Wir passen die Heizkurve an.

Because anpassen is a separable verb.

In a normal main clause, separable verbs split into:

• the conjugated verb part in the usual verb position
• the prefix at the end of the clause

So:

• infinitive: anpassen
• main clause: Wir passen die Heizkurve an.

This is very common in German:

• Ich rufe dich an. = I call you
• Wir stellen die Heizung ein. = We set the heating

It is part of anpassen, not the standalone verb passen.

Here:

• base verb: anpassen
• subject: wir
• present-tense form: passen
• separated prefix: an

So Wir passen ... an means we adjust ...

That is different from the independent verb passen, which often means things like:

• to fit
• to suit
• to be suitable

For example:

• Das Hemd passt. = The shirt fits.
• Das passt gut. = That suits well / That works well.

So in your sentence, you should understand the whole verb as anpassen.

Because wir takes the same present-tense ending as sie/Sie for most verbs.

For anpassen, the present tense is:

• ich passe an
• du passt an
• er/sie/es passt an
• wir passen an
• ihr passt an
• sie/Sie passen an

So Wir passen die Heizkurve an is simply the 1st person plural present tense: we adjust the heating curve.

Because Heizkurve is a feminine noun: die Heizkurve.

Also, it is the direct object of the verb, so it is in the accusative case. For feminine nouns, the accusative article is still die, so you see:

• nominative: die Heizkurve
• accusative: die Heizkurve

That means the form does not change here, even though the case changes.

It is the thing being adjusted.

A useful question is: What are we adjusting? Answer: die Heizkurve

That makes it the direct object, which in German usually takes the accusative case.

So:

• Wir = subject, the people doing the action
• passen ... an = verb, the action
• die Heizkurve = direct object, the thing affected by the action

It is a compound noun, which is extremely common in German.

It is made up of:

• Heiz- from heizen / Heizung relating to heating
• Kurve = curve

So Heizkurve is literally something like heating curve.

Important grammar point: in German compound nouns, the last part determines the gender.
Since Kurve is feminine (die Kurve), the whole word is also feminine:

• die Heizkurve

Because all German nouns are capitalized.

So in this sentence:

• Wir is capitalized because it starts the sentence
• Heizkurve is capitalized because it is a noun

This is a standard rule in German spelling.

In a German main clause, the conjugated verb usually comes in the second position.

In your sentence:

• Wir = position 1
• passen = position 2
• die Heizkurve = later in the clause
• an = separated prefix at the end

So even though the full verb is anpassen, the conjugated part passen still follows the normal verb-second rule.

Yes. In a subordinate clause, a separable verb usually becomes unsplit and goes to the end.

Main clause:

• Wir passen die Heizkurve an.

Subordinate clause:

• ..., weil wir die Heizkurve anpassen.
  = ..., because we adjust the heating curve.

So:

• main clause: passen ... an
• subordinate clause: anpassen

That difference is very important in German.

In a yes/no question, the conjugated verb comes first:

• Passen wir die Heizkurve an?

The separable prefix an still stays at the end.

So the pattern is:

• statement: Wir passen die Heizkurve an.
• question: Passen wir die Heizkurve an?

With separable verbs in the perfect tense, German uses:

• haben or sein as the auxiliary
• the past participle, which usually includes the prefix

For anpassen, the past participle is angepasst.

So:

• Wir haben die Heizkurve angepasst.
  = We adjusted / have adjusted the heating curve.

Notice that in the past participle, the verb is no longer split:

• infinitive: anpassen
• perfect participle: angepasst

Yes. Anpassen often means:

• to adjust
• to adapt
• to modify so it fits conditions

So it is a very natural verb for technical settings, controls, and parameters.

You can use it with many objects:

• Wir passen die Temperatur an. = We adjust the temperature.
• Ich passe die Einstellungen an. = I adjust the settings.
• Sie passen den Plan an. = They adapt the plan.

So the sentence is a good example of how German often uses anpassen for practical or technical adjustments.