Do you know of any electric re-heat systems for your soaking tubs?
Thank you for your interest in our japanese bathtubs.
You should use equipment available in your area.
I would recommend to contact a SPA equipment dealer/installer near you.
An ofuro can be treated as a regular spa/hot tub.
The equipment sizing will depend on the capacity of the tub.
I found this compact heater without tank (post-heating).
Of course it should be coupled with a small pump for recirculation and with a cartridge filter if you wish.
Since ofuros are made of solid wood, you can open holes for inlet/outlet almost everywhere.
Please let me know of any other question/problem.