Ian Mansfield

Hi Bill,

I have looked at your drawings with interest. Whilst I don't want to be negative I am concerned that your design neither follows Professor Richard C. Hill's design or that of a rocket heater.

Of course I may be wrong in my assessment and I hope I am.

A rocket heater's layout and dimensions are critical to get the necessary high draft of air and efficiency. Your water jacketed feeder tube is not necessary in a rocket design as the burning should occur in the burn tunnel and not the feed tube. In contrast in Professor Hill's design the burning of the timber takes place at the bottom of the feed tube with the assistance of the injection of forced air. The resulting gases are passed through a tunnel into the secondary chamber where burning is completed.

I can understand your fascination with rocket heaters and they have their place in the scope of things. However, they are not designed to burn large heavy pieces of timber like Professor Hill's design.

In the circumstances I think it would be prudent to build a prototype of your design using simple materials and test your theories.

Hi,

I have built a water heater that works and is completely safe. It can be viewed here: https://sites.google.com/site/mywoodfiredhydronicboiler/

A pump is not needed to circulate the water and natural syphoning keeps the cooler water in the vicinity of the heat exchanger. The water in the storage tank is treated with a tannin based corrosion inhibitor and the tank is open to the atmosphere so no pressure can accumulate.

The water that I circulate through my hydronic system is separated from the storage water by a stainless steel plate heat exchanger.

I agree with previous posters that a closed system that needs an electric pump is potentially highly dangerous. No insurance company would want to insure your home with that type of installation.

Hi Bill,

I was wrong it is working. I suggest you give it another try now.

Regards

Ian

Hi Bill,

I can confirm that there is a problem with uploads to the site. I tried to upload a couple of pictures last night and this morning without any success.

Hi Bill,

Are you still trying to upload your illustration?

This is a short but interesting video about the worth of injecting air into a rocket stove.

https://www.youtube.com/watch?v=qiKBIz4hwzY

Food for thought maybe?

Hi Bill,

I had some time today to re-read and consider the postings in your thread and I am interested to see a graphical representation of your design.

It is an interesting concept to use a part of Professor Hill's design and adapt it to work with principles from a rocket heater. However, by not using a forced draft inlet fan you are dramatically moving away from the Professor's design.

It would seem to me that before you spend a lot of money that you need to build a prototype to test your design and theories.

Not needing electric powered fans is certainly good if your power supply is interrupted but of course you will still need pumps to circulate the water that you heat.

Hi Bill.

To answer a couple of your queries the surface area of my heat exchanger totals about 2124 square inches and the stack temperature is generally in the range of 230 to 284 degrees F.

However, in Professor Hill's report in Section II titled 'The Problem of Burning Wood' he details all the variables and difficulties one encounters when burning wood. He then says:-

"Given this complexity, the only design approach is to cut and try. The only design rule is to keep the combustion zone hot and turbulent for a sufficient time to complete the reaction."

In another section of his report at V(2) he discusses experiments he conducted to eliminate the requirement for a forced draft fan.

He said when this fan was eliminated the fire burned in a traditional wood stove mode-

Yellow smokey fire, heat exchanger deposits etc. The high velocity stirring of the forced draft fan seems essential.

In my case I followed Professor's design fairly closely as I had already had two failures in trying to create heat with a reverse cycle heat pump and then with a coil inserted into a slow combustion heater.

Hi Bill,

I cast the sections of my burn chamber using Densecrete 145 Castable which I bought from the Australia supplier at this site: http://www.darleyfirebrick.com.au/castables.html

For refractory insulation I used Litecrete 1280 from the same supplier. Of course you will not be buying from this supplier but you could look up the site to get an idea of the specifications of the products I used.

I cast the burn chamber in five pieces because each piece was small enough that I could bake it in our home oven. Bigger pieces would not have fitted. I went further than that and took the baked pieces to have them professionally fired but the operator declined to do the job in case he did it incorrectly.

I then went ahead with the assembly on the basis that the pieces would be fired when the heater was being used. I took the precaution of lighting a couple of small fires before doing a full burn.

I would certainly recommend casting the burn chamber in a number of pieces as a monolithic structure will have no give and take. I butted each piece against the next piece and used kiln cement in the joins that I obtained from the Big Ceramic Store USA.

I would recommend making molds for each piece with very smooth surfaces. I followed the manufactures instructions in mixing the refractory and I vibrated the mixture in the mold. I allowed the pieces to cure for a couple of days and then put them in the sun to dry out before baking them for about eight

hours.



I would recommend building the burn and secondary chambers inside a steel jacket to hold everything together. The steel jacket will also prevent leakage of gas in the event that you do have some cracking. I used about one and half inches of refractory insulation to fill the gap between the refractory

pieces and the steel jacket.


I would recommend that you build your heater in modules so that if one component fails it can be replaced or repaired without having to rebuild the whole heater. Extensive use of isolating valves for the storage water is useful as having to drain hundreds of gallons of treated water is a pain.

The burn tube in my heater has walls about one inch thick. The structure if strengthened by the refractory insulation and steel jacket that surrounds it.

I think you will have a lot of fun and satisfaction in building your own heater. I know I did.

Hi Bill,

This is my wood fired water heater based on the design of Professor Richard Hill. I constructed it myself and it works very well. The device shown has had the benefit of several modifications and I am looking forward to it having a long service life.

There is plenty of information displayed on this web site: https://sites.google.com/site/mywoodfiredhydronicboiler/