I'm looking at the ebay item:
http://cgi.ebay.com/TITAN-TANKLESS-WATER-HEATER-N120-Whole-House-NEW_W0QQitemZ120070468154QQihZ002QQcategoryZ115967QQrdZ1QQcmdZViewItem

I have a hose bib connection on the outlet of the pump/heater. I was thinking of piping from this to a tankless water heater and then piping it into tub over the side in the back. I would have to get 4 gpm. I guess I could do a bucket test. (count seconds to fill 5 gal bucket and do the math). Then I would have to run another circuit from the breaker box to handle ~50A/220v. Would this be a good idea? If I couldn't get the recommended flow rate threw the heater, could I hook up another pump?

Dan

On a Hot Tub?

I wouldn't waste the time or money. On a typical spa installation that thing would probably be rotted out within a year or less. These heaters are designed for a very stable ph and limited sanitizer environment and just don't have the means to operate continuously with a system that will recirc contaminants and chemicals through them.

YMMV.