An indicator of space heating demand. The heating degree days for a single day equal 65 degrees Fahrenheit minus the average of the highest hourly temperature and the lowest hourly temperature for the day, if greater than or equal to zero.

The number of Heating Degree Days (HDDs) during a period is an index that is intended to relate to the amount of heating used during that period. Because heating is most often used during winter, HDDs are most often calculated over some or all of the winter period, and are designed to reflect how cold that period is. The number of HDDs on one day is defined to be the number of degrees by which the Average Temperature on that day is below a threshold, usually taken to be 65F. The number of HDDs over a period is just the sum of the number of HDDs on each day during that period. For instance, a single day of 60F corresponds to 5HDDs. Two days of 60F correpond to 10 HDDs, and so on. Days during which the Average Temperature is greater than 65F do not contribute any HDDs. This somewhat complicated formula is an attempt to create a linear relationship between a meteorological index and the consumption of power. Contrast with Cooling Degree Days (CDDs).

A Heating Degree Day (HDD) is a form of degree day used to estimate energy requirements for space heating. One HDD is obtained for each degree that the daily average temperature is below the base of 65 degrees F. For example, if the daily high temperature is 64 degrees and the daily low is 40 degrees, the average temperature for that day is 52 degrees F. The daily HDD is 13. If the average temperature is more than or equal to 65 degrees, the daily HDD is zero.

Each degree that the average daily temperature is below the base temperature (usually 65°F) constitutes one heating degree day. E.g., The temperature outside is 55ºF. That is 10º below the base of 65º, or 10 heating degrees for that day.

HDD): A measure of how cold a location is over a period of time relative to a base temperature, most commonly specified as 65 degrees Fahrenheit. The measure is computed for each day by subtracting the average of the day's high and low temperatures from the base temperature (65 degrees), with negative values set equal to zero. Each day's heating degree days are summed to create a heating degreeâ€“day measure for a specified reference period. Heating degree days are used in energy analysis as an indicator of space heating energy requirements or use.

Difference between the actual temperature, as determined by the average of the high and low daily temperatures, and 65 degrees F. For example, if the daily high temperature is 55 degrees and the daily low is 35 degrees, the actual temperature for that day would be 45 degrees. The HDD's for that day would be 20 (65-45). If the average temperature is greater than or equal to 65 degrees, the HDD's for the day would be zero

HDDs are a way to measure how much heating is required in some period of time. A large number of HDDs signifies that the building required a large amount of heating. Zero HDDs signifies that the building did not require any heating. In case you are interested, HDDs for each day are calculated as follows: HDD = (TBalance Point - TMean) * Nday+ Where TMean is the average of the high and low temperature for a day, and Nday = 1, and HDD must always be positive. For Utility Bill Analysis, HDDs are calculated separately for each day and then summed together into billing periods.

A quantitative index that reflects demand for energy to heat homes and businesses. A mean daily temperature of 65°F is the base for heating degree day computations. Heating degree days are summations of negative differences between the mean daily temperature and the 65°F base. Thus, a day with a temperature of 62°F would count as 3 heating degree days. Days with the following temperatures, 62, 61, 55, would result in 17 heating degree days.

A measure of how much below a standard reference temperature actual temperatures have been. A basis for computing how much electricity and gas are needed for heating purposes.

A form of degree day used to estimate the required energy for heating. One heating degree day occurs for each degree the daily mean temperature is below 65 degrees Fahrenheit.

A unit to measure "coldness". The number of heating degree days in any given day is the average temperature for that day subtracted from 65F. The number of heating degree days per year is used to estimate yearly heat loss in Btu's. Climate zones (approximate) on climate zone maps are differentiated by heating degree days per year and insulation recommendations will vary in accordance with these heating degree days, or climate, zones.

One heating degree day is given for each degree that the daily mean temperature is below 65 degrees a given temperature. It is used as an indication of fuel consumption. Refer to cooling degree day.

The number of degrees per day that the daily average temperature (the mean of the maximum and minimum recorded temperatures) is below a base temperature, usually 65 degrees Fahrenheit, unless otherwise specified; used to determine indoor space heating requirements and heating system sizing. Total HDD is the cumulative total for the year/heating season. The higher the HDD for a location, the colder the daily average temperature(s).

A unit measuring the severity of winter or heating energy conditions. Using a reference temperature of 65° F, degree days are determined by the difference in the mean daily temperature and the reference temperature. For example, a day with 50° F mean temperature has 15 HDD (65-50=15). The annual Heating Degree Days are the sum of the degree days over a calendar year.

Term used by heating and cooling engineers to relate the typical climate conditions of different areas to the amount of energy needed to heat and cool a building. The base temperature is 65 degrees Fahrenheit. A heating degree day is counted for each degree below 65 degrees reached by the average daily outside temperatures in the winter. For example, if on a given winter day, the daily average temperature outdoors is 30 degrees, then there are 35 degrees below the base temperature of 65 degrees. Thus, there are 35 heating degree days for that day.

A day in which the average daily temperature is less than 65 degrees Fahrenheit, and therefore likely to be a day in which people turn on their heat. A heating degree day is assigned a value that represents the number of degrees that days average temperature is less than 65 degrees. For example, if a day's average temperature is 45 degrees, the Heating Degree Day (HDD) value for that day would be 20 (65 45). If the average temperature is greater than or equal to 65 degrees, the HDD value for the day would be zero. (The day would not be sufficiently cold to require heating.)

useful in determining heating energy requirements. Defined as (65 - MT)= HDD,where MT is Mean Temperature (F). If MT is greater than 65 degrees F, HDD=0. MT= Mean (average) Temperature of the day. MT=(High Temperature+Low Temperature)/2

One heating degree day is given for each degree that the daily mean temperature is below 65°F. It is used as an indication of fuel consumption. Related terms: degree day or cooling degree day

Heating degree day (HDD) and cooling degree day (CDD) are quantitative indices demonstrated to reflect demand for energy to heat or cool houses and businesses. These indices are derived from daily temperature observations.