There are a several signals you should look into house ventilation, such as:
1. Enduring odors
If you have problems getting potent smells out of your house, you likely have a ventilation concern.
2. Musty air
The air in your rooms should be fresh, but stale areas mean you could have poor ventilation.
3. Disproportionate dust
Dust can get stuck more often in areas with poor ventilation.