Heat up vs. Hot up

What is the difference between Heat up and Hot up?

Heat is a verb and hot is an adjective, so it seems wrong to put an adjective together with a particle:

Hot up, hotting up

I consulted several sources and found:

OED:

verb (hots, hotting, hotted)

(hot something up or hot up) British informal

make or become hot:[with object]He hotted up the flaskbecome or make more lively or exciting:[no object] :the championship contest hotted up
The Merriam-Webster:

hot up

 verb

Definition of HOT UP

intransitive verb; chiefly British

: to increase in intensity, pace, or excitement <Air raids began to hot up about the beginning of February. — George Orwell>

transitive verb

chiefly British : to make livelier, speedier, or more intense

With a silky Southern drawl, the waitress asked, "Want me to hot up that pie?"

(Well, I doubt that, because most Americans have never even heard of 'hot up'.) Here is what an American from California had to say:

"I think it's simply that "hot" is an adjective and "heat" is a verb. I've also never heard "hot up".  You can also "reheat" your food in the microwave, if you're warming up leftovers, for example."

 

and The American Heritage Dictionary:

Hot up

Chiefly British Informal. to heat; warm (usually followed by up).

I heard it today, here:

http://www.euronews.net/2011/12/01/diplomatic-row-grows-between-tehran-and-london/
So you might think that 'hot up' is just a silly journalistic attempt at originality, but you'd be wrong.
Again, according to Merriam-Webster:

First Known Use of HOT UP

1878! 

 

It turns out that this informal British usage is not even new, and it's not slang either.
At least, it's not slang to say that a situation is 'hotting up'. Apparently, it is slang to 'hot up' a person, an audience or a situation. 


Being an American English speaker, I will always prefer Heat up to Hot up, but essentially both are correct.

More on Heat:
Meaning #2 - intensity of feeling, esp. of anger or excitement : Words few men would dare use to another, even in the heat of anger. 
You can also say> In the heat of the moment, when you are describing something said or done rashly.
• 'The heat' [informal] - intensive and unwelcome pressure or criticism, esp. from the authorities : A flurry of legal proceedings turned up the heat in the dispute.
Other interesting expressions with heat:

go hot and cold - experience a sudden feeling of fear or shock

have the hots for - [informal] be sexually attracted to

hot on the heels of - following closely: The mugger ran away from the scene of the crime, with the police hot on his heels.

hot to trot - impatient to begin some activity

hot under the collar - [informal] angry, resentful or embarrassed.

in hot water - [informal] in trouble: She landed in hot water for falsifying the documents.

ESL Spanish students:
Calor - heat 
Caliente - hot
Calentar - heat/ heat up (or hot up, if you must); 
Warm up is used in certain contexts, but I won't comment on that in this post.
Califacción - heating (n.) 


So...In summer you feel the heat.
If I ask,"How are you?"
in Spanish you might say, 'Tengo mucho calor' or 'Con mucho calor'
This cannot be translated directly.
You could say:


It's very hot/it's too hot today.
or
I'm overheated.(I feel the heat too much)
eg. She felt overheated after her run in the park.