The updated ASHRAE 62.2-2013 standard, titled Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings, has met with debate about what a ventilation “minimum standard” should be and what the implications are for their practical application.
The old ASHRAE 62.2 recommended 7.5 cfm per occupant + 0.01 cfm per square foot of area (with the assumption of 0.02 per square foot natural air infiltration ventilation).
62.2-2013 essentially abandoned the bogus assumption of 0.02 per square foot natural air infiltration and shifted it to the mechanical equation, now: 7.5 cfm per occupant + 0.03 cfm per square foot of area.
This change can have a dramatic effect on flow rates and equipment sizing, energy use and comfort. A typical 1,000 sf, two bedroom home goes from 32.5 cfm to 52.5 cfm. The rub is that with such increased ventilation rates, heat losses go up, energy use goes up, and it’s not clear that the interior air is any cleaner or healthy – it may make the air quality worse, particularly with exhaust only applications and in hot-humid climates.
Martin Holladay at Green Building Advisor (see here) and Allison Bailes at Energy Vanguard (see here, here & here) have reported on the 62.2 debate. And Joe Lstiburek of the Building Science Corporation has not only rejected the 62.2-2013 recommendations (see Unintended Consequences Suck) but offered his own alternate standard, Ventilation for New Low-Rise Residential Buildings Building Science Corporation Standard 01 — 2013 (BSC-01). Joe Lstiburek is right.
All the above makes for very interesting reading. But we also offer our abbreviated summation of the situation:
- The scientific evidence of direct links between health benefits and ventilation are scant – see Ventilation Rates and Human Health on GBA.
- Regardless, it is accepted that the build-up of indoor contaminants and toxins such as radon, VOCs, soot, formaldehyde, CO2, humidity and CO etc, should be avoided and good ventilation helps do this.
- And a poorly ventilated home can be “stuffy” and uncomfortable. Balanced ventilation helps avoid this, and should.
- Exhaust only systems are typically more unreliable at meeting the above goals and are more inefficient and uncomfortable than balanced and distributed systems.
- It was generally accepted that the old 62.2 sizing worked well, particularly where the systems were balanced and distributed. Joe Lstiburek even wrote back in 2006 that even the old 62.2 standard was excessive in his opinion, and suggested that the balanced and distributed systems should typically run at 60% of the old 62.2 sizing – making the 62.2 recommendation effectively a boost mode.
- The old 62.2 standard, done with balanced and distributed high-efficiency heat recovery ventilation, roughly corresponds to the Passive House Institute’s recommendations (see here, page 6).
62.2-2013 has two related and perverse considerations: a) It gives a sizing reduction break to leaky houses, as one may still calculate with the discredited natural ventilation allowance, much like before – meaning that if you build a proper airtight house you must do the full (over)ventilation rate. b) This is because 62.2-2013 also makes no distinction between the type of ventilation system – so it’s assuming a tight house with a crappy exhaust only approach. Escher meet ventilation.
- What should the minimum recommendation be? We think it should be to build airtight homes and install a balanced and distributed low volume ventilation system, with high-efficiency heat recovery. (See GBA post on Designing a Good Ventilation System.) Exactly how low is open to debate – but certainly a magnitude lower than 62.2-2013. Make it effective, comfortable and efficient.
Or as Joe might say, “Build tight and ventilate right”.