* All Costs assume electric appliances, billed @ $0.08 per KWH.
Gas prices are assumed billed at $1.00 per Therm.
(The gas furnace and range energy useage is rated in Therms -
all other appliances are electric, including the television.)

See Hot Water Costs for information about water heaters, and Comparisons for an energy comparison of gas vs. electric furnaces.

**** "Per Month" Usage Estimates are based on typical family of four.

If your browser doesn't properly display it, ° is the symbol for degrees.

Compare the costs of using a microwave and toaster-oven to prepare a typical TV dinner - 2 cents vs. 8 cents - a 4X cost increase! Then compare the range oven @ 12 cents, a 6X cost increase!

Light bulbs are not included for several reasons, an hour or two usage costs less than one cent, and no one leaves a light on for 20 hours at a time, so increasing the usage to 20 hours wasn't a clear example. Nor would it be any clearer keeping the time at an hour or so, and increasing the number of bulbs involved to 20. Giving a monthly estimate of a bulb is just too inaccurate, so no bulbs were listed. But you can easily compare values yourself - just remember 1 kilowatt hour is 1000 watts for one hour. If you burn one 100 watt bulb for 2 hours, you used 200 watt/hrs or 0.2 KWH. Of course if the bulb is fluorescent, you get a lot more light for the same wattage! See Fluorescent/Incandescent Wattage

** Furnace: for this example, the electric furnace is not a heat pump, but a standard unit with electric strips. A heat pump unit would be more efficient at outside temperatures above 40°F, and the same efficiency for colder days. During the times the heat pump is allowed to operate, it produces about 90° air, certainly enough to warm the house, but colder than body temperature. Warm your hands elsewhere.

On the other hand, gas furnaces more than 10 years old, and some of the currently less-expensive models, have efficiencies of 70 or less. So with 80000 BTU of heat at the burner, 30% may go up the exhaust flue, leaving you with about 56000 BTU of effective heat. So, the example shows the (70%) gas furnace running 2/3 hour to provide the same full 80000 BTU equivalent to the house. With gas furnaces, typical air output temperature is 130° or so. Under KWH usage, the number of gas THERMS are listed. The gas cost is assumed @ $1.00 per therm.

Also the gas furnace may have a pilot light that stays on constantly. More expensive models have an electronic ignition to light the burner each time it's needed, notice the monthly savings.

*** A/C - the A/C is electric, while gas A/C units exist, they are rare, like gas TVs. Some people leave the thermostat FAN switch ON to stir the air (much like a very efficient ceiling fan) - the costs are listed. Another factor to consider with the A/C is the number of little heaters you have scattered around the house, opposing the work of the A/C unit. These heaters are incandescent bulbs. About 90% of the energy used by an incandescent bulb is radiated as infrared heat - only 10% is visible light. So, three 100 watt bulbs represent about 270 watts of heat, or about 922 BTUs which is about 1/5th the maximum cooling capacity of a small window A/C. Using three 20 watt fluorescent produces the same amount of light yet reduces that A/C load to 123 BTUs, saving 799 BTUs or 0.234 KWH, or about 2 cents every hour! And that's just the A/C savings, the direct energy savings are 240 watts, or another 2 cents per hour! Not only do you save from drawing less power for the lights, you put out less heat for the A/C to remove and save money that way also!!

This is important, let's recap.
By switching from three 100 watt incandescent bulbs to three 20 watt fluorescent bulbs, you save 2 cents of power to the bulbs and 2 cents for the A/C to remove the bulb's heat. That's a savings total of 4 cents per hour, and the total cost to power the fluorescent bulbs is about 1/2 cent per hour (60 watts = 0.06 Kwh X $0.08 = $0.0048)!

Total cost to power incandescents, 4.5 cents,
total cost for fluorescents, 0.5 cents!
Do the math.

The typical (gasoline, diesel, natural gas - petroleum-powered) car has a battery to start the engine. The battery does not 'run' the car, it merely starts the engine. The alternator 'runs' the car by powering all the electrical systems, and recharges the battery as well. (Click for detailed battery information and the definitions of some of the terms used in this section.)

A typical car alternator produces between 60-90 Amps. Before 1970, most cars used generators. The major reason for the change to alternators was the alternator's ability to provide near maximum power at lower engine speeds, i.e. in heavy traffic. The mechanical regulators used with the old generators often over-charged the battery at highway speeds, and under-charged in city driving, causing many battery failures. Over-charging and heavily discharging caused the water to 'boil' or 'out-gas' from the battery's cells, requiring frequent refillings.

