I was thinking of ways to save money and heating is definitely one I could save on. (I live alone and really only want my desk area to be heated, the rest of the home is ok).

I have tried a really small butane heater but it still costs me about £2 per night to have on.

I've noticed people talking about using candles with some plant pot over the top to hold heat for longer, and this got me thinking...

I have to drive for much of the day/evening at work. The car gets very hot as all cars do after hours of driving. I was wondering if I could obtain some bricks or something that would hold in the heat and I could keep them under the bonnet as I drive home.

Then I could bring them in and put into some tray or something to heat the small room.

Just a mad idea from the mind of a maniac, but thought I'd ask here to see if this can be turned into a viable idea :D

  • 2
    You can try using those blue "bottles" which are used to "transport" cold - you keep them in the freezer when not needed, and then you add them to an insulated box to keep the temperature in the box low (I forgot their names, I call them "penguins"). MAYBE they work for hot temperatures, but maybe they explode - I have no idea. You can find them in different sizes.
    – virolino
    Commented Nov 25, 2022 at 7:48
  • Nice I like the thinking. I will look into it (but I can imagine them shattering in the heat (not that I have a clue what I am talking about :D ) Commented Nov 25, 2022 at 13:55
  • The amount of heat you could soak in or out of anything small enough to carry would just not be worth the effort at all, unless you put it inside your jumper like a hot water bottle. It would not heat a room. Scattering bricks down the road would not endear you to the local authorities.
    – Tetsujin
    Commented Nov 25, 2022 at 20:17
  • Wear clothing designed for cold weather that keeps your body heat in. Commented Nov 25, 2022 at 21:43
  • Already wearing too many layers and the temps will go down 10-20C more than this during full winter nights Commented Nov 26, 2022 at 14:21

2 Answers 2


I've been thinking about this as well. Black absorbs more heat so something black placed in a window in the sun that was able to store the heat for 12 plus hours kinda deal. I was thinking something like black recycled glass ( which is really beautiful anyway ) around a core of sand or oil or something that would absorb and slowly radiate the heat. Of course you still have to worry about cloudy days. You could try and incorporate a Fresnel lens (magnifying glass) of some sort but this involves more precision than I possess :) I'm sure there are some excellent strategies just around the corner as necessity is the mother of invention :) For now, just an extra sweater and pair of socks and slippers :)

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    – Community Bot
    Commented Dec 28, 2023 at 21:54

By far, the best material to hold heat is water. It has a heat capacity of 4.19 kJ/kgC. With density of 1 kg, that's 4.19 kJ/literC.

Bricks, not so good. Heat capacity is 0.8 kJ/kgC. Density is twice the density of water, so heat capacity is 1.6 kJ/literC.

The best possible material to hold heat would be a material that has a phase change at around the temperature you want to store and release that heat. However, such materials are hard to find at exactly correct phase change temperature, and probably very expensive as well.

Where bricks shine is if you can heat them burning hot. For example, wood-burning fireplaces have bricks that can become very hot, far above the boiling temperature of water (100 degrees Celsius). In these cases, bricks shine. But storing heat at around room temperature, bricks lose to water.

  • I feel like water would cool down too much. Like the material would need to hold the heat for longer to make it worthwhile. This was just a completely mad idea from me really haha. In reality it would need to be a nice convenient shape and size of bricks and some way to easily transport them from under the car hood (after long drive ie. big heat) to the home (ie. 50ft away etc). Commented Nov 29, 2022 at 12:43
  • If you want to prevent it cooling down, just prevent evaporation (sealed container) and add insulation like lots of clothes around it at the time the cool-down is most likely. However, if the environment of water is hotter than the water, it's not cooling down, it's heating up, so insulation should be minimized.
    – juhist
    Commented Nov 29, 2022 at 16:43

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