I remember this musty smell from when we lived in an apartment, years ago. Now I'm smelling it for the first time in 5 years.
Its the same musty smell, I believe coming from the air ducts. We have a single story house with a crawl space. The air handler and propane furnace is under the house, in the crawlspace. This unit is 5 years old. The compressor unit sits outside the house on one side. The return takes a 24 x 12 x 1" filter and I change it about every 2 - 3 months. Again, We have lived here for 5 years and this is the first time we have smelled this.
What should I check first?