Ancient Roman heated floors (Hypocaust)

It's neat seeing thermal mass and surface heating used in ancient times!

This video shows a reconstruction of a Roman hypocaust. I found it interesting that they got a much better draft when they decreased the entrance to the fire--it reminded me a lot of the small rocket mass heater doors and fireboxes:



And, this video shows the foundations of an actual ancient Roman hypocaust:

I really appreciate your historical posts like this one, thanks for sharing Roman, and other, stuff with us!

Wow, wow, wow what a video!  Genius.  I’m always astounded at the ancient world.  All the answers have been discovered somewhere on the Earth just need to work it back, have patience, and show folks.  A wonderful thermal mass experiment done very well.  We’ve been toying with the idea of a smaller hypocaust/rocket mass heating system for a connected barn/sunken greenhouse design.  With a highly conductive central Trombe wall and two level floor heating.   Curious in the video they were mainly interested in the heating but noticed the beginning temps indoor were notably below outdoor temps:). Both edges of the sword heating and cooling in one simple design.   Modern geothermal design is not that environmentally friendly and complicated, but lime plaster and rock, my favorite.  Intrinsic to many ancient designs the more proficient they ran it the more efficient the system became.  Really incredible 4 dimensional thinking here.  Double Cheers and brilliant, thank you!  Nicole.  

Quite interesting to watch these two videos. However, what a waste of wood to do this! They used 540 kilos of wood to heat essentially a tiny home for 8 days plus an extra day of "inertial" heat (and not even in very cold weather). In terms of efficiency, this is an abject failure. Could heat same home with, say, a good fireplace insert or a RMH, for a  fraction of that amount of wood, like less than 20%. Having a toasty floor is nice, but there's got to be a better way.

...was just thinking about this topic a bit more. Perhaps these modern Brits have the wrong idea of how the floor/wall hypocaust was typically used back then?  Perhaps the ancients chiefly used interior fire heat, like a hearth/chimney, and the hypocaust system was just used sparingly to take the "edge" off of the coldness of floor and walls, rather than to heat the house. It's hard to imagine the ancients using so much wood for so little heat return.

From what I'm seeing, hypocausts were usually in the homes of wealthy, or in public bathhouses.

From History Extra:

The hypocaust began as a public luxury, eventually exported to private homes. The earliest examples appeared in the great bath complexes (thermae) of the late republic and early empire. Roman baths were vast public leisure centres and required consistent, large-scale heating.

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“To have a hypocaust system in one’s house was a big sign of wealth. It would generally only have been present in examples of really opulent and wealthy dwellings: dwellings that, for example, might have their own private bathhouses.[/url]

No, it wasn't efficient and did take a lot of resources. There were a lot of ways they could have made it more efficient. But, it was also a thing for the wealthy, to show how rich they were.

Exactly Kit!   If you only seasonally use a heating system and can scale it up or down as people do today.  They limited the air intake aperture as they showed and extended the burn time lessening wood consumption.  I don’t run my thermostat in the house at 26C all winter, 13-14C.  If I had only hand tools wood to burn becomes gold.  The thermal monitoring noted temps well above 20C would be too much for people spending the majority out of doors.  The real brilliance of Hypocaust is thermal buffering 2-3C naturally cooler in summer, and with RMH built central in the design the circulation could heat a large structure very efficiently.   Just a scale change to the RMH.   Rebar and lower lime in modern concrete prohibits higher temp direct heating with fire as it will degrade structurally when cooling/shrinking.  Instead I imagine a long small burn/exhaust chamber the length of limecrete floor with a thermal wall above it transferring heat to a second floor.  
Compared to digging 50+ meters at 60K for the modern geothermal systems pumping 3-4 tons propylene glycol under your feet.  Imagines if that breaks physically… if the limecrete breaks you can patch and it will get stronger.  Absolutely brilliant.  Cool people live longer, scientifically speaking.  Cheers.  

All you really need to maintain the system is a dedicated staff of children to crawl in and clear out the ash. ; )

Fair and excellent point Sir Arthur.  Some work I do as work, and some work is to prevent my own entropy.  Have trouble telling the difference, yet winter heating is an excellent motivator.  I believe starting the fire with an high frequency oscillating vacuum pulling exhaust would fix the ash clean out as well locating the primary ceramic Venturi at the very front of the modified RMH.    Cheers.