Sizing Your HVAC System

In Heating & Cooling 101, Uncategorized by YounitsLeave a Comment

“What size HVAC equipment do I need?” is one of the questions we at get asked most often.  It seems like a simple question, but there are many factors that go into sizing air conditioner, furnace or other HVAC units.

At its’ simplest, 1 ton is equal to 12,000 BTU (British Thermal Unit), so if you are looking at a 3 ton system, the equivalent BTU is 36,000.  Cooling is commonly referred to in tons (although it can be identified by BTU) and heating as BTU/hr.

The main component in sizing your system is determining how much energy or power it takes to heat or cool your total square footage.  One ton, or 12,000 BTU/hr will generally heat or cool between 400 and 800 square feet.  This may seem like a big range, but square footage alone does not determine how big your hvac unit needs to be.  Other important factors include:

  • Climate.  Very hot summers (cooling) or extremely cold winters (heating) have a big impact on performance, so this must be taken into consideration in calculation your equipment size.
  • Sun exposure. Do you have a lot of shade around your house, or does your exposure get the heat of the sun at its’ hottest?  This means your air conditioner needs to work harder in the summer to keep home at a comfortable temperature and must be considered in the BTU calculation.
  • Insulation.  How new or well insulated are your doors and windows?  If they are old or poorly insulated, you will lose efficiency, resulting in the need for a larger capacity HVAC unit.
  • Ceiling Height.  This is not considered in the raw square footage of your building or home, but it does matter in the square footage of cooling and heating equipment.  Ceiling space is conditioned along with the rest of the space, so if you have high ceilings, you may need a bigger unit.

The best thing to do before purchasing your new HVAC unit is to have a contractor do a heat load calcuation.  This will give you the most accurate analysis for how big your heating and/or cooling system needs to be.  Keep in mind as well that your heating equipment may need to be a different size than your cooling equipment. representatives are happy to answer any questions you may have regarding sizing your system.  Call us M-F from 9 a.m. to 5 p.m. CST at 1-800-880-0199 or e-mail us anytime at

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