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Air Conditioning Sizing Tips

Air Conditioning for Old Houses

How in the world did people survive 60 years ago without air conditioning? I have worked in older brick buildings in the inner city of Cincinnati during the summertime. They can be stifling. My guess is that the people back then didn't know any better. Since there was no alternative, they simply sweated and took it easy.

Business productivity had to suffer. Air conditioning has to be one of the most innovative and useful inventions of the 20th century.

The Most Complex Aspect

Heating and air conditioning is by far the most complex aspect of building and remodeling. It involves physics, fluid mechanics, electricity and much more. A technician must have thousands of dollars of specialized testing and monitoring equipment. The equipment is constantly changing and improving. Plumbing and electrical work pale in comparison.

Few homeowners are prepared or able to make even the most simple diagnosis when a air conditioning problem strikes. The equipment is simply too technical. I myself am challenged when it comes to air conditioning troubleshooting and repair. I'm so glad that my best friend, Richard Anderson owner of Sergeant's HVAC, is a top notch heating and air conditioning service technician!

Environmental Control

Did you ever stop to think that your heating and air conditioning equipment and ductwork are probably the second most important component of your house? The first and most important is the roof - it keeps you and your possessions dry.

Your air conditioner keeps your environment ("house") comfortable and at a stable temperature - that is if it was designed and installed correctly. All too often builders and homeowners try to save money when selecting a heating/air conditioning contractor or air conditioning equipment.

This is a HUGE mistake. I have been in new houses where the room to room temperature can vary by 8 - 12 degrees! Air whistles from the ductwork or doesn't come out at all.

Your comfort level is directly related to the ability of the person you choose to install and service your air conditioning equipment. Low prices often mean low service and ability.

All Things Must Be Right

Air conditioning is so complex that all aspects of the system must be designed and installed right for you to be comfortable. This means that the condensing unit, the air handler and fan, the interior coil, the ductwork and the refrigerant must be right.

Imagine if all of the components are perfect except for the ductwork. If you have a two story house and the second floor is hotter than the first floor, something is wrong! Don't let a technician tell you this is normal. My two story house has the same temperature (+/- 2 degrees) in each room day or night.

This didn't happen by mistake. My friend Richard made sure that the supply duct to each room delivers enough cool air to handle the heat gain. He also installed a return air duct that vacuums the hot air from the ceilings. Do you have this design in your house?

Maintain Your Equipment

Air conditioning often performs poorly because of homeowner neglect. You hear it all the time about changing / cleaning air filters. The reason for this is simple. Air filters protect your equipment. They stop the buildup of dirt on the interior coil and the fan blades that move air throughout your house. If dirt builds up on the interior coil or the fan blades the coolness on the coil can't be delivered to the hot air that passes over the coil. It is that simple.

If you have the old technology fiberglass filters, you may want to consider newer polyester rinsable filters. I have these type in my system. I love them. You can readily see the dirt within the filters. They rinse easily. Many air conditioning contractors sell these or they are available where air conditioning equipment is sold.

Annual or bi-annual checkups may not be a bad idea. The service technician can check to make sure your refrigerant level is perfect. He can look for loose electrical connections. Fan speeds can be tested and adjusted. The drain line from the interior coil can be checked for cleanliness. Fans and motors that require lubrication can be oiled.

All of these things can prolong the life of your air conditioning equipment. Remember, air conditioning equipment breaks down when you most need it. You may have to wait for days for a repair person to help you. All of this can often be prevented with regular checkups BEFORE the cooling season arrives.

Do you cover your outdoor unit in the winter months? This may be a bad idea. Check with the manufacturer before continuing this practice. A cover may trap condensation. Just a quick tip........


Checklist for Locating Air-Conditioning Problems

What happens if one day your air conditioner just doesn't cool well or doesn't work at all? It worked fine last season or last week but all of a sudden acts up. The problem may be complex or it may be simple. There are some things you should check before you call the repair company. The simple fix items may save you a $100 service call. Some things you can't check easily. These have to be performed by a professional. I hope your air conditioning problem turns out to be something minor. If it doesn't and it is time to purchase a new outdoor unit, be sure to consider two things: Try to buy a unit with the highest SEER rating. This is a measurement of efficiency. The higher the SEER #, the more cooling you will get for your electricity dollar. Also make sure that the interior coil is matched to the outside unit! Don't underestimate the importance of this fact. Without proper matching you may loose your warranty AND the outdoor unit will NOT operate at the SEER rating as advertised! You must ask questions....!

