Usage of rental and rent

It is a rental car.
It is for rent.
They are not interchangeable. Rent in the sense of for rent is a noun. Rental is an adjective.

Thank you so much, but there must be cases where they are interchangeable, right?

ex) The quarterly rent / rental will be $20,000.

Or do you have any good examples?

Thank you.

I would say no. In the sentence you mentioned, the quarterly rent would be the correct option. In this case, again, rent is a noun, which you are explaining to be worth $20,000. If you said the quarterly rental will be... you are implying a noun anyway, but not stating it. The rental car, the rental house, etc. You can know this because in the sentence above, rental

Elanguest In the sentence you mentioned, the quarterly rent would be the correct option

I agree.

Elanguest If you said the quarterly rental will be... you are implying a noun anyway, but not stating it. The rental car, the rental house, etc.

The sentence would not be very natural if we added 'house', in my opinion. We'd need

What I meant was that rental in that context functions as a noun because it is a shortened form of an unstated phrase, for example rental car, as in "it's a rental." I agree with you that the sentence doesn't sound natural, which is why I gave the quarterly rent will be $20,000 as the preferred option.