Heating, Ventilation and Air Conditioning
What is the typical energy use of household appliances?
Like most things in life, nothing's average, but here is a table showing what can be thought of as typical energy use for different appliances
What's the most common mistake people make in trying to save energy around the house?
Common mistakes people make include:
We don't own a home; we rent an apartment. What can we do?
If your landowner pays the utility bills it should be easy to convince him or her to make efficiency improvements, since they will realize the economic benefits. If you pay the utility bills you are still not without hope, because there are inexpensive things that you can do to lower your bills and make your home more liveable.
Water heating costs can be reduced by putting a blanket on your heater. Blankets typically cost less than $10 and can save between 10 and 40% of your water heating costs. However, water heaters less than five years old already contain sufficient internal insulation, and should not be wrapped, otherwise they might overheat. You can also reduce water use and heating costs by installing low flow shower heads and faucet aerators.
Weatherstripping can reduce or eliminate drafts through windows and doors. It doesn't take long to install, increases comfort and reduces costs. Rope caulk provides a temporary seal during the winter months around windows that leak. You can remove this seal in the summer so that you can open and shut the windows. If your windows are very leaky, you can fit a piece of plastic over the window during the winter to form an inexpensive storm window.
Here are some other possibilities:
We have an older house. Which should we do first: insulate or replace the furnace?
Whether you should insulate or replace you furnace first depends on the situation in your house. Factors which influence this decision are the age and efficiency of your furnace, and the amount of insulation currently present in the house.
In general it is more cost-effective to upgrade insulation than it is to upgrade your furnace. However, if your furnace is old, and you are planning on replacing it anyway, you might want to upgrade the furnace if you have to choose between the two options. The average lifetime for a furnace is between 16 and 18 years. The efficiency of furnaces has increased over the years, so the older a furnace is the more likely that furnace is to be inefficient. The average efficiency of new furnaces has increased from 63% in 1972 to 83% in 1995. Older furnaces, and furnaces which are used a lot are more cost-effective to replace than newer or infrequently used furnaces.
Typically older houses were built with poor levels of insulation. As insulation ages, it compresses, becoming less effective at preventing heat transfer. Dust and moisture also contribute to the aging process in insulation. In temperate areas, if the insulation level in your house is less than 6 inches, the most cost-effective action is to increase the insulation up to R-30. For areas with extreme hot or cold temperatures, it is cost-effective to increase the insulation up to R-42
Here are approximate R-values of different insulation levels. The actual R-value of your insulation depends on the type and condition of the insulation, but these approximate values are helpful for judging whether adding insulation is the best plan for your house.
| Insulation Level | Approximate R-Value |
| 3 inches | R-9 |
| 6 inches | R-19 |
| 10 inches | R-30 |
| 13 inches | R-42 |
You might want to check out our Home Energy Advisor. It allows you to explore the costs and savings of replacing your furnace compared to adding additional insulation, making decisions of this sort easier...
My neighbor's bills are much lower than mine, even though they have children, and are home more than we are. Why are my bills so high?
There are a number of factors that cause differences in energy bills, so comparing your bill to someone else's is like comparing apples to oranges. The ages of major appliances, especially refrigerators and air conditioners, can make a dramatic difference in your bill. In addition, if your house leaks air like a sieve while your neighbor's house was just weatherized and insulated, you will have much higher heating and cooling bills. Other factors that can result in significant differences in bills are the number and kinds of lighting fixtures, thermostat settings for heating and cooling, the number of loads of laundry, old refrigerators out in the garage, and hobbies which result in electricity use.
What's the single biggest user of electricity in my house?
If your house has central air conditioning, the air conditioner will probably be the biggest user by far. Although used only a few months of the year, the annual cost can be much greater than the annual cost of your refrigerator, which is typically the next largest user. In hot climates, the annual air conditioner cost can exceed a thousand dollars. You can get a very rough idea of what your air conditioner is costing you by subtracting the electric portion of your bill in a spring month when you aren't using your air conditioner from the electric portion of the bill in the summer when you do use it. This gives you the monthly cost. Multiply this by the number of months you use your air conditioner to arrive at your approximate annual cost.
