Op het balkon drinken wij thee, maar als de kachel uitgaat, gaan we naar binnen.

Because Dutch main clauses usually follow the verb-second rule: the finite verb comes in the second position.

So:

• Wij drinken thee op het balkon. = neutral order
• Op het balkon drinken wij thee. = the location is placed first for emphasis

Once Op het balkon takes the first slot, the verb drinken must come next, and the subject wij comes after it.

This kind of inversion is very common in Dutch.

Yes, op het balkon is the normal Dutch expression.

Dutch treats a balcony as a surface or platform you are on, not something you are in. So:

• op het balkon = on the balcony
• in het balkon would sound wrong in normal Dutch

This is one of those preposition choices you mostly have to learn as a fixed phrase.

Both wij and we mean we.

The difference is mainly one of style and stress:

• we = the usual unstressed, everyday form
• wij = the fuller, more stressed form, often used for emphasis, contrast, or a slightly more formal tone

So:

• Op het balkon drinken we thee sounds very natural and conversational.
• Op het balkon drinken wij thee is also correct, but a bit more deliberate or formal.

Using wij in the first clause and we in the second is not wrong. It may just reflect a slight difference in emphasis.

Because uitgaan is a separable verb.

In a normal main clause, separable verbs split:

• De kachel gaat uit.

But in a subordinate clause, the verb moves to the end, and the parts stay together:

• als de kachel uitgaat

So the pattern is:

• main clause: gaat ... uit
• subordinate clause: uitgaat

This is a very important Dutch grammar pattern.

Here uitgaan means something like:

• to go out
• to switch off
• to stop burning

With de kachel, it means the heater or stove stops giving heat, or its flame/fire goes out.

So this is not the other meaning of uitgaan as in going out socially.

Context tells you which meaning is intended.

Because the whole clause als de kachel uitgaat comes first in that part of the sentence.

Dutch still wants the finite verb of the main clause in second position. So the structure is:

• first position: als de kachel uitgaat
• second position: gaan
• then the subject: we

That is why you get:

• maar als de kachel uitgaat, gaan we naar binnen

If you put the main clause first, you would get:

• maar we gaan naar binnen als de kachel uitgaat

Both are correct, but the emphasis is slightly different.

It can mean either, depending on context.

In Dutch, als often covers both ideas:

• if the heater goes out
• when the heater goes out

If the speaker is talking about a possible condition, English may prefer if. If the speaker means something expected or habitual, English may prefer when.

So Dutch als is often a bit broader than either single English word.

Naar shows direction: movement toward somewhere.

So:

• naar binnen gaan = to go inside
• binnen zijn = to be inside

In this sentence, the speakers are moving from the balcony to the inside, so naar binnen fits well.

Dutch also sometimes allows we gaan binnen, especially in speech, but naar binnen gaan makes the movement especially clear.

Because Dutch nouns belong to different grammatical genders/categories:

• het words
• de words

You generally have to learn the article together with the noun:

• het balkon
• de kachel

Unfortunately, there is not always a simple rule you can guess from the meaning alone. This is just something learners gradually memorize.

Kachel can refer to a heating device such as a:

• stove
• heater
• space heater

The exact English translation depends on context. In this sentence, heater is often the safest general choice, but stove may also fit in some situations.

The important part grammatically is that it is something that can uitgaan.

The commas follow normal Dutch punctuation rules.

• The comma before maar separates two main parts of the sentence.
• The comma after uitgaat marks the end of the fronted subordinate clause als de kachel uitgaat.

So the punctuation helps show the structure:

• first clause: Op het balkon drinken wij thee
• second clause begins with maar
• inside that second clause, the subordinate clause comes first: als de kachel uitgaat
• then the main clause follows: gaan we naar binnen

Yes, a Dutch speaker could say it, but a slightly more everyday version would often be:

• Op het balkon drinken we thee, maar als de kachel uitgaat, gaan we naar binnen.

Another very natural version is:

• We drinken thee op het balkon, maar als de kachel uitgaat, gaan we naar binnen.

The differences are mostly about emphasis:

• Op het balkon first = extra focus on the location
• We drinken thee op het balkon = more neutral everyday order
• wij instead of we = slightly more formal or emphatic