Luft-til-luft-varmepumpen varmer stuen.

Norwegian very often builds compound nouns by joining words together.

Here, luft-til-luft-varmepumpen breaks down like this:

• luft = air
• til = to
• luft = air
• varmepumpe = heat pump
• -en = the (definite singular ending)

So the core noun is varmepumpe = heat pump, and luft-til-luft- tells you what type it is: an air-to-air heat pump.

The hyphens are helpful because the first part is already a multi-word expression. Norwegian often uses hyphens in compounds like this to keep them readable.

In Norwegian, the is usually attached to the end of the noun instead of being a separate word.

So:

• varmepumpen = the heat pump
• stuen = the living room

This is very normal in Norwegian. Compare:

• en varmepumpe = a heat pump
• varmepumpen = the heat pump

and:

• en/ei stue = a living room
• stuen / stua = the living room

Because stuen is also in the definite singular form.

The base noun is stue = living room.
In this sentence, it means the living room, so it becomes stuen.

This does not happen because it is the object of the sentence; it happens because it is definite. Norwegian marks definiteness on nouns whether they are subjects or objects.

Varmer is the present tense of the verb å varme, which means to heat or to warm.

So:

• å varme = to heat / to warm
• varmer = heats / warms
• varmet = heated / warmed

One nice thing for English speakers: Norwegian verbs do not change for person.

So you get:

• jeg varmer = I heat
• du varmer = you heat
• han/hun varmer = he/she heats
• vi varmer = we heat

The verb form stays the same.

This sentence uses the basic subject–verb–object order:

• Luft-til-luft-varmepumpen = subject
• varmer = verb
• stuen = object

So it works very much like English:

• The air-to-air heat pump heats the living room.

However, Norwegian also follows the V2 rule in main clauses, which means the verb must stay in the second position. For example:

• I dag varmer luft-til-luft-varmepumpen stuen.
  = Today, the air-to-air heat pump heats the living room.

Notice that varmer still comes second.

Yes, very often.

In Bokmål, many feminine nouns can appear either with:

• common-gender style: en stue – stuen
• feminine style: ei stue – stua

So both of these can be correct:

• Luft-til-luft-varmepumpen varmer stuen.
• Luft-til-luft-varmepumpen varmer stua.

The choice depends on writing style, dialect, and personal preference.
The version with stuen may look a bit more neutral or formal to some learners, while stua is also extremely common.

The same kind of variation can happen with varmepumpe:

• en varmepumpe – varmepumpen
• ei varmepumpe – varmepumpa

Yes, you can, but the nuance is slightly different.

• varmer stuen = heats the living room
• varmer opp stuen = heats up the living room

Adding opp can make the action feel a bit more like bringing it up to a warm temperature. Without opp, the sentence is more neutral and general.

In a sentence about what a heat pump does, varmer stuen is perfectly natural.

Yes. It is a standard way to describe a type of heat pump.

For example:

• luft-til-luft-varmepumpe = air-to-air heat pump
• luft-til-vann-varmepumpe = air-to-water heat pump

So luft-til-luft is not just random wording here; it is a technical label that tells you how the system transfers heat.

Because Norwegian normally expresses definiteness by adding an ending to the noun.

English:

• the heat pump
• the living room

Norwegian:

• varmepumpen
• stuen

This is one of the biggest structural differences English speakers notice early on. Instead of putting the before the noun, Norwegian often puts the definite marker on the noun.