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.