Not to mention the Этот in front of it, which is the masculine declension for "this". It has to agree with the gender of чайник, reaffirming that it's masculine.
This fact points out a good method for determining gender: enter "this [thing]" into an online translator, and see what you get. I entered "this kettle" in Google Translate and got "этот чайник" - the masculine declension of это = этот reassured me that чайник is indeed masculine.
I usually also enter "these [things]" to see what the nominative plural is - often a great way to remind myself about the Russian spelling rules, when an ending doesn't match the declension table. I've also discovered some irregular plurals this way.
Sometimes, "this" doesn't work well, so I use possessive pronouns like "my [thing]".
I'd think the short-form adjective here would be appropriate: Этот чайник очень горя́ч
The hotness is hardly a permanent condition, for one. Examples I've seen of other short-form adjectives include adverbs like очень.
The short-form declension:
Plur горячи́ (Russian spelling rules change the usual -ы to -и after ч)