Learn Swedish: Vilken golvvärme låter du installeras i badrummet? - Which underfloor heating are you having installed in the bathroom?

This is the causative passive construction. We use låta (here as låter) plus an object and a passive infinitive (which ends in -s) to mean 'having something done'. Since the heating is being installed by someone else, we need the passive s-infinitive installeras rather than the active installera.

How does the word order work in this causative construction since it is a question?

Normally, the object sits between låter and the passive infinitive. But because this is a question, the object is the question phrase itself (Vilken golvvärme) and gets pulled to the very front. The verb låter still takes the second position, followed by the subject du, and then the passive infinitive installeras.

Why is it Vilken golvvärme and not Vilket golvvärme?

The gender of a compound word is always determined by its final part. Here, the final word is värme (heating), which is an en-word (en värme). Therefore, the question word 'which' must agree and take the en-form Vilken.

Could I say 'Vilken golvvärme har du installerad' to mean the same thing?