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I noticed that the specific heat capacity of brick is around $(900-1000)~\rm\frac{J}{kg~K}$ whereas water is $4180~\rm\frac{J}{kg~K}$.

If my understanding is correct then the water heater would store more heat at the same temperature compared to the brick heater. In fact around 4 times more.

So why are brick filled storage heaters used instead of water filled ones?

Brick is denser than water which means the heater would be heavier which would be another reason to choose the water over the brick.

Though a water heater may be prone to leakage and possible breakage due to thermal expansion, which would be at least one disadvantage of the water heater.

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    $\begingroup$ That first specific heat capacity is way off. The specific heat capacity of brick is around $1000~\rm\frac{J}{kg~K}$, not $1$. $\endgroup$
    – Chris ♦
    Commented Dec 10, 2017 at 11:33
  • $\begingroup$ Thanks Chris. I read the data online in kilo form and then forgot to prepend the k. Though I did later mention "4 times" when comparing the s.h.c. values, so I hope people recognized my typing error. $\endgroup$
    – Kantura
    Commented Dec 10, 2017 at 11:44
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    $\begingroup$ No convection, so slower heat transport, will stay warm longer? $\endgroup$
    – user137289
    Commented Dec 10, 2017 at 12:41
  • $\begingroup$ Thanks Pieter. That's interesting, I never thought of the effect of convection. I wonder if that does in fact slow down the rate of heat given off. $\endgroup$
    – Kantura
    Commented Dec 10, 2017 at 13:51
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    $\begingroup$ What does it come out to in $\frac{J}{K\ m^3}$? $\endgroup$
    – The Photon
    Commented Dec 10, 2017 at 16:43

3 Answers 3

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There are a number of things that make working with water more difficult, but I suspect the major one here is the boiling point of water. A quick search shows that a typical storage heater runs at temperatures from $200-650~\rm^\circ C$. These temperatures are well above the boiling point of water, so a storage heater using water would either have to be huge (defeating the purpose of using water) or containing enormous pressures.

While you could probably make one under pressure that still operates fine, it would presumably be more expensive, and far, far more dangerous, since at those pressures it basically turns into a bomb the first time something goes wrong.

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in addition to the points made above, a water tank can leak, but a basement full of stacked bricks will not, nor will the bricks support growth of mold, bacteria or algae. the bricks can be easily stacked with gaps to admit air but this is harder to accomplish with water. the bricks have structural strength but water requires a container to take loads.

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And, of course, bricks are denser so the water wouldn't hold about 4x as much heat for a heater of the same size but only about roughly twice as much.

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