Ventilation Status
Current: — ACH | Recommended: — ACH | Status: —
Recommendation Summary
| Room volume | — |
| Target air changes | — |
| Required airflow | — |
| Recommended fan | — |
| Status | — |
Ventilation Reference Chart
| Space | Recommended ACH |
|---|---|
| Bedroom | 4 – 6 |
| Living room | 6 – 8 |
| Bathroom | 8 – 10 |
| Kitchen | 15+ |
| Garage | 6 – 10 |
| Workshop | 8 – 12 |
| Office | 6 – 8 |
| Gym | 10 – 15 |
| Server room | 15 – 20 |
How Much Ventilation Do I Need?
Ventilation is measured two ways: air changes per hour, or ACH, which is how many times the air in a room is fully replaced each hour, and CFM, the cubic feet of air per minute a fan must move. This calculator turns your room into a fan recommendation. Choose the room type to get a target ACH, enter the dimensions, and it returns the required airflow in CFM, the fan size to buy, and whether your current ventilation is adequate. Switch modes for exhaust fan sizing, ASHRAE fresh-air requirements, or occupancy-based ventilation.
CFM vs ACH
The two connect through one simple formula: required CFM equals room volume times ACH divided by 60. Room volume is floor area times ceiling height, so a 400 square foot room with 8 foot ceilings is 3,200 cubic feet. To turn that over six times an hour you need 3,200 times 6 divided by 60, or 320 CFM. ACH tells you how vigorously a space is ventilated; CFM tells you what fan delivers it. Dividing back the other way, CFM times 60 divided by volume gives the ACH a given fan actually provides.
Negative Pressure in Garages and Workshops
When an exhaust fan pulls air out faster than it can flow back in, the room goes into negative pressure and the fan starves, moving far less air than its rating. It can also backdraft combustion appliances, pulling exhaust gases back into the space. The fix is makeup air: an intake opening, louver, or cracked window sized to match the exhaust. In garages and workshops where you exhaust fumes, dust, or solvents, always pair the exhaust fan with a fresh-air inlet so the air actually moves through the room.
Fresh Air Ventilation
Modern homes are built tight to save energy, which is great for heating bills but can trap moisture, odors, and pollutants indoors. Mechanical fresh-air ventilation deliberately brings in outdoor air, often through an ERV or HRV that recovers heat from the air it exhausts. The ASHRAE 62.2 residential standard sizes this at roughly 0.03 CFM per square foot of floor area plus 7.5 CFM per occupant, counting bedrooms plus one. The fresh-air mode above applies that formula.
Ventilation and Indoor Air Quality
Good ventilation is the simplest lever for indoor air quality. It dilutes carbon dioxide that builds up from breathing, clears cooking smoke and bathroom moisture before it causes mold, and flushes out volatile compounds from finishes, cleaners, and hobbies. Spaces with more people or more pollution sources, like gyms, kitchens, and workshops, need higher air-change rates, which is why their recommended ACH values are well above a bedroom. If a room feels stuffy or odors linger, it is usually under-ventilated.