Tepelné ztráty bez izolace jsou velké.

Because tepelné is an adjective agreeing with ztráty.

The dictionary form is tepelný = thermal / heat-related. But in a sentence, Czech adjectives change their endings to match the noun in gender, number, and case.

Here:

• ztráty = feminine plural
• subject of the sentence = nominative
• so the adjective must also be feminine plural nominative

That gives:

• tepelný → tepelné

So tepelné ztráty = thermal losses / heat losses.

Here ztráty is nominative plural, because it is the subject of the sentence.

The basic singular form is:

• ztráta = loss

Plural:

• ztráty = losses

You can also tell from the rest of the sentence:

• jsou = are → plural verb
• velké = plural adjective

So the sentence structure is basically:

• Tepelné ztráty = subject
• jsou = verb
• velké = predicate adjective

Because the subject is plural.

The verb být = to be has these present-tense forms:

• je = is (3rd person singular)
• jsou = are (3rd person plural)

Since ztráty means losses, not loss, Czech uses the plural form:

• Tepelné ztráty jsou velké.

If the noun were singular, you would get:

• Tepelná ztráta je velká. = The heat loss is large.

Because velké is an adjective linked to ztráty, and Czech adjectives must agree with the noun they describe or refer to.

Here:

• ztráty = feminine plural nominative
• so velký changes to velké

Compare:

• velká ztráta = a large loss
• velké ztráty = large losses

Even though English often leaves adjective forms unchanged, Czech does not.

The preposition bez = without requires the genitive case.

So:

• bez
  • genitive

The noun here is:

• izolace = insulation

After bez, it must be in the genitive:

• bez izolace

A useful detail: for this noun, the nominative singular and genitive singular happen to look the same:

• nominative: izolace
• genitive: izolace

So the form does not visibly change here, even though the case does.

You know it from the preposition.

In Czech, many prepositions always require a certain case. Bez always takes the genitive, so izolace must be genitive here, even though the form looks identical to the dictionary form.

This is very common in Czech: sometimes the case is shown clearly by the ending, and sometimes you identify it mainly from the grammar around it.

So in:

• bez izolace

you should understand it as:

• without
  • genitive

Usually it means without insulation in a general sense.

Czech has no articles like a or the, so context decides whether something is definite, indefinite, or generic.

In a technical sentence like this, bez izolace normally means:

• without insulation
• if there is no insulation
• in the absence of insulation

So it sounds general, not necessarily like one specific piece of insulation.

Czech word order is fairly flexible.

The given version:

• Tepelné ztráty bez izolace jsou velké.

is a normal, neutral way to say it.

But other orders are also possible, depending on emphasis, for example:

• Bez izolace jsou tepelné ztráty velké.
• Velké jsou tepelné ztráty bez izolace. (more marked/emphatic)

English relies much more on word order for grammar. Czech relies more on endings, so word order can shift to show topic, focus, or emphasis.

Because Czech does not have articles like English a/an and the.

So a Czech sentence often leaves that distinction unstated unless context makes it clear.

That means:

• Tepelné ztráty bez izolace jsou velké.

could be understood in English as something like:

• Heat losses without insulation are large.
• The heat losses without insulation are large.
• Heat loss without insulation is high.

The exact English wording depends on context, but the Czech sentence itself does not need an article.

Yes. Tepelné ztráty is a common technical expression meaning heat losses or thermal losses.

It is used in contexts like:

• buildings
• heating systems
• insulation
• energy efficiency

So this is not just any random combination of words; it is a very natural collocation in technical Czech.

In careful pronunciation, jsou is pronounced with the j.

But in normal everyday speech, many speakers pronounce it more like sou.

So you may hear both:

• careful: jsou
• common spoken: sou

This kind of reduction is very normal in spoken Czech. As a learner, you should recognize both, but in writing you still use jsou.

They are:

• tepelný = thermal, heat-related
• ztráta = loss
• bez = without
• izolace = insulation
• být = to be
• velký = big, large, great

Seeing the dictionary forms helps explain the sentence forms:

• tepelný → tepelné
• ztráta → ztráty
• být → jsou
• velký → velké