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The 2018 Building Code Makes a Change in Ventilation

Ventilation Energy Enthalpy Recovery Ventilator Erv Humidity

Ah, ventilation. One of the easier topics in building science. Everyone agrees: We need airtight houses. Airtight houses need mechanical ventilation. Build tight. Ventilate right. No problem! We’re all on board. There’s nothing to disagree about. Right?

Ah, ventilation. One of the easier topics in building science. Everyone agrees: We need airtight houses. Airtight houses need mechanical ventilation. Build tight. Ventilate right. No problem! We’re all on board. There’s nothing to disagree about. Right?

Well, not exactly. If you’ve followed this blog for any amount of time, you know there’s plenty of disagreement to be found in the realm of ventilation for homes. Earlier this month I wrote about a new amendment that RESNET has out for public comment now. I mentioned in that article that the building code  has adopted a new ventilation rate. This happened last year and will go into effect in the 2018 editions of the International Residential Code (IRC) and International Energy Conservation Code (IECC).

This is connected to RESNET because of something I wrote about three years ago. In the last code cycle (the codes get updated every three years), the IECC adopted another compliance pathway. It’s a performance, as opposed to prescriptive, path and meeting the code is based on hitting a certain number on what they call the Energy Rating Index (ERI). That index is basically the same thing as the HERS Index and is in the 2015 IECC.

That ties RESNET to the building codes pretty strongly. Actually, RESNET is tied in pretty strongly already because the HERS reference home is based on the 2004/2006 IECC.

So, the code hearings keep happening because they’ve got to keep up with their three year cycle of publishing updated codes. Since the 2015 codes came out, they’ve taken up the issue of ventilation rates. Through the 2015 IRC, the ventilation rate was set at the ASHRAE 62-1989 rate:

0.35 air changes per hour but not less than 15 cfm/person

Last year at the code hearings, that rate was updated to:

(0.01 cfm/square foot of conditioned floor area) + (7.5 cfm/person)

That’s basically the rate from the 2010 version of ASHRAE 62.2. There’s no acknowledgment of the differences between ventilation strategies, though. It’s the same rate whether you do exhaust-only, supply-only, or balanced.

This change has happened already. It has passed. It will be in the 2018 IRC/IECC.

But now they have to make another change because of the ERI. RESNET has to change its standard if it wants its HERS Index to qualify as an Energy Rating Index. The code also has to make a change because even if RESNET adopts that amendment, the code language for the ERI points to RESNET’s old standard.

So, they’re working to fix that, too. The language to do so is:

The ERI reference design ventilation rate shall be as specified by Equation 15-1 of Section M1507.3.3 of the International Residential Code.

If that language gets adopted and RESNET passes its amendment, the ERI will be based on the new IRC ventilation rate. If the code amendment passes but RESNET’s doesn’t, RESNET will have to make changes to calculate the ERI separately from the HERS Index. (Won’t that be fun!) If the code language above does not pass, the ERI path probably won’t be as appealing to builders because they’ll take a hit in ERI points for meeting code instead of ASHRAE 62.2-2013.

We’re all in agreement, right? Isn’t it fun to get into the world of ventilation standards and codes! But guess what. This isn’t new. Here’s a quote from the book Ventilation and Heating by John Shaw Billings, M.D.:

“It is in the determination of [the ventilation rate] that the young architect or engineer is likely to find his chief difficulties, owing to the great divergence of opinion among the authorities to whom he will probably refer for guidance.”

That was written in 1893. As it says in the Bible, there’s nothing new under the Sun.


Related Articles

The Great Ventilation Battle Shifts to RESNET

The Great Ventilation Debate – Live at Affordable Comfort!

The 2015 Energy Code Will Have a HERS Rating Compliance Path


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This Post Has 8 Comments

  1. Is no one considering the
    Is no one considering the results of research regarding the apparent connection between CO2, ventilation rates and increases in cognitive function?

    Harvard TH Chan School of Public Health October 26, 2015


    Lawrence Berkeley National Laboratory “Elevated Indoor Carbon Dioxide Impairs Decision-Making Performance” Elevated Indoor Carbon Dioxide Impairs Decision-Making Performance October 17, 2012

    To this casual observer, there appears to be little objective data supporting current ventilation performance decisions.

    Other than such HSPH and LBNL data, I am a loss to see reason to support any particular ventilation standard other than subjective body effluent /odor.

    Unless of course, such research conclusions are invalid of no value. If so, let us discuss.

    If not, why not let them enter into ventilation standard considerations?

