordinary heater converted to include a coil of some description but I am not sure what type. 
The second issue is that I dont think it is safe or legal to connect an uncontolled heat source to a pressure system unless it is vented to atmosphere. In a solar hot water set up for pool heating a relief valve is used I think, for pressure build up as a solar system is also considered an uncontrolled heat source. Would this type of valve be suitable for such a system? 
Are there any other issues with this which need to be considered?
thanks.

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## Moondog55

Well I can think of several solutions 
Don't heat the pool water at all, re-tile using black tiles on the pool base and a pool blanket 
Heat a heat exchange medium like "Glaubers salts" which sit in a separate cylinder by boiling clean water in the wet back and run the pool water through the exchange in plastic pipe, I think you can get plastic pipe that is good to 88C for hot water ( Don't know for sure) 
I have to ask why you want to heat the pool in summer tho

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## stan250

> Well I can think of several solutions 
> Don't heat the pool water at all, re-tile using black tiles on the pool base and a pool blanket 
> Heat a heat exchange medium like "Glaubers salts" which sit in a separate cylinder by boiling clean water in the wet back and run the pool water through the exchange in plastic pipe, I think you can get plastic pipe that is good to 88C for hot water ( Don't know for sure) 
> I have to ask why you want to heat the pool in summer tho

  If this year is anything to go by here, we aren't really doing 'summer' - it must be that global cooling thing.
Comfortable pool water is around 23 degrees+ -you would be hard pushed to achieve that for any significant length of time here. Couple of cold nights, no pool heater, back to square one. 
The minimum temp forecast for this week here is around 6 degrees and this is mid November. To have a pool and to be unable to use it
for a large part of the year when there is abundant fuel all around, seems rather stupid.

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## Moondog55

When I worked at Falls Creek ski resort we found that a pool blanket ( the HD roll-away insulated type) gave us the best bang-for-buck in terms of efficiency winter and summer. 
Same in the highlands of Nugini where it gets a lot colder than that.
Retain the heat you have and you need to add less, and yes modern firewood heaters are efficient, but why not use the same unit to heat you house and house hot water too??  Pivot Stove & Heating Company  
Add a 1000liter or bigger heat exchange tank to this unit

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## stan250

> When I worked at Falls Creek ski resort we found that a pool blanket ( the HD roll-away insulated type) gave us the best bang-for-buck in terms of efficiency winter and summer. 
> Same in the highlands of Nugini where it gets a lot colder than that.
> Retain the heat you have and you need to add less, and yes modern firewood heaters are efficient, but why not use the same unit to heat you house and house hot water too??  Pivot Stove & Heating Company  
> Add a 1000liter or bigger heat exchange tank to this unit

  
Pivot said I can either do one or the other but not pool heating and house.
Was going to use a pool blanket as well.
He also said I would need a separate open vented header tank and separate pump as the pool pump will pump too fast. As usual with these things, it is more complicated (and expensive) to do than it first looks! But the cost of an electric heat pump and the cost of running it when you really need it, makes this still a much more cost effective way to heat the pool.

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## Moondog55

_I have talked to pivot as well and the bloke I talked to had never heard of Glaubers salts, so I would research further with real experts_  
Pivot had ( or at least the salesman I talked to last year) also had no experience with multi tapping HW storage tanks which I found surprising as it a standard way of using stored heat 
50kwatts is a hell of a lot of heat and that is the rating without a turbo unit on the flue and I wonder if that 1kwatt per square meter is realistic in a fully insulated house with the thermostat set at a reasonable level. 
Comment on pool pump pressure is a good point tho

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## stan250

> _I have talked to pivot as well and the bloke I talked to had never heard of Glaubers salts, so I would research further with real experts_  
> Pivot had ( or at least the salesman I talked to last year) also had no experience with multi tapping HW storage tanks which I found surprising as it a standard way of using stored heat 
> 50kwatts is a hell of a lot of heat and that is the rating without a turbo unit on the flue and I wonder if that 1kwatt per square meter is realistic in a fully insulated house with the thermostat set at a reasonable level. 
> Comment on pool pump pressure is a good point tho