Refrigerators are typically the largest users in houses without air conditioning or in climates where the air conditioners are used only a few days of the month during the cooling season. If your refrigerator is more than ten years old you might want to consider replacing it. New efficiency standards went into effect in 1992, and older refrigerators are typically two to three times more expensive to run than a new unit. For more information go directly to the American Council for an Energy-Efficient Economy's list of most efficient refrigerator-freezers.
I was trying to find an estimate of the expected savings of an Energy Star NEW HOME (30% better than Model Energy Code) versus an "average" existing home. Your estimates seem to be oriented to retrofits using Energy Star equipment, as was clear once I got into the details. Have you also done, or do you have a reference on the savings with the Energy Star new home? That would presumably come out somewhat better than the full retrofit case.
A conservative estimate of energy consumed by average existing homes is 100 million BTUs per year, at a cost of about $1,280.
The energy consumed by the average new home is about 90 million BTUs for around $1,250. This consumption is driven largely by appliances and gadgets.
Energy Star new homes are designed to save 30% of HVAC (heating, ventilation and air conditioning) and hot water. These two end uses typically make up around 60% of the total bill, so the Energy Star new home will save about 20% of the total bill. These homes have no restrictions, or rules about the appliances and gadgets that the owners can bring in, so there aren't savings in these areas.
If you were to retrofit an existing home with the equivalent measures used in an Energy Star new home by making HVAC and hot water improvements and bringing in efficient appliances, you conceivably could realize greater savings than an Energy Star New Home, depending on the quality of your retrofit job. The next question is: would it would be cost-effective to do so? Retrofits on existing housing are generally more expensive than incorporating the same efficiency measure into the construction of a new home, and they may not work as well, depending on the quality of work. Visit our Home Energy Advisor to see the potential savings from retrofiting your house...
What information can you give me on air-to-air heat pumps for the home?
Air-to-air heat pumps are basically air conditioners with the capability of running backwards in the wintertime. During the summer, air conditioners remove heat from your house, and shunt it outside. Air source heat pumps have a switching system that allows them to operate in reverse in the winter, removing heat from the outside air, bringing it into your house. Since air source heat pumps are not actually creating heat, but moving it from one place to another, they are less expensive to operate than electric resistance heaters, and depending on the costs of both natural gas and electricity, possibly gas furnaces as well.
Gas is sufficiently cheaper than electricity that an air source heat pump is generally more expensive to operate than gas furnaces. For those who are unable to receive gas services, the air source heat pump is probably the best bet.
One drawback to air source heat pumps is that they get less efficient when the outside air temperature gets colder. It is harder to extract the residual heat from colder air. Electric resistance furnaces become more cost effective when the average winter air temperature is below 30°F.
Another option is ground- or water-source heat pumps. These units extract heat from the ground by using an underground loop, or from water, through an open or closed loop. Since the average ground temperature hovers around 50°F year round for most of the United States, this is a very good source for heat in the winter, and cooling in the summer. Although putting in a ground loop is expensive and repairs can be costly, ground-source heat pumps are good options for some people.
For further reading, see the section on heating in our Librarian:
Does it pay to run a large duct from the outside of the house to the furnace to provide outside air for combustion? Contractors provided a passive supply of air along with the installation of our new furnace in St. Paul, Minnesota and we are wondering if it is worthwhile with a 30-year old furnace in Macomb, Illinois.
Most older furnaces are provided with combustion air from ducts leading into the furnace closet, or from openings to either the crawlspace or the attic, depending on the furnace location. To determine whether your furnace needs additional combustion air, look into the furnace closet. Using a flashlight, look at the walls and ceiling in the closet. You should see one of a couple of things. There might be registers (or simple openings) to what look like ducts on the walls near or in the ceiling, or near the floor of the closet. Alternately, the ceiling of the closet might be open to the attic of your house. If any of these are the case, your furnace is getting sufficient combustion air, and you do not need to worry.
If you do not see any ducts or openings, then check the door to the furnace closet. As long as the door is undercut by about 3/4 to one inch, your furnace can get plenty of air. Again, no problem, unless your house is very airtight.
The reason to provide extra combustion air is to prevent a backdraft where combustion gases are coming into the house rather than exiting through the flue. This is a very dangerous situation when it occurs, and can cause serious health problems, as well as death from carbon monoxide poisoning.
