When It Comes to Air Conditioning, Size Matters

Homeowners tend to keep their air conditioning units for a long time. Yet, if saving money is your goal, it could pay to weigh the operating and maintenance costs of your aging, less-efficient unit against the savings of upgrading to a new, efficient unit.

When you upgrade, avoid the common mistake of oversizing. Many people who have been struggling with an unreliable, older model think getting a larger capacity unit will make everything cooler. They believe since the unit will not be stressed, they will save operating costs. Not so.

A system that is too large not only costs more, and costs more to install, it operates inefficiently. A unit that is too large will breakdown more often and cost more to operate. Oversized heating equipment often creates uncomfortable temperature swings in the home. And oversized air conditioners do not run long enough to dehumidify the air. This gives rooms a clammy feel and even permits unhealthy mold growth in humid areas.

Often, when replacing their system, homeowners simply buy the same size they had before. Many older units were sized before the era of tightly constructed homes. It was not uncommon to install systems that were two to four times beyond the necessary capacity. If you have added new windows, caulking, weather stripping, or insulation over the years, you might be better served by a smaller system than the one you are replacing.

A popular formula to use for correct sizing is found in Manual J: Residential Load Calculation, published by Air Conditioning Contractors of America. It requires measuring walls, ceilings, floor space, and windows to determine room volumes. It considers your insulation’s resistance to heat flow (R-value) and estimates air leakage with a blower door test.

A good estimate also includes inspection of ducting and placement of the supply and return registers. Even the orientation of the house affects heat gains and loss. For example, overhangs can reduce solar gain through windows. Shortcut methods of sizing are only useful to get a ballpark estimate. Sizing based on gross square footage is not a good way to size for a final choice. The rule of thumb is one ton (12,000 BTU per hour) per 500 square feet of living space. This does not take into account design, construction, insulation, and other factors.

Replacing your air-conditioning unit with a new, more efficient model can lead to a windfall of energy savings. However, if you choose the wrong company to size your home and install your system, it can lead to a long list of headaches. Too many contractors will give you an estimate on a new system simply because it’s the system they have taking up space in their warehouse or it’s the cheapest system for them to sell!

We take your comfort, energy savings, and satisfaction to heart. We also do our best to provide air conditioning units for maximum value at the lowest price. If you know you need a new A/C, but have been putting it off, give us a call at (360) 558-3242. We’re happy to give you a free estimate.