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Room Airflow and Balance Calculator

Calculate CFM from an explicit air-change target or sensible load, then compare design and measured room airflows without hiding individual deficits.

Use this result well

Inputs that matter
Room volume (ft³), Specified air-change target (ACH), Sources and assumptions, Room sensible load (Btu/h), and 4 more
Output to expect
Airflow from a specified room air-change target, Airflow for a documented sensible load, Room airflow balance record
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Airflow from a specified room air-change target

Convert a room volume and an independently specified air-change target to airflow. The selected rate must come from the applicable design and must identify outdoor or total air. This worksheet does not choose cooling airflow, a register size or an occupancy standard.

CFM = room volume in cubic feet × specified ACH ÷ 60.

Airflow for a documented sensible load

Calculate the airflow corresponding to a documented room sensible load, an established supply-to-room temperature difference and an appropriate air heat-capacity coefficient. Outdoor ventilation, latent loads and outlet selection remain separate design checks.

CFM = sensible Btu/h ÷ (air coefficient × temperature difference in °F).

Room airflow balance record

Compare measured room supply airflow with each room's documented design flow. Report signed differences and an explicitly chosen review tolerance. A balanced total can hide a deficient room; every row stays visible.

Room difference = measured − design CFM; relative difference = difference ÷ design × 100 when design is positive.

Updated: September 2026

Example Scenarios

The built-in example is an arithmetic illustration. Replace it with your own verified measurements or planning assumptions.

→ 151.2 CFM

The built-in example is an arithmetic illustration. Replace it with your own verified measurements or planning assumptions.

→ 150 CFM

The built-in example is an arithmetic illustration. Replace it with your own verified measurements or planning assumptions.

→ 2 rooms outside chosen tolerance

FAQ

Yes. The room balance record compares each room individually with its design airflow and chosen tolerance, even when the total measured flow matches the total design flow.

Use the actual source documents, units and operating conditions shown in the selected mode. Replace illustrative examples with your records, enter explicit zeros only where valid and retain unresolved assumptions.

Choose Save planning case for local history. Copy MD retains current inputs, notes and interpretation; Download CSV exports the result breakdown. Export a separate copy before changing devices or clearing browser storage.

About Room Airflow and Balance Calculator

Convert a room volume and an independently specified air-change target to airflow. The selected rate must come from the applicable design and must identify outdoor or total air. This worksheet does not choose cooling airflow, a register size or an occupancy standard. Calculate the airflow corresponding to a documented room sensible load, an established supply-to-room temperature difference and an appropriate air heat-capacity coefficient. Outdoor ventilation, latent loads and outlet selection remain separate design checks. Compare measured room supply airflow with each room's documented design flow. Report signed differences and an explicitly chosen review tolerance. A balanced total can hide a deficient room; every row stays visible.