the period of the year during which heating a building is necessary to maintain comfortable conditions. UK standard - approx 33 weeks a year.
Found on http://www.encyclo.co.uk/local/20842
The period from early fall to late spring (in the northern hemisphere) during which additional heat is needed to keep a house comfortable for its occupants. Found on https://www.encyclo.co.uk/local/21033
The coldest months of the year; months where average daily temperatures fall below 65 degrees Fahrenheit creating demand for indoor space heating. Found on https://www.encyclo.co.uk/local/22819