Fresh-air and ventilation systems
When a filtered fresh-air system is worth it, what specs to ask for, and how it fits with room purifiers.
A filtered fresh-air system (also sold as “fresh air purifier”, “ERV” or “HRV”) brings outdoor air in through a filter, often balancing it with exhaust air. It’s a bigger investment than room purifiers and usually suits renovations or new homes.
When it’s worth considering
- You’re renovating and can run ducts or mount a through-wall unit
- Closed rooms get stuffy (high CO₂) but opening windows lets smog in
- You want the home kept at slight positive pressure, so leaks push air out instead of in
Specs to ask for
| Spec | Look for |
|---|---|
| Filter on the incoming air | MERV 13 minimum, ideally a HEPA stage (H13) |
| Airflow | Sized to give the rooms served a sensible fresh-air rate. Ask the installer to show the calculation |
| Heat / energy recovery (HRV/ERV) | Recovers heat or coolness from outgoing air, which cuts AC and heater running costs |
| Positive pressure option | Supply slightly more than exhaust |
| Filter access and cost | Easy to replace. Price and stock of replacement filters known |
| Noise | dB at the speed used at night |
| Sealed installation | Ducts and wall penetrations sealed so unfiltered air doesn’t bypass |
What it doesn’t do
- It doesn’t replace room purifiers during severe episodes: fresh-air systems add filtered air but usually don’t recirculate a room’s air fast enough on their own.
- It doesn’t remove gases such as NO₂ unless it has substantial carbon or other gas filtration.
Things that work against you
- Evaporative (“desert”) coolers pull large volumes of unfiltered outdoor air into the home. Avoid them on polluted days.
- Window ACs and split ACs mostly recirculate indoor air. Their standard mesh filters don’t capture PM2.5.
- Exhaust-only ventilation (bathroom and kitchen fans) pulls replacement air in through gaps. That’s fine, but be aware it can draw in outdoor air.