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Musings of an Energy Nerd

Revisiting Ventilation

An updated overview of residential ventilation systems

Builders can choose from among a wide variety of ventilation appliances. The pulled-apart cylindrical appliance at the top is a Lunos e2 fan manufactured in Germany. The rectangular applaince at the bottom is a Renewaire energy-recovery ventilator (ERV) manufactured by Soler & Palau, a company with headquarters in Barcelona, Spain.
Image Credit: Lunos and Soler & Palau

My comprehensive article on residential ventilation systems, “Designing a Good Ventilation System,” was published back in 2009. A few things have changed in the last eight years, so it’s time to revisit the topic.

Code requirements

Most building scientists aren’t willing to provide a simple answer to the question, “At what point is a home so tight that the home requires a mechanical ventilation system?” A typical answer is, “It depends — but unless your house is very leaky, it’s better to err on the side of caution and install a mechanical ventilation system.”

Building codes aren’t so vague, however. According to the 2012 and 2015 versions of the International Residential Code (IRC), any new home with a blower-door test result of less than 5.0 ach50 is required to have a whole-house ventilation system. This code requirement can be found in Chapter 3, section R303.4, and in Chapter 15, section M1507.1 of the IRC.

Since the new IRC code requires homes in all zones except Zones 1 and 2 to achieve an airtightness result of no more than 3 ach50, the code effectively mandates a whole-house mechanical ventilation system for homes in Zones 3 through 8. If you live in Zones 1 or 2, and if your blower door test came in at less than 5.0 ach50, your home is also required to have a whole house ventilation system.

The bottom line: If you’re getting your advice from GBA, you’ll be building a tight house — so your house needs a mechanical ventilation system.

The building code is vague concerning the details of a mechanical ventilation system; it doesn’t really tell builders what type of equipment is needed to comply with the code. The code is specific, however, about ventilation rates. Here are the minimum airflow rate requirements according to the 2015 IRC, section M1507.1:

These code-mandated ventilation rates are…

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  1. Expert Member
    Dana Dorsett | | #1

    Missed one.
    Among the "Lunos-type fans" let's not forget the Lunos Nexxt, which can deliver 53cfm per pair at the full 20 watt highest speed. (~$1600/pair through 475 High Performance Building Supply.)

  2. ethant | | #2

    My understanding is that the Minoair Boreal has been replaced by the CATU-V12 ( The cooling capacity has been upgraded; I'm not entirely sure what else has changed... The website is only partially updated, so if you click on the Canadian flag ( you'll still see the Boreal - or maybe the Boreal is still the preferred model in Canada - that I'm not 100% sure about it because it seems the changeover is happening right now...

    In a well insulated house with perhaps another source of heat (wood), the Minotair (especially with the resistance heat booster) can be used as an all-in-one heating, cooling, venitilation, and dehumidification solution, which should be factored into the installed cost calculations.

  3. Reid Baldwin | | #3

    What changed from 2009?
    I looked back at your 2009 article and I didn't notice major changes since then. As in 2009, building scientist recognize ventilation as important, but most homeowners still don't. Building scientist still argue about the appropriate rate. The vast majority of builders and contractors still look for the cheapest way to satisfy the code inspector. Inclusion of a ventilation requirement in the model codes may have resulted in a ventilation requirement appearing in more local codes than in 2009. But inspectors still seem to accept a fresh air inlet with no controls and no commissioning as satisfying the requirement.

  4. GBA Editor
    Martin Holladay | | #4

    Response to Dana Dorsett (Comment #1)
    Thanks for alerting me to the Lunos Nexxt. I have edited my article in include information on the Nexxt.

    It could be argued that the Nexxt resembles the Zehnder ComfoAir 70 more than it resembles the original Lunos fans -- falling into a category that might be called "Low-airflow-rate wall-mounted ventilation appliances."

  5. GBA Editor
    Martin Holladay | | #5

    Response to Armando Cobo (Comment #2)
    The airflow rates you mention -- 40 cfm to 120 cfm -- will indeed cover most U.S. homes. While it's possible to buy an ERV for $1,500, as you point out, installing the ventilation system will usually add several thousand dollars to the final cost for the homeowner.

  6. GBA Editor
    Martin Holladay | | #6

    Response to Ethan T (Comment #3)
    Thanks for your comments. As I pointed out in my article on the Montair, the heat pump provides only 9,400 Btuh at an outdoor temperature of 47 degrees F -- and even less heat output as the outdoor temperature drops. That means that it's unlikely to be suitable as a whole-house heating system for a cold-climate home.

  7. GBA Editor
    Martin Holladay | | #7

    Response to Reid Baldwin
    Since I wrote my 2009 article, the model building codes have changed, and many builders are now required to install residential ventilation systems. As you point out, however, builders' ventilation system knowledge and installation skills fall woefully short, and the vast majority of residential ventilation systems installed by builders simply don't work. For an in-depth discussion of this issue, see my article, Ventilation Failures and Vocabulary Lessons.

    The weakness in new code requirements for ventilation, as your correctly point out, is that (a) the code doesn't tell builders what they need to install to meet code requirements, so that a system that amounts to a hole in the wall (with a duct connecting the hole in the wall to a furnace plenum) meets code requirements, and (b) most code officials don't know much about ventilation and are unlikely to understand whether a system meets code requirements.

