Hot days = loss of appetite?

At night I might think so, but not two days running and not avoiding food in the early morning. 
 
In total honesty, I've made that mistake before -- hating to run to the vet "for nothing" or blaming "the heat" on things (and I'm in Florida -- at 11:30 it was already 90F in the *shade*).  But honestly, more often than not it's a mistake to think that way.
 
ANY time the dog goes off food for more than a meal or two, I take it seriously.  When you go to the vet take a fecal and urine sample if at all possible. 
 
If hot days are only beginining you shouldn't see heat problems unless the dog has been super over-active.  If the dog is drinking a lot (which you kind of implied) that's all the more reason to have a vet have a look -- and the fecal and urine samples are important.  Fecal because it could be parasites, urine because it could be kidney.  Put both on ice and get them there as soon as possible.

I would check just to make sure that everything is ok. I'm getting temps in the 90's and humidity is so high, I'm stuck to the computer chair. I feed Sara at night when it is this hot, but she doesn't refuse to eat. Have him checked just to be sure.

I allow one day off feed but that's it.  One more, or off feed and some other symptom like not drinking or lethargy or funny color, and I'm on the phone to the vet.  Blood tests aren't that expensive and can help spot a serious problem early - or put fears to rest.