The fact that the furnace is thirty years old, leads me to believe that it should get plenty of combustion air, unless you have had problems with backdrafts in the past. Most older houses have a lot of air leakage through the walls of the house, sufficient to provide combustion air for furnaces, water heaters and fireplaces. If you have recently altered the house in a way that could reduce air leakage, such as installing wall insulation where previously there was none, or if you have had the house wrapped with Tyvek when replacing siding, you might consider adding a duct to provide combustion air. If your water heater is gas, and inside the house (rather than in the garage), check the air supply for its combustion as well.
This is more of a safety issue than an efficiency issue, so there won't be substantial monetary savings from providing outside air for combustion.
How can I tell if the contractor who is putting in a Goodman furnace is gouging me on the price?
What you're experiencing is a major problem with large appliances that require contractors for installation. Scary as this may seem, there is no price list available in this type of situation. Prices can vary widely by contractor or area. It is even difficult to get wholesale listings from manufacturers, since they may charge different amounts to different contractors. If a local home repair store carries the brand of furnace you are interested, you can get a general idea of the unit cost. Unfortunately this does not cover labor and installation costs.
The best way to figure out if a contractor presents a reasonable bid is to shop around. Before you sign a contract, get several bids from different contractors, five to seven would be ideal. For each bid, get all of the details in writing, and make sure the bids are comparable. Be careful if one of the bids is dramatically lower than all of the others. Make sure that the same work is actually being bid on. In addition, check with the local Better Business Bureau and find out if any of the contractors have complaints against them, and get details about complaints if you can.
There are a lot of good contractors who do quality work for reasonable prices. However there are also a lot of contractors doing shoddy work, and contractors who overcharge consumers because they can.
How do I decide whether I should reinstall a heat pump or convert to natural gas? We have been very unhappy with our current heat pump after one year in our new Reston, VA home (age 14 years).
A decision about whether to reinstall a heat pump would be easier if you knew why you were unhappy with the performance of your current heat pump. It could be because the heat pump is really not meeting your heating needs, or because you have expectations based on previous experience with other types of furnaces.
If your heat pump runs constantly, and your house is still uncomfortably cold, you might want to consider converting to natural gas, provided your heat pump is fully charged, and operating properly. Have your heat pump serviced to confirm the unit is fully charged with refrigerant, and has no other mechanical problems. Since air-source heat pumps rely on the outdoor air for the warmth used to heat your house, they are not the optimal choice in really cold climates. In some areas, winter air temperatures are so cold that the heat pump is unable to extract sufficient heat your house up to the thermostat setpoint, even with continual operation. When the outside air is below 35°F, air-source heat pumps operate below their rated efficiencies, reducing your savings compared to a more efficient unit. You might want to consider switching to a ground-source heat pump in this circumstance. Ground-source heat pumps take heat from the ground, or from a water source such as a lake or well. These areas typically have very stable temperatures (approximately 50°F) year-round, enabling the heat pump to work at optimum efficiency.
Its also possible that you might be dissatisfied due to misunderstandings about the way that heat pumps operate. Understanding how they work, and ways to work around their limitations can alleviate the problem.
Heat pumps produce lower quality heating than a furnace, maintaining warmth in your house by cycling frequently. The air exiting a heat pump is only warm, when compared to the heat emitted by a furnace. This lower temperature makes it difficult for a heat pump to be "turned on," heat up your house, and then be "turned off." Many people are accustomed to using furnaces in this manner. They are often disappointed with the performance of a heat pump. Heat pumps heat best when they are connected to a thermostat kept at a steady temperature, and allowed to cycle on and off frequently, maintaining a constant temperature.
If you've been accustomed to the flow of hot air from your furnace, you may be disappointed in the air temperature coming from the heat pump. Once again, this is because of the lower temperatures. It doesn't mean that your house is colder, overall. However, areas near registers may now seem drafty, because the exiting air is closer to your body temperature. Placing deflectors on registers to direct air away from places that you linger in will help.
If I shut off my heater or air conditioner when I'm gone from the house, doesn't it cost more to heat or cool the house back to the right temperature once I return?
The rate of heat transfer from your house to the outside, or vice versa, is dependent partly on the temperature difference between your house and outside. More heat is transferred when the difference is greater, so it takes more energy to keep your house at 72°F when it is 40°F outside than to heat your house back up to 72°F after you return.
