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Building Science

Should Balanced Ventilation Be Required?

Aspen’s new energy code requires balanced mechanical ventilation with recovery

An energy-recovery ventilator (ERV) provides balanced ventilation with heat recovery and moisture recovery.
Image Credit: Energy Vanguard

“You know where this is going, right? Codes will eventually require balanced ventilation.” I’ve heard people say this more than once in the past year or so. As someone who has been attending the semiannual meeting of the ASHRAE 62.2 committee, I’ve been skeptical. Then I read the new Aspen energy code and saw the first evidence that this really could happen.

Yes, I held out on you in my last article. I published that article about Aspen’s Simplified Equivalent Compliance Alternative, but I didn’t tell you about any of the other provisions in their new code. Here’s another one that, as far as I know, isn’t required anywhere else yet.

Section R403.6.2 Balanced ventilation [added section]. Dwelling units shall be provided with a mechanical balanced ventilation system. Heat or energy recovery ventilation systems shall have a minimum sensible heat recovery efficiency of 65% determined in accordance with CSA 439 at 0° C and at an airflow greater than or equal to the system’s design whole-house mechanical ventilation airflow.

Of course, they also added “balanced ventilation” to the list of definitions:

BALANCED VENTILATION SYSTEM. A mechanical ventilation system providing simultaneous outdoor airflow and exhaust airflow within 20% of each other.

Aspen is a cold climate. That means the skiing isn’t as good during the summer as in winter. It also means nobody with any experience in the area would use a supply-only ventilation system. That’s for hot and mixed humid climates. But there’s plenty of exhaust-only ventilation systems. The problem is they suck.

Balanced ventilation is definitely the way to go. The problem is it’s more expensive, especially if you’re going to require that it be done with some kind of heat recovery, which is what Aspen requires in their new code.

I imagine no one will be able to afford the houses there anymore and the place is just going to become another piece of American carnage, victim of a bunch of city bureaucrats that overreached with economy-strangling regulations. At least I hope that happens so I can afford to move within 100 miles of the place some day.

Seriously, though, Aspen’s new code will require all new homes to have a balanced whole-house ventilation system with heat recovery that’s at least 65% efficient. This is a big deal. Will it be coming to a jurisdiction near you soon? We’re in the process of adopting the 2015 IECC now in Georgia, and I’m pretty sure we won’t go that far. Who knows what might happen in our next code cycle, though.

Here’s another little confession for you. This isn’t the only thing I’ve kept secret from you. I’ve got one more big revelation for you about the Aspen energy code, so stay tuned.

Allison Bailes of Decatur, Georgia, is a speaker, writer, building science consultant, and the author of the Energy Vanguard Blog. You can follow him on Twitter at @EnergyVanguard.


  1. STEPHEN SHEEHY | | #1

    Aspen is already unaffordable
    The median home price in Aspen is over $3 million. Anyone building a house there isn't worried about the cost of ventilation.

  2. SwitchgrassFarmer | | #2

    Balanced Ventilation - Added Preventive Maintenance Cost
    I am curious how mechanical contractors handle preventative maintenance in homes with HRV/ERV systems. It takes me a few hours, a couple times a year, to clean the filters, wipe down the cabinet and fans, and wash the HRV heat exchanger core. Is there a typical charge for that added service?

    BTW, I slipped up on HRV cleaning last year. I looked inside the unit early fall and it wasn't too dirty. However a few days after the very first cold spell water was dripping out of the discharge side. I opened the cabinet latches and a few gallons of water blew the door out of my hands. Turns out a number of brown marmorated stink bugs had decided the HRV was a good place to overwinter; they died and perfectly plugged up the condensate drain! (The lesson to this story: the timing of HRV cleaning is important.)

  3. Expert Member
    ARMANDO COBO | | #3

    Supply-only ventilation
    The link provided is not working, so please expand on supply-only ventilation in hot and mix-humid climates. Do you want to bring hot and humid air inside a house during the summer months? Add another 1/2 ton min. to the system! Balanced is the way to go.

  4. Expert Member

    BC Codes
    Our building code already requires full-time balanced ventilation except for single story houses under 1800 sf.

  5. JustHousing | | #5

    It's required in MN
    With the new 2015 energy code, balanced ventilation is now required in MN residential new construction. Section R403.5.

  6. GBA Editor
    Martin Holladay | | #6

    Response to Armando Cobo
    Thanks for letting us know about the broken link. I have fixed it. The link was to an article about climate zones.

    I don't agree with everything that Allison Bailes writes here. For most homes, the volumes of air needed for residential ventilation are relatively low -- in many cases, in the range of 60 cfm to 100 cfm. That's why exhaust-only ventilation systems in hot climates, or supply-only ventilation systems in cold climates, don't really lead to moisture problems in walls.

    That said, you are correct that operating any ventilation system during the summer in a hot humid climate will increase the sensible and latent load for the house. An HRV or ERV will lower the added load slightly when compared to an exhaust-only or supply-only system. No matter what type of ventilation you have, it's important to avoid overventilating during hot, humid weather.

    -- Martin Holladay

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