Sizing Lunos e² through-wall ventilation units

Sizing Lunos e² through-wall ventilation units

How To Size Lunos e2 Systems

Components of the Lunos through-wall ventilation system

To understand sizing of the Lunos system, we must first review the two types of fan units available to install:

Lunos Comparison Chart

For larger spaces, installing multiple systems can achieve higher ventilation requirements while still achieving significant savings compared to high efficiency centralized systems. To make sure that homes achieve proper ventilation levels, we offer the following guidelines for sizing your Lunos system, based on 2021 International Residential Code (IRC) ventilation rates which is required by many jurisdictions, AHJ and code officials.

Lunos Air Flow Diagram
Caption: The Lunos e2 system provides continuous ventilation with one unit providing fresh air in and the other unit exhausting stale air out and then reversing in 70 second intervals. For the full video, click here.

In the past, when considering design ventilation rates, we’ve considered recommendations from ASHRAE, Building Science Corporation, and IRC. We’ve since simplified to only presenting the IRC Chapter 15 route. For more on why we’ve chosen this pathway, we recommend watching this video from Christine Williamson: The Controversy About Residential Ventilation Rates. It’s the most clear and concise explanation regarding the differences and methodologies behind each means of measurement.


IRC Chapter 15 prescribes the following calculation:

7.5 CFM per occupant (determined by the number of bedrooms + one)
+ (area x 0.01)
reduce by 30% (credit for balanced ventilation)
= Required Minimum CFM

Using the above calculations as a starting point, we assume an average rate of 20 CFM per pair of Lunos fans, then remove the 30% balanced ventilation credit (take times 70%). Here’s how the size/configurations change:

  • 450 sf studio = 7.5cfm*1 + (450 x 0.01) x 70% = 8.4 cfm minimum [One pair]
  • 650 sf one bedroom = 7.5cfm*2 + (650 x 0.01) x 70%= 15.4 cfm minimum [One pair]
  • 1,000 sf two bedroom = 7.5cfm*3 + (1,000 x 0.01) x 70% = 22.75 cfm minimum [Two pair]
  • 1,500 sf three bedroom = 7.5cfm*4 + (1,500 x 0.01) x 70% = 31.5 cfm minimum [Two pair]
  • 2,000 sf four bedroom = 7.5cfm*5 + (2,000 x 0.01) x 70% = 40.25 cfm minimum
    [Three pair]

Although the minimum flows required can be reduced by 30% credit for balanced ventilation - the Lunos system requires placing a fan in each bedroom as well as other living spaces. The fact that e260 units allow for odd numbers of fans on one controller won't change the equation in most circumstances. If an odd-number setup is beneficial, please contact us to consult before purchasing, as this may require additional controllers and changes in wiring or layout for your fans.

The need to place one fan in each room functionally makes Lunos sizing the same as IRC calculations without this 30% credit. It may, however, provide some leeway in certain situations, so engineers, architects and designers should use that option if needed.


The ultimate number of fans may also be affected by the layout of the home. As there should be a Lunos e2 in each bedroom at minimum, to ensure indoor air quality in each bedroom. Then depending on the layout the living areas may act as a pass-through space for circulation of the air between bedroom fans. Consequently, there may be opportunities to be more or less efficient in the number of units required depending on the specifics of the layout.

The Lunos e2 systems are installed in the living areas of the home - including bedrooms, living rooms, offices. Bathrooms require separate, dedicated ventilation systems. For these spaces, our best practice recommendation is to install the Lunos eGO unit for optimal comfort and efficiency.

eGO Room Ventilation
eGO Room Ventilation

Alternatively, traditional exhaust fans can be used with intermittent operation. The exhaust fans should have timers, motion sensors or switches to limit their use and their impact on the overall ventilation efficiency.

If you still have questions, email us at and we can help you optimize your e2 and eGO layouts.