terry ive got both of these machines , altec comes with a heating elment in the machaine in the clean water side great at keeping water hot ,but if you go to flat and its only got cold water it takes abit to heat it up ,great machine , the twin vac air flex is a lot lighter great for flats , i also bought in line heater from them , fantitic peice of kit , would recomend it , even if you only got cold water it heats it up instantly you will get great services from both companys never had any probs happy carpetcleaning, if you do alot of flats air flex is the lighter of the 2, which you should serious consider