Τον χειμώνα το καλοριφέρ στο σαλόνι μένει ανοιχτό όλο το βράδυ.

Τον χειμώνα means in winter or during the winter.

It is in the accusative, because Greek often uses the accusative for time expressions without a preposition. This is sometimes called the temporal accusative.

So:

• ο χειμώνας = winter
• τον χειμώνα = in winter / during winter

English uses in, but Greek does not need a preposition here.

Greek very often uses the definite article in general time expressions, especially with seasons, parts of the day, and similar expressions.

So τον χειμώνα is the normal Greek way to say in winter.

This is one of those places where Greek uses the more naturally than English does.

Το καλοριφέρ means the radiator or the heater/radiator unit.

It is a neuter noun, which is why it takes το.

It is also a loanword, and in everyday Greek it usually keeps the same form rather than changing endings much. The article often tells you the gender and case:

• το καλοριφέρ = the radiator

Στο is a contraction of σε + το.

So:

• σε = in / at / to / on
• το = the
• στο = in the / at the / to the

Here it means in the:

• στο σαλόνι = in the living room

Μένω can mean several related things:

• live
• stay
• remain

In this sentence, μένει ανοιχτό means stays open/on or remains on.

So:

• Μένω στην Αθήνα = I live in Athens
• Το καλοριφέρ μένει ανοιχτό = The radiator stays on

The context tells you which meaning is intended.

Μένει ανοιχτό emphasizes that the state continues.

• είναι ανοιχτό = it is open/on
• μένει ανοιχτό = it stays open/on, it remains on

So in this sentence, μένει gives the idea that the radiator is left on for the whole night, not just that it happens to be on at one moment.

Because καλοριφέρ is neuter singular, and adjectives in Greek must agree with the noun in gender, number, and usually case.

So the forms are:

• ανοιχτός = masculine
• ανοιχτή = feminine
• ανοιχτό = neuter

Since the sentence has το καλοριφέρ, the correct form is ανοιχτό.

Yes, ανοιχτό literally means open, but Greek often uses it where English would say on, especially for things like:

• lights
• heating
• taps
• electrical devices

So in this sentence:

• το καλοριφέρ είναι ανοιχτό = the radiator is on

This is very natural Greek usage.

Όλο το βράδυ means all night or the whole night.

Breaking it down:

• όλο = whole / entire
• το βράδυ = the night / the evening-night period

Together, it means that something lasts for the entire night.

This is also a time expression in the accusative, showing duration.

Both can mean all night, but they are built from different nouns:

• το βράδυ = evening / night period
• η νύχτα = night

So:

• όλο το βράδυ = all evening/night long
• όλη τη νύχτα = all night

In many contexts they are very close in meaning. Here, όλο το βράδυ sounds completely natural.

Greek word order is more flexible than English word order.

This sentence begins with Τον χειμώνα to set the time frame first:

• Τον χειμώνα = In winter

Then it gives the subject and the rest of the information:

• το καλοριφέρ = the radiator
• στο σαλόνι = in the living room
• μένει ανοιχτό = stays on
• όλο το βράδυ = all night

So the order is natural, but some parts could be moved around for emphasis without changing the basic meaning.