  He said that they had tried to do both before and it didnt work. I asked if it was because there was insufficient room for two coils at the heater and he said yes. He also said there wouldnt be sufficient heat to do both at once.
Thinking about this if you had two separate heat exchangers (ie two separate systems) in the header tank then you could run both simultaneously or one at a time. I suspect that drawing water heated by water rather than by direct heat to the coil perhaps wouldnt get hot enough. Dont really understand how heat exchangers work, or wetbacks for that matter.  
Just spoke to him again and he said you cant put two heat exchangers in one header tank, its not safe or legal for some reason.
The deal is one heater, one header tank with ballcock plumbed to house system. One titanium heat exchanger, one thermostat, one 120 watt pump, one separate pipe system to and from pool, conditioners (whatever they are)+ freight - all up about $7000..... ouch. 
Anyone think of another way to heat the water with wood???

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## Moondog55

Yeah I follow that, but that is the exact reason you use a storage tank, you can make the storage tank as big as you need ( assuming the space is available) and tap it off as needed.
Glaubers salts is one of the few materials which have a greater heat storage capacity than water and it does this by phase change solid until it reaches a certain energy level and then melting.
I know people who have done this very well; heating a ski lodge at Harrietville as well as all the hot water and the spas in the lodge

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## Moondog55

**   **   *Quote from Wiki*  **   *Thermal storage* 
 The high heat storage capacity in the phase change from solid to  liquid, and the advantageous phase change temperature of 32 °C (90 °F)  makes this material especially appropriate for storing low grade solar  heat for later release in space heating applications. In some  applications the material is incorporated into thermal tiles that are  placed in an attic space while in other applications the salt is  incorporated into cells surrounded by solarheated water. The phase  change allows a substantial reduction in the mass of the material  required for effective heat storage (83 calories per gram stored across  the phase change, versus one calorie per gram per degree Celsius using  only water), with the further advantage of a consistency of temperature  as long as sufficient material in the appropriate phase is available.

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## Moondog55

> Just spoke to him again and he said you cant put two heat exchangers in one header tank,

    Can he cite the regulation?/ I seriously doubt that claim unless things have changed recently

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## stan250

> Can he cite the regulation?/ I seriously doubt that claim unless things have changed recently

  he got rather testy when I asked about using two exchangers.....dont know why.

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## Moondog55

It is beginning to sound as if you have been talking to the same bloke who told me ( emphatically I may add ) that you cannot have mains pressure wood fired hot water.

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## stan250

Spoke to another wood fired boiler specialist who builds them and it seems there is no way around the header tank layout. Relief valves wont really do the job safely enough and we get lots of power outages here meaning the pump will stop and the thing could explode.
Its a bit strange that the yanks seem to build these things for pools without all this palava especially as they are by inclination notoriously litigious - I guess they must have worked out a simpler system.
Here is a sample of their wares and not a header tank in sight: Wood Stove Pools, WSP Profile, www.woodstovepools.com - The Best Wood Burning Pool Heater On The Market! - Welcome to Warmwatersolutions.com - Extenda-Swim Wood Fired Burning Swimming Pool Water Heaters - The Only Wood Pool Heater http://extendaswim.com/  
Edit: quote from one of the websites above "Make sure your pump is running and is flowing through the unit, if for any reason the water flow is interrupted (power outage, etc.) extinguish the fire immediately". I just wonder what happens if you are out or asleep or you didnt notice the pump wasnt working in time. oops

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## Moondog55

Header tank vented to atmosphere?? OK but that does sound just like the domestic systems of the 30s - 60s, but the header tank is only part of the system.
HMMMMM!! I'm going to do some more research as this does not sound correct to me, how big a storage tank was the second bloke talking about??
We need an experienced plumber or three to jump in here

