"It's very hot in this room". Why "it" is used in this text?

It's = it is It is very hot in this room. "It" and "it's" is used whenever describing something that doesn't have a gender like an event or the status of something. *it* was a tragic day. *It's* windy outside.

You can’t start a sentence without a subject. Yes there are exceptions but this rule is so universal that it’s almost insane. In this context you start with a subject “it” to refer to the topic of conversation which comes later. As a general rule you can say something general like “It’s hot”and then add clarifying information like “in this room” afterwards and most of the time it’s understandable the one exception is long sentences that can lose the meaning of the original phrase.

I could be wrong, but, due to the lack of conjugation, English often requires an explicit subject of a sentence.  Here,  "it" refers to the ambient conditions, essentially "the room".

It is the place. It is the subject of the sentence. Starting a sentence with “very hot” doesn’t make sense. Very hot! On its own would be fine as an exclamation, but it would have to be a response.

"it is" is used when you want to describe the environment using adjectives, "there is" is used when you want to describe the environment using nouns. Eg: It is hot. (hot is an adjective) There is a person. (person is a noun) hope this helps!

It is a pronoun, it can be a neutral pronoun, a dummy pronoun. Your main language is probably one of those that don't need a pronoun to talk about certain things like the weather and stuff. But English always needs a pronoun, when that isn't a specific pronoun like I, he, she, then it's it. In this example, it is there only to support the verb to be, because you can't simply say "is". I'll use Portuguese, which is my main language: Está bastante quente neste quarto. In Portuguese, we have something called hidden pronouns and something called undefined pronouns. In cases like this, we'll never use a pronoun, because our grammar and structure don't demand us to, but they kind of exist through the rules I mentioned, but you can't do that in English, so whenever you want to start sentences and there's no specific person or object, noun, you're probably going to end up with "it". As I also mentioned, it is used for verbs of nature such as to rain, to snow: you can't say "snows today", it's gotta be "it snows today", that "it" doesn't mean anything, it's just there to complement the verb. I also so someone commented that you use "it is" for adjective and "there is" for nouns. But that's not 100% true. There is is a verb form all by itself, it comes from the expression there to be which is used to talk about things that exist and their amount. But you can say: it's a person which simply means you're referring to something that is a person. Also there to be is conjugated according to the amount as I mentioned, so you'll say: there is a person here and there are two people here. But if you're asked for example something like this: oh, hey, man, what's that over there? Your answer will be: it's people. It's some people... It's a river. It's 5 birds.

"It" is being used as a [dummy pronoun](https://www.thefreedictionary.com/Dummy-Pronouns.htm).

In English sentences need a subject to be complete. “It” is often used for weather, time and general conditions. In English we are allowed to use “it” as a sort of placeholder (dummy) pronoun for things like time weather and general conditions. “It is 3:00”. What is 3:00? I suppose the moment we are experiencing is 3:00, but who wants to say all that? “It is hot in this room” what is hot in this room? “A condition of this room is hot in this room”. That’s just silly so we use “it”. Bottom line, English allows it so we do it.

Thank you all, guys!

"It" = "The temperature" = subject of the sentence

It's is "it is". "It", is in place of something along the lines of "the temperature". So "the temperature is very hot in this room", although this doesn't completely work as it would be "the temperature is very HIGH in this room" or "this room has a very high temperature". I haven't given a perfect explanation, but "it's" is used in place of an object. "The coffee cup is hot" to "it's hot".

It is the state of the room, you are using it in place of "The state of this room is very hot" instead, we shorten because the subject is implied. -"It's very hot in this room."

In that sentence, "it" doesn't refer to anything specific. It's used as a "dummy subject" or "empty subject." We use "it" like this when we talk about the weather, temperature, time, or distance. There's no real thing that "it" is pointing to. It's just a grammatical way to start the sentence when we want to describe the condition of something, in this case, the temperature in the room. So, "it" here is just a placeholder subject needed to make the sentence grammatically correct in English when talking about the weather feeling hot.

What is hot? The room is hot? Not really. The air is hot, the environment is hot. The general surroundings are hot. But it's easier to just say "it".

It’s = it is, in this case.

"It" means the environment or situation. "It is raining" means that rain is happening in the current situation

What is your first language? It might be interesting to compare how you would say this in that language. We also use it for weather: It's raining. That is also common in romance languages. I don't know how it works in other germanic languages.

It's just referring to an understood/assumed noun. "It's hot in this room." What is hot? The temperature. "It's nine o'clock." What is nine o'clock? The time. "It's humid today." What is humid? The weather. Same as if someone asked, "What color is your car?" You *could* answer."My car is blue," but the subject is already known from context, so you can instead just reply with, "it's blue."

It's worth mentioning that 'it' as a dummy pronoun can be the **subject** or **object** of the clause. Examples of a dummy 'it' as a subject: >*It's sunny today.* >*It's a shame that you have to leave.* >*It's hard to hear you clearly.* >*It seems weird that she's not here.* Examples of a dummy 'it' as an object: >*I hate it when he's right.* >*I tried to catch the bus but I didn't make it.* >*Fuck it.* It's also possible to use those verbs above with 'it' where it's *not* a dummy pronoun too.

"It" is a substitute for "The temperature".

It's a contraction of it is

The "impersonal" subject it is something English borrowed from French. I assume your native language is not from the Latin family? How would you translate LITERALLY your way of saying CASUALLY that it is hot in this room?

It means the "state of the area".  Like you'd say "it's late". Or "it's smelly".

"It" is the temperature. You can find this construction in weather phrases, eg. "It's raining". Because it's obvious what you're talking about, the pronoun does not need to have a clear antecedent.

Because you are talking about the room. And "it" is used to refer to something which is not a person, like objects and things.