Residential Ventilation: Why I like BSC-01 better than ASHRAE 62.2 2013

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Last week at the Westford Symposium on Building Science (aka “Summer Camp”), Joe Lstiburek formally announced the release of BSC-01, Ventilation for New Low-Rise Residential Buildings, an alternative standard to ASHRAE 62.2 2013.

The disagreement between Lstiburek and the ASHRAE 62.2 Committee’s latest revision has been well reported by Martin Holladay and Allison Bailes in particular. A lot of the hallway talk, though, is about the horserace and controversy and tactics, and few people are saying publicly what the better approach is. That is a mistake. Two competing standards does create confusion as Paul Francisco suggests. That’s unfortunate. It would indeed be better to have one. Perhaps not what Francisco means, though, unless 62.2 2013 gets fixed, that standard should be BSC-01.

Read the standards. Hear the arguments. Having done that, I can only conclude that BSC-01 is the better standard, so much so that ASHRAE 62.2 2013 shouldn’t be used by those who build or fix homes or adopted by code jurisdictions or other standards by reference. With the current science—what we know and what we don’t know—it is a much more sensible solution for providing ventilation in homes.  Here’s why.

Size Matters

Okay, what I really mean is flow rate matters. And based on what we know about both the health effects of ventilation and the costs of over-ventilation, 62.2 2013 goes too far.  Using the discussion example Lstiburek gave in Westford, in a 2000 square foot, three-bedroom house, with 8 foot ceilings, the standard calls for 90 cfm. Too much. It’s too much in Duluth in January and too much in Atlanta in July.

First the health effects. We just don’t know. Back when I was with EPA’s indoor air program, we trotted out the Yaglou research and others’—and the changing standards over time.  (For some of the history see “The History of Ventilation and Temperature Control”, pdf ) We couldn’t say much about the health effects then, and we can’t say much now. The research just isn’t there. We can talk about comfort, odors, “stuffiness”. And we can be prudent knowing that in many cases the levels of some contaminants can be much higher indoors than outdoors. Based on what we do know, some ventilation is good.

At the same time, too much ventilation creates real problems. In hot humid climates, sucking in a lot of moisture from the outside has the potential not just to create comfort problems, but also to create conditions ripe for mold growth and dust mites with their own health consequences. And we can help rot down buildings. In cold climates, overventilating can lead to overdrying of both furnishing and nasal cavities. Now, one could theoretically add dehumidification in those hot humid climates or humidification in cold climates. But that comes at a real cost, both first cost and operating cost. Pulling in moisture in South Carolina is a bad idea. And residential humidifiers, as suggested as a solution to the overventilation of 62.2 2013, scare me more than low ventilation. I’ve seen some natsy humidifiers that weren’t maintained, and adding a humidifier to correct a dryness problem introduced by providing too much ventilation is madness without a very compelling justification. This is a big deal. See the preceding paragraph—we don’t have that justification.

Energy use matters, too. And higher ventilation rates use more energy. We shouldn’t do that without a compelling reason. See above.

I like the BSC-01 standard better. It calls for a reasonable flow rates based on what we know now, 50 cfm in that same example house. I also like engineering in additional capacity as suggested by the folks at Building Science should the occupant decide to boost rates, but more on that in a moment.

Configuration Matters

When does 90 cfm not equal 90 cfm not equal 90 cfm? (Or better, when does 50 cfm not equal 50 cfm not equal 50 cfm?) When we’re talking about how ventilation is delivered and distributed in a house. I’ll accept exhaust only ventilation. I’ve used it in my own homes (I live in Vermont, a strong heating climate). It kinda works. However the distribution is not great. Using a bath fan, the bedrooms don’t get as much outdoor air. This works ok if a furnace fan kicks on and mixes the air, but not as well without the mixing. And with exhaust-only, I can’t be sure of where the make-up air is coming from, or even whether it’s better than the air I’m exhausting. More generally, without a balanced system, I’m more concerned about the quality of the air, and this means I want to compensate by adding more ventilation (even saying that seems nutty!) Similarly, if I can’t distribute the air well, I would again provide more ventilation to compensate.  I would—I have.

This is reasonable, and desirable. BSC-01 addresses this by assuming a penalty for systems that are unbalanced, lack distribution, or both (or look at it as a bonus for systems that are balanced and distributed, if you prefer). 62.2 2013 does not. It assumes all configurations are equal—and they clearly are not. Research supports differing effectiveness for different systems. There is no research suggesting all configurations are equal.

Control Matters

This issue isn’t spelled out very clearly in the standards without parsing standard-speak, but proponents of the two standards are generally taking opposing position.

Regardless of interpretations of standards, occupants should have control of the ventilation systems. They should be able to turn them up (especially if designed with extra capacity, an approach I’m fond of) or down. Not recognizing comfort needs or outdoor air considerations is arrogant and wrong. In some areas at some times, ozone levels can be higher outdoors than in. Some places spraying with pesticides is done to control for mosquitos and it’s recommended or desired turn off ventilation systems during these times. There are things like wildfires which increase fine particulate counts. The standards do not consider every potential scenario, and as such occupants need to be able to easily adjust if needed.

