If you were asking about the temperature of something wouldn't you ask "Ist es dir warm?"? I guess what I'm really asking is whether this sentence is ambiguous in the same way "Sie ist heiss" is.
Also, the pronunciation sounds a bit weird to me. Shouldn't it be the single syllable vahrm ?
Edit: I checked with the audio and IPA on Wiktionary.com and it should. I guess Duo sort of sounds like the Austrian woman but it sounds strange to me. Maybe not bad enough to complain about but here we are.
"this" is a demonstrative pronoun -- it "points" to something, generally something new that you are introducing to the conversation by pointing to it.
"it" is a personal pronoun that refers back to something that had already been mentioned earlier in the conversation.
eksunhirro as a first language English speaker, I cant describe why sometimes one term is used but other times it is the other.. or sometimes it is either of these can be used.
"Is it warm?" is something one may ask say if the other person has checked the weather reports and you want to know generally what the weather or if someone was bringing a plate of food to another and wanted to check if something had been heated so asks "Is it warm?."
Both "is it warm?" and "is this warm? would be equally commonly used in the example where someone is handing you a plate of food in which you didnt know if it had been heated but wanted to know.
BUT in the other example above re weather you would not use "is that warm?" it would be "Is it warm?" being asked (the example of where both are inside and one has checked the weather and the other is wanting to know generally say if about to get dressed to go outside one may ask "Is it warm?" refering to weather outside.
So anyway, sometimes these terms are used interchangably but other times they are not. I dont know thou how to describe the difference so just have given you these examples.
I'll give another example. Someone has just gave the weather in Fahrenheit instead of the celsius a person is used to the weather being reported in.. in this case the person may not having a clue on the meaning of the reading could ask "Is that warm?".
Just because a word is listed as a definition doesn't mean that it's interchangeable. For example, groß can mean either "big" or "tall" depending on context, but it doesn't always mean one or the other (although it's "big" most of the time). It's the same with es: it can mean a bunch of things because of how English and German match up, but most of the time, it will be "it".