    1. Okay lets get back to our
      Okay lets get back to our environmentally friendly healthy living environmental enclosures. What are our objectives (a) control the enclosure environment (i) for most efficiently (ii)most healthy (b) by enclosure sealed or completely air tight so can control (i) this saves energy and provides economy but builds up toxic environment unless enclosed air is healthy (note did not say by ventilation)(ventilation just brings in the outside toxic air that in high vehicle traffic areas can at times be worse that existing indoor air)CO2 build up is one of the good monitoring healthy air indicators
      It is my company objective for creating a healthy living environment is to scrub or clean the air vs air exchange started in 1978 because of the air sealing of UFFI and scrubber guaranteed control of indoor product emission result (reacted off some nitrogen to increase the oxygen level and in turn reduce the CO2 …Comments? AIR CHANGE VOLUME SHOULD NOT BE OUR OBJECTIVE; ENVIRONMENTALLY FRIENDLY HEALTHY LIVING ENVIRONMENT SHOULD BE; RESPECTFULLY THAT IS BEST ACHIEVED BY AIR SEALING CONTROL AND AIR TREATMENT BY PERHAPS AIR CHANGE BUT IS GUARANTEED BY AIR SCRUBBING (

      1. Friendly FYI, your ALL CAPS
        Friendly FYI, your ALL CAPS makes your last 4 lines harder to read and more likely to be overlooked than if you simply wrote them in lower case. Only lawyers think that ALL CAPS makes things clearer but they get paid when they increase confusion whereas we need to decrease it. In general.

  2. We can not even get simple
    We can not even get simple attic ventalation understood to midagate or eliminate mold so good luck with the new venalation standards.

    1. Jack the key is not attic
      Jack the key is not attic ventilation It is attic air circulation and humidification Ventilation in the attic corners is often obstructed by too much air entrance into the attic in the central areas and not creating the draw from the corners or dead air areas Respectfully treat the breathing air for the enclosed occupants but also the breathing of the building components COMMENTS? (

  3. Allison,

    You wrote: “This change has happened already. It has passed. It will be in the 2018 IRC/IECC.”

    While this proposal has passed in the Committee Action Hearings, the Public Comment Hearings for the 2018 Codes is scheduled for October 19th – 25th in Kansas City, Missouri. While a proposal that passes the Committee Action Hearings can be automatically approved at the final hearing without discussion, this only happens if there are no public comments received by the ICC about the proposal. Any proposal that receives public comment will have to be approved at the Public Comment Hearings before it will become code. So the bottom line is that none of this is set in stone – yet.
    The online public comment period ended last week (July 22nd). Until the public comments are posted, we will not know if this proposal will be discussed in October. I suspect that it will. Therefore there is still opportunity for the measure to be defeated, supported, or modified during the final hearings.

    1. Ron, the part I said has
      Ron, the part I said has passed and will be in the 2018 code is the ventilation rate. That’s in the mechanical section of the IRC. It’s already gone through the whole process and was approved at the final action hearings in Long Beach. So we do know that the ventilation rates will be in the new code.

      If you were thinking I was talking about the change to the ERI, you’re absolutely right. That gets voted on in Kansas City in October.

  4. Is it of interest to anyone
    Is it of interest to anyone (other than me and Harvard School of Public Health and LBNL) that Lawrence Berkeley National Laboratory researchers advised that by achieving a ventilation goal at around 600 parts per million CO2 instead of 1100 and higher, that cognitive function would be increased by 100% to 300%?

    By the way, what is the carbon dioxide level in your breathing zone?

    In a 2013 Tundra pickup, two occupants, with the AC on and Vent off, at highway speed, CO2 climbed to 3600 ppm in about nine minutes. Is that worth knowing if you are driving your wife and chiildren anywhere in heavy traffic? Should we be indifferent toward 100% to 300% impairment in motor vehicles operation from high CO2? What equivalent in beer intake would match driver impairment resulting from 3600 ppm or higher CO2?
    Would a driver’s cognitive function be improved by 100% to 300% by keeping the vent open?

    Hmmmm . . . manufacturer’s liability for wrongful death and personal injury for not warning drivers or providing automatic means for CO2 control? Slam Dunk?

    1700 square foot home, energy efficient, two occupants plus a cat. Auxiliary Ventilation system off, normal AC operation, 1800 PPM CO2 overnight at 6 am.
    Same home, same occupancy, auxiliary variable speed ductless ventilation system, speed controlled by a CO2 controller set to maintain 600-700 ppm im breathing zone.
    RESULT? Constant 590-650 ppm CO2 in breathing zone. Average air delivery rate 20-22 cfm. Great Sex!

    Has anyone considering ventilation code, rates and effects on real people read the LBNL and HSPH research reports?

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