Calculating the correct size of HVAC unit for your home is not as simple as matching the square footage to a particular unit. The amount of insulation, size and type of windows, ventilation system, attic space, number of rooms and floors within the home all determine the type of system that will be most efficient. Since so many factors affect the performance of an HVAC unit and it is such a large investment, it's best to consult with an experienced contractor licensed to work with HVAC systems to determine the best unit for your situation. The contractor can also inspect the existing ductwork and advise whether or not the unit you're considering will be compatible with existing components.
The size of the HVAC unit has a direct impact on its efficiency, which affects not only the amount of comfort it provides, but also the long-term cost of operation. A unit that is too small will be forced to run too much and may even freeze up on hot days. On the other hand, a unit that is too large will not provide better comfort, but will cycle on and off frequently, consuming more energy than an HVAC unit that is sized properly for your home. Look for units that match the size recommendations made by your contractor.
Energy ratings for HVAC units include SEER and SHR. The SEER rating, or Seasonal Energy Efficiency Ratio, offers insight into how much heat the unit removes for each kilowatt of energy it consumes. The higher the rating number, the more efficient the unit. The SHR rating stands for Sensible Heat Ratio and reveals the percent of energy the unit uses to cool, versus the amount of energy used to remove excess moisture from the air. The ideal rating is around 0.7, which is equal to 70 percent of the energy expended on cooling, and 30 percent on removing moisture. In order to achieve the energy efficiency ratings listed, the unit must be the correct size and installed properly.
Price and Warranty
A good price on an HVAC unit is not always the lowest price. Quality, durability, efficiency and the length of the warranty should all be factored in as part of the final cost. A unit with a low initial price may cost more in the long run if it does not run efficiently and requires frequent repairs. On the other hand, an expensive unit with a lot of extra features may not be worth the price if you don't use the features regularly or don't require special filtering or exact humidity levels. Look for a unit that is built to last and has a warranty that backs up the manufacturer's claims.