"especially when you consider that 5 to 7 ACH was considered acceptable a few years ago"
5 to 7 being considered acceptable is ACH50. 5ACH at 50 pascals is what my house exchanged prior to any serious air sealing which happened to be mostly loads of leakage from the garage into the house through the sill boxes.
5ACH naturally infiltrated would chill a house in the winter really quick and if you changed the air out 5 times per hour your furnace would be a huge monster and I couldn't imagine the energy bills. You'd feel the air moving constantly and the comfort would be terrible because of it.
0.35ACH of ventilation either through forced ventilation or infiltration is quite a lot of air to move. In Minnesota the ACH50 to nat factor is 17. So if I take my previous 5ACH50 and divide by 17, I get about .3ACH natural. So basically a house built to have even a little thought to the basics of air sealing will probably need forced ventilation. If I had 4 adults in this house or a smelly baby, I might agree with ASHRAE or code requirements but I don't.
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