With air conditioning systems, the equipment runs at peak efficiency when it operates for long periods. Cooling your house back to the comfortable temperature will use less electricity than the unit would use cycling on and off for short periods to maintain the set temperature. If your house takes too long to get back to a comfortable temperature, you might investigate getting a programmable thermostat, and set it to start heating or cooling your house an hour or so before you return. You could also set the thermostat back, to a lower, for heating, or higher, for cooling, temperature while you are gone, rather than turning it off completely.
Will putting in a digital thermostat help out on the ac consumption?
Yes, digital thermostats will normally reduce the energy used for air conditioning or heating by quite a bit. Programmable thermostats, not always digital, save money by turning the air conditioner to a higher setting (or heater to a lower setting) when no one is present in the house, or in the evenings when it is cooler. You can achieve the same savings without the programmable thermostat, but you would have to remember to change your thermostat every day when you leave the house, and turn it off every night when you go to bed. In addition, if you are using the thermostat to regulate your heater, you would wake to a cold house. The programmable thermostat does all of the remembering for you once it is set. A sample of a heating schedule you might program into a thermostat is:
| Wake up | 6:00 am - 9:00 am | 72°F |
| Leave | 9:00 am - 5:30 pm | 50°F |
| Evenings | 5:30 pm - 11:00 pm | 68°F |
| Sleep | 11:00 pm - 6:00 am | 50°F |
This way your house is always comfortable and you can save money on heating. You can make a similar schedule for air conditioning.
| Wake up | 6:00 am - 9:00 am | 75°F |
| Leave | 9:00 am - 5:30 pm | 80°F |
| Evenings | 5:30 pm - 11:00 pm | 75°F |
| Sleep | 11:00 pm - 6:00 am | 78°F or off |
My central air conditioning blows cool but not cold air and seems to be always running. I have heard that dirty coils in the condenser could cause this. Is this something I can check and clean myself and, If so how would I go about it?
There are a couple of things that can cause the symptoms you describe.
Things to do:
Ducts can be disconnected by a simple bump when storing the luggage away in your attic. A disconnected duct wastes energy by heating or cooling your attic or crawlspace instead of your home. In addition, pollutants and dust can be sucked into your house through a disconnection. If you find a disconnected duct, reconnect it with sheet metal screws and mastic for metal ducts or zip-ties and butyl-backed tape (not duct tape, which degrades rapidly) for flexible ducts. If you wish you can hire contractors to go over your entire duct system sealing it for leaks, or do it yourself. This will help lower your heating and cooling costs.
We are purchasing a new air conditioner and the contractor mentioned something about "duct sealing." What is this and would this be a good thing to do?
The duct systems in most houses leak. Leaks can be as small as pinholes or tiny cracks and as large as completely disconnected ducts. However, any leak is wasteful, since it allows conditioned air to escape into your attic or crawl space. Duct sealing is a process of stopping leaks by pressurizing the ducts with a tracer substance, such as smoke, and then physically locating and patching leaks. A new aerosol method is under development at Lawrence Berkeley National Laboratory, which would seal ducts without the need for a laborer to manually reach and plug every leak.
You recommend insulating attic access doors; how do I do it? I can see the light through mine even when its closed!
Keep in mind that you are actually trying to address two problems there: heat loss and air flow. So you need to both insulate and air seal. The U.S. Department of Energy offers a detailed web page with more information.
On windy days I can feel drafts coming from the baseboards in my house. How can I stop these drafts?
The best way to prevent drafts in your house is to stop the air from penetrating the outside shell. Typically, air comes in through cracks along the foundation, near the exterior of the chimney, water faucets and electrical outlets, and along doors and windows. A good quality outdoor caulk will prevent air flow through these areas. For cracks larger than 1/4 inch, fill the gap with insulation or some other filler material, then caulk over the area.
Some parts of my house are never comfortable, no matter what I do. The rest of the house is fine, but one room is always too hot or too cold. Why is that, and what can I do to fix it?
Your problem is probably caused by disconnected or leaking ducts. This problem reduces the amount of conditioned air reaching a room. Disconnected ducts waste the energy intended for heating or cooling your attic or crawlspace, and contribute to indoor air pollution by increasing dust in the house or by drawing exhaust fumes from gas appliances back into the house.
