On Monday, October 5, 2015 at 4:14:21 PM UTC-4,

The 15 amp plug-in type hot tubs operate a little differently than what you had. Because of the small power supply, the hot tub will only heat water when it is not in use. When you have the jets blowing bubbles, the heater will not operate. This is fine if you don't use the tub for extended periods where the water would cool down while you are in it.

John Grabowski
http://www.MrElectrician.TV

+1

My first spa, I made that mistake too. When I found out the disadvantages
it was still new, so I got the company to switch out the controller pack
for a 240V one.

To summarize, there are two issues:
First is what John pointed out, that the heater will not heat while the
pump is on high and the blower is going. That may not be so bad, because
usually you're not going to be in it long enough for the water to cool
down much. But it does mean that whatever temp it's at when you get in,
it's only going down.

Second is what GFRE pointed out, that at 240V it will heat at 4X the
rate as 120V. To me, that makes a big difference, especially in one
that is outside. I keep mine at the lowest temp, 50F, which obviously
saves a lot of energy in the winter. When I'm going to use it, I turn
it up. It still takes a few hours to get to 100F. It would take 4x
that with 120V, meaning you'd have to plan a long way in advance.
Or you could keep it on a timer, but I don't use mine that regularly.

Another factor is from what I've seen, the 120V ones are limited to
very small ones. I think if you're getting one, it doesn't cost all
that much more to get a bigger/better one.

If he really wants 120V, then converting that circuit over isn't a
big deal.