How to Tell What Size HVAC Unit I Have
Everyone has a HVAC unit in their residence, but not all know what size it is. It is important to know what size HVAC unit you have if you need your HVAC unit replaced. You can ensure the HVAC contractor is replacing the unit with one of the same size. Sometimes HVAC contractors try to sell a model that is a few sizes bigger than the one you have. This benefits them because they make more money, but it costs you more money, with an increase in energy costs. With a few tools and a little time, it is easy to tell what size HVAC unit you have. Does this Spark an idea?
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Instructions
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1
Turn off power to the HVAC unit. This is located on the side of the unit and is usually a regular switch. Switch it to the "off" position.
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2
Open the door of the HVAC unit. Sometimes they lift off; other times you'll need to take a screwdriver, loosen up a few screws, and then pull the door off.
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Take your flashlight and look at the unit tag. This is usually a sticker and can be found either on the inside of the unit or on the back of the door you took off. It will contain all the data about the HVAC unit. See reference 1 for a picture of a sample HVAC unit tag.
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Locate where the tag states "BTU input." This is how many BTUs the unit uses and is how HVAC units are sized. However, the BTU input is not the same as the BTU output. BTU output is equally important because it's how many BTUs go into heating the residence. The difference between BTU input and BTU output is determined from the efficiency of your HVAC unit.
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Calculate the BTU output. To do this, determine the efficiency of your HVAC unit. This should also be stated somewhere on the tag or elsewhere on the unit. If it isn't, rough estimating is easy. If your unit vents to the chimney with a metal pipe, it's approximately 80 percent efficient. If it utilizes one or two PVC pipes and vents to the exterior of your house, it's approximately 90 percent efficient. Multiply the BTU input by the efficiency of your unit to get your BTU output. (e.g. Your BTU input is labeled as 75,000 BTU. Your HVAC unit is 80 percent efficient. 75,000 times 0.80 equals 60,000 BTU. This would be your BTU output.)
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Replace your HVAC unit's cover and turn the power to the unit back on.
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Tips & Warnings
Some units may have the BTU output listed on the equipment tag. This is not common but will save you a bit of math if it is listed.
You need to figure out the BTU output because when a BTU requirement is figured out for a building, the BTU output is the final number that is determined. Then, depending on the unit's efficiency that you are purchasing, you need to convert to BTU input to purchase the unit. (e.g. Your building needs 85,000 BTU to heat it. You want a 90 percent efficient unit. You take 85,000 and divide it by 90 percent. You end up with 94,444 BTU. This number is the BTU input you are looking for. You'll probably have to round up to 100,000 and purchase a 100,000 BTU HVAC unit.)
Always turn the power off to the HVAC unit before taking the cover off. Parts of the unit have 120 volts of electricity that is live at all times, even when the unit isn't operating.
