I'm sure I'm about to lose it and yell at my dad for bringing in more furniture
Why do you think this is worth yelling over?
I'm just annoyed that there is more furniture in the house.
If you think this behavior is problematic, you probably should speak to him about it.  Hoarding is a mental illness and needs to be treated.  Just be respectful though, instead of yelling!
I'm not sure about that. I just hate all this furniture.
Well he's wrong to keep getting furniture if the house is too crowded, but yelling at him is disrespectful and won't solve anything. If you want him to see your point you can't make him feel attacked. He probably doesn't even know you have a problem with his furniture collection.