Humidity in home is really low. 15% in basement, 25% on first floor and 28% on second floor.

New home owner, bought the home in August but didn't renovations that took some time.

Over the summer the humidity in the house was 40-55 (except basement)

The windows are not drafty(except basement windows, they need to be replaced. I have sealed up everything that I am aware of....

I have baseboard heating. What can I do to increase the humidity in my home?

It's fridgid out like 20 degrees and inside I have the heat set to 67-70.