What Are BTUs and How Do They Factor into Your Commercial HVAC System?
As you work with your HVAC professional to evaluate furnaces, heat pumps, and air conditioners, you’ll most likely encounter the abbreviation BTU. By understanding BTUs and what they mean to your commercial HVAC system, you’ll have a better idea of what is needed to heat and cool your facility and how your HVAC equipment does its job.
What is a BTU?
A BTU is, at its simplest, a measurement of heat energy. BTU stands for British Thermal Unit, and it represents an amount of heat that must be added to your indoor environment to produce heating or taken away to produce cooling.
One BTU is equivalent to the amount of heat it takes to increase the temperature of one pound of water by one degree Fahrenheit. Some sources define BTU as the amount of heat generated by burning one average kitchen match from end to end. Furnaces are rated by how many BTUs it takes per hour to achieve this type of heat increase.
In practical terms, one BTU is a relatively small amount of energy, and by itself, it doesn’t mean much. Heating and cooling equipment, however, is rated in thousands of BTUs. A typical furnace, for example, may be rated at 80,000 or 100,000 BTUs. At that level, BTUs become a significant indicator of HVAC system performance.
BTUs and Efficiency
The BTU rating of heating and cooling equipment indicates how much energy a furnace uses to produce heat or an air conditioner uses to remove heat. It also serves as a measure of how much of the heat produced by the equipment makes it into your home.
For example, a gas furnace rated at 100,000 BTU input will consume 100,000 BTU of energy per hour. This base level of function is then affected by the furnace’s overall efficiency, as expressed by its AFUE (annual fuel utilization efficiency) rating. A high-efficiency furnace with an AFUE of 90 will convert 90 percent of the input into usable heat, while the other 10 percent will be wasted through exhaust, ventilation, and other factors. In this example, 90,000 BTUs of energy will be turned into heat while 10,000 BTUs of energy will be lost.
When it comes to air conditioners, the BTU rating indicates how much energy is used to remove heat from the air. BTUs are an important element of cooling equipment tonnage, which is another measure of heat removal.
The use of ton to measure heat removal is thought to have originated when buildings were cooled by ice. It takes 286,000 BTUs to melt a literal ton of ice (2,000 pounds). Divided by 24 hours, that means it takes approximately 12,000 BTUs per hour to melt a ton of ice back to liquid form over the course of a full day. By these measures, a one-ton air conditioning system will be able to remove 12,000 BTUs of heat per hour. Each additional ton of capacity adds another 12,000 BTUs of heat removal — a 2-ton cooling system removes 24,000 BTUs of heat per hour, and so on.
BTUs and Equipment Sizing
When choosing heating and cooling equipment, carefully consider the equipment’s size. In this context, size does not refer to physical dimensions but to heating or cooling capacity. If you use a system with more BTUs than recommended for your facility, the equipment will work too hard, cycling on and off frequently and wearing itself out early. HVAC equipment with lower-than-recommended BTU ratings will not be able to produce the amount of heating or cooling you want, leaving your indoor spaces uncomfortable. Consult with your local trusted HVAC professional for expert recommendations.
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