Ugh. I feel I just can't seem to win with this hardwood. So as per previous thread, we noticed a bit of gapping and I was becoming concerned the humidity levels might be too low. Had hardwood flooring guy in, he said the ideal target for the product I have is 40% RH.

So, I got a central humidifier installed, and over last two or three days have inched up from about 30% to about 36% (based not only on the dial, but on a humidistat we have upstairs, so I trust the reading).

Then we get a bit of a cold snap overnight (-18c, 0f) and I notice heavy condensation on the windows this morning. To the point it's even dripping down to the sill...

So I do a bit of research and note that the standard humidifier recommendation for temp -18c/0f outside is no more than 25% RH inside! It's not even a window quality issue, as I read countless tales of window experts who say even triple pane high quality windows will steam up at 35% RH if outside is -18c/0f... AND if it gets colder -28c/-30f -- which it absolutely does where I live -- they say it should not be more than 15% humidity!

So I feel like I just flushed a few hundred bucks down the drain getting a humidifier installed, to try to move humidity up a few % to a zone that I can't because my windows will sweat too much. I've basically turned the humidifer off already, and now can't imagine when we'll even use it since we never dropped below 30% RH in the first place.

Am I missing something?

That is a real cold snap! One of the incidental things about humidification is that you will notice the comfort of being in the house. Very dry air is not comfortable to breath all the time. You may be able to use a clock to set the humidifier to run just part of the time. Even with thermo-pane windows with storms you will get some condensation with normal humidity when it is very cold outside.
Sorry you have the problem.

This is the winter battle for most canadians with real wood floors - In many cases its about striking a balance between an acceptable level of gapping and the condensation on the windows. One might affect you more than the other; excessive dryness is bad for your health so I'd be willing to look past the wet windows a few days of the year in favor of an overall better living environment.

I've had success with these tricky balances by using a smaller portable unit in the main areas with hardwood only, instead of bringing the whole house up, we just add moisture to the worst rooms, the house remains dry heated, but the cool moisture sinks to the ground and into the floor.

Also had some luck with pans of water left to evaporate in the worst rooms. Your mileage may vary.