Notice the current needed to start the engine. Say it takes 250 Amps to crank, and you do it in 4 seconds. For an 80 Amp alternator to replenish the power takes at least 13 seconds, IF several conditions are met. First, there are always other devices sharing the alternator's output - the engine computer, amd perhaps the sound system, the interior heater/AC fan motor, and the lighting system. The second requirement is the battery must be able to accept the charge that quickly. Many rechargeable batteries are meant to be charged at roughly 1/10th the normal output current, and increasing the time to 40 seconds is still quite reasonable.
With all the accessories and lights on, there may be little surplus current to recharge the battery after cranking the vehicle. The situation worsens if after-market electrical equipment has been added. What happens when drawing more power than the alternator can provide? Simple - the excess is drawn from the battery - and the dashboard emergency warning, 'Alternator' or 'Battery' lights. Naturally, this can't go on forever.

If the excess is not too large, the battery can supply the power for a while - perhaps an extra 5 Amps all night long. Then during the next day, the savings from NOT using the lights may allow the alternator to slowly recharge the battery, although it may take all day to fully recharge. Don't forget, every crank causes another substantial loss!

When a battery must be 'jumped' to start the car, it may mean the battery is defective, or that it was simply discharged. Once cranked, the alternator may need several hours of charging to fully recharge the battery. Within 10 minutes or so, the alternator should charge the battery sufficiently to re-crank the engine later.

A battery with a RC (Reserve Capacity) of 90 minutes, indicates the battery can supply 25 Amps for 90 minutes. Should the alternator fail, this provides perhaps 90 minutes of power to reach a repair facility. Although if your vehicle was already drawing more than the alternator could produce (90 Amps, for instance), then the battery might only be able to provide 10-15 minutes of additional drive-time.

Turning off all the unncessary equipment, including the stereo and heating/AC fan saves a substantial amount of power.

And since the lighting system typically draws 20+ Amps., daylight range is much further. Only the engine computer and few other internal systems powered might have a current draw of less than 10 Amps, which would more than double the 90 minute emergency drive-time!

Remember, just one crank might use 10-20 minutes of your emegency reserve time!

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Parasitic Discharge is a term for the power drawn from the battery while the vehicle is not used, for things such as the radio memory, engine computer memory, and theft deterent systems. This value should not be greater than 35 milliamperes (0.035 Amps.), else the battery may not last the typical maximum of 4 weeks between crankings. Ambient temperature greatly affects the length of time a vehicle may sit without cranking.

See Illumination Conversions for more information about light.

* CCF X BTU Factor are natural gas terms and may appear on your bill. (CCF = 100 Cubic Feet of gas.)
The BTU Factor is determined by the gas supplier, depending on the exact energy content; 1.035 is a typical value. Using those values,
1 therm = 100,000 BTU or 0.966 CCF

** SEER or EER = 'Seasonal Energy Efficiency Number or Energy Efficiency Number (SEER is the BTU/watt for a peak day -- EER is for the seasonal average day)
They are ratings placed on appliances indicating the BTUs produced (heating) or removed (A/C) divided by the wattage necessary. The more the BTUs per watt, the more efficient the product.
(Note: watts = volts X amps. Most often, window A/C units are marked with volts and amps, rather than in watts. Do the math.)
Ex: 12,000 BTU A/C draws 10 Amps at 115 Volts. (12,000 / (10 X 115) = 10.4 EER rating.
(Also see Degree-Day)

*** COP = Coefficient of Performance - older term used for efficiency before EER.
Example from above: 12,000 BTU A/C draws 10 A at 115 V. (12,000s BTU / 1.150 Kwh, 1.150 Kwh = 3925 BTUs, so 12000 / 3925 = 3 COP)

**** Sunlight = 704 watts / sq. m. at the earth's surface, with no clouds, no pollution, direct noon summertime sun. At the top of the atmosphere, the power is 1380 watts, but 30% is reflected back into space, 19% is absorbed by the atmosphere, leaving 51% reaching the earth's surface.

Insolation is solar radiation energy from the sun. Insulation protects your house from insolation! See R-value

Important: Calories are defined as small heat units and large heat units.
Medical scientists use small units, while engineering science, biologists, and dieticians use the large units. Elsewhere on this site, all references to 'calorie' are to the kilocalorie. It is recommended to use the Joule term with SI units to prevent confusion.

Notice the Metric systems use a mass of water and the English system uses the weight of water as the standard unit. (See Standards Compared)

Water serves as a standard substance for defining units of measure.
The weight of air is measured at the standard of 32° F.

STP Conditions are with standard temperature and standard pressure.
Most precise measurements are done under STP conditions, for air, a standard temperature is 69.8° F and standard pressure of 29.92" Hg. or 760 mm. (Mercury).

k = BTU / hr./sq.ft./in. thickness / degree F.
k is the reciprocal of the R-value. (1/ R)

Tog is an insulation measurement for clothing, bedding, carpets, etc.
A clo is the insulation needed to keep a resting person warm in a 70°F room.

