Sustained heat across a whole house
A household circuit limits how much heat a portable machine can produce, and that heat degrades as solution travels the hose and sits on the floor. An engine-driven heat exchanger holds temperature consistently from the first room to the last. On a large job this is the difference between a strong result in the living room and a noticeably weaker one in the back bedrooms, which is a pattern homeowners often notice without knowing the cause.