here is some more testing
today it was cold and breezy at my house.

32 ounces of water
9:40am......64.5 degree water out of tap........27 degrees outside temperature 6 mph wind
10:10........140.1 degrees..............................32 degrees outside temperature 8 mph wind
10:30.........174.2............................... ...........34 degrees outside temperature 11 mph wind

I didnt get the temperature to rise after the last entry. you could still cook meat at that temperature. its not hot enough to boil 32 ounces of water right now. But, it should be plenty warm to cook most foods.

Keep in mind I am also still using the dull HVAC tape. If you were to get something more reflective, I am sure your temperatures would rise.