Cast iron doesn't need supplemental heaters unless you sleep in the tub.

So I assume this answer means a cast iron tub keeps tub water the same temperature longer then other tubs , but how much longer before the water drops by 5 degrees ? I like to keep the tub water at 110 degree for atleast for 45 minutes at a room temp of 68.

There are a few options:

• Hydrosystems has something called Hydrofusion which is supposed to be silent pump that recirculates the water.
• Hydrosystems also has something called the Hydro Blanket that is an integrated heating pads into the tub that heats up targeted areas.
• MTI tubs has a systems called Radiance that is also the integrated heating pads into the tub.
• MTI tubs also has an inline heater.

These are a few options that I am aware of from these manufacturers. I think other manufacturers have the same options but they may have different names.

Good luck!

I'm not aware of any pure soaking tubs that circulate water. You'd need some sort of water circulation to reheat the water. Unless you went uber-low tech with a bucket immersion rod. Okay, maybe not, lol.

I have added aftermarket inline heaters to circulating tubs that didn't have a built-in heater. Quite easy to install. Heaters are roughly 1500W and run about $175 or so.

Check out Neptune Tubs. We are getting the Neptune Wind with the air bubbles and optional heated back. It isn't freestanding, but an off set corner tub. But if they make that one with back heat I am thinking others come with it too. They are made in Canada and have a pretty good reputation from what I can find out. http://www.produitsneptune.com/en/produits/bains/

Mongo,

The hydrosystems and MTI are pure soaking tubs. I did not want an air tub or whirlpool.