Saturday, September 14, 2013

A simple gravity hot water system from the wood burning stove


I am not sure when I found the time, perhaps it was the pressing need to have a shower (as the sun is not as warm as it was to heat the hose pipe outside!) but I managed to reinstall the hot water tank! Last spring our tank sprung a leak and the company which I bought the tank from wonderfully paid for the tank to be posted back and a new tank to be sent over from the UK. It is a small tank designed for boats and has 2 internal coils and on one of the coils I have built a system inside the old water heating section on our wood fired kitchen range. Have a look at this old post to see the construction of the heating coil in the range: http://jonsarna.com/?p=597   I used a jig to ensure that the coil I made to fit into the tank were soldered all at the correct angle to ensure water flow and no air gaps. I just used an old piece of plaster board with screws screwed in to it to hold the pipes in place. It was also easy to draw on all the angles etc, and was fire proof to solder afterwards!

The photo below shows the tank and the pipes going down through the wall into the kitchen. These pipes were the problem as the 2 different tanks fittings were not in the same place.....ahhhhh....they were about 2 cm apart...... 


This meant that I had to undo the solder joints, clean all the solder off them, and redo them. I hate doing plumbing, however I have done so much now it is becoming easier and easier and perhaps I do not hate it as much as I used to!! On the top left is an old expansion tank from a scrap car I got from one of our neighbours. This means that the heating system is an open system which is a much safer system as there is no risk of explosion! All the pipes from the wood stove are sloping upwards so there is no need for a pump, I have built it carefully and it works pretty well and we are really pleased with it. We just need to win the lottery so that we can afford a couple of sacks of copper "dust" which we could pack in around the pipes in the stove as this would drastically improve the efficiency of the tank. At the moment we bought loads of rolls of aluminium foil and rolled it into balls and packed it around the pipes to try and improve the transfer of the heat from the fire box wall across to the water filled pipes. Air is not a good conductor!
You can see that there is about a 10 degree difference between the hot pipe on the top and the returning colder pipe on the bottom.


This picture shows the pipes on the back of the wood burning stove, the hot one, behind the insulation on the top and the colder one with no insulation. Although I insulate both pipes for most of their journeys I leave the last little bit of the cooler pipe uninsulated so that there is some cooling which helps (I think) with the natural flow of the circulating water. It works better if there is a temperature difference between the pipes.


The photo below shows the not very pretty pipes disappearing through the wall to the hot water tank. But is a small price to pay for a system which takes up minimal space, uses an existing heat source and it works! This does not heat it up to really hot, but we have installed a small immersion heater in the tank, 800W, and this on sunny days will just blast the tank using our solar panels to power it...... Lovely hot water out of a tap.... Luxury!!!


UPDATE:
I have just found this picture showing the coil I made which fits in the wood burning stove. Maybe it is a duplicate of the photos on our other site! This also shows how I fixed it on the sheet of plasterboard to hold it at the correct angles for water flow.



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