Insolation is solar radiation energy from the sun. Insulation protects your house from insolation!

Even the Carbon Zinc battery has about 60% of its original capacity after 5 years on the shelf, but could not power a flashlight with more than a very weak beam of light.

For the Gel Lead and Lead Acid rechargeable cells, "Life" is the useful lifetime of the cell, and those cells must remain charged, even while stored! NiCads should be stored uncharged. The 500 charge/discharge cycles specification of NiCads can usually never be reached during the 2 year 'lifetime' of the cell, so don't be concerned about the number of recharges.

Don't confuse the estimated life of the NiCad cells (2-3 years) with usefulness. The typical NiCad cell loses 10% or more per week and up to 30% of the charge per month, giving up as much as 90% in 8 weeks! If they weren't rechargeable, you couldn't pay people to take the things.

(Read the notes after the other battery topics.)

* Cell cannot supply this current for any length of time!

Currents in parenthesis are the low and high discharge rates. At higher discharge rates, the Amp-Hr rating is naturally less.

All ratings are typical for the size and type of battery. Premium batteries usually have better specifications (unless near the end of their life...), and economy batteries may have better or worse specs. It depends.

The actual ratings for Button cells as well as the 6 volt and 12 volt batteries vary depending on the model and SIZE of the particular battery. For the 6 volt battery, the model was the typical "lantern battery", for the Carbon-Zinc and Alkaline. While the Gel Lead and Lead Acid values show a range of Amp-Hr ratings from 7 AmpHr for the Gel Acid up to about 100 AmpHr for the Lead Acid batteries.

(Read the notes after the other battery topics.)

The Maximum Current Ratings are almost a short circuit condition. Of course this can't be a normal mode for any battery, but often occurs briefly in devices powering motors or inductive loads.

(Read the notes after the other battery topics.)

Internal Resistance is precisely that. It's internal to the battery and it causes a resistance to current flow. A "dead" flashlight battery is a good example. Most times, measured with a meter (while the battery is not under a load), it might measure anywhere from 0.5 to maybe 1.3 volts, yet in the flashlight, it seems dead. The reason is the internal resistance increases with age, decreases with temperature, and increases with the number of charge cycles of rechargeable cells.

A typical 2-cell flashlight bulb, the PR-2, draws 0.5 Amp, and has about 5 ohms of resistance when lit. The Carbon Zinc D cell has about 0.3 ohms internal resistance when new, and when powering a PR-2 bulb, each cell drops 0.15 volts or 0.3 volts total, leaving about 2.7 volts to operate the bulb. But when the battery's life is gone, the internal resistance increases to 20 or 30 ohms or higher. Consider the bulb's resistance is only 5 ohms - adding an additional 30 ohms means only 14% of the battery voltage gets to the bulb, the rest is dropped across the internal resistance inside the battery - the bulb may not even glow!

The internal resistance also plays a role when trying to charge a cell. If the resistance is high, when the charging voltage is applied to the battery, the battery terminals instantly (or quickly) rise to the fully charged voltage level, indicating no further charging is necessary. Yet most of that voltage is dropped across the internal resistance and the battery can only charge very slowly, if at all - perhaps only at 100th the normal charge rate, making the battery useless.

(Read the notes after the other battery topics.)

See Energy Equivalents for more information comparing light and energy.

Luminous Intensity is the brightness of a source, previously measured in candles, now in candelas. The intensity depends on the direction from which it is measured. The average power was previously called spherical candlepower, now * MSCP, Mean Spherical Candela Power. Most bulbs produce light in a spherical direction. LEDs are different and are measured in ** MCD, MilliCandelas (1/1000 MSCP, but measured only in the major axis of an LED's beam).

Luminous Flux is the actual energy in the visible spectrum, measured in lumens. Most of the energy from a bulb is not visible, but in the form of heat; about 90% for most incandescent bulbs.

Illumination is the density of the luminous flux on a surface, or how brightly lit a surface appears, measured in lumens per sq. ft. (flux per area).

A 100 W. Incandescent bulb produces about 130 candela. With no reflector, what Illumination will a bare bulb produce 2 feet from the bulb (when the bulb is on)? The illumination drops inversely as the square of the distance (meaning if the bulb were 2 ft from the surface, it would be 2 ^ 2 or 4 times dimmer.) 130 candela / 2^2 = 32.5 lumen / sq. ft.

