daidokoro no kankisen wo tukeru to, kuuki ga yoku narimasu.

の connects two nouns. Here it means something like the kitchen’s ventilation fan or the ventilation fan in the kitchen.

So:

• 台所 = kitchen
• 換気扇 = ventilation fan / exhaust fan
• 台所の換気扇 = the kitchen ventilation fan

This is a very common noun-linking pattern in Japanese.

換気扇 usually means an exhaust fan or ventilation fan, especially the kind that removes air, smoke, steam, or smells.

In a kitchen, it often refers to the fan over the stove or cooking area.

Breakdown:

• 換気 = ventilation
• 扇 = fan

So the word literally relates to a ventilation fan.

を marks the direct object of the verb.

The verb here is つける, which in this sentence means to turn on.
So 換気扇をつける means to turn on the ventilation fan.

Even though English says turn on, Japanese uses the simple transitive verb つける with the thing being turned on marked by を.

Examples:

• 電気をつける = turn on the light
• テレビをつける = turn on the TV
• 換気扇をつける = turn on the ventilation fan

That is a very common point of confusion. つける has several meanings depending on context.

Some common meanings are:

• to attach / affix
• to put on (some things)
• to turn on (lights, TV, machines, etc.)

Here, because the object is 換気扇, the meaning is clearly to turn on.

For example:

• 電気をつける = turn on the light
• エアコンをつける = turn on the air conditioner

So this is a standard use of つける.

Here と means when or if, but with an important nuance: it often suggests a natural, automatic, or expected result.

So 換気扇をつけると、空気がよくなります means roughly:

• When you turn on the ventilation fan, the air gets better
• If you turn on the ventilation fan, the air improves

This と is often used for:

• general truths
• habitual results
• cause-and-effect situations
• automatic results

Examples:

• 春になると、暖かくなります。
  When spring comes, it gets warm.
• このボタンを押すと、ドアが開きます。
  If you press this button, the door opens.

So in your sentence, turning on the fan leads to the result that the air improves.

In Japanese, verbs before many grammar patterns appear in the plain form, even if the whole sentence is polite.

So:

• つける = plain form
• なります = polite form

This is completely normal.

Many clause-linking patterns work this way, such as:

• 〜と
• 〜から
• 〜けど
• 〜ので
• 〜たら

So the sentence is not “mixing styles incorrectly.” It is following standard Japanese grammar.

Because 空気 is the subject of the second clause, not the object.

The second part is:

• 空気がよくなります

This literally means the air becomes good/better.

With なる (to become), the thing that changes is typically marked by が.

So:

• 空気がよくなる = the air becomes better
• 部屋が静かになる = the room becomes quiet
• 天気がよくなる = the weather becomes better

If you used を, it would sound like you are directly acting on the air as an object, which is not what なる does.

Because the sentence is expressing change.

• いいです = is good
• よくなります = becomes good / gets better

The verb なる means to become, so Japanese uses it to show that a state changes.

Also, よく is the adverbial form of いい.

So:

• いい = good
• よくなる = become good / improve

This is a very common pattern:

• 大きい → 大きくなる = become bigger
• 寒い → 寒くなる = become colder
• よい / いい → よくなる = become better

So 空気がよくなります means the air improves.

Because いい is irregular.

Although the dictionary form is usually いい, its other forms often come from よい.

So:

• dictionary form: いい / よい
• adverbial form: よく
• past: よかった
• negative: よくない

That is why you get:

• 空気がよくなります not
• 空気がいいくなります

This is something learners simply need to memorize.

That is a good question, because よく can mean different things.

It can mean:

1. well / in a good way
2. often

In this sentence, よく means better / well, because it is part of よくなる.

So:

• 空気がよくなります = the air gets better

It does not mean:

• the air often becomes...

Context makes that clear.

Compare:

• 彼はよく来ます。 = He comes often.
• 気分がよくなりました。 = I felt better.

Same word form, different meaning depending on usage.

Yes, it is understandable and fairly natural. It means the air becomes better or improves.

Depending on context, native speakers might also say things like:

• 空気がきれいになります。 = The air becomes clean.
• 空気がよくなります。 = The air gets better.
• 換気がよくなります。 = Ventilation improves.

So your sentence is fine, though in some situations a speaker might choose a slightly different expression depending on whether they want to emphasize:

• the quality of the air
• the cleanliness of the air
• the quality of ventilation

Yes. Both can refer to a kitchen.

• 台所 = kitchen, a native Japanese word
• キッチン = kitchen, a loanword from English

In many everyday situations, キッチン sounds modern and common, especially in housing or interior contexts. 台所 can sound a bit more traditional or practical.

So both of these are possible:

• 台所の換気扇
• キッチンの換気扇

The nuance changes slightly, but the meaning is basically the same.

No, standard Japanese normally does not use spaces between words.

The sentence would usually be written as:

台所の換気扇をつけると、空気がよくなります。

Spaces are often added in learning materials to help beginners see word boundaries more clearly. That is helpful for study, but it is not normal everyday writing.

So the spaced version is a teaching aid, not standard orthography.