kama ha atui.

It is read:

かま は あつい。
Romanized: kama wa atsui.

A few notes:

• 窯 = かま
• は is the particle wa here
• 熱い = あつい

In normal Japanese writing, you would usually see it without spaces: 窯は熱い。

窯（かま） means kiln.

It is not one of the most common everyday words for beginners, so it may feel a little specialized. You might see it in contexts like:

• pottery
• ceramics
• brick-making
• traditional crafts

So the sentence is talking specifically about a kiln, not just any general heating device.

When は is used as the topic particle, it is pronounced wa, even though the character itself is normally read ha.

So in this sentence:

• written: 窯は熱い
• pronounced: かまわあつい

This is just a standard feature of modern Japanese grammar.

は marks the topic of the sentence.

So 窯は熱い literally has the structure:

• 窯は = as for the kiln
• 熱い = is hot

A very natural English translation is simply The kiln is hot, but the Japanese structure is closer to As for the kiln, it is hot.

Japanese does not need a separate word for is in this kind of sentence.

熱い is an i-adjective, and i-adjectives can act as the predicate by themselves. So:

• 窯は熱い。 = The kiln is hot.

You do not need something extra after 熱い.

This is very normal in Japanese:

• 水は冷たい。 = The water is cold.
• この部屋は暑い。 = This room is hot.

熱い（あつい） is used for something that is physically hot to the touch, or has a high temperature as an object.

That fits 窯 very well, because a kiln is a heated object.

By contrast, 暑い（あつい） is usually used for:

• weather
• air
• a room feeling hot

So:

• 窯は熱い。 = correct for a kiln
• 今日は暑い。 = Today is hot

This is an important distinction in Japanese.

Yes, you could, but the nuance changes a little.

• 窯は熱い。 = As for the kiln, it is hot.
  This sounds like you are presenting the kiln as the topic.

• 窯が熱い。 = The kiln is hot. / It is the kiln that is hot.
  This can sound more like you are identifying the kiln specifically, or emphasizing it.

For a simple beginner sentence, 窯は熱い is completely natural and easy to understand.

Yes. 熱い is an i-adjective.

Its dictionary form is already 熱い, and it can change like this:

• 熱い = hot
• 熱くない = not hot
• 熱かった = was hot
• 熱くなかった = was not hot

So you can make related sentences like:

• 窯は熱くない。 = The kiln is not hot.
• 窯は熱かった。 = The kiln was hot.

Not in normal Japanese writing.

A native-style version would be:

窯は熱い。

Spaces are sometimes added in teaching materials to help beginners see the parts more clearly:

• 窯
• は
• 熱い

So the spaced version is useful for learning, but the standard written form has no spaces.

窯は熱い。 is in the plain style.

A more polite version would be:

窯は熱いです。

Both mean the same thing, but:

• 熱い。 = plain, casual, dictionary-style
• 熱いです。 = polite

Textbooks often introduce the plain form so learners can see the basic grammar clearly.

Yes, there are two useful points:

• 窯 is a somewhat less common kanji for beginners, so many learners may know the word only after seeing furigana: 窯（かま）
• 熱い is a common adjective, and the kanji 熱 often relates to heat

So this sentence mixes:

• a more specialized noun: 窯
• a very common adjective: 熱い

That is one reason the reading かま may be the part learners are most likely to ask about.