*** In the 1920's the accepted work surface lighting was only 5 to 10 footcandles (lumens / sq. ft). By the 1960s, it reached over 100 footcandles. When color TV was introduced, it increased the requirements on a football field to 200 footcandles or more.

An EPROM computer chip, without the protective cover over the erase window, could be left in full sunlight for at least a week before being erased. Under a typical office fluorescent fixture, it could last about 3 years.
(A non-defective chip.)

Daylight and Sunlight are not the same. Sunlight is the light from the Sun. Daylight is the light from the Sun mixed with the light from the sky.

By warned different manufacturers of similar bulbs may have widely varying color temperatures, and the exact line voltage usually has an effect (100 or 120 volts?)

Most digital cameras do a remarkable job guessing the correct 'white balance' adjustment, that is, automatically compensating for whatever strange illumination values are present and then adjusting so the colors appear natural. Once in a while, an unusual background color or pattern may cause a totally unpredictable picture.

If the color temperature (K) is doubled, radiated energy increases 16 times!

°F. = Fahrenheit and °C. = Celsius aka Centigrade

* Water at sea level and 30 inches barometer

** A degree-day allows measurements of how much energy it takes to heat or cool a home on a given day. It's a 15 degree-day, if the average temperature for the day is 80°, (80-65 = 15). The number of degree-days for the month can be summed and compared with your actual energy usage. Often the weather pages on websites of local TV stations provide the local degree-day information.
(Also see SEER)

Pressure changes the boiling point of water, where at 30 psi, it increases to 272° F (133° C).

To convert from degrees F to C, subtract 32, multiply by 5, divide by 9
To convert from degrees C to F, multiply by 9, divide by 5, add 32

There are 4 major temperature scales:
Fahrenheit (F) and Rankin (R), and Celsius (C) and Kelvin (K).
The R and K scales are 'absolute', they both equal 0 at absolute zero -
(-460° F and -273° C), and are convenient to use with cryogenics.
You must use a formula to convert from F to C or from R to K because
the heat change of 1 degree C or K = 1.8 degree F or R.
To convert from F to R, merely subtract 460. From C to K, subtract 273.
F and R are incremented exactly the same, with R offset by 460 degrees
C and K are incremented exactly the same, with K offset by 273 degrees

F = C @ -40° and R = K @ 0° (absolute zero)

Even though steam and boiling water are at almost the same temperature, steam burns far more severely because it contains 540 more calories per gram than the boiling water. The boiling water only needed 100 calories per gram to raise its temperature from freezing to boiling!!

Liquid heated in an oven (or microwave oven) may become 'superheated', higher than 212° F, yet it will not boil until it's moved and the surface can cool slightly, then it will violently and explosively boil.

For Color Temperature of Light, see Light Color Temperature

Super trick to wow your camping buddies: Listen for a cricket,
count the number of chirps the insect makes in 15 seconds, add 40, and you've got the temperature in °F!!

* AWG = American Wire Gauge
** mil = 0.001 inch or 0.0254 mm. or 25.4 um. (microns)
*** circular mil = cross-sectional area of the wire

The physical size of a wire (the diameter) gets larger as the 'wire size' nomenclature gets smaller. Originally, wires were sized by how many of a particular size would fit through a specified hole diameter. The larger the wire, the fewer would fit.

For wire sizes in extension cords, see below.

Determine the total current draw (Amps) through the cord, the cord's length, and use the table below to determine the minimum AWG Wire Size for that current. Naturally, using a cord with an even LARGER wire size, with greater current capability, than the minimum is fine -- and actually provides slightly less energy losses.

Hint: A 100 Watt device draws about 1 Amp (at 110 volts). So, 300 Watts draws 3 Amps, 1000 Watts draws 10 Amps, and 1500 Watts draws 15 Amps. Simply add the wattages of the device(s), and divide by 100, for the approximate Amps that are drawn through the cord. Choose a cord with at least that size wire.

The labels on some cords may list the maximum current allowed, or the Wire Size, or both.

* N.W. = NO WAY, move closer to power source.

If you connect two 50 ft. cords together, drawing 10 Amps, BOTH cords must at least 16 AWG wire. (Even though ONE 50 ft. cord with 18 AWG wire could handle 10 Amps, having TWO connected end to end is the same as ONE 100 ft. cord. And both would need to be a minimum of 16 AWG wire.

Exceeding the current or lengths in the table may have more than one destructive effect. Trying to force too much current through too small a wire size causes the wire to heat, and may cause a fire. Do not extinguish the fire with water until the cord is disconnected. The energy lost heating the wire inside the cord reduces the voltage at the end of the cord, resulting in dim lights, and possibly damaging motors by overheating while operating at the reduced voltage. Some electronic equipment may refuse to operate, or may operate erratically.