What an ERV Does for Indoor Air

Houses that are tightened up hold moisture, cooking smells, and whatever the people and the cleaners put in the air. An ERV gives those houses a controlled way to trade air with outside. One fan exhausts. One fan supplies. A core sits between the streams so they do not mix freely, but heat and some moisture move across. In winter that means the incoming air is not quite as cold as the raw outdoor air. In summer it means you are not dumping all of your cooling into the yard.

What improves, and what does not

Used as designed, an ERV lowers the stale-air complaint and helps with humidity that comes from people and showers, because it is actually exchanging air. It does not cool a room the way a condenser does. It does not filter wildfire smoke just because it is running. Smoke is outdoor air, and the ERV’s job is to bring outdoor air in. During heavy smoke, more outdoor air can be the wrong move. Filters on the ERV catch dust. They are not a claim about medical air.

A heat recovery ventilator, an HRV, is the cousin that transfers heat but is built to pass less moisture. The wet side of the climate is why an ERV is the one people mean in the Portland metro more often than not. The right choice is still about the house, how tight it is, and whether a bath fan and a dryer are already the only ventilation.

What has to be true for it to help

• The outdoor intake has to be away from a dryer vent, a garage, and the condenser’s discharge.
• The core needs to stay clean. A packed core stops recovering anything and just becomes two weak fans.
• Balancing matters. An ERV that blows harder than it exhausts, or the reverse, fights the furnace and the doors.

If the house is stale and the filter on the furnace is already clean, ventilation is a fair question on a diagnosis. It is not the first part we sell when the real issue is a dead return or a coil that is dirty.

Common questions