Сегодня так жарко, что без кондиционера в комнате трудно работать.

Because жарко is not an adjective here. It is a predicative word used to describe a general state or condition, especially weather or surroundings.

• Сегодня жарко = It’s hot today
• жаркий день = a hot day

So:

• жарко describes the situation
• жаркий describes a noun

In this sentence, Russian is talking about the overall condition of the day, not describing a specific noun like day or room.

It means so ... that ...

So:

• так жарко, что ... = so hot that ...

This is a very common Russian structure for showing degree and result:

• Он так устал, что сразу уснул. = He was so tired that he fell asleep immediately.
• Было так холодно, что мы не вышли. = It was so cold that we didn’t go out.

In your sentence, the result is:

• так жарко, что ... трудно работать
  = so hot that it’s hard to work

Because что introduces a subordinate clause.

The sentence has two parts:

1. Сегодня так жарко
2. что без кондиционера в комнате трудно работать

In Russian, subordinate clauses introduced by что are separated by a comma. This is required punctuation.

Yes. Russian often leaves out the present-tense form of to be.

So Сегодня так жарко literally feels like:

• Today so hot

But in natural English, you translate it as:

• It is so hot today

This is especially common in weather and impersonal expressions:

• Холодно. = It’s cold.
• Темно. = It’s dark.
• Трудно работать. = It’s hard to work.

Russian does not need a subject like it in these sentences.

Because the preposition без always takes the genitive.

The dictionary form is:

• кондиционер

But after без, it becomes:

• без кондиционера = without an air conditioner

More examples:

• без сахара = without sugar
• без машины = without a car
• без друзей = without friends

So this is simply a case rule: без + genitive.

Because this sentence describes location, not motion.

• в комнате = in the room or inside the room
• в комнату = into the room

Here, no one is going anywhere. The sentence says it is hard to work in the room, so Russian uses:

• в + prepositional for location
  → в комнате

Compare:

• Я работаю в комнате. = I work in the room.
• Я иду в комнату. = I’m going into the room.

Because Russian often uses трудно + infinitive to mean it is difficult to do something.

So:

• трудно работать = it is hard to work

This is an impersonal construction. It does not focus on a specific subject like I work or we work. It describes the general difficulty of the action.

Other examples:

• Трудно понять. = It’s hard to understand.
• Легко забыть. = It’s easy to forget.
• Невозможно спать. = It’s impossible to sleep.

Yes, the sentence is intentionally general and impersonal.

Трудно работать means something like:

• it’s hard to work
• working is difficult

It does not specify exactly who finds it difficult. That can be left general, like in English.

If you want to add a person, Russian can do that:

• Мне трудно работать. = It’s hard for me to work.
• Нам трудно работать. = It’s hard for us to work.

In your sentence, the point is the condition itself, not the person.

Yes. Russian word order is flexible, and different orders can sound more natural depending on emphasis.

Your sentence:

• Сегодня так жарко, что без кондиционера в комнате трудно работать.

A possible alternative:

• Сегодня так жарко, что в комнате трудно работать без кондиционера.

Both are grammatical and mean basically the same thing. The difference is mostly emphasis and flow.

The original order puts без кондиционера earlier, which highlights the lack of air conditioning as an important condition.

Yes. In everyday Russian, кондиционер commonly means air conditioner.

Depending on context, it can also refer to conditioner for hair, but in this sentence the meaning is clearly air conditioner because of the heat and the room.

So here:

• без кондиционера = without air conditioning / without an air conditioner

This is a very common question.

For weather, climate, or how the air feels, Russian normally uses жарко:

• Сегодня жарко. = It’s hot today.
• В комнате жарко. = It’s hot in the room.

горячо is more often used for something physically hot, heated, or hot to the touch:

• Кофе горячий. = The coffee is hot.
• Здесь горячо! can sometimes work, but it often sounds more like intensely hot or heated, not the normal weather word.

So in this sentence, жарко is the natural choice.

Because the sentence is talking about the general activity of working, not completing a single piece of work.

• работать = to work in a general or ongoing sense

The idea is:

• it is hard to work
• not it is hard to finish one work task

Imperfective is normal after words like трудно, легко, приятно, невозможно when speaking about an activity in general.

A natural stress pattern is:

• Сего́дня так жа́рко, что без кондиционе́ра в ко́мнате тру́дно рабо́тать.

A few useful stress notes:

• сего́дня
• жа́рко
• кондиционе́ра
• ко́мнате
• тру́дно
• рабо́тать

Also, in normal speech, что is often pronounced more like што. That is standard in spoken Russian.