gongyong gongganeun maeil hwangihaeyo.

은 is the topic marker. It marks 공용 공간 as the thing the sentence is talking about.

So 공용 공간은 매일 환기해요 is roughly:

• As for the common/shared space, [we] ventilate it every day.

In natural English, we usually would not say as for, but that is the basic grammar idea.

Why not 공용 공간을?
Because this sentence is presenting 공용 공간 as the topic, not just as a plain object. Korean often does this when talking about general rules, routines, or instructions.

Korean often uses a singular noun in a generic sense, where English might prefer a plural.

So 공용 공간은 can still mean:

• the common/shared space
• common areas
• shared spaces

It depends on context. Korean does not always match English singular/plural patterns directly.

공용 공간 means a shared space or common area.

Breakdown:

• 공용 = for public/shared/common use
• 공간 = space

So together, it refers to places used by multiple people, such as:

• a shared kitchen
• hallway
• lounge
• office common area

It sounds practical and fairly standard, especially in building rules, office notices, or housing guidelines.

환기해요 comes from the verb 환기하다, which means to ventilate / to air out.

This is a 하다 verb:

• 환기 = ventilation
• 하다 = to do

So:

• 환기하다 = to ventilate
• 환기해요 = ventilate / airs out / do ventilation (polite present style)

This pattern is very common in Korean:

• 청소하다 = to clean
• 공부하다 = to study
• 운동하다 = to exercise

Both are possible, but 환기해요 is the more natural, standard fused form.

Compare:

• 환기해요 = normal and common
• 환기를 해요 = also grammatical, but often sounds a bit more separated or emphasized

In everyday Korean, noun + 하다 verbs are very often conjugated as one unit:

• 공부해요
• 청소해요
• 환기해요

So 환기해요 is what learners should expect to hear most often.

The subject is omitted, which is extremely common in Korean.

Depending on context, this could mean:

• we ventilate the shared space every day
• people ventilate it every day
• you should ventilate it every day
• it is aired out every day

Korean often leaves out the subject when it is obvious from context or not important.

In signs, rules, manuals, or workplace instructions, this kind of sentence often feels like a general statement or routine practice rather than a fully specified we sentence.

매일 means every day, and it functions as a time adverb.

In Korean, time expressions commonly come before the verb:

• 공용 공간은 매일 환기해요.
• topic + time + verb

This is very natural Korean word order.

You could also move things around a little in Korean, but this version is simple and standard.

In Korean, the present form often covers both:

• a present action
• a habitual action
• a general rule

So 환기해요 here is most naturally understood as a habitual/general statement:

• ventilate every day
• is aired out every day
• we air it out every day

Because 매일 is included, the sentence clearly describes a repeated action, not just something happening right now.

Grammatically, it is a statement. But depending on context, it can feel close to an instruction or rule.

For example:

• In conversation: We ventilate the common area every day.
• In a notice or policy: The common area should be ventilated every day or Please ventilate the common area daily might be the intended sense.

Korean often uses plain statements in places where English might use commands, passive forms, or official wording.

Yes, you could.

The difference is mainly in focus:

• 공용 공간은 매일 환기해요
  = As for the common area, we ventilate it every day.
  This sounds topical and general.

• 공용 공간을 매일 환기해요
  = We ventilate the common area every day.
  This treats it more directly as the object of the verb.

In many real situations, both are acceptable. The 은 version is especially common when stating routines, rules, or general practices.

Yes. 환기하다 is broader than just running a machine.

It can mean:

• opening windows to let fresh air in
• airing out a room
• ventilating a space in general

So in everyday use, it often refers to the practical idea of letting the air circulate, not necessarily a specific method.

Yes. A more formal style could be:

• 공용 공간은 매일 환기합니다.

This uses 합니다 style instead of 해요 style.

Compare:

• 환기해요 = polite, everyday speech
• 환기합니다 = more formal, official, written, or business-like

So if this were on a notice, building policy, or workplace guideline, 환기합니다 might be more likely.