Ég á það til að hnerra þegar kaldur vindur kemur inn um gluggann.

In this sentence, að eiga það til að + infinitive is an idiomatic expression. It means:

• to tend to ...
• to be prone to ...
• to have a habit of ...

So Ég á það til að hnerra means something like I tend to sneeze or I’m prone to sneezing.

Even though á normally comes from eiga (to own / to have), in this expression the whole phrase functions as one unit. It should usually be learned as a chunk:

• ég á það til að ...
• þú átt það til að ...
• hann/hún á það til að ...

This is much more natural in Icelandic than translating word-for-word from English.

Here, það does not refer to a specific thing. It is part of the fixed expression eiga það til að ...

So in this sentence, you should not try to translate það literally as it. It works more like a placeholder inside the idiom.

Compare:

• Ég á það til að hnerra. = I tend to sneeze.
• not literally: I have it to sneeze.

This is a very common feature in languages: some words appear because the expression requires them, not because they carry their usual concrete meaning.

Because hnerra is an infinitive here: to sneeze.

In Icelandic, after eiga það til að, you use að + infinitive:

• Ég á það til að gleyma. = I tend to forget.
• Hún á það til að hlæja. = She tends to laugh.
• Ég á það til að hnerra. = I tend to sneeze.

So að here is the infinitive marker, similar to English to.

Here þegar means when:

• þegar kaldur vindur kemur inn ... = when a cold wind comes in ...

That is a very common meaning of þegar.

However, þegar can also mean already in other contexts:

• Ég er þegar kominn. = I have already arrived.

So the meaning depends on context. In your sentence, because it introduces a time clause, it clearly means when.

Because kaldur vindur is the subject of the clause, so it is in the nominative case.

In þegar kaldur vindur kemur inn um gluggann:

• vindur = subject
• kemur = verb
• therefore vindur is nominative singular
• the adjective must agree with it: kaldur

So you get:

• kaldur vindur = a cold wind (nominative singular masculine)

If it were an object in a different sentence, the case might change. For example:

• Ég finn kaldan vind. = I feel a cold wind.

There vind is the object, so it is accusative, and the adjective changes too: kaldan.

The ending -ur shows agreement with vindur, which is:

• masculine
• singular
• nominative

In Icelandic, adjectives must agree with the noun they describe in:

• gender
• number
• case

So:

• kaldur vindur = masculine singular nominative
• kalda konan = feminine singular accusative/weak forms depending on context
• kalt barn = neuter singular nominative/accusative

In your sentence, kaldur matches vindur exactly.

Because the subject vindur is singular.

The verb koma (to come) agrees with the subject in person and number. Here the subject is kaldur vindur = a cold wind, which is third person singular, so the verb is:

• kemur = comes

Examples:

• Vindurinn kemur. = The wind comes / is coming
• Vindarnir koma. = The winds come / are coming

So kemur is used because there is one subject, not several.

Inn um gluggann means in through the window.

It has two parts:

• inn = in, inward
• um gluggann = through the window

Together they describe motion entering through an opening.

This is very natural in Icelandic for something moving from outside to inside through a window, door, etc.

Compare:

• Hann kom inn um dyrnar. = He came in through the door.
• Vindur kemur inn um gluggann. = Wind comes in through the window.

So inn gives the inward direction, and um marks the path.

Because um takes the accusative case here, so gluggi becomes gluggann in the definite accusative singular.

Forms of gluggi (window) look like this:

• nominative: gluggi = a window
• accusative: glugga
• nominative definite: glugginn = the window
• accusative definite: gluggann = the window (as object / after certain prepositions)

Since the phrase is um gluggann, the noun must be in the accusative.

That is a very common question, because um has several meanings.

Yes, um can mean:

• about: við erum að tala um bókina = we are talking about the book
• around: ganga um húsið = walk around the house

But with motion through an opening, um can also mean through:

• inn um gluggann = in through the window
• út um dyrnar = out through the door

So here um is not about. It marks the route by which something passes.

The basic structure is:

• Ég — subject
• á það til að hnerra — main predicate
• þegar kaldur vindur kemur inn um gluggann — time clause

So the sentence is built like this:

1. Ég á það til að hnerra
   = I tend to sneeze

2. þegar kaldur vindur kemur inn um gluggann
   = when a cold wind comes in through the window

This is a very normal Icelandic sentence structure: main clause first, then a subordinate clause introduced by þegar.

Yes, you could, but the meaning changes slightly.

• Ég hnerra þegar kaldur vindur kemur inn um gluggann.
  = I sneeze when a cold wind comes in through the window.

This sounds more direct and factual.

• Ég á það til að hnerra þegar kaldur vindur kemur inn um gluggann.
  = I tend to sneeze when a cold wind comes in through the window.

This version suggests a tendency or repeated pattern rather than just stating the event plainly. It is a little softer and more idiomatic in the sense of this often happens to me.

Yes, hnerra is the normal verb meaning to sneeze.

A pronunciation point learners often notice is the beginning hn-. In modern Icelandic, this is usually pronounced with an n sound, and the h is not pronounced separately the way an English speaker might expect. So learners often hear something close to nerra.

The important thing grammatically is that it is a regular infinitive here:

• að hnerra = to sneeze

And in the present tense:

• ég hnerra = I sneeze
• hann hnerrar = he sneezes

It is most naturally understood as a general situation.

Because the sentence says:

• kaldur vindur = a cold wind
• not kaldi vindurinn or vindurinn

the meaning is general: whenever cold wind comes in through the window, the speaker tends to sneeze.

So this sounds like a habit or recurring reaction, not one single event.

Yes. It is a productive and very useful pattern.

Examples:

• Ég á það til að gleyma nöfnum. = I tend to forget names.
• Hún á það til að vakna snemma. = She tends to wake up early.
• Við eigum það til að tala of hratt. = We tend to speak too fast.

So once you learn the pattern, you can use it with many infinitives to describe habits, tendencies, or things that happen repeatedly.