The Great Ventilation Debate, Live at the ACI Conference
Joseph Lstiburek and five members of the ASHRAE 62.2 committee discussed mechanical ventilation in Detroit last week
Last week at the Affordable Comfort Conference (also known as ACI), I co-moderated a panel called The Great Ventilation Standard Debate.1 Duncan Prahl of Ibacos proposed the session and rounded up a collection of some of best building science folks in North America to be on the panel. And if you’ve been paying attention to this blog, you know who one of them was.
The photo above (taken by Nate Adams) shows the cast of experts on the panel. From left to right, they are Joseph Lstiburek, PhD, PE, Iain Walker, PhD, Paul Francisco, Michael Lubliner, Rick Karg, and Don Stevens. All but Lstiburek are on the ASHRAE 62.2A standard for residential mechanical ventilation systems established by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. Among other requirements, the standard requires a home to have a mechanical ventilation system capable of ventilating at a rate of 1 cfm for every 100 square feet of occupiable space plus 7.5 cfm per occupant. committee. In addition, there were 3 or 4 other members of the 62.2 committee in the audience.
And speaking of the audience, we had a great crowd. I haven't heard an official number, but it was probably 150 to 200. The photo below (taken by Bethany Profaizer) gives you a view from the back.
A brief history of the debate
I’ve written about the issue of mechanical ventilation and the ongoing debate several times over the past year and a half. Here’s the short version, with links to the articles I’ve written.
First, everyone agrees that airtight houses need mechanical ventilation. (Also not up for debate is that homes need to be airtight. A house does NOT need to breathe.) Since we agree that ventilation is necessary in airtight homes, we need some guidance on how to do that. “Build tight; ventilate right” is a great mantra, but that second part needs to be fleshed out.
That’s where ASHRAE comes in. They’ve got a ventilation standard for homes, and it’s gone through several updates since the 1989 version. Since 2003, it’s been called ASHRAE 62.2: Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings. The standard covers a lot of ground, but at the heart of it is a method for determining the amount of ventilation air a home needs. And that’s where the debate begins.
Joseph Lstiburek, PhD, PE, has argued loudly against the way that rate is determined. His biggest complaints about 62.2 are that:
So Joe introduced his own standard last year - BSC-01. (It's really more of a set of guidelines than a standard, though, because it hasn't gone through a consensus process like 62.2 has.) BSC-01 is for new homes only and allows systems that are balanced, that distribute the air throughout the house, and that mix the air to run at lower rates.
The opening punches
We opened the panel discussion by asking each of the six panelists to introduce themselves and make an opening statement. The five 62.2 members were diplomatic in their words. Lstiburek opened by saying that 62.2 isn't based on science, costs people money they don't need to spend, and makes homes too dry in cold climates and too humid in humid climates. Further, he said, it's worthless because no one is adopting it.
The discussion was civil throughout, although there were some pointed disagreements. Francisco talked about the justification for the rates and opened his comments by saying, "ASHRAE 62.2 is wrong 99% of the time for most homes." He said the purpose of the standard is to recommend ventilation strategies that can do the most good for the most homes.
Francisco (or was it Walker?) referred to a study from Scandinavia that would justify even higher rates than we're using now. Lstiburek jumped in at that point and said that study was wrong and the real takeaway from it wasn't that we need higher rates but that we need to fix moisture problems before they become indoor air quality problems.
Rick Karg asked Lstiburek a few questions at one point in the discussion, one of which was, If you're criticizing 62.2 rates for not being supported by the science, what science supports the rates you recommend? It was an excellent question, and Lstiburek didn't have a good answer for it. (How I think he should have responded is that since there's no health science to support either 62.2 or BSC-01 rates, we should do what causes the fewest problems.)
A serious problem with exhaust-only ventilation
The debate didn't focus as much on the problems with exhaust-only ventilation as I thought it would, but Lstiburek did make a compelling point on that issue. In multifamily buildings, using bath fans and the kitchen range hood to satisfy 62.2 is nearly impossible to do effectively. "If the building is compartmentalized," Lstiburek said, "good luck with makeup air. What are you going to do? Leave a window out?"
Hope for the future of 62.2
Francisco had the best line of the day. We asked the panelists all to make a closing statement and tell us where they see things going. When it was his turn, Francisco began, "I don’t know where we’re going, but I do know how we got in this handbasket."
The debate at ACI was lively and interesting yet friendly. Lstiburek was laughing with Walker over private comments at one point, and the group found some things to agree about. The biggest point of agreement was that kitchen exhaust is really important, and we need range hoods with good capture efficiency, not just high ventilation rates. Francisco, the chair of the 62.2 committee, even called for a vote to document that agreement.
Toward the end of the discussion, Lstiburek made an announcement. "I'd like to get back on the committee, if you'll have me," he said. "I may have to beg and grovel, but I'd like to be a member again."
It was a great discussion at the ACI conference by some of the most expert minds on the topic of ventilation. Both sides made good points. Both sides made bad points. We also had some great comments and questions from the audience, including one from a gentleman who works in weatherization of existing homes. When he has to add a ventilation system, he said, that means less money to improve the insulation, air-sealing, and HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. system.
As he wrapped up the discussion, Duncan Prahl reminded everyone that the ASHRAE 62.2 committee members are all volunteers and that anyone can contribute to the evolution of the standard. It's easy to criticize something you don't like. It's harder to get involved and make it better. My sense after this discussion is that the 62.2 standard is about to take the next steps forward and address some of the issues that led Lstiburek to go rogue last year.
- Nate Adams
- Bethany Profaizer
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