An Idea from the Harrogate Show.
Inside Hall 1 I came across a stall by the Leeds Allotment Society
As you see it quoted CHEAP HEAT. In fact its free heat
It consisted of an old central heating radiator painted black, this was placed in a box with polystyrene insulation behind it and a double glazed panel in the front.
From the top of the radiator a 22mm pipe comes out and up along to an expansion vent, from there the pipe goes along then down into a raised bed in a polly tunnel where it splits into two under the soil. It emerges from the raised bed and back into the radiator.
The idea is the sunlight is attracted to the black radiator, ( much like you see steam coming off a tarmac road when its been wet and the sun suddenly comes out ) this heats up the water in the radiator, hot water rises and cooler water takes its place, Gravity pump.
The chap I spoke to said it makes at least three degrees Celsius difference. Obviously its not for the faint hearted and some DIY skills would be required but what a good idea I thought.