Kunsthalle Helsinki has decided to offer free entry to all exhibitions on the first Wednesday of the month 6-8pm again, starting on Feb 5th. You are welcome to write your review in the comments, if you visit it!
If you want to visit another museum in Helsinki for free, you may want to take a look this post. Please note, that I haven’t checked the times since I did the post, so you may want to recheck open hours and entrance fees on the homepage of the museum.
Free But Fun 
I’ll definitely have to check out your list before touring the museums of Helsinki – there seem to be a few free days which are always good to know about!
Most of the museums have once a month a couple of hours of free entry, which is handy on a rainy day!