Existing Homes Cop-out

Now, BSC-01 is intended for new construction. At the release announcement in Westford, Joe indicated that they are NOT planning on version of BSC-01 for existing homes, saying it should be up to judgment of the expert visiting the building. Why can’t one argue the exact same thing for new construction? What’s good for the goose is good for the gander. Yeah, things get messy fast with existing homes, but we need a standard applied to existing homes, too.


In his interview with Allison Bailes, Paul Francisco indicates “I don’t think it’s going to help the market. There are a fair number of items in the BSC standard that really do have merit, and it certainly speaks to people who don’t want to have to do as much ventilation as 62.2 specifies. In general, I think it’s just going to increase confusion and frustration further.”

And I think the confusion is probable. In that light, one could argue about the appropriateness of Joe’s approach in moving forward with an alternative standard. However, BSC-01 corrects some bad problems with 62.2 2013, problems that make 62.2 2013 unsuitable for use in its current form. Sometimes you can win the fight inside. Sometimes you have to take it outside. Paul and others on the 62.2 Committee have indicated they think Joe’s arguments have merit and that they could support the recommendations. They ought to revisit this quickly.

In the meantime, I believe BSC-01 is the more appropriate standard for providing ventilation in homes. What do you think?

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About the Author:

Mike Rogers is the President of OmStout Consulting. A nationally recognized expert in residential energy-efficiency, he works with contractors and programs to scale sustainable market approaches to improving homes. More on Google+


  1. Javier P.  December 1, 2013

    62.2 does require that the occupant be provided with a control allowing him/her to turn the system on/off, and that the control be readily accessible. Your piece implied that a control is not required.

    • Mike Rogers  December 1, 2013

      Hi Javier, I don’t think I implied that.

      What I said “This issue isn’t spelled out very clearly in the standards without parsing standard-speak, but proponents of the two standards are generally taking opposing position.”

      What I mean: I don’t think the control issue is well defined in 62.2 “without parsing standard-speak”. I’ll stand with that for now, at a very minimum as a matter of degree. This is particularly relevant since can argue control is more than on/off. I’ll continue to argue that occupant’s ability to alter ventilation rates below the standard rates is desirable.

      The second part of my statement about control is not about the standard, per se. With my “proponents of the two standards are generally taking opposing position,” I take the discussion outside of the standard itself and get to the intent of those developing and promoting the standard. If you read the referenced discussions and interviews, you’ll find statements by proponents of 62.2 arguing against occupant control. Read Max’s comments referenced in the articles by Allison Bailes and Martin Holladay. For starters, you might read Allison’s interview with Paul Francisco, who happens to be the Chair of the 62.2 committee. In it you’ll find statements from Mr. Francisco such as:

      “What we would like to do is develop some kind of control we can include this in the standard that says, if you have this type of control then it reduces the ventilation when conditions are more extreme, it increases the ventilation when conditions are more mild. It has benefit on the energy side since you would have less ventilation when it costs the most to heat or cool, more when it doesn’t cost very much.”

      This implies that the control issue isn’t yet fully baked into the standard, no? But even more telling:

      “Yeah, I do think it should be difficult to turn it off completely, especially when you get to tighter houses. I’m not going to say that we should have ventilation police going around and making sure that people have it at the full rate as specified by 62.2. People are in charge of their homes. We should not be taking that away but I also don’t think we should be making it easy for people who live in really tight homes to fully shut down their ventilation system.”

      “If they’re really intent on it, they can always go and snip wires to fully disable it but I don’t think we should be, especially in tight houses, just be providing a switch that says, turn me off if you don’t want me right now.”

      This certainly implies that there should be practical limits on the degree of control given to occupants. Most people would not consider the need to “snip wires” a reasonable control strategy, even an on/off strategy. Now, these statements are not part of 62.2, but it’s hard to disagree that proponents of 62.2 argue against occupant control with this type of statement.


  2. Ted Kidd  August 17, 2013

    “Two competing standards does create confusion as Paul Francisco suggests. That’s unfortunate. It would indeed be better to have one. Perhaps not what Francisco means, though, unless 62.2 2013 gets fixed, that standard should be BSC-01.”

    Hey Mike, tell us how you REALLY feel. (seems to get thrown my way a lot, so happy I can use that on someone else).

    Excellent writing, again. I think and hope your summary is helpful for those who want to understand thevissue without taking a deep dive into the details.

    And kudos for taking a strong position even though it could make some powerful folks unhappy with you.

  3. Green Curmudgeon  August 14, 2013

    Good points, Mike. I lean towards the BSC standard, first because it addresses climate issues, second because it addresses distribution, and third, because it is much easier to read and understand than 62.2. It will be interesting to see how this all fleshes out over time. What I think is important is to develop a system for builders and designers to use to determine the best way to ventilate a house. Standards are useful for determining the technical details, but getting the work designed and installed properly in the field is much more complicated -we need to provide a decision matrix so people can decide the best system to use, how to size it, and good diagrams and instructions on how to install them so they actually work, as well as detailed instructions on how to commission them so we know they work well. Maybe we’ll see this someday soon.


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