“Fresh-Air” Intake - What We’ve Learned
Note: We’re homeowners piecing this together while a CBH warranty request is still pending (no repair date yet as of writing this post).
The Issue
| Item | Observation |
|---|---|
| Fresh-air flex duct | Runs from an exterior hood into the main return plenum. In theory this should supply fresh outdoor air. |
| Small blue filter screen | Was missing during the home inspection. Our independent home inspector flagged the absence, so CBH added a light‑blue screen afterward. It arrived with no label, no MERV rating, and no guidance on when or how to replace it. The screen also had holes and gaps around the edges, letting air bypass it. |
Because CBH never provided a rating (or even basic maintenance instructions for the screen), it was impossible to know whether the material could handle smoke, pollen, or fine dust.
During an attic check we also discovered the flex duct had completely pulled away from the intended exterior wall outlet. It looks like the duct’s weight or tension tore the plastic collar clean off, right through the screw holes where it was originally mounted. There was no collar left in place, only a zip tie loosely holding the duct near the wall. As a result, the system is now grabbing a mix of attic air and outdoor air.
Detached duct in the attic
What We Did
We replaced that unknown screen with a darker-blue MERV-1 pad (photo below).
All incoming outdoor air now passes through this pad before it mixes with return air from the house, but MERV-1 only stops coarse debris. Fine smoke and pollen still get through.
Original Filter
Updated MERV-1 Filter after only 2 months during fire season (Summer 2024)
| Scenario | Before any pad | With MERV-1 pad |
|---|---|---|
| Boise wildfire smoke events | Indoor readings jumped to “Unhealthy” within an hour. | Peaks now settle near “Moderate.” An improvement, but still not ideal. |
| High-pollen days | Noticeable spikes on the monitor. | Spikes are lower, yet still present. |
Takeaways
- A fresh-air duct only helps if it’s sealed and uses a properly rated filter.
- If the builder supplies an unlabeled screen with no maintenance guidelines, consider what is coming into your home unfiltered.
- In wildfire or high-allergy regions, filtering the intake air to MERV 8–13 before it hits the return plenum can make a big difference.
- Periodically verify that the duct is still clamped to the exterior hood; vibration and settling can loosen fittings.