Без увлажнителя воздух становится слишком сухим, особенно когда включён обогреватель.

Because the preposition без (without) always takes the genitive in Russian.

• увлажнитель = a humidifier
• без увлажнителя = without a humidifier

This is a very common pattern:

• без сахара = without sugar
• без воды = without water
• без машины = without a car

So here, увлажнителя is simply the genitive singular form of увлажнитель.

After the verb становиться (to become), Russian normally uses the instrumental case for the noun or adjective describing what something becomes.

So:

• воздух становится сухим = the air becomes dry

The adjective сухой changes to the instrumental form сухим.

This is a very important pattern:

• Он стал врачом = He became a doctor
• Она стала счастливой = She became happy
• Погода становится холодной = The weather is becoming cold

If you said воздух слишком сухой, that would mean the air is too dry. But воздух становится слишком сухим means the air becomes too dry / is getting too dry.

Становится is from the verb становиться, which means to become or to get.

In this sentence:

• воздух становится слишком сухим = the air becomes too dry

The -ся ending is part of the dictionary form становиться. In some verbs, -ся has a reflexive origin, but you should learn становиться as a whole verb meaning to become.

Conjugation here:

• становлюсь = I become
• становишься = you become
• становится = it/he/she becomes

Since воздух is grammatically masculine singular, the verb is становится.

Because воздух is the subject of the sentence.

The sentence is saying that the air does something:

• воздух становится... = the air becomes...

Subjects in Russian are usually in the nominative case, just like in English.

Слишком means too in the sense of excessively.

So:

• сухой = dry
• слишком сухой / слишком сухим = too dry

It works like this in other sentences too:

• слишком холодно = too cold
• слишком дорого = too expensive
• слишком поздно = too late

Here it modifies сухим, telling us the air does not just become dry, but too dry.

There are really two things going on:

1. особенно = especially
2. когда включён обогреватель = when the heater is on

The part starting with когда is a subordinate clause, and Russian normally separates that kind of clause with a comma.

So the comma marks the added clause:

• ..., особенно когда включён обогреватель.
• ..., especially when the heater is on.

This punctuation is very natural and standard in Russian.

Включён means switched on / turned on.

It is the short form of включённый.

Russian often uses these short forms in sentences like is turned on, is ready, is open, etc.

Compare:

• включённый обогреватель = a heater that is turned on
  
  • long form, used like an attribute before a noun
• обогреватель включён = the heater is turned on
  
  • short form, used as the predicate

In your sentence, the full idea is:

• когда обогреватель включён = when the heater is turned on

Russian allows this word order too:

• когда включён обогреватель

That order is a bit more literary or descriptive, but completely normal.

Both are possible.

• когда обогреватель включён = when the heater is on
• когда включён обогреватель = when the heater is on

The second version puts a little more focus on the state turned on. Russian word order is more flexible than English word order, so the speaker can shift emphasis slightly.

For a learner, it is often easiest to understand когда обогреватель включён first, because it lines up more closely with English structure.

Not exactly.

• обогреватель usually means a heater or space heater — a device used to heat a room
• радиатор can mean radiator
• батарея in everyday Russian often means a heating radiator in a home, not only a battery

So in this sentence, обогреватель suggests an actual heating device that is switched on, often an electric heater.

Yes, but the meaning is slightly different.

• Без увлажнителя воздух слишком сухой = Without a humidifier, the air is too dry.
  
  • This describes a state.
• Без увлажнителя воздух становится слишком сухим = Without a humidifier, the air becomes too dry.
  
  • This emphasizes a change or process.

So the version with становится is better if you want to highlight that the air gets drier, especially under certain conditions.

Yes. Увлажнитель is the standard word for humidifier.

It comes from the verb увлажнять / увлажнить = to moisten / to humidify.

Related words:

• влажный = damp, moist
• сухой = dry
• увлажнение = humidification, moisturizing
• увлажнитель воздуха = air humidifier

In everyday speech, people often say simply увлажнитель if the context is clear.

It works very naturally as a general statement.

Russian often uses the present tense for things that are generally true:

• Без увлажнителя воздух становится слишком сухим...
• Without a humidifier, the air becomes too dry...

So this sounds like a general observation, especially in homes during heating season.

If you wanted to talk about one specific past situation, Russian would change the tense:

• Без увлажнителя воздух стал слишком сухим = Without a humidifier, the air became too dry

So the present tense here is best understood as a general fact or regular occurrence.