Well, yippee, it finally got up to 35% today. It's been about 9 days since I started from 22%. I checked with the flooring distributor/ expert to get his views, and he counseled me to wait until something in the 40% range and then let it acclimate for a few days before installing. Based on the slow humidification rate I bought a big ass humidifier at Best Buy (pushes out 9 gallons a day) and it's starting to make a difference.
Really surprised how long this has taken. In prior years, when I have not forgot to turn the WHH on, we've had no problem keeping it at the right level. I wonder if there is a latent effect due to not just the air, but everything in the house such as furniture and carpets etc having been so dried out (after all, it did start at 22%...). SWMBO thinks I'm more insane than ever (obsessing about humidity and checking the readings every five minutes) but the thought of having the floors buckle in the humid summer scares the crap out of me.