Q: How can I determine the proper size air conditioner / heater for my home?Bigger Is Not Better
A: Bigger is Not Better
Why an Oversized Air Conditioner Is Bad News?
- Oversized air conditioners run up your utility bill. An oversized unit short-cycles (runs for shorter periods of time than it should), and uses more electricity than a properly sized unit. Air conditioners operate more efficiently the longer they run continuously, and should be sized so they don’t turn on and off frequently on hot days.
- Oversized air conditioners cost more to buy and don’t last as long. The larger system will cost you hundreds of dollars more and give you fewer years of service— and bad service besides.
- An oversized air conditioner makes your house clammy. A unit that’s too big can’t dehumidify the air effectively because it runs for only short periods at a time. The indoor coil never gets cold enough to do its job of removing moisture from the air. An oversized unit will leave your home cold and clammy, especially in humid climates.
- Oversized air conditioners are noisy. The bigger the air conditioner the faster the air rushes through the ducts and grilles. Often the ducts and grilles are not designed for the larger unit, so the noise will get even louder as air tries to force its way through the small openings.
Studies show that 1/3 to 1/2 of all home air conditioners don’t work the way they should because they are oversized! There is no happy medium with an oversized unit. It delivers noisy blasts of frigid air, then shuts off while moisture builds. On hot days, it will do this repeatedly, making the home more and more uncomfortable as the day passes.
You'll pay hundreds of dollars more for an oversized air conditioner. Then you'll pay higher electricity bills to run it because an oversized unit is so inefficient.
Investing a little more in a good contractor who will take the time to properly size and install your system may be a very wise investment – both for your comfort and for your pocketbook.
Q: How can I make the uneven temperatures in some areas the same as the rest of the house?
A: Here are some different solutions for different scenarios.
Scenario #1: Each system serves no more than one story or level.
This is a temperature imbalance problem that can be resolved by increasing the amount of cooling or heating to specific areas. This can be accomplished in different ways.
Go to the warm room. If the air coming from the outlet feels like it has good velocity then the duct(s) are doing all they can but are too small. They need to be replaced with larger duct(s) or an additional duct installed for this area. Another cause, although less common, is that the duct is so long that the extreme attic temperature has caused the air to lose its coolness. Use better insulation on long duct.
The ducts may be large enough but poorly installed. Re-install correctly. A common misconception is that a larger unit will help. This can make matters worse due to the shorter run times and longer intervals where no cooling occurs. Imagine filling 2 bathtubs, one is 10’ away from the water heater the other 60’ away. Now consider there is a device that shuts off water flow to both faucets after one minute. The tub near the water heater is steaming, the tub that is 60’ away may have begun to get warm water just as the water is turned off. If new equipment is to be installed take care to assure proper sizing of the system.
Scenario #2: One system serves two or more stories or levels.
This is a basic design flaw. This is usually the result of cost-cutting during construction. This system should have never been designed this way if comfort is important.
A 2nd system should be installed. The current system capacity will then be too large for the smaller area it serves. Because it is ok for the outdoor unit to be up to about 30-40% smaller than the indoor equipment’s rated capacity you may be able to install a smaller outdoor unit and reuse the furnace and maybe the indoor coil. Most furnaces have adjustable blower speeds allowing this option.
A single system, such as Trane’s XL20i dual compressor, variable airflow furnace coupled with a Zoning System may be the best solution available. The cost for this system is typically comparable to the cost of two 12 SEER systems that have mid-range quality, efficiency and quietness. You get the individual temperature control just as 2 systems offer but the similarities end there:
- It’s all-new equipment. There are no re-used components planning the next expense for you.
- The highest efficiency system in the world (or lowest operating cost) with efficiencies ranging from 16.0 to 20.0.
- Superior humidity control
- Improved filtration due to the inherently fewer cycles of the XL20i
- Since there are roughly half as many components, fewer breakdowns are expected and the XL20i has a 10-year warranty on all components. That’s the longest standard warranty in the industry.
- If you want improved filtration for asthma or allergies you need to purchase only one of Trane’s specially designed filters. This saves hundreds of dollars now and in ongoing expenses when compared to 2 systems
Care should be taken to assure proper sizing. A common misconception is that a larger unit will help. That can make matters worse due to the shorter run times and longer intervals where no cooling occurs.