Ducts can become disconnected or develop leaks in many different ways, such as accidental bumping, when someone moves around the ductwork. In addition, over time duct tape can degrade and ducts, especially those under the flooring of houses, can simply fall apart. Disconnected ducts are not only a problem in old housing-the ducts in new houses are often accidentally disconnected during construction. Have your ductwork inspected and make sure any connections are airtight, and held together with zip ties, or sheet metal screws and mastic to create a good seal.
I've heard that if we make our house too tight, the air won't be healthy to breathe.
If you're building a new house from scratch, this can be a real concern. Your architect should be able to design adequate ventilation as part of the plan. But if you have an older house, there are usually so many ways for air to get into your house that tightening up will save you energy but still leave an adequate supply of fresh air.
I am trying to find some information concerning attic fans (i.e. the pros and cons).
Mechanical ventilation is typically accomplished with a small fan located on a dormer vent. These fans are usually hardwired into a house's electrical system and are controlled by a thermostat. They usually draw electricity in the range of 2 to 70 kWh per year, depending on local weather conditions and your attic temperatures. The cost of this energy of course depends on the local price of electricity.
Approximately one square foot of ventilation is recommended for every 150 square feet of floor area. You would have to check the specifications of the particular fan you are considering to determine the equivalence to regular vents.
One alternative to mechanical venting is a combination of ridge vents and eave or soffit vents (see diagram below). Ridge vents run along the ridge of your roof, and eave and soffit vents are located at the base of the roof. With this combination, the natural convection of the hot air in your attic powers the venting. In addition, because of the locations of the inlet and outlet vents, virtually the entire attic space is vented, reducing the likelihood of pockets of hot air.
Mechanical venting, can provide adequate venting for your house, but is dependent on electricity. Other forms of venting, such as the ridge/soffit combination mentioned above, provide superior venting, but requires modification of your roof to install. If you were already planning on installing a new roof, you should seriously think about a ridge/soffit combination.
I keep getting ads in the mail for companies offering to replace our windows with "energy-efficient" windows. How much can these save me?
For a typical house, windows can account for 10% to 30% of the heating and cooling bill. Upgrading from single-pane windows to 'superwindows' can cut this in half or better, so savings of up to 15% of your current bill are reasonable. Depending on where you live, this can amount to $50 to $100 per year. Spread over 20 years, this means $1,000 to $2,000. You can get a better estimate by running our Home Energy Adviser.
But the big thing to keep in mind is that many of these window replacement firms use simple double-pane windows; for just a little more money up front, you can save a lot of energy over the long haul by asking for windows with special low-e coatings and inert gases, such as argon or krypton, which fill the space between the panes of glass. Some manufacturers even offer 'superwindows' with one or two thin plastic films sandwiched between the panes of glass. These windows can reduce energy loss to one-half as much energy as standard double-pane glass, and one-fourth as much as single-pane glass.
Ask the salesperson to tell you the "U-value" of the windows they offer. This is sort of like the miles-per-gallon rating for new cars; an independent agency performs these ratings. In this case, lower is better: the best you can buy today have U-values of around 0.2, while a typical double-pane window is around 0.5.
Note: One thing to keep in mind is that retrofit windows may not be very cost-effective. The cost of replacing windows in existing housing is quite expensive and you typically get payback periods of 20 to 30 years or more. However, retrofit windows will make a substantial difference in the comfort of your home, which could well be worth the cost. Also, double-paned windows typically add to the value and saleability of your home if you put it on the market. In new construction, the labor costs are equivalent regardless of the quality of window installed, so buy the best you can afford.
Over the winter, fog appeared between the panes of my double pane windows, but during the summer it went away. Why did this occur?
Fog, or condensate, on multiple pane windows is caused by moisture between the glass layers. When it is cold, the moisture condenses on the outer glass pane, very much like water beading up on the outside of a cold glass of water.
There are several reasons why the condensate might have disappeared. One is that your windows might be double-paned, but not sealed. These windows generally have a small air tube connecting the air space between the glazings to the outside. If this tube becomes completely or partially blocked, perhaps by snow or mud, condensation would build up during the colder months. In this case, the blockage could have cleared during the warmer weather. Check for the presence of an airtube in your windows and make sure it is unobstructed. If your double pane windows have been installed for a long time, it is very likely that this is the problem.