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## Moondog55

OK so the header tank is there to provide the water pressure in a low pressure tank, the tank is vented to the air and the exit is just above the header tank, this is the standard system I'm used to, can be wood or electric. this is the storage tank. 
you don't use the storage tank for hot water, inside the storage tank you have coils of pipe, usually copper, these copper coils are the heat exchange and can run at whatever pressure the pipes and fittings are rated to, you can tap off these heat exchanges to what-ever you want.
Most storage tanks are just too small to be useful and very poorly insulated

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## stan250

> Header tank vented to atmosphere?? OK but that does sound just like the domestic systems of the 30s - 60s, but the header tank is only part of the system.
> HMMMMM!! I'm going to do some more research as this does not sound correct to me, how big a storage tank was the second bloke talking about??
> We need an experienced plumber or three to jump in here

  
45 litres.
If I have this correct, basically a small pump circulates water between the boiler coil and the header tank and then out to a heat exchanger where it meets water circulating in the pool system utilising the pool pump. 
The second guy also has a few additional safety features on his boilers but they 'aint cheap but they sound like they know what the are talking about. Tubulous Australia: Wood Boilers & Hydronic Central Heating
These things look like they came out of catalogue from about 1890, built like battleships- amazing.

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## stan250

> OK so the header tank is there to provide the water pressure in a low pressure tank, the tank is vented to the air and the exit is just above the header tank, this is the standard system I'm used to, can be wood or electric. this is the storage tank. 
> you don't use the storage tank for hot water, inside the storage tank you have coils of pipe, usually copper, these copper coils are the heat exchange and can run at whatever pressure the pipes and fittings are rated to, you can tap off these heat exchanges to what-ever you want.
> Most storage tanks are just too small to be useful and very poorly insulated

  In my set up I wont be storing water, the water needs to pass through, get heated and be on its way. I think you are talking about a system for heating and storing hot water to have on tap and not a circulating system. My water needs to be separated from the coil to header system as does yours but the difference is yours is pressurised from a storage tank and mine is pressurised from a circulating pool system.

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## Moondog55

Yes but they both need to be great big storage tanks or they loose heat too quickly, the storage tank at the place in Harrietville was about 3000 liters and it had to be that big to warm the water for the spas ( spas run fairly hot 42C at Falls Creek) 
Even if you only have one coil for the swimming pool passing through the heat storage tank you storage tank needs a certain volume to maintain the temperature differential, I reckon you could use high pressure black polypipe as the heat exchange material with no problem if the heat storage tank was only at 50C.
You don't store hot water, you store energy in the form of heat, then extract what you want when you run the pool pump

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## stan250

> Yes but they both need to be great big storage tanks or they loose heat too quickly, the storage tank at the place in Harrietville was about 3000 liters and it had to be that big to warm the water for the spas ( spas run fairly hot 42C at Falls Creek) 
> Even if you only have one coil for the swimming pool passing through the heat storage tank you storage tank needs a certain volume to maintain the temperature differential, I reckon you could use high pressure black polypipe as the heat exchange material with no problem if the heat storage tank was only at 50C.
> You don't store hot water, you store energy in the form of heat, then extract what you want when you run the pool pump

  If you need to heat say spa water quickly and on demand then yes I can see that you might need to have some sort of big heat sink but pool water heating dosent work that way. The boiler boils away for a couple of days then ticks over on slow combustion to keep the temp up with the help of pool cover and in my case a winter time polytunnel covering the pool for as long as I can be arsed to fill the thing with wood. It's just not possible to heat a pool right up to a comfy temp quickly in the shoulder seasons or in winter so I dont think the tank option would work or would be something I would want to set up - I'm trying to reduce the equipment needed, not add to it!!

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## Moondog55

> If you need to heat say spa water quickly and on demand then yes I can see that you would need to have some sort of big heat sink but pool water heating dosent work that way. The boiler boils away for a couple of days then ticks over on slow combustion to keep the temp up with the help of pool cover and in my case a winter time polytunnel covering the pool for as long as I can be arsed to fill the thing with wood. It's just not possible to heat a pool right up to a comfy temp quickly in the shoulder seasons or in winter so I dont think the tank option would work or would be something I would want to set up - I'm trying to reduce the equipment needed, not add to it!!

