An ERV (energy recovery ventilator) and an HRV (heat recovery ventilator) solve the same problem: a tight, well-sealed home needs a steady supply of outdoor air, but you don't want to throw away the energy you spent heating or cooling the air you exhaust. Both use a core that lets outgoing and incoming air streams swap energy without mixing.
The difference is moisture. An HRV transfers heat only. An ERV transfers heat and a portion of humidity — commonly 40 to 60 percent — between the streams. That one distinction drives the choice by climate. In hot, humid markets like coastal Texas and most of Florida, an ERV is usually the right call: in summer it keeps much of the muggy outdoor moisture from riding in with the fresh air, so the AC isn't fighting it. In cold, dry northern winters an HRV is often preferred because it ventilates without trapping indoor humidity that an ERV would partly hold back.
For a homeowner the takeaway is that 'fresh-air system' isn't one product. A contractor in a humid launch state proposing an HRV, or vice versa, should be able to explain the moisture logic. Either device should also be sized to an ASHRAE 62.2 airflow target rather than picked off a shelf — the recovery core saves energy, but only the airflow rate determines whether the house is actually ventilated.