Maybe about 50 kilos. 3 g / cubic cm
This would mean 16666.666666667 cubic cm of stone
Heat storing capacity is 3 J/cubic cm K
If the stones are heated to 150 degrees celcius from 10 degrees celcius...
the energy stored to the stones would be about 2 kwh.
We usually warm up the stove every other day during the winter time, so
- times - 45 (summer) = 105 times a year.
- * 2 kwh
210 kwh.
Electricity costs about 0.1 eur per kwh.
At the end savings would be 21 euro per year.
Since the materials were free, the only cost would be work.
Say 10 euro per an hour..that would mean payback in one year.
Hope i got the calculation right.
They use this same method in commercial applications too.
In these applications the whole stove is wrapped in
stainless steel net and the gap is filled with stones.
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