Ef húsvörðurinn kæmi fyrr á morgnana yrði anddyrið hlýrra og hreinna.

Because this sentence is expressing a hypothetical situation, not a simple fact.

• kæmi is the past subjunctive of koma (to come)
• yrði is the past subjunctive of verða (to become / be)

In Icelandic, unreal or less-real present/future conditions often use the past subjunctive, especially after ef (if). So this sentence is like English:

• If the caretaker came earlier in the mornings, the lobby would be warmer and cleaner.

If the speaker meant a more real or open condition, Icelandic would usually use the indicative instead:

• Ef húsvörðurinn kemur fyrr á morgnana verður anddyrið hlýrra og hreinna.

No. They are past-looking forms, but here they do not mainly indicate past time.

In this kind of sentence, the past subjunctive shows hypothesis, distance from reality, or non-factual meaning. So the sentence is about a possible present or future situation, not about something that actually happened in the past.

This is similar to English using past forms in sentences like:

• If he came earlier...
• ...it would be warmer.

That does not necessarily mean past time in English either.

Because Icelandic main clauses normally follow a verb-second pattern.

Here, the whole ef-clause comes first:

• Ef húsvörðurinn kæmi fyrr á morgnana

That first clause takes up the first position in the sentence. So in the main clause, the finite verb comes next:

• yrði anddyrið hlýrra og hreinna

That is why yrði comes before anddyrið.

If you put the main clause first, the order would be more straightforward:

• Anddyrið yrði hlýrra og hreinna ef húsvörðurinn kæmi fyrr á morgnana.

á morgnana means in the mornings or every morning.

The word morgnana is a plural form, because Icelandic often uses the plural when talking about repeated times or habitual actions. So the idea is not one specific morning, but mornings in general.

This kind of time expression is very common in Icelandic.

fyrr means earlier or sooner.

In this sentence it modifies kæmi, so it tells you when the caretaker would come:

• kæmi fyrr = came earlier

It is an irregular comparative adverb. In many contexts, it corresponds to the comparative idea of snemma (early), even though the form is not what an English speaker might expect.

They are comparative forms:

• hlýr = warm

• hlýrra = warmer

• hreinn = clean
• hreinna = cleaner

They appear in the form hlýrra and hreinna because they agree with anddyrið, which is:

• neuter
• singular
• the subject of the clause

After a verb like yrði (would become / would be), Icelandic predicate adjectives agree with the subject. Since anddyrið is neuter singular, the comparative adjectives are neuter singular too.

Those endings are the definite article, which Icelandic usually adds to the end of the noun.

So:

• húsvörður = caretaker / janitor
• húsvörðurinn = the caretaker / the janitor

and

• anddyri = entrance hall / lobby
• anddyrið = the entrance hall / the lobby

This is one of the big differences from English: Icelandic often puts the onto the noun itself instead of writing it as a separate word.

The main noun forms are:

• húsvörðurinn — nominative singular
  It is the subject of kæmi.

• anddyrið — nominative singular
  It is the subject of yrði.

• morgnana — accusative plural
  It appears in the time expression á morgnana.

So even though English speakers may focus first on word order, Icelandic is also showing grammatical roles through case and endings.