i have a maax living air tub & they say the air & the back rest on one end is heated by the heat the pump puts out. it's not enough to notice, but it also has a water temp display & i typically gain a degree or two throughout the 20-30 minutes in the tub, with no insulation around the tub or anything.

if you do a search, i have seen other posts talking about this as well, when i was doing my own research.

I have a Bain Ultra Air Tub. The backrest gets noticeably warm but it's directly related to the speed of the turbine. The higher the speed, the warmer the backrest. I think on the two person tubs, there's an in line heater. I have a single person tub and yes, the water is cooled off by the air after awhile. The way I've learned to work around this is to not fill the tub as high as I ultimately want it, turn off the cold and let the hot water finish filling the tub at a slower output or just add hot water when I need it. I love my airtub! If/when I do feel a coolness, it's towards the end of a long bath but for the most part, this isn't a problem for me.
Monica

Most manufactures are using heated air systems, think of the air motor as a glorified hair dryer they will heat the air to approx. 30 degrees above the air/room temperature they draw in, so if your motor is drawing in room temp say of 70 degrees the air coming into the tub is then heated to approx. 100, most people will bath in 100-102 so the heated air will help to maintain the water temp in the tub. Some company's are now adding an In line Heater option to their air tubs, the In line Heaters used to be only available on whirlpools models. I personally love Air tubs but I would be hard pressed to choose between a whirlpool or Air so I would have to do a Combo tub with both!
One of the company's that now have the In line Heaters on their Air tub is Hydro Systems.

Here is a link that might be useful: tubz.com

Thank you all for your advice. I love lolling in the tub from time to time, but it always cools off before I am ready to get out. I love the image of a glorified hair dryer.

I guess I want to feel like a lobster being boiled! Heat and bubbles until I turn pink.

Toadangel, thanks, I did find more info when I searched.

dedtired, SO funny you mentioned "lobster". Before I had my air tub, I used to call my HOT soaks "lobster baths". Now I'm "boiling" in my lobster bath :) Really, the water stays hot enough, long enough, most of the time. If it does cool down a little before I'm ready to get out, I just add more hot water. One thing Bain Ulta suggests to keep the water hot longer, is to run the blower a few minutes before starting your water.
Monica

The process sounds very much the same, however I'd prefer to come out alive and not on the plate of someone wearing a bib.

I am getting over a cold right now and the thought of bubbling away in a warm steamy bath sounds like heaven.

I love my Bain Ultra air tub. I does tend to cool off a bit after 20 minutes or so, even though the air is heated. I will have to try the tip Monica suggested. Also, I found that I wanted a gentler range of settings, as the air jets are plenty enough for me. There is a way to choose a gentler program, and this also helps keep the water warm longer.