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Q: How important is it to have your air ducts cleaned, and do you provide that service?

A: Although many companies will tell you that there are health benefits to cleaning your air ducts and that it is recommended by the EPA (Environmental Protection Agency), it just isn't true. The average household should not need their air ducts cleaned if they regularly change their air filter. There is a short list of reasons why you might want to have your ducts cleaned, which you can read more about here on the EPA website. Trusted Heating and Cooling does not offer this service because it is rarely ever needed and usually is just a frivolous cost that many companies want to add to your bill. We only recommend and provide services that you need and will truly add a benefit to you and your home/family. If you really think your ducts are dirty and need cleaning, there are hundreds of AC companies in Austin that do provide that service.

Q: What effect does closing my doors and registers have on my air conditioning system?

A: A properly installed air conditioning system will be balanced so that sufficient cold air is delivered to and returned from each room of your house. Closing doors and air conditioning supply vents disrupts this balance, causing your system to run at less than its designed efficiency. It also causes air pressure to increase in the ductwork, which magnifies the negative impact of any leaks you may have in your ductwork and reduces the efficiency of the air conditioning fan itself.

You can close doors to unused rooms if there is enough space under the door to allow for sufficient air circulation. If you do decide to close some registers, never close off vents to more than 10% of your total conditioned space.

Q: My roommate keeps his bedroom window open during the summer for one to three hours a day, but keeps his bedroom door shut. Does the open window in his room make the whole system less efficient?

A: Because heat travels from hot to cold, the heat that is entering through the window remains in the house and therefore has to be removed by the air conditioner. Even with the door closed, the heat that builds up in the room will eventually travel to a cooler section of the house to be removed by your air conditioning.

Q: I have heard that you should not run an evaporative cooler and central air unit at the same time or in the same day because it would cause the two systems to work against each other. Is this true, and if so, how does it work?

A: It is true that you do not want to run the two systems together because of the humidity. Air temperature feels different at different humidity levels. During the summer you will feel cooler and therefore more comfortable in your home at lower humidity levels, just like you feel more comfortable outside without the humidity of the monsoon.

While air conditioning units do dehumidify, it will take some time for the unit to remove the excess humidity from the air, the carpet, the furniture and anything else in your home. During this time, you may feel uncomfortable enough to lower the thermostat, increasing the cost of operating your system.

When switching over from evaporative cooling to air conditioning, make sure you close off the damper that isolates the ductwork and separates the two units. Without a tight seal between the two sections, hot outside air will be drawn in through the cooler and will mix with the conditioned air.

Q: Which requires more power -- running a house's air conditioning system or its heating system?

A: The answer depends on what type of heating you have. Typically, you use more energy to air
condition than you do to heat, due to the environment your air conditioner has to work in. The
hotter the outdoor temperature, the harder your unit works. As the outdoor temperature rises, the less efficient your air conditioning becomes and the more energy it uses to keep you cool. 
If you are referring to the operation of a heat pump, it takes more energy to run the cooling side of a heat pump than it does the heating side.

The following two factors cause this to be true:

  1. The cooler outdoor air temperatures of winter are easier on the compressor resulting in increased efficiency and lower energy consumption.
  2. The heat generated by the motor of the compressor itself is added to the air delivered to your home, resulting in increased capacity. What this means is that during winter the capacity of your system increases and the energy consumption decreases.

Q: I have a one-year-old home with 12 SEER dual air conditioners mounted on a concrete pad on the west side of the house where they are exposed to full afternoon sun. Since the house is new, the trees aren't big enough to shade the unit. Would building a two-by-four-foot shaded structure, with adequate ventilation around each unit, create any significant energy savings?

A: Studies have show that shading air conditioners and especially just shading condensing sections is of little value. In fact, improper installation can actually cause restricted airflow to the unit resulting in increased run time and higher operating costs.

Q: Despite numerous efforts to reduce my electric bill, it is still high. I replaced my 35-year-old air conditioner with a new 12 SEER unit, and installed a new, energy-efficient washer, dryer, range, water heater dishwasher. I also had a new roof installed a year and a half ago. Since these replacements, my equal monthly payment has gone up $4! I expected a significant reduction in energy costs. Why isn't my bill lower now?

A: Replacing your old air conditioning unit with a new system should be showing you summer air conditioning savings. However, in comparing one month to another, or one year to another, you must also account for weather and temperature differences.

Next, try to determine what portion of your monthly bill actually went to air conditioning. To do this, subtract your March bill -- a month when people typically do not use any cooling or heating -- from your July bill. The difference between these two months gives an estimate of your cooling cost.

