Converting a heat loss calculation to energy use

[RISolar]

HI folks. I am developing a spreadsheet for solar thermal design. Is there a general formula that I could work with that will convert a manual J heat loss calculation into actual energy consumed on a monthly basis. I have experimented with "Heat loss*24/65-design temp*heating degree days". I don't have confidence in it and was hoping there is another formula I can use.
Thank you in advance for your help

 

[Zapster]

Take a look at 3Eplus, it is a free heat loss program. It may not be what you want; however, it may be good to verify your model.

http://www.pipeinsulation.org/