Dad’s short answer: Heat genuinely helps on set-in stains and anything greasy, so it's worth having if you're choosing between two similar machines. But understand what you're getting — most of these warm the water rather than producing real steam, and warm water plus a good formula does most of the work.

What heat actually does

Warm water dissolves and loosens more than cold does, particularly on grease, oils and sugary spills. It also helps the cleaning formula work faster, which means fewer passes.

Where you'll notice it most is a stain that's already dried in. Cold water and a scrub tool will improve it; warm water and dwell time will often finish it.

What heat doesn't do is replace technique. Spray, let it sit for a minute, agitate, then extract. That sequence matters more than the temperature.

Heat versus steam, and the safety part

Most heated spot cleaners heat the water on the way out or simply keep the tank warm. That's not steam. A true steam function is a different mechanism, and a handful of machines in this category do offer it — but far more listings imply heat that's closer to warm.

One genuine caution: heat can set certain stains rather than lift them, most notably blood and some protein stains. For those, cold water first. This catches people out.

And check your carpet. Some synthetic fibers and some wool don't love high heat, and on a rug of any real value the manufacturer's guidance beats mine. Test an inconspicuous corner first — that goes for any new machine or formula, heated or not.

Dad’s Take: Heat helps on grease and set-in stains. Use cold on blood — heat sets it, and that's a mistake you can't take back.