Although you replaced other appliances, their impact will be minimal. However, changes to your windows can produce very large returns for a small investment. Almost 40% of all the heat that enters your house in the summer comes in through the glass. Installing simple and inexpensive exterior window shading on sun-struck windows can dramatically reduce the load on your air conditioner.

Q: I've heard that if you can't see through a furnace or air conditioning filter, it is no good. I've also heard that if you can see through them, they are letting too much dirt and dust pass. What are the differences among filters, and are the cheaper ones adequate, or should I invest in more expensive filters?

A: Different types of filters rely on different methods of filtration to do their job. The inexpensive filters rely on a fine coating around each of the fiberglass strands to help catch the dirt as the air passes through it. As this coating attracts more and more dirt, it becomes less and less efficient. If you wish to use these filters just make sure that you replace them at least once a month and maybe even more often during the summer.

Another kind of disposable filter uses pleated paper as its filtration medium. The pleats enable a large amount of filter paper to be installed in the filter frame thus increasing the filters efficiency. Even though it has more filtering surface area, it still needs to be checked monthly and replaced when necessary.

There are also permanent filters that can be operated by natural electrostatic charges or by electronic circuitry. While these filters do not need replacing, they can be expensive to purchase.

The bottom line is, unless you have a medical condition that requires high levels of air purification, disposable filters will work just fine. The thing you have to remember is that they must be replaced regularly. If they become clogged, your air conditioning system will not get the air it needs to run efficiently, resulting in higher-than-necessary cooling costs.

Q: What is the difference between Seasonal Energy Efficiency Ratings (SEER) and tons? Is a bigger air conditioning unit better?

A: SEER is a measurement of the efficiency, while tons is a measurement of size. One ton of air conditioning is equivalent to 12,000 BTU. A BTU is a British Thermal Unit, and it is simply a measurement of heat. One BTU is roughly equivalent to the amount of heat generated by burning one wooden kitchen match. Simply put, this means that a one-ton air conditioner can remove 12,000 BTU from a space per hour.

To determine what size air conditioner a house needs, a contractor will conduct a heat gain/heat loss calculation, which enables the contractor to match the size of the unit to the BTU requirements of the specific house. A general rule of thumb for an average home is about 500 sq. ft. per ton.

Bigger definitely is not better. A larger-than-necessary system will turn on and off more frequently and cost more to operate than a properly sized system. A unit is operating at its lowest efficiency when it initially starts. The longer a unit runs the more efficient it is. Be sure to look for a properly sized system.

Q: I need to know which air conditioner would be best in our new 2,000 sq. ft. house. The builder is installing a 10 SEER as standard equipment, and charging extra to upgrade to a 12 SEER. How do I know which SEER is best for a home of this size?

A: The SEER rating has basically nothing to do with how well a unit will cool your home. It simply refers to how much it will cost to operate the unit when it is running. The size of the system is the determining factor on how well it will cool your square footage. The builder's air conditioning contractor should have done the load calculations on your home and determined the size of the unit based upon them. 
Going to a 13 SEER can save you about 15% to 20% annually on air 
conditioning costs.

Q: Is it better to let my air conditioning run all day at 85 degrees or turn it on when I get home?

A: Turning your unit off in the morning when you leave the house and then waiting until you return at night to turn it back on will save you the most money. The problem is that not only will the air in your house have a chance to heat up but the furniture, carpet, walls, etc. will also heat up. With all this heat it will take your air conditioner longer to bring the temperature back down to a comfortable level.

The continuous operation of the unit is actually very efficient. Without all the starts and stops of a typical cycling unit, you're able to run the system at its peak efficiency. However, setting the thermostat at 85 will also save you money (perhaps not as much as turning the unit off), while not taking as long to re-cool your house. Both options work, it's just a matter of how much discomfort you're willing to put up with.

Q: How long should it take for a functioning air conditioner to lower the temperature from 84 to 80 degrees? We live in a 1,550 sq. ft. home with no direct sun exposure and have a 3.5-ton air conditioner. We have been unable to bring the temperature down in our home when we set it around 84 degrees during the day. 
Should we be able to raise the temperature to 86 degrees and then lower it to 78 to 80 degrees when we come home? If so, how long should this take, and do you think a 3.5-ton unit is adequate?

