I was cleaning out my furnace and noticed the label on the inside of the unit recommends a 18" x 25" filter. But the actual size I have is a 14" x 20". This seems to be a rather large difference. The furnace came with the house when I bought it 7 yrs ago. How significant of an issue is this?
The furnace is a Goodman GMPN080-4
Thanks
Mike