Laboratory exhaust planning

Multi-Fume-Hood Exhaust Planner

Compare fully connected exhaust with a user-defined active and standby hood scenario.

Created · Updated

Build an airflow scenario

Use documented full-open and standby flows. The calculator does not choose diversity or room-pressure criteria.

Hood group A

Hood group A

Hood group B

Hood group B

Enter values and calculate.

Total hood counthoods
Fully connected exhaustCFM
Scenario exhaustCFM
Scenario / connected ratio%
User-set makeup airflowCFM

How to use this planner

  1. Group hoods that share the same full-open and standby airflow.
  2. Enter total and simultaneously active counts for the scenario being reviewed.
  3. Enter a project-defined makeup-air fraction; do not treat the default as a requirement.
  4. Compare the result with exhaust controls, supply-air capacity, room-pressure strategy, and failure modes.

Formula

Connected exhaust = Σ(quantity × full-open flow)
Scenario exhaust = Σ(active × full-open flow + inactive × standby flow)
Makeup airflow = scenario exhaust × user-set makeup fraction

Worked example

Four hoods are split into two identical groups. Each group has two hoods, one active at 600 CFM and one at 150 CFM standby. Connected exhaust is 2,400 CFM; the operating scenario is 1,500 CFM, or 62.5% of connected flow. A user-set 90% makeup fraction produces 1,350 CFM for that scenario—not a universal requirement.

Result interpretation

This calculator exposes the assumptions behind one operating scenario. It does not prove that hoods may be diversified, select minimum flow, establish room offset, model door transfer, size a fan, or validate control response. Laboratory exhaust and makeup systems require a coordinated design and owner-approved sequence.

Frequently asked questions

Is the scenario ratio a diversity factor?

It is the arithmetic ratio for the counts and flows you entered. Whether a diversity concept is allowed and how it is defined are project decisions.

Why is the makeup-air fraction user supplied?

Room pressure depends on all supply, return, transfer, and exhaust paths. No single generic fraction can represent every laboratory.

Can I enter constant-volume hoods?

Yes. Enter the same full-open and standby flow for that hood group.

Related resources

Sources