ACH calculator — air changes — Sim your flow
Compute air changes per hour from room volume and airflow.
What the fan really does in this room
The same fan is a high air-change rate in a small bedroom and a low one in a large living room. ACH is that measure. Home then shows whether the turnover is even, or only happens next to the fan.
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Frequently asked questions
What is Sim your flow? A 3D, real-time, browser tool where you see how air and temperature behave in a home. You draw or open an example, place a fan or AC, and follow the air live.
Do I need to know how to draw or be technical? No. Start from a ready example home, move the fan and AC, open a door, and watch what happens. If you draw your own home it does not need to be exact — rough rooms are enough to get a feel for it.
Can I test whether an AC or fan reaches the bedroom? Yes — that is one of the main jobs in Home. Place the unit, open or close doors, and see whether air and cool air get there — or stall in the living room. Move placement until it looks more reasonable.
What do I see in the live simulation? Air in motion, still corners, and how temperature changes across rooms. Colors and particles help you read the situation. It is a live picture of the field — fast feedback, not a recording after the fact.
What does the report give me? When the simulation has settled, the report sums up the result: an Airflow Score, still zones, how air spreads, and room-by-room numbers — including whether cooling or heating is heading toward the target. You can take it out as a PDF.
Is it free? Do I need to install anything? You run it in the browser, no app. Free is enough for example homes, visualization, and moving fans/AC. Pro unlocks drawing and editing your own home, saving, optimizing placement, and creating a report on your drawing.
© 2026 John Flemström · Sim your flow