A gázszámla alacsony, hacsak nem nagy az energiafogyasztás.

Hacsak nem is a fixed expression meaning unless.

So:

• hacsak nem nagy az energiafogyasztás = unless energy consumption is high

A native English speaker may want to translate it word by word, but that is misleading here. The nem is part of the set phrase hacsak nem; you should learn it as one unit.

A similar example:

• Elmegyek, hacsak nem esik. = I’ll go, unless it rains.

So even though nem normally means not, in this structure you usually should not treat it as a separate English not.

Hungarian often leaves out van (is) in the present tense, third person when the predicate is a noun or adjective.

So:

• A gázszámla alacsony. = The gas bill is low.
• Nagy az energiafogyasztás. = Energy consumption is high.

There is an understood is, but Hungarian does not say it here.

This omission does not happen in every situation. For example:

• Past tense: A gázszámla alacsony volt. = The gas bill was low.
• Future: A gázszámla alacsony lesz. = The gas bill will be low.

So in this sentence, the missing is is completely normal Hungarian grammar.

They are the same definite article, just in two forms:

• a before a consonant sound
• az before a vowel sound

So:

• a gázszámla because gázszámla starts with a consonant
• az energiafogyasztás because energiafogyasztás starts with a vowel

They both mean the.

Compare:

• a ház = the house
• az autó = the car

Yes. Hungarian very often forms compound nouns as one word.

Here:

• gázszámla = gáz
  • számla = gas bill
• energiafogyasztás = energia
  • fogyasztás = energy consumption

This is extremely common in Hungarian. English often writes similar ideas as two words, but Hungarian prefers compounds much more often.

So a learner should get used to seeing long nouns built from smaller parts.

Both are possible, but they are not used in exactly the same way.

• Nagy az energiafogyasztás puts the emphasis on nagy (high).
• Az energiafogyasztás nagy sounds more like As for energy consumption, it is high.

In this sentence, nagy az energiafogyasztás is very natural because the important new information is that the consumption is high.

Hungarian word order is flexible, and it often reflects focus or information structure, not just basic grammar.

English and Hungarian do not use articles in exactly the same way.

In this sentence, az energiafogyasztás refers to the relevant energy consumption in the situation being discussed, so the definite article sounds natural.

Hungarian often uses the definite article where English might use no article at all.

So:

• az energiafogyasztás here does not sound overly specific or strange in Hungarian
• it is just the normal way to talk about the energy consumption in context

A few important ones here are:

• sz = English s in see
• cs = English ch in church
• gy = a soft sound, roughly like dy in during for English speakers
• ny = like ny in canyon
• á = a long vowel, roughly like a in father

So in this sentence:

• gázszámla has sz
• alacsony has cs and ny
• energiafogyasztás has gy and sz

Also, Hungarian stress is normally on the first syllable of the word.

No. Hungarian has no grammatical gender like masculine, feminine, and neuter.

So adjectives do not change because of gender.

That means:

• alacsony can describe something masculine, feminine, or neuter in English translation
• nagy works the same way

This is one reason Hungarian can feel simpler than many Indo-European languages in this area.

The adjectives here are also singular because the nouns are singular. If the subject were plural, Hungarian could show that:

• A számlák alacsonyak. = The bills are low.

So number can matter, but gender does not.

Yes. A close alternative would be:

• A gázszámla alacsony, kivéve, ha nagy az energiafogyasztás.

This also means something like:

• The gas bill is low, except if energy consumption is high.

But hacsak nem is a very natural and compact way to say unless, so the original sentence is perfectly good Hungarian.

So as a learner, the main thing to remember is:

• hacsak nem = unless
• present-tense is is omitted here
• word order can shift to highlight what is important