  Valid point, I must say the polytunnel idea is also a very good one. 
Been an interesting discourse tho, i learnt something

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## Geoff2005

Nice technical challenges here but what I wouild be thinking about is running a wood heater inside house in summer and increase fire risk etc. 
I have been a pool owner for 10 yrs in Perth. Our weather is fairly similar to Adelaide. We have a solar heating arrangement (36m2 for 55000l) and is always used in tandem with a blanket. Up until 2 yrs ago I have always used the cheapest blanket. The WA gov had a rebate scheme for blankets so I went for an 8 yr life blanket which is considerably thicker then what I had in the past. Last year I didnt run the solar heating at all, pool was even a bit on the warm side in some instances. The pool is nice temp now. 
My point is just a good blanket will most likely be all you need. Reduces evapouration too.

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## Moondog55

Good blankets save heaps of heat, but a lot does depend on annual lowest temperature, if air temp drops much below freezing you need to add extra heat to the pool, even if it is Olympic sized

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## stan250

This is what I mean; with the steam 'n all.
[ame=http://www.youtube.com/watch?v=NlVon8q6LMU]YouTube - James U. Winter Outdoor Pool Heated - Free Heat Machine Outdoor Wood Furnace[/ame]

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## applied

I have created sutch a beast last summer just for giggles I lit a large fire in a 44gallon drum and screwed a 22gallon drum inside. I filled the smaller drum with second hand coolant I drained from a motor and coiled one of those small dia grey water hoses in the smaller drum. Using a small bilge pump of eBay circulated the water. 
Definitely works but I live in a medium density suburb so wasn't popular with the neighbors and firewood supply is a problem.

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## Geoff2005

Looking at he vid that guy lives in a forrest so has lots of "free" fuel. And probably lots of free water to replace the water evapourating off. He would run that furnace 24/7 to keep the pool like that, it wont happen in an hour or a day of burning (raising water temp from 10 to 25 degrees). 
Don't know too many people that are planning on increasing the amount of fuel they consume these days, and for the excersise this will take a lot of fuel regardless of the location of a plantation and if you get it free.

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## stan250

> Looking at he vid that guy lives in a forrest so has lots of "free" fuel. And probably lots of free water to replace the water evapourating off. He would run that furnace 24/7 to keep the pool like that, it wont happen in an hour or a day of burning (raising water temp from 10 to 25 degrees). 
> Don't know too many people that are planning on increasing the amount of fuel they consume these days, and for the excersise this will take a lot of fuel regardless of the location of a plantation and if you get it free.

  As I said at the beginning I have more fallen timber than I could ever use (about 50 acres of forest on my block).
Also have far more rainwater than  I could ever store - tanks are overflowing after first month of winter rains. Plus I have an abundant supply of fairly saline groundwater which is suitable for a salt water pool/chlorinator.
I will be using a thick pool blanket to reduce heat loss and evaporation (about 97%) when pool is not being used for swimming plus a winter-time polytunnel again to reduce heat loss and evaporation from cold and winds.
Whilst we do get an occasional light frost at night here (blanket in place) the chance of similar daytime temps as in the vid, are not likely.
Providing I put in a sufficiently large firebox, it shouldnt need loading too much and I wont be heating it every week but a set up like this would mean I would have the option use the pool for quite a lot longer than the 4 or 5 months it can be used for presently and some central heating for the house.
I put the video up to demonstrate that even in the worst winter conditions in Northern Idaho, this would work - it was also meant to be a bit tongue in cheek but you seem to have missed that.

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## Moondog55

I for one would love you to keep us posted on the results, not for swimming but for a heated spa, DIVINE!

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## stan250

> I for one would love you to keep us posted on the results, not for swimming but for a heated spa, DIVINE!

  
I dont think you would need to store heated water for a spa. A decent sized boiler will heat a whole swimming pool by 1degree F per hour, so a spa should I reckon, be ready to go in no time at all- after all they dont hold that much more water than 2 or 3 large baths. Set up costs would be cheaper without storing the water.