Air Conditioning Operates - But Little Cool Air

  • Check Furnace or Air Handler filters. Clogged or dirty filters slow air flow past the interior coil.
  • Check tension of belt on Furnace or Air Handler Fan if belt driven. A loose fan belt slips. This causes insufficient air to pass by the interior coil.
  • Look for a water puddle below furnace or air handler. Water may be a sign that the interior coil has frozen. If ice forms on the interior coil, the air passing by the coil just doesn't get cold enough. Ice formation can usually be traced to dirty filters.
  • Check interior coil for dirt buildup. This is only possible by removing the inspection panel on the ductwork that surrounds the interior coil. This is not always easy. A dirty coil is only a problem if your filters have not been changed regularly.
  • Outdoor condensing unit maybe low on refrigerant. This can only be checked by a professional.
  • Check interior registers. These may be blocked by boxes or furniture or are closed/restricted.

System Will Not Function - No Cool Air

  • Check all circuit breakers. Look at main electric panel and outdoor disconnect switch at condensing unit. Turn to off position then back on.
  • Check thermostat switch / setting. The switch to cool position mat not be engaged. Thermostat may need adjustment. Turn switch off then on again.
  • Startup capacitor may not be functioning properly or worn out. Can only be checked/serviced by a professional.
  • Check furnace on/off switch. It may have been turned off inadvertently. This will shut off the power to the furnace/air handler fan.
  • Check Compressor Auto Shut Off. Compressor may be failing. Can only be checked/serviced by a professional.


Air Conditioning Sizing Tips

Quite possibly the biggest reason for air conditioning discomfort is that the equipment is simply too small. Imagine using a lawn mower engine to power a freight train. It just simply can't do the job. Air conditioning condensing units (that big mechanical 'thing' outside your house) are sized like shoes. They are measured in tons. A ton is a unit of measure. One ton equals the amount of BTUs (12,000 BTUs) it takes to melt one ton of ice in a 24 hour period. You will often here your air conditioning person tell you that you need "...a 3.5 ton unit.." or something like that. Well, how in the world did they know that?

Heat Gain

The only way air conditioning equipment can be sized PROPERLY is to perform a heat gain calculation. 20 years ago I used to have to do these by hand. It could take hours. Air conditioning companies now have nifty computers to do it quickly. You need to feed the computer data. It wants to know how large your house is - that is, how much wall area is exposed to the outside temperatures. It wants to know how large and what type of windows/doors you have, the amount of wall and attic insulation, which direction your house faces, how many people live in the house, etc. Once all of this data is fed into the computer, it will tell you the heat gain in BTUs for your house. This is exactly how to do it. There is NO OTHER WAY. Don't let the person tell you that your neighbor's house across the street is the same design and square footage and as such requires the same AC unit. That is not necessarily true! The reason lies in the fact that the house orientation is different. They may have more glass surface facing west!

Interior Coils and Fan Speed

The big machine outside that makes noise compresses the Freon or other refrigerant into a liquid. The liquid is pumped or suctioned into your house. There it passes through a coil inside of your furnace or air handling unit. Within this coil the refrigerant evaporates into a gas. This makes the interior coil very cold. The air passing over the coil creates air conditioning! We need this component to be sized correctly as well. If the interior coil is not matched to the outside unit, it will not evaporate all of the refrigerant. It will not produce enough "cooling effect". The fan that forces air through the ducts must be sized right too. If it is not large enough or does not spin fast enough then not enough air will get cold to combat the heat gain your house is experiencing.

Ask Questions

If you are building a new house or installing new air conditioning, you must ask all of these questions. Make the air conditioning technician prove to you that they have all of the components sized correctly. The simple fact that you are asking the right questions will frighten the non-professional. Look for numbers on the nameplate of the outdoor unit. It will often have a number like 42,000 or some multiple of 6,000 in it. These refer to BTUs. If you have a 3.5 ton unit, then you better see the number 42,000 somewhere! Some manufacturers may drop the three zeros, look for that as well - you may just see the number 42.


Air Conditioning Systems for Old Houses - Ones Without Ducts

Do you own an old house - one with hot water heat? Installing large traditional sheet metal ducts may be impossible. Two companies in the USA make very nifty systems to overcome this hurdle. The systems use high velocity air that passes through smaller flexible ducts. The main trunk line (it's flexible too!) is often 9 inches in diameter or less! the individual branch lines that feed into the rooms are only 2 inches in diameter. Small holes are cut into the ceilings to accommodate the piping. Special liners and orifices are used that reduce and eliminate air noise. The principles of cooling the air are the same as with traditional units. It is just the delivery of the cool air that differs. These companies have been in business for years. The techniques and equipment are time tested and reliable. Often the installers in each city have undergone rigorous training. Make sure you ask about this when you call for information and installers in your city. I would absolutely call both companies and ask for information.

  • SpacePak
    260 North Elm Street

    Westfield, Massachusetts 01085
  • Unico, Inc.
    7401 Alabama Ave.

    St. Louis, Missouri 63111-9906

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