Όταν κάνει καύσωνα, προτιμώ να μένω σπίτι με τον ανεμιστήρα ανοιχτό.

Όταν means when. It introduces a time clause:

• Όταν κάνει καύσωνα = when there is a heatwave / when it’s extremely hot

In Greek, this kind of clause often uses the present tense for something habitual or generally true, just like English can say When it’s hot, I prefer...

Literally, κάνει καύσωνα is something like it makes heatwave, but that is not how it is understood. It is a fixed Greek expression meaning:

• there is a heatwave
• it’s scorching hot

Greek often uses κάνει in weather expressions:

• κάνει ζέστη = it’s hot
• κάνει κρύο = it’s cold
• κάνει καλό καιρό = the weather is nice

So κάνει καύσωνα is a natural idiomatic way to talk about extreme heat.

Yes, όταν έχει καύσωνα is understandable and natural too. It means when there is a heatwave.

The difference is mostly one of style and idiomatic preference:

• κάνει καύσωνα sounds very common and weather-like
• έχει καύσωνα also works, with more of a there is sense

Both are used, but κάνει καύσωνα is especially typical in everyday Greek.

After προτιμώ (I prefer), Greek normally uses να before the following verb:

• προτιμώ να μένω = I prefer to stay
• προτιμώ να διαβάζω = I prefer to read

So να is required here. English uses to; Greek usually uses να + verb.

This is about aspect, which is very important in Greek.

• να μένω = imperfective aspect, focusing on the action as ongoing, repeated, or general
• να μείνω = perfective aspect, focusing more on a single, complete event

In this sentence, the speaker means a general preference in hot weather:

• I prefer staying home
• not I prefer to stay home one specific time

So να μένω is the natural choice.

Compare:

• Προτιμώ να μένω σπίτι όταν κάνει καύσωνα. = I prefer staying home when it’s extremely hot.
• Προτιμώ να μείνω σπίτι σήμερα. = I’d prefer to stay home today.

Both can exist, but they do not feel exactly the same.

• μένω σπίτι = I stay home / I stay at home
• μένω στο σπίτι = I stay in the house / at the house

In everyday Greek, σπίτι without the article is very common in the sense of home as a general place, just like English often says stay home rather than stay at the home.

So here:

• να μένω σπίτι = to stay home

is the most natural phrasing.

Here με means with:

• με τον ανεμιστήρα ανοιχτό = with the fan on

It describes the situation in which the speaker stays home. So the idea is:

• I prefer to stay home, with the fan on.

This is a very common Greek pattern:

• με την πόρτα κλειστή = with the door closed
• με τα φώτα αναμμένα = with the lights on
• με το παράθυρο ανοιχτό = with the window open

Because ανεμιστήρας is a masculine noun, and after με here it appears in the accusative singular:

• nominative: ο ανεμιστήρας
• accusative: τον ανεμιστήρα

So:

• με τον ανεμιστήρα = with the fan

This is a normal article + noun pattern in Greek.

Because ανοιχτό must agree with τον ανεμιστήρα in gender, number, and case.

The noun is:

• ανεμιστήρα = masculine, singular, accusative

The adjective ανοιχτός changes form:

• nominative masculine: ανοιχτός
• accusative masculine: ανοιχτό

So:

• τον ανεμιστήρα ανοιχτό = the fan on/open

This is why ανοιχτό is correct here.

Yes, ανοιχτός / ανοιχτή / ανοιχτό literally means open, but in Greek it is also often used where English says on, especially for appliances or things functioning.

So:

• ο ανεμιστήρας είναι ανοιχτός = the fan is on
• η τηλεόραση είναι ανοιχτή = the TV is on

Greek can use open in situations where English uses on.

The comma separates the introductory time clause from the main clause:

• Όταν κάνει καύσωνα, = when there is a heatwave,
• προτιμώ να μένω σπίτι... = I prefer to stay home...

This is similar to English punctuation in sentences like:

• When it’s hot, I prefer to stay home.

Yes. Greek word order is fairly flexible. This sentence could also be rearranged, for example:

• Προτιμώ να μένω σπίτι με τον ανεμιστήρα ανοιχτό όταν κάνει καύσωνα.

This still makes sense, but the original version is very natural because it sets the condition first:

• When there’s a heatwave, ...

So the original word order feels smooth and typical.

Yes, καύσωνας is a noun meaning heatwave.

Its forms are:

• nominative: ο καύσωνας
• accusative: τον καύσωνα

In the expression κάνει καύσωνα, the noun appears in the accusative, because that is how this idiomatic construction works.

So even though English says there is a heatwave, Greek uses the expression κάνει καύσωνα.

A very natural English rendering would be:

• When it’s scorching hot, I prefer to stay home with the fan on.

Other natural translations include:

• When there’s a heatwave, I prefer staying home with the fan on.
• When it’s extremely hot, I prefer to stay home with the fan running.

This helps show that Greek and English do not always match word-for-word, even when the meaning is straightforward.