Heat Exchanger

When the weather is overcast, the solar geyser will not heat up the water. I do have an electrical element backup, but decided to build a heat exchanger to see how well it would work. It is fired up by the tsotso stove. I heat a 40litre volume from 20degC to 45degC in about 1hr15min, with ambient temp of 20degC.
 
 
I used a copper array made of 2 lengths of 22mm copper and 1 length of 19mm - it is what I had in my garage. The pieces are soldered together. I had to trim the elbow and T-pieces, so that it could slide into the 100mm round tube.
 
The length shown here was about 2.5m but I cut it down to about 2.2m, so that it could thermsyphon into the tank in the ceiling, without a pump. This array slides inside the 100mm round steel tube.
 The bottom cold water feed, is a 15mm polycop pipe insulated with 20mm irrigation pipe. The cold and hot water pipe is connected to the water tank of the solar geyser. The storage tank is about 5m distance from the heat exchanger/chimney.
 
 The top hot water outlet is a 22mm pipe insulated with 25mm irrigation pipe. The 100mm pipe was 2m length and was extended using one piece of 102mmW galvanised stove pipe with a hat attached. I had two pieces of 140mm stove pipe and used it as  insulation for the 100mm round pipe - this is optional.
 
 The tsotso stove flame is sucked up by the draft of the chimney and heats up the copper pipes. I will be adding 0.3mm aluminium sheeting around the triangular base, to prevent wind from affecting the flame.
 
 I had firstly installed the heat exchanger inside the fireplace chimney, but there was insufficient heat to warm up the water - the drum and oven takes up most of the heat. So I built a seperate chimney and it heat up the water quicker. .