Should I be concerned about how many tons my HVAC unit is or needs to be?

Air conditioners come in many different sizes, whether they are window air conditioners or central air conditioners. These units should be sized to cool the size of your home with the most efficiency.

I have often been asked if a smaller or larger unit would be better. Smaller BTU units will continually run, just trying to keep up. This will increase your electric bill and it is unlikely the unit will be able to cool the area effectively, whereas, an air conditioner too large can be overkill. To dispute the rumor that bigger is better, an air conditioner too large will cool more quickly, but that may impede the reason for running the air conditioner in the first place. You see, one of the functions of your air conditioner along with cooling the air, is to extracting moisture from the air (humidity) that makes all of us feel hot and sticky.

Although the air may be cooler, if the unit doesn’t run long enough, the moisture cannot be extracted from the air properly. You can equate this to being outside camping on a cool, clammy, foggy night. Remember the feeling when your skin is moist and you get goose bumps when cool air flows over it, well an air conditioner too large will cycle on and off frequently and deprive you of feeling cooled.

Over-sizing will furnace may result in a different set of problems. When you oversize the gas furnace you could potentially overheat the furnace. This is mostly caused because in the case of an oversized furnace the existing ducts in the home will not support such high volumes of air flow, which can cause pressure to build-up in the return air duct and therefore overheat your furnace. Also, do keep in mind that the maximum level of efficiency with the gas consumption of a gas furnace, this maximum level is only achieved when the right size of furnace is installed in your home. In fact, the right size furnace should almost continuously run during the coldest day of the year. Of course, it should be able to satisfy your desired temperature.

How do I figure out the right size for my house? The short answer is you really should get a contractor to determine the proper size of HVAC equipment needed. To calculate the proper size of heating and cooling equipment for your home requires use of an engineering procedure such as ACCA/ANSI Manual J. Using short-cuts or ‘rules-of-thumb’ typically results in equipment that is incorrectly sized for your home.

Some of the other factors that are involved when determining what size of an air conditioner or furnace would have the required power output to cool or heat your home. These factors include the extent of exposure to the sun and the outside air, the thickness and type of outside wall insulation, the size, type and number of windows and outside doors, the ceiling height, etc.

Another misconception is also the belief that by going with a bigger size furnace or air you will save cost on your fuel/electricity bills as a result of the units working less, which is certainly not the case. You always require the same amount of energy in order to heat or cool your house. The factor that determines this consumption is not the power rating; it is the efficiency of the unit. When the furnace or A/C is more powerful, it will use more power in a shorter period whereas a smaller size furnace or A/C would end up using the same energy but in the manner of less power in a longer period – which works out to have the same consumption levels. In fact, in the case of an oversized unit, some energy is wasted and the maximum efficiency of the unit would not be achieved.

For more information contact McDonald Plumbing, Heating and Air at (916) 233-4194.

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