Using 200L plastic Drums for Space Heating

If you fill a 200L drum with moderately hot water (50 deg.C), and place it in a reasonably cold room (10 deg.C), it will radiate heat in a similar amount as a 1kW electric heater. (It's possible to work it out by using the surface area of the plastic, the coefficient of heat conductivity, the thickness, the difference in temperature, etc., but it's easier to just try it!)

It will continue to radiate useful heat until the drum temperature drops below approximately 30 deg.C. (Assuming that the room temperature doesn't rise too much - although we do want it to rise somewhat - after all, that's the object of this exercise!)

I've done some calculations around this theme, and they look good!

A 1-KW bar heater radiates heat at the rate of 3.6MJ per Hour

A 200-Litre plastic tank of hot water at 50 deg.C holds 15MJ of Useful Heat ("Useful" is defined as being above 30 deg.C)

So, each 200-litre tank which you can fill with hot water from your solar panel during the day, will radiate 3.6MJ per hour into the air of your house at night, for about 4 hours.


Build a wooden, insulated tunnel, big enough to hold about TEN 200-litre plastic drums, side-by-side, with an air gap between and around them. (A gap of around 100mm should do)

Set up some air ducting and a fan, to draw air from the coldest part of the house and blow it through the (hot) tunnel and back into the living area of the house.

Set up your 30 sq. metre (7kW) solar panel so that it pumps the hot water it generates into the plastic drums, which are connected in SERIES so that the hot water flows in one end, out the other, and back to the panel again after coming out of the last drum.

During the day, the solar panel will heat up the drums at a rate of around 20MJ per hour (that's what my solar panel does, anyhow), and assuming that most of that is actually stored in the plastic drums, you'll have around 50 to 80MJ of useful heat stored after four hours of reasonable sunshine.

Then at night-time, you turn on your fan and open the air duct into your living area... and at the rate of 10MJ per hour, you can run it for around 5 - 8 hours!

Ok, now sit back and enjoy all your hot air!

(I DO intend to set up a design like this, so watch this space...)
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