A: A properly running air conditioner installed on an energy efficient house should be able to bring the temperature down from 85 to 80 degrees within one to two hours. If your unit is not able to do this nor maintain a specific set point, then I'm guessing that you either have equipment problems. It could be incorrect refrigerant charge; air distribution problems, where the unit is producing the cooling but it is not being distributed throughout the house or is being mixed with hot attic air; or thermal problems with the house, such as missing or poor insulation.

A general rule of thumb is that one ton of air conditioning can handle 500 sq. ft. of conditioned space. So your 1,550 sq. ft. house should have a little over three tons.

Considering that your unit appears to be oversized and yet is not able to provide adequate cooling, I recommend that you have the system tested and your house inspected.

Q: I have a two-story home with two split-unit air conditioners with programmable thermostats. I am on SRP's Time-of-Use plan and would like to take advantage of these prices by pre-cooling my house in the early morning, then allowing the house to warm slightly during the day. What temperature and time settings would best accomplish this?

A: Pre-cooling works best when your house has a lot of mass built into it, also known as heavy construction. In a heavy house, pre-cooling tile-over-slab floors, masonry fireplaces, granite counter tops, masonry perimeter walls etc. allows the house to store a lot of the pre-cooling energy and coast well into the on-peak period without requiring additional air conditioning. Light house construction (frame construction, carpeted floors, laminate countertops, drapes etc.), on the other hand, will not have enough mass to store much of the pre-cooling energy.

Any pre-cooling strategy has to be operated long enough to cool the structure and not just the air. If your house is heavy, I'd recommend pre-cooling it down eight to 10 degrees for a good four to six hours prior to the on-peak period. If your house is light then a four- to six-degree pre-cool for a couple of hours should be fine.

Q: We live in a 13-year-old, two-story home and have decided to replace both air conditioning units. What SEER rating should we be looking for?

A: Replacing a 13-year-old air conditioning unit with a new 13 SEER system can save you 40% to 45% on your air conditioning bill.

While SRP recommends a minimum 13 SEER, you should rely on your contractor to help you decide what level of efficiency is best for you. Before you buy any system, make sure that the contractor performs a heat gain and loss calculation on your house. This will ensure that you buy the correct unit size for your house. Systems that are larger than necessary will not only have higher initial equipment costs, but also higher operating costs.

With regard to the manufacturer, all the major brands manufacture high quality equipment that will last 15 to 20 years. When shopping, manufacturers, look at their warranties as a sign of their quality.

Q: I am replacing my 22-year-old, four-ton, roof-mounted air conditioning system. What factors should I consider in choosing the best system for my house? Should I be concerned about the depletion of the Freon supply over the years and its potential rising cost, or should I look for the environmentally friendly Puron refrigerant for its longevity?

A: Have your contractor calculate the cooling requirement for your house. Just replacing an old unit with a new unit of the same size may not be in your best interest. Your cooling loads may have changed over the years due to changes to your house. Installing larger-than-required equipment costs more to purchase and costs more to operate each month. Make sure your contractor also checks your home's air distribution system to ensure proper airflow is being delivered to and from the unit. Duct leaks can reduce the efficiency of the unit, causing increased operating costs.

The industry says that Freon R12 will be around for many years, but there is no guarantee of how much it will cost. I recommend a system that uses the new refrigerants, as they are not limited to quantities on hand. In addition, a SEER 12 will save you approximately 10% in cooling costs over a SEER 11 system.

Q: How do air conditioners work?

A: Air conditioners perform two basic functions, heat removal and moisture removal. Even though you live in Arizona, we do have our monsoon season with its higher-than-normal humidity levels. The lower the humidity level, the more comfortable you will feel at a given temperature.

As your warm indoor air is drawn up through the filter, it passes over a very cold coil that removes the heat and moisture. If you've ever noticed a plastic pipe running off your roof that drips water, that is the moisture the unit has removed from the inside of your home.

Q: I set my air conditioning at 80 degrees, but over the course of an hour, the unit runs for over half an hour and then only turns off for about 10 minutes. This does not seem normal. What is a normal cycle?

A: How long a unit runs at any one time is dependent on many things, including the size and efficiency of the air conditioning unit, the operating condition of the unit and the temperature swing of the thermostat. While typical cycle times are approximately 10 minutes on and 10 minutes off, the longer the unit runs, the more efficient it is. However, longer-than-necessary run times can indicate a problem with the unit.

To see if your system is performing like it should, get a hold of a couple of quick response thermometers and put one in the return grill (the grill where your filter goes) and the other one in the supply register (the vent that blows the cold air into the room) closest to the return grill. You should see about a 20-degree difference between the two readings. If not, it can indicate that you have refrigerant or air flow problems.

