Both sentences are grammatically correct. However, they are used in different ways: He takes a vacation at his grandmother's house. You can use this sentence if you are referring to a single vacation, or if you are referring to a habitual action that is defined within the sentence, like the following example: He takes a vacation at his grandmother's house during the summer/every couple of months. He takes vacations at his grandmother's house You can use this sentence if the person is taking vacations in a habitual manner without defining the time frame in the sentence. This is different from the above sentence because in order to use that syntax, you have to define a time frame.

He takes a vacation at his grandmother's house This is correct - vacation is a noun He takes vacations at his grandmother's house This would be "He vacations at his grandmother's house" - here, vacation is used as a verb

Hey Victor, how are you? Firstly, you should know that "take a vacation" means "to go somewhere for a vacation; to stop work to have a vacation." I must say that I agree with Chris upon the difference in the usage of the word ''vacation'''. So, your first sentence, which is "He takes a vacation at his grandmother's house" sounds correct to me. As for your second one, it does not sound correct as "take vacations" is not considered to be a standard idiom in English (that is why I disagree with Nick upon his second statement). However, you might use the word "vacation" as a verb and say "He vacations at his grandmother's house" or ''During his vacations, he stays (or ''would stay'', if you were to express a repeated or habitual action in the past) at his grandmother's house.'' Below you shall find a set of useful examples: E.g.: "Sara took a vacation at the Grand Canyon last year." E.g.: "I need to take a vacation and relax." E.g.: ''I have heard he is planning to take a vacation by the end of this month.'' E.g.: ''Where do you usually take a vacation (at)?'' *NOTICE: The form ''have a vacation'' is also permissible in English. You could say, for example ''I had a one-week vacation at my uncle's farm'' or ''I plan to have a vacation next month''. Hope that helps! Should you have any further questions/doubts regarding English grammar, do not hesitate to contact me. I shall be pleased to help.