How do I get rid of the musty odor from my house when it is closed up?

I would open up the windows and use a few fans to get the air moving.

I like to diffuse lemon essential oil when my house has odors.

Frebreeze Air spray, and a fan blowing into the room from a door/window, and then another fan blowing air out of the room.... its an air current going to replace the air quickly. If its musty from high humidity, you could add a dehumidifier or some of those Damp Rid containers to get the excess moisture out. I get those Damp Rid containers at the Dollar Tree.

These ideas might help: https://m.youtube.com/watch?v=hpNVGRDVYs8

Hi Sue, hope this link help you out,

https://www.wikihow.com/Remove-Musty-Odors