I was at a training seminar for the new title 24 2013 measures. The subject of ventilation came up and how it was required. The new code roll out requires that cfm is tested. I was a bit disappointed when I heard a comment that was then agreed with by the presenter. Simply over specify the fan during design and avoid problems later.
With the recent change in standards for 62.2 v 2013 has brought prescriptive ventilation standards up quite a bit. In fact they are about 13 percent more than the 1989 standards which were thought too high by many. Take the 2010 standard and add a whopping 62 percent. I realize that the "infiltration credit" will bring the numbers down but who will honestly know that number during the concept phase. So how will a builder or custom contractor comply? Over sizing the fan will be a good strategy for compliance.
I took the percentage numbers from my home and in 1989 I was required 76 cfm, in 2010 53 cfm, in 2013, 86 cfm. So the best strategy will be a fan between 100-120 on paper for compliance
As we tighten our home and increase the ventilation are we doing the right thing? I think the 62.2 committee misses this one. They are encouraging high ventilation rates and not prescribing how we ventilate. Certainly a balanced system approach is best practice but more expensive. The most cost effective and straight forward solution will be a exhaust only fan oversized.
Will the homeowner accept this as a IAQ solution or will they simply turn the fan off because of noise or perceived energy waste? In my opinion as we move forward only balanced recovery systems make sense. It is difficult to convey that leaving a bathroom or laundry room fan on 24/7 will increase ones health. I think it will be seen more as an annoyance and will simply be turned off. Furthermore I believe a separate system which is designed for IAQ will be perceived as such and will be more likely to be left on.
If our goal is truly indoor are quality a oversized bath fan does not seem like a solution.