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Japanese bathtubs originate from the technology of boat building. (which are actually build to keep the water outside and not inside!)
About the shape, the rectangular tubs evolved from the method of building boxes.
The round and ingot shape tubs from the manufacturing of buckets.
Therefore the shapes are different in their origin not only in the design but also in their functionality and purpose.
Ofuros have not been designed. They have been shaped by everyday use.
I think this is a splendid example of the expression “the form follows the function” expressed by the architectural modernist movement.

Said that, here I will mention some DEMERITS of the two shapes:
1) round, ingot shape: as the planks are orientated vertically and have their cross section (which is more porous) facing up: they are more prone in becoming stained on the section by black mold (but this is not always true out of the extra humid japan)

2) rectangular tubs: the corners unnecessarily hold some a larger amount of water..!
I am not sure I answered your question…

What is your budget? If you want to use it in 2 people you need at least 1500 of length.
But if you make it deeper and add internal seats… it becomes quite expensive.

Therefore I recommend to use it without seats – which enables to have a shallower tub and also use less water.

For the weight, consider that water weights 1000 Kg per cubic meter.
Therefore it depends on the sizes but a 1500x750xD600mm will hold 670 liters (670 Kg) when filled to the rim.
This translates in 120 p/sf so I think you would need some reinforcing if the bathroom is on the 2nd floor.

Sorry, we do not know of any public ofuro in the US (we supplied ofuros to Singapore and Hong Kong spas.)
For the question about re-heating the water, please check FAQ 71.

All the Best//

iacopo

Please note:
1) A wooden bathtub placed on a radiant floor will dehydrate and crack. No matter if the wood is coated or not.

2) Besides this, coating only one side only is never a good idea as the wood will be unbalanced and start to warp

3) In case of a japanese bathtub, we never coat it as it would lose its aroma. To make the maintenance easier we suggest to use a full penetration water repellent product (Kihada ichiban)

to solve the problem in your case I recommend:

A) to sand the outside of the tub to remove the coating completely

B) To keep the tub always full to the rim while the radiant floor is on. Even when you are not taking a bath

C) If you want, we can sell the water repellent. It prevents stains and the formation of mold.

Please let me know if you have additional questions.

In Japan most of the hot water heaters are equipped with a re-circulation circuit and have a small pump built into the system.
But of course we cannot export a HW heater with the tub (you would not be able to do maintenance or find spare parts) so the only way is to build a system ad hoc.
This can be easily achieved by putting together some machines used for spas such as a pump, cartridge filter and post-heater (gas, electric or heat pump).
US is the land of private pools and spas so you have the best selection of equipment with makers such as certkin, jandy, pentair, waterways etc. If you prefer a low tech approach, you could cover the tub to avoid heat loss due to evaporation and in the morning you can add 10 liters of very hot water (60deg. centigrade) to raise the temperature.
Please let me know if I answered your question.