Novitherm™ Heat Reflectors – Calculating Savings

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Heating Degree-Days
Heating Degree-Day (HDD) is an index used to determine the duration and intensity of winter cold. The index, originally developed in 1927 by the American Gas Association, is widely used to estimate home heating requirements. The concept is quite simple. Once the outdoor temperature falls below 18° Celsius, space heating is required in a building to maintain a comfortable indoor temperature. For every degree of temperature below 18° C, 1 HDD is accumulated. On a day where 30 HDDs have accumulated, three times as much fuel is required to heat a building as on a day when only 10 HDDs have accumulated.

HDDs are also used comparatively to measure the relative severity of a winter. The total daily HDD values for a winter season may be compared to previous winter totals or a long term average.

Canada’s fuel industry uses HDDs to maintain adequate fuel supply levels and to anticipate consumer needs. By accumulating HDDs, home heating suppliers are able to estimate fuel consumption. This allows for more efficient scheduling of deliveries and eliminates shortages between deliveries.

HDDs are also used in building design to calculate insulation and heating requirements for new buildings and in retail sales of insulation to establish guidelines for the type and amount of insulation required for a particular location. Homeowners themselves may use HDD and energy consumption figures to determine the effectiveness of recent energy conservation measures to their homes such as increased insulation, caulking around windows and doors, lower thermostat settings, installation of Novitherm Heat Reflectors, etc.

Calculating Heating Degree-Days
HDDs are calculated simply by subtracting the mean daily temperature (C°) from 18° C. The daily mean temperature is arrived at by averaging the maximum and minimum temperatures for the day. Where the daily mean temperature is above 18° C no degree-days are counted. These daily values are then added together to obtain a cumulative total for the period of record (i.e., week, month, year).

HDDs may be calculated on a day-to-day basis from weather information published in most Canadian daily newspapers. Monthly and annual summaries of accumulated HDDs are available from Environment Canada’s Weather Office.

Using Degree-Days to determine your home’s heating efficiency
The relationship between HDDs and residential gas consumption becomes quite obvious when one examines a typical heating year. This relationship may also be used by individuals to determine the heating efficiency of their dwelling on an individual basis.

By dividing fuel consumption (from monthly heating bills) over a period of a week, month or year by the accumulated HDDs for the same period, the homeowner calculates how much fuel is consumed per single degree-day. This figure is referred to as the heating factor. It would be expected that this heating factor would remain constant from year to year unless conservation measures were adopted to increase heating efficiency within the home.

Canadian Consumers can visit Environment Canada’s Weather Office for more information and to calculate savings.

Go to www.climate.weatheroffice.ec.gc.ca/climateData/canada_e.html and follow these steps:

click on customized search
1. in Search By Province box, select your province and click on search
2. select the centre closest to you
3. under Data Interval select daily
4. select month and year and click on GO

The resulting chart will list Heating Degree Days in the fifth column. There is also a print feature should you wish to record the data.