Skip to content
Calculation Machine

ERV / HRV Sizing Calculator

Balanced ventilation airflow for a home.

Reviewed by the Calculation Machine team · How we check our maths

Your values

ⓘ Live results

Results
Continuous ventilation
90 CFM
Unit size to specify
90 CFM
In L/s
42
Occupants assumed
4
Intermittent equivalent (50% duty)
180 CFM

Quick answer

Balanced ventilation is sized at roughly 0.03 CFM per square foot plus 7.5 CFM per occupant.

The formula

CFM = 0.03 x sq ft + 7.5 x (bedrooms + 1)

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Floor area2000 sq ft
  • Bedrooms3

Result

  • Continuous ventilation90 CFM
  • Unit size to specify90 CFM
  • In L/s42
  • Occupants assumed4
  • Intermittent equivalent (50% duty)180 CFM

How to use the ERV / HRV Sizing Calculator

  1. 1Enter conditioned floor area and bedroom count.
  2. 2Choose a unit rated at or just above the result at 0.4 in wc.
  3. 3Balance supply and exhaust within 10% at commissioning.

Frequently asked questions

ERV or HRV?

ERV transfers moisture as well as heat — better in humid summers or very dry winters.

Can it replace bath fans?

A multi-port ERV can, if each wet room gets a dedicated exhaust pickup.

About this calculator