## Home Energy Definitions

Return to the main Home Energy index

Please enter here the area of the heated (and/or cooled) space in your house. Ideally, this is the total
area inside the walls, but it is necessarily somewhat approximate. Real estate agents like to count the
area of a stairwell twice, because it occupies two floors. This number is a proxy for the window area
and number of people in residence.

This is a sum of the difference between the average daily outside temperature and 65 degrees F, added up
over a whole year (usually). The calculator can be used for shorter periods if you don't have an entire
year of utilities summarized, you would enter the heating degree days for the period you have bills here.
When the temperature outside exceeds 65F, you don't subtract heating degree days, instead you add cooling
degree days (CDD). The temperatures are computed and subtracted for each day, assuming that the house
has sufficient heat capacity and insulation to average over that long a period. 65 F is used as the
standard because all houses capture and store heat to some extent. If you don't know your HDDs, you
can leave this blank, enter your zip code, and I will make an attempt to find an estimate on
the web for your climate.

This is the sum of the difference between the average daily outside temperature and 65 degrees F, when
the average outside temperature exceeds 65F. You need to enter this number if you want to compute
HCI, but then you also need to know how much electricity you are using for cooling. This calculator
assumes only electricity is used for cooling, running heat pumps, air conditioners, or swamp
coolers. I have defined CDD exactly like HDD because I want to compute HCI just like HHI, with
the same sort of assumption about the way houses damp out temperature swings with insulation and
thermal mass.

This is your US or Canadian postal delivery code, which tells me where you are located. If you
are not in the United States, feel free to enter the name of your city/town and country in this
blank. The javascript calculator that fills in the HHI and HEI blanks doesn't use this information.

This optional blank is for entering the location of your house website for publication in my
table. It's not useful if you are not requesting publication or have no website.

This blank is for the total electricity used by your house and all the things inside it.
I don't want you to subtract the electricity you generate from the electricity you use
for this blank, because this page is devoted to computing energy consumption of housing,
and generation is a separate question. If you generate electricity, please enter it in
the next blank. Electricity is converted to BTUs at a rate of 3340 BTU/KWH, and heats
the house after it powers appliances and other equipment inside. If you
want to see live updates of your HHI and HEI, do not enter any commas in this number.

Enter the electricity you generate at your house in this blank. Most people will enter
zero. Most people who generate electricity do so with photo-voltaic (PV) panels, and so
you could estimate how much you generate if you know the rated capacity of your system
and the number of hours full sun you get a year, but then you must have a grid inter-tie
in order to make use of your excess capacity. People who have no grid inter-tie will
generate an amount equal to their use.

Enter the electricity used to run your cooling system. This requires sophisticated
instrumentation to measure. If you are in a hot climate, you might approximate it
by comparing summer and winter electricity bills. Subtract your other electrical
uses from your summer bills and add up the difference over the hot months.

Enter your annual total natural gas use in therms. Even though most of us use
natural gas to cook and heat water in addition to heating our houses with it, the
other uses should still be counted toward heating the house, since the cooking and
hot water are used inside the house. Cooking is a very small use compared to space
heating anyway. Natural gas is converted to BTUs at a rate of 100,000 BTU/therm.
If your bill is in MCF, thousand cubic feet, multiply by 10.31 to get therms.

Enter your annual total propane use in gallons. Even though most of us use
propane to cook and heat water in addition to heating our houses with it, the
other uses should still be counted toward heating the house, since the cooking and
hot water are used inside the house. Cooking is a very small use compared to space
heating anyway. Propane is converted to BTUs at a rate of 91600 BTU/gallon.

Enter your annual total wood burned in cords. A cord is enough wood to completely
fill the bed of a large pickup truck, stacked to the top of the cab. Heating with
wood can be quite significant, but it is one of the most difficult fuels to measure.
Wood is converted to BTUs at a rate of 20,000,000 BTU/cord.

If check the box for including this house in the public table, that will be recorded along with the rest of your data
when you save. Then the administrator of this page will manually add your data to the table.
### Home Cooling Intensity

The ratio of BTUs used for cooling to the square feet cooled and the Cooling Degree Days (CDD) is defined
as the Home Cooling Intensity (HCI). Like the Home Heating Intensity (HHI) it has units of BTUs per
square foot per degree day, with degrees in Fahrenheit. It is a measure of the efficiency of the cooling
system and the efficiency of the house design for cooling. Better insulation and fewer sunny windows
make an efficiently cooled house.
### Home Heating Intensity

The ratio of BTUs used for heating to the square feet heated and the Heating Degree Days (HDD) is defined
as the Home Heating Intensity (HHI). Like the Home Cooling Intensity (HCI) it has units of BTUs per
square foot per degree day, with degrees in Fahrenheit. It is a measure of the efficiency of the heating
system and the efficiency of the house design for heating. Better insulation and more sunny windows
make an efficiently heated house.