A fűtésszezon hosszú.

In Hungarian, the verb to be is usually left out in the present tense, third person when it links a subject and an adjective or noun.

So:

• A fűtésszezon hosszú. = The heating season is long.

But in other persons, Hungarian does use the verb:

• Én magas vagyok. = I am tall.
• Te magas vagy. = You are tall.

So the missing is is completely normal here.

Hungarian has two forms of the:

• a
• az

Which one you use depends on the sound that follows:

• a before a consonant
• az before a vowel

Since fűtésszezon begins with f, which is a consonant, you say:

• a fűtésszezon

If the next word began with a vowel, you would use az instead.

It is a compound noun:

• fűtés = heating
• szezon = season

So:

• fűtésszezon = heating season

This kind of compounding is very common in Hungarian. English often uses separate words where Hungarian may prefer one compound word.

Because the first part ends in s and the second part, szezon, begins with sz.

So when combined:

• fűtés + szezon → fűtésszezon

In writing, both parts stay visible, and the consonants come together naturally. You do not simplify it to one s in spelling.

This is normal in Hungarian compounds.

A rough guide:

• fűtésszezon ≈ fyoo-tays-seh-zon
• hosszú ≈ hos-soo

A few important sound points:

• ű is a long front rounded vowel. English does not really have it, but it is somewhat like saying ee with rounded lips.
• é is like a long ay sound.
• sz is pronounced like English s.
• Hungarian s by itself is pronounced like English sh.
• So in hosszú, the sz is an s sound, not z.
• The ú is long, so hold it a bit longer.

Stress in Hungarian normally falls on the first syllable:

• FŰtésszezon
• HOSZszú

No. In Hungarian, adjectives do not agree with nouns in gender, and Hungarian has no grammatical gender at all.

In this sentence, hosszú is a predicate adjective:

• A fűtésszezon hosszú. = The heating season is long.

Predicate adjectives normally stay in their basic form.

Also, unlike in some other languages, Hungarian adjectives do not change just because the noun is masculine/feminine/neuter, because those categories do not exist in Hungarian grammar.

Yes. Hungarian word order is quite flexible, and changing it often changes the focus or emphasis.

These are both possible:

• A fűtésszezon hosszú.
  Neutral: The heating season is long.

• Hosszú a fűtésszezon.
  More emphasis on long: The heating season is long / It’s the heating season that is long.

So the original sentence is a neutral, straightforward version.

Yes, but that creates a different structure.

• A fűtésszezon hosszú.
  = The heating season is long.
  Here, hosszú is part of the predicate.

• A hosszú fűtésszezon...
  = The long heating season...
  Here, hosszú directly describes the noun inside a noun phrase.

So hosszú after the noun means is long, while hosszú before the noun means long as an attributive adjective.

Both main words are in the nominative (basic dictionary form):

• fűtésszezon = subject
• hosszú = predicate adjective in its basic form

There are no visible case endings here because the sentence is just a simple subject + adjective statement.

Yes, you can also say:

• A fűtési szezon hosszú.

This also means The heating season is long.

The difference is mainly structural:

• fűtésszezon = a compound noun
• fűtési szezon = a noun phrase with an adjectival form

Learners may hear both. In many contexts, fűtési szezon may sound a bit more common or transparent, but fűtésszezon is also understandable and correct.

In normal Hungarian, you usually need the article here:

• A fűtésszezon hosszú.

Without the article:

• Fűtésszezon hosszú

this sounds unnatural as a standard sentence.

Hungarian often uses the definite article with singular nouns when talking about a specific thing or a recognized category in a general statement. So the version with a is the natural one.