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## tricky4000

How about one of these to circulate the water G Store - pumps - hot water recirculating pumps
Maybe use plastic piping?

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## stan250

> How about one of these to circulate the water G Store - pumps - hot water recirculating pumps
> Maybe use plastic piping?

  yea the supplier suggested a Grundfos pump but they are quite pricey I see!
For the pipework outdoors in the US they seem to use the insulated Pex system which has very low heat loss over long distances but is quite pricey and probably more so over here. Regular pipe suitable for hot water under pressure and insulated with foam tube; for our conditions and (buried) over fairly short distances, would suffice I would have thought

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## jago

Stan not sure if this has been discussed couldnt see it but have you thought of using geothermal heat  there are a few companies not sure of the set up cost   Australian Geothermal Heating - Direct Energy - Swimming Pools & Spas | Direct Energy   :2thumbsup:

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## stan250

> Stan not sure if this has been discussed couldnt see it but have you thought of using geothermal heat  there are a few companies not sure of the set up cost   Australian Geothermal Heating - Direct Energy - Swimming Pools & Spas | Direct Energy

  hmm, that's a new one on me. Looks like it might cost quite a bit to install.

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## jago

Not pushing this company http://www.directenergy.com.au/wp-co...rochureweb.pdf 
In London there are several large office buildings heated and cooled in this way very succesfully.  I'm sure you are correct the cost is in the set up like solar systems but then there is minimal running costs. 
Google geothermal heat  pumps and see whats on offer its something I am looking at for the house as well as the pool as solar is proving problematic  for me. :2thumbsup: If I get a handle on prices I will post.

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## stan250

> Not pushing this company http://www.directenergy.com.au/wp-co...rochureweb.pdf 
> In London there are several large office buildings heated and cooled in this way very succesfully.  I'm sure you are correct the cost is in the set up like solar systems but then there is minimal running costs. 
> Google geothermal heat  pumps and see whats on offer its something I am looking at for the house as well as the pool as solar is proving problematic  for me.If I get a handle on prices I will post.

  
I am assuming that this system relies on the use of some sort of reverse cycle electrical heat pump, the only main difference between this and a regular pool heat pump being that the heat is taken from the ground rather than the air.
If this is the case, whilst the costs of running this in winter would be lower than a heat pump using air as its heat source, the actual cost in electricity of running a regular pool heat pump is not as insignificant as 'they' would have us believe! especially if you aren't able to run it solely on the off peak tariff.
So I would be careful to check on the running costs if an electrical heat pump is used as the electric cost of running a regular heat pump for a pool in July would be around $250.
Also electricity is likely to keep rising considerably over the next few years so I would be wary of tying myself to running anything major like heating which uses electricity in any significant amounts.

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## GraemeCook

> Stan not sure if this has been discussed couldnt see it but have you thought of using geothermal heat  there are a few companies not sure of the set up cost   Australian Geothermal Heating - Direct Energy - Swimming Pools & Spas | Direct Energy

  
Jago 
I got some estimates on geothermal about a year ago.    Started off at $10,000+ to drill the hole(s) for the bore, then started to get expensive.  Ballpark $35,000. 
But very cheap to run! 
Cheers 
Graeme

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## jago

> Jago 
> I got some estimates on geothermal about a year ago.    Started off at $10,000+ to drill the hole(s) for the bore, then started to get expensive.  Ballpark $35,000. 
> But very cheap to run! 
> Cheers 
> Graeme

  %#$@^@8  ,  thanks Graeme back to the $20k solar ideas then,

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## stan250

Just a safety note for anyone considering a wood fired pool heater.
An electrician must be consulted before trying this as I understand that, any pool heater must, amongst other safety issues, of which there seem to be many, be double insulated and probably earthed and bonded for equipotential hazards. 
All in all this is a complicated set up with some dire consequences if not done correctly, therefore experienced licensed professionals in the area of heating, plumbing and electricity must be consulted before attempting this.

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