Learn Hardcore German: Die Heizung funktioniert nicht, deshalb ist das Zimmer jetzt kalt. - The heating doesn’t work, therefore the room is cold now.

funktionieren means “to work” or “to function” (like a device). So Die Heizung funktioniert nicht literally means “The heating isn’t working.”

Why is nicht placed after funktioniert and not before it?

In German you normally put nicht immediately after the finite verb when you’re negating the verb itself. If you want to negate a noun, you’d use kein before that noun (e.g. keine Heizung).

Why is there a comma before deshalb, and why does ist come right after deshalb?

deshalb is a sentence adverb (Konjunktionaladverb) that links two main clauses. You separate main clauses with a comma. When an adverb like deshalb is in first position, German’s verb-second rule kicks in, so the conjugated verb (ist) must follow in second position.

Could I use weil instead of deshalb, and what would change?

Yes. But weil introduces a subordinate clause, so the verb goes to the end of that clause. You’d say:
Weil die Heizung nicht funktioniert, ist das Zimmer jetzt kalt.

What’s the difference between deshalb, darum, and deswegen?

All three mean “therefore” or “so.” They’re interchangeable here:
…, deshalb ist…
…, darum ist…
…, deswegen ist…
Each one still sits in first position and triggers verb-second word order.

Why are die Heizung and das Zimmer using different articles?

German nouns have grammatical gender. Heizung is feminine, so it takes die in nominative singular. Zimmer is neuter, so it takes das.

Why are Heizung and Zimmer capitalized?

German orthography requires that all nouns are capitalized, regardless of where they appear in a sentence.

Where does the time adverb jetzt fit into the sentence?

Adverbs of time generally come after the verb (and subject) but before manner or place. In ist das Zimmer jetzt kalt, jetzt sits between subject and predicate adjective to show when the room is cold.