If you have sealed windows, it is possible that the amount of moisture that leaked into the airspace is very small, small enough to remain in the air as water vapor when the air is warmer. If this is so, you can probably expect it to return next winter.
Another possibility is that the leakage is very large. Once the weather warmed up, the moisture equalized with the outside air, clearing up the fog. In either case, check the warranty on your windows. Most sealed double-paned windows have some form of warranty against leakage. A lot of warranties have a limited life, but some are lifetime. Generally, once the seal on a window has leaked, there isn't much you can do to repair it, and you will probably have to replace the window.
Is there any rating for electric water heaters? I would be interested in knowing the ratings for brands.
There is a rating for water heaters in general. Appliance standards require that electric water heaters achieve a certain number of points on the scale. The rating for water heaters is called the Efficiency Factor (EF), based on the use of 64 gallons per day. The national appliance standards require the following EFs for electric water heaters:
| Size | Efficiency Factor (EF) |
| 30 gallon | 0.91 |
| 40 gallon | 0.90 |
| 50 gallon | 0.88 |
| 60 gallon | 0.87 |
The most efficient electric water heaters have EFs around 0.94 to 0.96.
This Energy Factor translates into an estimate of annual consumption, once again based on the assumption of 64 gallons/day. This estimate, in kWh/yr is the number you will see on the yellow Energy Guide sticker. We have a list of the most efficient water heaters, compiled by the American Council for an Energy Efficienct Economy (ACEEE) in our web site at:
Here are some general trends in water heater efficiency:
1. Larger tanks tend to be less efficient than smaller tanks, because they have more surface area through which to lose heat.
2. Electric water heaters are more efficient than gas or propane heaters because the latter lose heat from the exhaust gases in the burner. As a result, some of the heat produced just goes up the chimney.
3. Heat pump water heaters are more efficient than electric water heaters because they don't generate the heat used to make the water hot, they just move heat from one place to another. They are also much more expensive than other types of water heaters.
What is the average setting on an electric hot water heater?
Typically, water heaters have three temperature settings: high, medium and low. These settings correspond roughly, depending on the age and condition of the water heater, to about 160°F for high, 140°F for medium, and 120°F for low. Most people have the temperature set to medium, or around 140°F. If it is not already there, you should consider lowering the thermostat to 120°F, which will save you about 3 to 5% in water heating costs for each 10°F reduction. You might want to consider a timer for your water heater that turns it off when not in use, say between 10 or 11 pm to 6 am. This would also lower your water heating costs by cutting down the amount of energy lost through the walls of the tank during the night.
If you turn your hot water heater off during the day, won't it cost more because you then have to heat up the whole tank and wait minutes before taking a shower? Also, isn't it kind of an inconvenience?
No, it uses more energy to heat water up and keep it hot than it does to heat it up once, because heat is lost through the sides of the tank. The same energy is required to heat up the water regardless of whether it is heating a little bit at a time, or all at once. Heat losses through the tank walls or pipes simply add to the cost.
If you turned your hot water heater off during the day, it would be an inconvenience any time you wanted to use it. Putting a timer on that turns it off or to a lower temperature during the night generally poses no inconvenience at all. These timers can be set to turn the heater back on an hour or so before you get up in the morning, so your hot shower is ready to go when you are.
We're putting in a home office. Do computers and fax machines really use that much energy?
If you use a PC built before 1994, it can use around 200W, and a laser printer can use around 100W; if you leave this on 24 hours per day this can add up to $225 a year. But many PCs and printers built since 1995 have "ENERGY STAR" capabilities, which save a lot of energy when you make sure they are turned on.
Should I leave my computer on all the time, or turn it off when not in use?
Only you can decide whether to leave your computer on, or turn it off. There are reasons for each strategy. While I can't say for sure about your specific system, the typical computer draws around 100 Watts, or 2.4 kWh/day. Multiply this by your electricity rate per kWh to come up with the cost per day. Leaving a typical computer on all the time would cost about 21¢/day (2.4 kWh * 8.6¢/kWh). This may not seem like much but it adds up to close to $75/year. If you don't have any particular reason to leave your computer on, that money would be needlessly spent.
There are reasons to leave your computer running 24 hours per day. One is if you use it as a web server, or if you use it to receive faxes 24 hrs/day, for your at-home business. If these do not apply to your computer, then it makes sense to turn off your computer when it is not in use.