It is very hard to determine if your cycling pattern is normal without an inspection of the system. I recommend having a contractor inspect the unit.

Q: I have a 25-year-old, two-and-a-half or three-ton heat pump in my 1,400 sq. ft. house. It just keeps on running. If I installed a new high efficiency unit, would I recoup the cost with lower energy bills?

A: Replacing the old heat pump with a new unit you should save you at least 50% on air conditioning costs. SRP recommends a minimum efficiency rating of 13 SEER; however, you should rely on your contractor to determine the best unit for your specific situation.

Proper sizing is very important. A larger-than-necessary unit will cost more to purchase and will also cost more to operate each month. Make sure your contractor performs a heat gain and loss analysis on the house, which will help you select the proper size unit.

Q: We have a two-story house that is five years old. We have two air conditioners, and we have consistently had problems with one of them running out of Freon. Last year, the contractor replaced the compressor in the unit. The drainage pipe that runs out of the house is constantly dripping water at a pretty steady pace. Is that a bad sign?

A: It means that your unit is removing the moisture from inside of your house and depositing it outside. However, the output of the condensate drain should vary as the indoor and outdoor humidity rises and falls.

During normal operation, the evaporator coil located inside your air conditioner becomes very cold. As the air from inside your house is drawn through this coil, the air is cooled and the moisture is removed. The cold air is returned to your house through the supply registers and the moisture drains to the bottom of the coil, into a drain pan and out the condensate drain.

Q: I thought a central air conditioner was supposed to remove humidity from the home and blow cool, dry, air. But the more ours runs, the higher the humidity, up to 30 to 40%. We had it checked and were told there is nothing wrong.

A:The longer a properly operating air conditioner runs, the lower the humidity should be. Several things could be wrong with your unit:

  1. There is a drainpipe, usually a white plastic pipe, coming out of your unit that should be dripping water this time of the year at a pretty good volume. This water is the moisture from your house. If it isn't able to discharge this water when your air conditioner is running, it will continually put it back into your home, increasing the humidity level.
  2. There could be a leak in the ductwork that distributes the cold air to the rooms of your house. The leak can add hot, humid air to the air being distributed to the rooms.

Q: We are away from our house four months during the summer. I've always left the thermostat set at about 85 degrees. Would it be better to shut it completely off?

A: If your house is well-insulated and tightly sealed, turning your air conditioner off completely is probably the best approach. In a newer, well-insulated home the interior temperature typically doesn't rise higher than the mid to upper 80s when the unit is turned off.

By turning your thermostat up and not turning it off completely, you will protect any fine wood furniture or other items that can be damaged by the heat and dryness. I also recommend placing several buckets of water in your bathtub. The water will slowly evaporate and add moisture to the air.

If you have an older, less insulated home, you should continue to turn your air conditioner up to a high setting as you have in the past, as the temperature in older homes can rise into the 90s.

You should also turn off the power to your refrigerator, prop open the door, and turn your electric water heater off. If you don't, the higher temperatures can cause your refrigerator to run twice as long and the water heater will continue to cycle on and off all summer.

Q: I have a 14- by 70-foot mobile home. I've heard that leaving the air conditioner on when we are gone will keep it from drying out. I had set my thermostat at 90 degrees and left buckets of water in the bathtub and kitchen sink. I had a two-inch insulating foam layer sprayed on the roof to further cut down on heat gain and have shaded the home's sides with awnings. 

Despite my efforts, my bills are still high, even when we are away for a month at a time. How can I reduce our electric bill when we are gone?

A: The insulation you added to the roof of your home should reduce the heat gain and lower your air conditioning costs. However, since only about eight to 10% of the heat that enters your home actually comes in through the roof, the actual effect of the insulation will be limited.

About 40-50% of the heat comes in through the windows. While your awnings help divert sunlight, you might want to consider adding shading screens to the outside if any of your windows receive direct or reflected sunlight. 
If you're going to be gone for the summer, in addition to setting your thermostat to its highest setting or turning it completely off, you should consider emptying out your refrigerator, propping the door open and unplugging it. If you leave it operating, it will run almost 24 hours a day because of the hotter temperature inside your home. This can add a significant amount to your monthly bill.

Because heat travels from hot to cold, the heat that is entering through the window remains in the
house and therefore has to be removed by the air conditioner. Even with the door closed, the heat that builds up in the room will eventually travel to a cooler section of the house to be removed by your air conditioning.