IRC Ventilation Requirements and HERS Scores Explained
The International Residential Code (IRC) sets minimum ventilation requirements for homes, including spot ventilation and whole-house ventilation. HERS scores measure home energy performance, and efficient, airtight, properly sized ventilation products can help builders meet IRC requirements while supporting lower HERS scores.
What Are IRC Ventilation Requirements?
The International Residential Code (IRC) is a comprehensive, stand-alone residential code that creates minimum regulations for one- and two-family dwellings of three stories or less. It brings together all building, plumbing, mechanical, fuel gas, energy and electrical provisions for one- and two-family residences.
Recent IRC model code versions have required minimum spot/local airflow rates and whole-house ventilation. The spot ventilation requirement, for instance, requires 50 CFM of actual delivered airflow in bathrooms. Based on typical ducting installations being less airflow-friendly than where bath fans are rated, typically a fan rated at 80 CFM is needed to ensure the inspector will actually measure at least 50 CFM.
Today’s tightly built homes are great for lower utility bills but can also cause problems with indoor air quality. These codes require a minimum amount of essentially continuous ventilation airflow based on the size of a home. This airflow can be met either through exhaust, supply or balanced ventilation.
- Exhaust ventilation: Pulling stale air out.
- Supply ventilation: Pushing fresh air in.
- Balanced ventilation: A combination of both.
For more background on code pathways, read Single-Family Ventilation Codes Explained: Requirements, Standards and Compliance.
What Changed in the 2018 IRC?
A key change introduced in the 2018 IRC was the requirement that all exhaust equipment serving single dwelling units such as bath ventilation fans and range hoods need to be listed and labeled as providing the minimum required airflow in accordance with ANSI testing standards.
This essentially means that they need to be certified by a certification body – usually the Home Ventilating Institute (HVI) in the case of residential ventilation. Electrical distributors should make sure the exhaust ventilation products they carry are certified. A certified products directory can be found at hvi.org.
Ohio adopted a Residential Code based on the 2018 IRC effective July 1, 2019. Code adoption varies by state and municipality, so builders should verify the version enforced in their local jurisdiction. Municipalities and states continue to adopt newer code editions on different timelines. We’ve found that with past code revisions, a handful of states and key municipalities update each year.
To learn more about how building codes and green building programs work together, read Ventilation Codes, Green Building Programs and Compliance Explained.
What Is a HERS Score?
The Home Energy Rating System (HERS) Index is the industry standard by which a home’s energy efficiency is measured. It’s also the nationally recognized system for inspecting and calculating a home’s energy performance.
HERS scores are calculated using software modeling which incorporates a number of energy-related inputs including how airtight the home is based on a blower door test, how it is insulated, etc. Like a golf score, the lower the better. A score of 100 corresponds to a 2006 code minimum reference home and score of 0 corresponds to a Zero Net Energy home.
Home builders strive for low HERS scores so that they can market the energy efficiency of their homes to prospective homeowners and potentially enjoy utility company rebates. They also have the option in some versions of the energy code to meet performance path requirements based on achieving a maximum HERS score for their climate zone.
Suppliers want to be able to offer products that will help builders lower their HERS score. RESNET created the HERS rating system and certifies the HERS raters who are specially trained to rate homes.
IRC Requirements vs. HERS Scores
| Topic | IRC Ventilation Requirements | HERS Scores |
|---|---|---|
| Primary purpose | Establish minimum residential ventilation and building requirements. | Measure and compare a home’s energy performance. |
| Key ventilation concern | Minimum spot ventilation and whole-house ventilation airflow. | Energy efficiency, airtightness and performance modeling. |
| How ventilation products help | Properly sized, certified products help deliver required airflow. | Efficient and airtight products can support better modeled energy performance. |
| Who uses it | Builders, inspectors, code officials, contractors and distributors. | Builders, HERS raters, energy consultants and homeowners comparing energy performance. |
Ventilation Product Features That Support Code Compliance and HERS Performance
From a product standpoint, some key products that can help builders comply with the IRC or enhance the HERS index include ventilation products that are:
- energy efficient in terms of CFM of airflow per Watt.
- airtight in order to help their blower door airtightness measurements.
- powerful enough to ensure they will move the required amount of air even after installation with some added static pressure, or duct resistance.
- quiet because homeowners are not likely to use ventilation fans if they are too loud, leaving open the possibility for callbacks or worse yet, liability concerns due to excess moisture.
Broan offers a number of highly efficient, HVI-certified bath ventilation fans to meet code requirements including these, which all feature DC motors. Most feature LED lighted options as well.
Lo-Profile DC
Also CFM selectable at 50, 80 or 100, this series is great for tight spaces and multi-family applications as it features shallow housings that fit into 2x4 construction.
Flex DC
Great for new construction or roomside retrofits, this series offers selectable CFM of 50, 80 or 110 and extremely airtight housings and dampers. Humidity sensing models are also available.
Frequently Asked Questions
What ventilation does the IRC require for bathrooms?
The IRC requires minimum spot ventilation in bathrooms. In many applications, the requirement is 50 CFM of actual delivered airflow, which means the installed fan and duct system must be able to deliver that airflow in real-world conditions.
Why might an 80 CFM fan be used for a 50 CFM requirement?
Fans are rated under test conditions, while installed duct systems often add resistance. A fan rated at 80 CFM may be needed so the inspector can measure at least 50 CFM after installation.
What changed in the 2018 IRC for exhaust ventilation products?
The 2018 IRC requires exhaust equipment serving single dwelling units, such as bath fans and range hoods, to be listed and labeled as providing the minimum required airflow in accordance with ANSI testing standards.
What is a good HERS score?
Lower HERS scores indicate better energy performance. A score of 100 corresponds to a 2006 code minimum reference home, while a score of 0 corresponds to a Zero Net Energy home.
Can ventilation products affect a HERS score?
Yes. Efficient, airtight ventilation products can support better energy modeling inputs, especially when they help reduce air leakage, use less energy and still deliver required airflow.
Who certifies HERS raters?
RESNET created the HERS rating system and certifies HERS raters who are trained to rate homes and calculate HERS Index scores.