Buy another Alkota Just like the one you have and run them together then you will get 3000 @ 10gpm.. If you put a bigger Motor and a bigger pump and a larger burner , bigger coils ..etc.. you might as well buy a second machine... Heck my Honda 13 Hp elec. start sales for about 900 to 1200 my 3500 @ 4 pump sales for about 375 to 500... so you can see where this is going... You Could buy a Cold water 3000@5gpm and T it in with your machine but your burner will not heat the water worth a crap... Best bet is to buy an identical machine to yours and run 2.. Ask the Hot Water Wizard or Russ Johnson they can tell you how to hook up two machines together,,