Everything You Need To Know About HVAC Load Calculations

So you’re getting ready to choose a new HVAC unit! As you surely know, this is a big decision. Keep in mind that bigger doesn’t mean better when it comes to your HVAC unit, so don’t let the biggest unit on the market draw you in.

You home won’t necessarily cool quicker or use less energy just because you have a large unit. In fact, a unit that’s too large could potentially do more harm than good. When determining what HVAC unit is right for you and your home, you might want to try some heating and cooling load calculations.

What Is HVAC Load?

HVAC “load” is the amount of heating or cooling that a building needs in order to maintain a proper temperature. The load is affected by a lot of things, including the climate, insulation grade, square footage, sun exposure, number of windows and doors in the home, how many people live in the space, and more.

Heating and cooling load calculations determine both the size and scope necessary for an air conditioning unit. Contractors will go to great lengths to calculate the accurate load, including details like the type of home, the kitchen, air type, and more. Adding up all the information helps determine what kind of power is needed to keep the home cool.

Why Is Calculating HVAC Load Important?

Finding the right size unit for your home isn’t about getting the biggest size, or alternatively, spending the least amount of money. Incorrect heating and cooling load calculations will lead to an incorrectly sized HVAC unit which will lead to headaches down the road.  

A wrong size unit can result in poor air quality, high energy bills, and a unit that breaks down well before its time. For an oversized unit, it will end up having a shorter lifespan since it will have to turn off and on more often. For an undersized unit, it will have a shorter lifespan since it has to work much harder than it was made to work.

Both an oversized and undersized unit will affect your air quality. An oversized unit will result in a clamminess to your air quality since it will cool the space too quickly to have time to reduce the humidity. An undersized unit won’t be able to process the air as it should.

How is HVAC Load Calculated?

Heating and cooling load calculations are determined by measuring the efficiency needed in tons and BTU’s (British Thermal Unit). These measurements are a way for contractors to determine a general estimate.

If you’ve been looking into HVAC units, then you may be familiar with a “three-ton air conditioning unit” or some other size. This doesn’t mean the unit weighs three tons, but rather this is the unit’s cooling and heating capacity.

Traditionally, BTU’s are used to measure heat, and tons are calculated as BTU’s per hour. The more tons or BTU’s a unit can handle, the more powerful it is. Follow these steps to calculate your HVAC load to get the right measurements for your unit.

Step 1: Measure Your Square Footage.

Determine your home’s square footage. You can do this by looking at your home’s blueprints, or, if you don’t have those available, measure the space room by room. Measure the length and width of each room, then multiply those numbers to get a rough square footage. Alternatively, you can measure your home’s exterior and then subtract any spaces that won’t need to be heated or cooled, such as the garage. 

Keep an account of the height of your rooms. Ceilings that are taller than average tend to require more BTU’s to cool and heat.

Step 2: Add Up Insulation, Windows, and Other Factors.

Check what grade of insulation was used in building your home (if you’re unsure, U.S. Standard Insulation is a good guess). You’ll also need to track how many windows you have, your home’s air-tightness, sun exposure, heat-producing appliances, and so on. A good way to estimate these is by adding up BTU’s like the following:

  • Each home resident: 100 BTU’s
  • Each window: 1,000 BTU’s
  • Each exterior door: 1,000 BTU’s

Step 3: Add Everything Up!

This is what the heating and cooling load calculation would look like for a house with 2,500 square feet, 12 windows, 3 exterior doors, with 5 people living in it:

  • 2,500 x 25 = 62,500 (this is your base BTU)
  • 3 people x 100 = 300
  • 10 windows x 1,000 = 10,000
  • 4 exterior doors x 1,000 = 4,000
  • 62,500 + 300 + 10,000 + 4,000 = 76,800 BTU

If you’re having trouble determining what heating and cooling load you have for your home, consider talking with a professional who can be your own personal HVAC calculator.

Ready to Calculate Your HVAC Load?

Knowledge is power when it comes to projects around the home! If you’re looking to replace your existing HVAC system, no matter the reason, make sure you get the right set up that is effective and efficient for your home. Get in touch with the heating and cooling experts at John C. Flood to discuss your HVAC project today. Call us at (703) 214-5611 or contact the Flood HVAC team online.

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