Einen Nachmieter zu finden ist schwerer, als ich gedacht habe, weil unsere alte Küche so klein ist.

Nachmieter means the next tenant or replacement tenant: the person who moves into a place after the current tenant leaves. It is a very common word in housing situations in German-speaking countries.

The basic noun is der Nachmieter, so it is masculine.

Because finden takes a direct object, and direct objects are usually in the accusative case.

• nominative: ein Nachmieter
• accusative: einen Nachmieter

Since Nachmieter is masculine, the article changes from ein to einen in the accusative.

This is an infinitive construction with zu. It means to find a replacement tenant or, more naturally in English, finding a replacement tenant.

The whole phrase Einen Nachmieter zu finden acts as the subject of the sentence:

• Einen Nachmieter zu finden = finding a replacement tenant
• ist schwerer = is harder

So the structure is basically:

Finding a replacement tenant is harder ...

In German infinitive phrases, the infinitive usually comes at the end. So the object appears before it:

• einen Nachmieter zu finden

That is the normal German order. English also does something similar in phrases like to find a replacement tenant, where the verb and object stay together, but German strongly prefers the infinitive at the end of the phrase.

Yes. That would also be correct and very natural.

Compare:

• Einen Nachmieter zu finden ist schwerer ...
• Es ist schwerer, einen Nachmieter zu finden ...

The version with Es ist ... often feels a bit more conversational and easier to process. The original version, with the infinitive phrase first, is also perfectly normal, but slightly more formal or written in tone.

Because the whole infinitive phrase Einen Nachmieter zu finden is treated as one single thing, so it takes singular verb agreement.

German treats an action or activity expressed this way as a singular idea:

• Einen Nachmieter zu finden ist ...
• Deutsch zu lernen ist ...
• So spät anzukommen ist ...

So ist is correct.

Here schwerer means more difficult or harder, not heavier.

The adjective schwer can mean:

• physically heavy
• difficult / hard

In this sentence, it clearly means difficult.

Schwerer is the comparative form of schwer:

• schwer = difficult
• schwerer = more difficult / harder

After a comparative in German, you use als for than:

• schwerer als ich gedacht habe = harder than I thought

So here als means than, not when.

Both are possible.

• als ich gedacht habe
• als ich dachte

The version with gedacht habe is the present perfect, which is very common in spoken German. The version with dachte is the simple past.

In many everyday contexts, German prefers the perfect tense where English might simply use the past. So als ich gedacht habe sounds very natural.

Also, because als introduces a subordinate clause here, the finite verb goes to the end:

• als ich gedacht habe

The participle gedacht comes before the auxiliary habe.

Because weil introduces a subordinate clause, and in standard German subordinate clauses send the conjugated verb to the end.

So:

• main clause: Die Küche ist klein
• subordinate clause: weil die Küche klein ist

That is why the sentence ends with ist.

Küche is a feminine noun: die Küche.

In the clause weil unsere alte Küche so klein ist, Küche is the subject, so it is in the nominative singular.

That gives:

• unsere = our, feminine nominative singular
• alte = old, with the weak adjective ending -e
• Küche = kitchen

So unsere alte Küche means our old kitchen.

No. So klein means so small or that small, emphasizing the degree.

• so klein = so small
• zu klein = too small

That is an important difference. In this sentence, so klein says the kitchen is very small, and that helps explain why finding a replacement tenant is difficult. It does not automatically mean too small, even though English might sometimes translate it that way depending on context.

The commas are there because the sentence contains multiple clauses, including subordinate clauses.

Structure:

• Einen Nachmieter zu finden = infinitive phrase acting as subject
• ist schwerer = main clause
• als ich gedacht habe = comparison clause
• weil unsere alte Küche so klein ist = reason clause

German normally uses commas before subordinate clauses like those introduced by als and weil. So the commas here are required.