The capacity of everything from refrigerators to air conditioners is rated in BTU’s or Tons. So what is a BTU, and how do they relate to Tons of Air Conditioning?
You’ll find a Video of this article if you prefer to watch, just scroll to the bottom.
Definition of a BTU
First of all what does a BTU stand for, “British Thermal Unit”
The definition of a BTU is “ The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit”. It doesn’t matter whether you are adding heat or taking away heat from water, it’s the same definition and calculation.
One Ton of Refrigeration or Air Conditioning
So, how did they come up with the term Tons. This comes from the fact that a TON (2,000 Lbs.) of ICE will absorb 288,000 Btu’s in 24 hours. And, since everything is rated by the hour, we divide by 24 hours to get the equivalent of 12,000 Btu/Hr.
288,000 Btu’s / 24 Hours = 12,000 Btu’s/Hr.
It’s still hard to wrap your head around just how much a BTU is in relationship to everyday common items around you. So. Here are some interesting facts about various outputs of BTU’s.
Heat (BTU’s) Generated by People
One of the factors contributing to the heat gain of a space is people. Depending on what people are doing they generate various amounts of Btu’s. The more active, the more heat (Btu’s) added to the space. (See diagram below)
Heat (BTU’s) Generated by Lights
With the transition away from Incandescent lights there is a corresponding savings in the heat output. A 100 watt Incandescent lightbulb puts out about 341 Btu/hr, while an equivalent lumens LED of 15 Watts produces 51 BTU/Hr.
Of course when doing a Heating and Cooling load there are more factors involved, but this gives you an idea of how various activities and items generate heat (Btu’s).
Refrigerators, Air Conditioners and Gas Stoves
When looking at Refrigerators, Air Conditioners or Gas Stoves, and you see the Total BTU’s, but realize that this is the amount of heat that can be absorbed or produced within an hour. It’s BTUH (BTU’s per Hour).
How Air Conditioners are Advertised
You can see that Air Conditioners are advertised using three different indications of its size.
#1. The first one there shows that it produces 24,000 Btu’s, which is a 2-Ton unit as we learned earlier. Take the 24,000 Btu’s/(12,000 Btu’s/Ton) = 2-Tons
#2. The second example shows that it’s a 3-ton unit, so we know that this produces 36,000 Btu’s/Hr. Take the 3-Tons x 12,000 Btu’s/Ton = 36,000 Btu’s
#3. The third example indicates that it produces 24k BTU, which in this case “k” stands for thousands, so this is a 24,000 BTU/Hr. air conditioner, or a 2-Ton unit. (24,000 / 12,000 = 2)
Refrigerators
With refrigerators there is almost no mention of capacity in terms of BTU’s or Tons. Instead it’s all about the width, or cubic volume of the interior space. How much food can you get in the refrigerator. You don’t worry about the BTU’s as its assumed that whatever size refrigerator you buy will be able to handle the heat from whatever you decide to put in it.
Gas Appliances
With gas stove tops or other gas appliances it’s important to check out the BTU rating of the total unit, and for each of the individual burners. As can be seen in the sales image below, the advertised information is related to the appliances size. Of course the size is important when selecting a stove top or gas appliance, but so is its BTU capacity. The larger the BTU burner capacity, the faster your food will cook.
Check the specifications of the appliance to see what each burner is rated for, could be anywhere from 500 to 18,000 Btu’s per burner, a big difference. You can see in the image above that the burners vary in their diameter, which is indicative of their Btu capacity.
BTU Calculation Example
For example, if you had a Gas Stove and one of its burners was rated for 5,000 BTU’s, you could calculate how long it might take to heat your water, realizing and ignoring that there are losses to the surrounding space. Not all heat gets absorbed, but just for simplicity this is how the calculation would work.
Starting with 2 Lbs. of water at 65F, and wanting to raise it to 210F, just before the boiling point of 212F.
BTU’s = Weight of Water (Lbs.) x Temperature Difference
BTU’s = 2 Lbs. x (210F – 65F)
BTU’s = 2 x 145
BTU’s = 290
290 BTU’s / (5,000 BTU/Hr.) = 0.058 Hrs. or 3.48 Minutes
So, what is a BTU or Ton of Air Conditioning? We now know that a Ton of Refrigeration or Air Conditioning is equivalent to 12,000 Btu per hour.