  8. Expert Member
    ARMANDO COBO | | #8

    Mini ERV Options
    We install in all our houses Honeywell, Fantech and Panasonic ERVs, with capacities from 40-120cfm for $1000-1500. It covers pretty much all houses.
    Revised: This is an installed price.

  9. Expert Member
    ARMANDO COBO | | #9

    Response to Martin
    The prices for the ERVs I gave above are installed prices, and with metal ducts. I fact, after my post I talked to the HVAC contractor we use in all my builder's jobs, and he said that a Fantch model we've used is 150 cfm,

  10. user-5975040 | | #10

    Supplying fresh air to bedrooms
    @Martin -
    When supplying fresh air to bedrooms - have you heard of complaints on very hot or very cold days about hot/cold air blowing directly into the bedrooms?

  11. GBA Editor
    Martin Holladay | | #11

    Response to Adam W
    Q. "When supplying fresh air to bedrooms - have you heard of complaints on very hot or very cold days about hot/cold air blowing directly into the bedrooms?"

    A. Yes -- specifically, about cold air in very cold weather. The complaints apply to poorly located passive air inlets -- I'm not a fan of passive air inlets in any case -- as well as poorly located registers that deliver air from an HRV.

    Obviously, you don't want the supply air register to aim the airflow at the head of the bed. You want to locate the register somewhere far from the head of the bed. Some builders locate the fresh air register in the closet, and equip the closet with louvered doors.

  12. GBA Editor
    Martin Holladay | | #12

    Response to Armando Cobo (Comment #9)
    Congratulations -- you're getting great prices from you ventilation system contractor if you are getting your ERVs installed for $1,500. In many parts of the U.S., that price is unrealistic.

    Talk to owners of Zehnder HRVs, and you'll learn that they paid $7,000 to $10,000. (Obviously, Zehnder equipment is more expensive that the equipment you install -- but still, you're getting good pricing.)

  13. user-5975040 | | #13

    Response to Martin (comment #11)

    My scenario would be using an ERV in Northern Virginia. I'm guessing your "very cold weather" is more likely to apply to the Northeast?

  14. GBA Editor
    Martin Holladay | | #14

    Response to Adam W (Comment #13)
    I think there is less likelihood of complaints when the outdoor temperature is 20 degrees F than when the outdoor temperature is -10 degrees F. That said, think ahead about where you want your fresh air registers to be installed. Don't direct the fresh air flow at the head of your bed.

  15. mangler66 | | #15

    An other alternative for whole house and wet room venting?
    I have been looking for an HRV specifically designed to provide dedicated, on demand wet room venting that rivals a dedicated bath fan. So far I have only found one system that shows promise, because it actually has flappers that will close when a boost fan is triggered to isolate the wet room and provide maximum local flow:

    If anyone knows of competing systems with similar features, I would be very interested to hear about them.

  16. GBA Editor
    Martin Holladay | | #16

    Response to Mai Tai
    Mai Tai,
    The Aldes system you linked to is the only one with the features you're talking about, although plenty of HRVs can be controlled from a bathroom (with a "boost" switch to increase the ventilation rate when needed).

    For more on this issue, see Does a Home with an HRV Also Need Bath Fans?

  17. STEPHEN SHEEHY | | #17

    Response to Mai Tai
    We've found that the boost switch on our Zehnder hrv works fine to clear moisture from the bathroom after showers. It can be set to run for 10, 30, or 60 minutes. Usually, 10 is enough.
    If you are unconvinced, why not just install a separate bathroom fan?

  18. mangler66 | | #18

    I'm trying to avoid


    I'm trying to avoid additional penetrations in the insulated shell, so no dedicated fans are planned. The issue with most standard HRVs is that once you press the boost button, it boosts flow at every inlet in the house. Some mitigate this by having multiple inlets at the main box, with only a few connected to the boost fan (I believe Zehnder is one of those). This works, but tends to complicate installation and increase tubing/duct costs. The Aldes is the only system that I have found to combine standard ducting and prioritized flow at the boost site.

  19. STEPHEN SHEEHY | | #19

    Reply to Mai Tai
    I understand your reluctance to making another hole in the building envelope. I've never heard of the Aldes hrv, but if it has decent specs, install one. But I think you'll be fine with a typical hrv and a boost, even if the boost isn't limited to a single location. We use the boost to clean out the kitchen air if we're cooking something smelly or smoky.

  20. JohnProctor | | #20

    Actual ventilation rates from balanced and unbalanced
    Martin, you may have mentioned and I didn't notice the difference between unbalanced (exhaust only or supply only) and balanced systems. Balanced systems moving the same CFM through the fans provide approximately twice the actual ventilation as unbalanced systems of the same rated CFM.

  21. GBA Editor
    Martin Holladay | | #21

    Response to John Proctor
    I think you're referring to the Point Five Rule. Here's what I wrote about the Point Five Rule in an "Editor's Note" inserted into a 2015 blog by Reid Baldwin:

    "...The Point Five Rule was first stated in 1992 by Larry Palmiter and Tami Bond. The Point Five Rule states that the use of an exhaust fan or a supply fan that moves less than twice the natural infiltration rate will cause an increase in airflow equal to half the flow rate of the fan. This phenomenon occurs because operation of an exhaust fan raises a house's neutral pressure plane, causing some of the wall leaks that were outlets to become inlets. Similarly, operation of a supply fan lowers a house's neutral pressure plane, causing some of the wall leaks that were inlets to become outlets."

  22. barkingeater | | #22

    Has anyone used the Twinfresh ductless thru the wall unit

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