Household item, popular, used around 40% of rooms (4)
I believe the answer is:
iron
'40% of rooms' is the definition.
I can't judge whether this definition defines the answer.
'household item popular used around' is the wordplay.
'household item' becomes 'ro' (I can't explain this - if you can you should give a lot more credence to this answer).
'popular' becomes 'in' ('in' can mean trendy).
'used around' means one lot of letters goes inside another.
'ro' going within 'in' is 'IRON'.
Can you help me to learn more?
(Other definitions for iron that I've seen before include "Smooth - press - club" , "Smoother - metal" , "The one who was 'not for turning'" , "uncompromising" , "sort of club" .)