1 The freezer time shown is for best quality only â foods kept constantly frozen at 0Â° F will keep safe indefinitely.  How long does baked ham last at room temperature? Bacteria grow rapidly at temperatures between 40 Â°F and 140 Â°F; baked ham should be discarded if left for more than 2 hours at room temperature.
Using this to calculate theoretical water-chilling capacity: 1 ton of refrigeration (12,000 BTUs per hour) will chill. 12,000 lbs. water/fish 1Â°F in 1 hour. Theoretically, then, a sample application to chill seawater and fish: 40 tons refrigeration (480,000 BTUs per hour) will chill. 120,000 lbs. water/fish 20Â°F in 5 hours.
Scientifically, one Btu is the amount of energy required to change the temperature of 1 pound of water by 1 degree Fahrenheit. In terms of air-conditioner capacity, the rule of thumb is that it takes around 25 Btu to cool 1 square foot of room floor area. 12,000 Btu unit could cool a room 25 feet long by 20 feet wide that has 500 square feet of floor area. Manufacturers give their own ratings as to how much room area they believe their units can cool.