Mass hot water heater

Hello from down under. Does anyone have any experience in heating a hot tob of about 1200 gallons its curremtly heated via a heat pump .
I think a rocket stove through a heat exchanger would work well. My current plan is to pump the tub water through a car radiator placed in a 50 gallon drum inside a heat box fed from the rocket stove. lokking for input and ideas. We live in subtropical brisbane australia so not as much intence heating as other places
this hot tub is made from concrete in the ground which is about 60degree f its covered with foam and there is sometimes a frost.
Any commnets would be appreciated

Hi John.

Another ozzie, Tim Barker has come up with a great design for hot water. http://permaculturenews.org/2012/11/23/rocket-stove-hot-water/

As you will see the high preasure water is heated by the tank of water that is heated by the rocket stove. This allows you to use high preasure water without the risk of explosion. I think you would get much better heat transfer than your suggestion of a radiator in an oven

Good luck with your project

GdayAlan
Thanks heaps for your input i have seen this stove at the PRI when i did my PDC, I am impressed!

The reason i thought of the car radiator was that it would be in a hot water drum over the rocket stove not in a oven as my previous communication may have suggested.

I imagined there to be a big pot like the old style copper washing pot my parents used and into that pot put 1 or 2 radiators into the bouiling water as a heat exchanger.

The reason for this type of heater exchanger was the volume of water that could go through it as opposed to 13mm coper pipe and this could be used with the current pool pump which runs a 38mm pipe.

i understand the pressure water system at the PRI but was after more water flow and cant see how i can get additional pressure in this appliacation.

Thanks again for your past and future input
regards john

Hi John, now I understand better.

Have you had a look at institutional rocket stoves? They seem to be similar to what your thinking of. There are how to videos and design hints about the use of insulation arround such as https://www.youtube.com/watch?v=VdhLWMW7IXA and http://www.aprovecho.org/lab/rad/rl/stove-design/category/1

Perfect now I can see a direction of how to build
So what do you think of the radiator as a heat exchange

Thanks
John

Things to think about
How many Kw will you need to heat the pool. You will need a rocket stove to deliver that so 6" 8"??

Radiators are designed to have a flow through them to exchange heat, will sitting them in hot water do that? You could use more than one if you have to.

Will the pumps flow rate suit the radiator/s and get the heat exchange you need. It might be worth hooking a radiator up to the pump and seeing what happens.

I don't know the answers to these questions but maybe just build it and see

Just came across some comments about using radiators (1/2 down page) http://donkey32.proboards.com/thread/1096/hot-water?page=9

Welcome John,
Here is a link to another recent discussion of using radiators to heat hot tub water: https://permies.com/t/44409/rocket-stoves/Rocket-stove-water-heater-radiator

If you search the forums there are many other discussions on this topic also.
AL

I'm not sure why this won't work I think I'll use the gas pot idea shown to try this before I build the rocket stove.
The institution stove does not have the J entrance for timber is this an enhancement???

My understanding is that many people here prefer the J tube to the L tube if only because it's easier to feed.

The j tube would only require a little change.

There is also a preference for using "ceramic" burn tunnels (fire bricks, cast etc) to steel as steel burns out at the high temperatures that an efficient rocket stove can reach.

Another alternative (maybe the best) is using a batch box as you have so much water to heat. The design of these is more complex and if I was you I would start with one of the others and see how it goes.

There is another thread that has some good ideas https://permies.com/t/44930/rocket-stoves/rocket-bath A link Rose Pinder posted to this NZ product might give you some ideas http://kiwitub.co.nz/home.htm

The Aprovecho-designed stoves are generally all L-shaped, I think to fit with common practices in third world cultures where their work is focused. The J-tube has been found to work better than the L, and is also much more ergonomic for American cooking styles.

Ok it looks like the J style will be my choice is hebel any good to use as an insulator the hebel specs state up to 1800degrees f
Has any one have ideas on this

I don't know if everyone understands that Hebel is autoclaved aerated concrete

It might work as surrounding material, but not as the hot face. A well-running RMH can get to 2000 F or more in places.

I've seen a design somewhere of a clay moulded fire bricks for the chimney of the fire box. Can anyone point me in the right direction to make this or should his time be bought as fire bricks

Not sure exactly what you mean by "clay molded firebricks", but if you want to cast a riser, look at David Eaks' videos in his 12/10/14 post in this thread:
https://permies.com/t/42108/rocket-stoves/Heat-riser-material