
Heat Storage Hypocausts: Air Heating in the Middle Ages (2017) - KirinDave
http://www.lowtechmagazine.com/2017/03/heat-storage-hypocausts-air-heating-middle-ages.html
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keeganjw
If you want to learn about an ancient solution to the opposite problem, air
conditioning, I recommend this:

[https://en.wikipedia.org/wiki/Windcatcher](https://en.wikipedia.org/wiki/Windcatcher)

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bliblah
Thanks for posting this, the gallery section left me speechless. I hope
tensions die down so I can go visit Iran one day; i'm always impressed by the
historical architecture that is present in the Middle East.

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oh_sigh
You can go there now as an American, and it may be even safer than going there
as a non-American, because you will have a government minder spend every
waking moment with you.

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pagutierrezn
In some rural areas of Spain where access to wood used to be limited
hypocausts still exist, work great and are heavily used because they are very
efficient. I've seen lots of them and their construction is practically the
same described by Romans

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billbrown
The podcast 99% Invisible had an episode[1] earlier this year that featured
some of these passive innovations like India's stepwells[2]

[1] [https://99percentinvisible.org/episode/thermal-
delight/](https://99percentinvisible.org/episode/thermal-delight/) [2]
[https://en.wikipedia.org/wiki/Stepwell](https://en.wikipedia.org/wiki/Stepwell)

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pseudolus
If you're in the UK or visiting the UK the Roman Baths in Bath, UK offer an
amazing experience to see saunas heated with hypocausts.

[https://www.romanbaths.co.uk/](https://www.romanbaths.co.uk/)

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dsfyu404ed
>A furnace's dimensions would depend on the size of the room to be heated. In
private homes, where only the bedroom was heated, it would be one to two
metres long, a little more than a metre wide and 50 to 60 cm high. In public
buildings and monasteries, where large halls and rooms had to be heated, the
furnaces would be much larger.

This is massive compared to the size of a wood stove. It's amazing what a
thousand years of incremental refinement will do.

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KirinDave
These systems do predate mass production of steel, so no surprise there.

It is interesting to contemplate what solar or geothermal variants of this
system could do. Nearly every home has a crawlspace of those dimensions
underneath the ground floor.

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dsfyu404ed
Nitpick:

I think you mean cast iron. Steel is kind of tricky to cast and we've only
been casting it for ~100yr and even then not for large things in high volume.
The largest high volume production (i.e. consumer item sold by the thousands)
cast steel thing I know of is steering knuckles on the newest Ford trucks. In
contrast we've been casting things of all sizes and shapes our of iron since
the 1800s. Considering the mechanical requirements of a wood stove it doesn't
make sense to cast it out of steel.

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KirinDave
You know, I thought that specific parts being switched to steel was a reason
for the uptake of popularity in a wood burning stove, but I see this is only a
case in a very specific market of wood burning stoves. Thanks for the
correction!

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dsfyu404ed
Which parts switched to steel? Other than fasteners and misc. hardware that
has to be strong and fairly malleable to withstand owner abuse (hinges,
handles, latches, etc) I don't see much of a need for steel in a wood stove.

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VBprogrammer
These are a fore-bearer of the masonry heater. Very similar to what some off-
grid types have built and called a rocket mass heater. Very interesting
principle but unfortunately (or fortunately if you are so inclined) they will
never compete with the ease of operation of a gas (or oil) central heating
system.

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KirinDave
Well, what's an interesting question about these systems is, "In a modern
context where we understand science much better and have much more
sophisticated materials available, could we use these principles?"

The real trick here is using available materials for heat storage, using air
convection to circulate heat but not waste gas, and tightly limiting oxygen
flow to make the most of minimal materials.

It's definitely not bad, from an efficiency standpoint, to be compared to
rocket heaters. They're still some of the most efficient systems we have.

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adrianN
We could probably improve the dimensions quite a bit if we used something
other than granite for heat storage. Something that changes phase, like in
those pocket warmers, would probably be more effective.

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yetihehe
There is fireclay [1], and I have fireplace with several bricks made from it.
When fired in the evening for 2-3h, will keep warm until morning.

[1]
[https://en.wikipedia.org/wiki/Fire_clay](https://en.wikipedia.org/wiki/Fire_clay)

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pagutierrezn
More info on existing and still in use hypocausts in Spain
[https://en.m.wikipedia.org/wiki/Gloria_(heating_system)](https://en.m.wikipedia.org/wiki/Gloria_\(heating_system\))

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failrate
Fun fact: even modern Korean condominiums have a modern equivalent of an
ondol.

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abrowne
I wish more housing in cold-winter North America (like here in Minneapolis)
had something like that.

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agumonkey
primitive technology dude built himself a hut with some form of hypocaust
(fire tunnel beneath clay tiles)