Don't worry about wear on the computer from turning it on and off repeatedly. This was once a problem in the early days of personal computers, but now your computer undergoes more wear from running constantly than from being turned off when not in use.
I have a Powermac 8500/180 and am wondering what I can do to lower its energy use. You mention that some new computers have Energy Star compatibilities. My computer was made in 1996. Please help, my energy bill skyrocketed the month I plugged the computer in.
From the Apple menu, select Control Panels and then "Energy Saver." This lets you set your energy use features-how quickly it turns the monitor off after the computer has been idle, and how quickly it allows the disk drive to spin down to a stop. Start by setting these to blank the screen after five minutes of inactivity, "Sleep" after 15 minutes, and "Shut Down" after one hour.
If you have been using a screen saver, you might reconsider. It's fun to look at, but your are paying for that entertainment.
The 8500 has a maximum power consumption of about 200 W, and the monitor an additional 100 W. (The *maximum* the 8500 box itself can draw is 200 W, if there are a lot of high-powered cards installed; usually it uses much less). In "sleep" mode, it draws less.
With this information, you can figure out that the worst-case consumption should be something like 300 W x 24hr/day = 7,200 Whr/day, or 7.2 kWh. If your electricity is 10¢/kWh, this costs a maximum of 72¢/day, or $21/month.
Do you really think my answering machine uses more electricity than my computer? Did I do something wrong or is your database totally bonkers?
Surprising though it may seem, most answering machines use more energy than most computers. Here's how it breaks down:
| Answering Machine | Computer | |
| Energy Consumption | 5 Watts | 200 - 250 Watts |
| Typical Usage | 8760 hrs (always on) | 10.5 hrs/month or 126 hrs/yr |
| Annual Consumption | 43.8 kWh/yr | 25 to 32 kWh/yr |
The equation to derive the annual consumption is:
Annual consumption = Energy Consumption (Watts) * 1 kWh per 1000 Watts * Usage per year
Obviously there are assumptions about typical usage and typical consumption. The numbers used in the Home Energy Advisor are national average numbers, which may not accurately reflect your particular use and computer system. If you work at home and use your computer every day, the module will not portray the energy consumed by your computer accurately.
This type of assumption is present throughout the Home Energy Advisor for end-uses that do not typically result in a significant portion of household energy consumption. Simplifications like this one shorten the time required to enter inputs, without greatly reducing the accuracy of the model.
My utility company tried telling us to use more fluorescent lights to save energy, but I hate how fluorescent lights flicker when you turn them on and then make that annoying hum. And they make everything look sort of blue and cold. Isn't there anything better?
Yes, there's a new kind of fluorescent technology, called "electronic ballasts." You have to ask your lighting store specifically for them. Unlike the older magnetic or transformer ballasts, electronic ballasts eliminate that annoying hum and flicker and allow the bulbs to emit light which is a much better. And instead of slowly getting brighter as they warm up, they turn on instantly.
Fluorescent bulbs are available now that have better color. When purchasing bulbs there are two things to look for: the Color Rendering Index (CRI) and the Correlated Color Temperature (CCT). The CRI rates the ability of the bulb to render an object's true color when compared to sunlight. Look for lamps with a CRI of 80 or higher. The CCT refers to the color objects emit when heated to a certain temperature on the absolute temperature scale (Kelvin). The lower numbers correspond to reddish color and the higher to blue-white color. For color similar to incandescent lighting look for CCTs around 2700.
| Lamp | CRI | CCT |
| Incandescent | 90-95 | 2700 |
| Cool-White Fluorescent | 62 | 4100 |
| Warm-White Fluorescent | 51 | 3000 |
| Compact Fluorescent | 82 | 2700 |
| Halogen | 95+ | 2950 |
Is it better to turn lights off when you leave the room? I heard somewhere that it uses more energy to turn lights off and on than to leave them running.
That used to be the case with fluorescent lights, but advances in technology, especially in ballasts, have resulted in lights that do not use appreciably more energy to start up. Turning fluorescent lights on and off does slightly shorten the lifetime, in hours, of the bulbs, but you will have to replace the bulbs less frequently if they are not running all day long. Incandescent lights do not require additional energy to start, in any event, so if you are leaving the room for more than a couple of seconds, you will save by turning the lights off, for both fluorescent and incandescent bulbs.