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# How to apply heating degree days to gas bill

Member Posts: 307
After doing some improvements to my one-pipe steam residential heat system, I got my first gas bill after the improvements. Heating degree days in December were 909 and in January were 894 (Harrisburg, Pennsylvania). That is a difference of about 1.7% warmer in January. With the temperature that close, if my gas bill shows that I used 10% less gas in January than in December, am I reasonably accurate in calculating that I improved my system efficiency by 10%? Nothing else changed. No changes to the house or its insulation, and the thermostat was set at a constant 68 the entire 60 days of comparison. I am new to this type of calculation and need some expert guidance.

• Member Posts: 5,477
I divide the total BTU's consumed by the degree days to get a number. I did some work on the house this summer and my BTU's/DD number improved by about 33% this winter over last winter.

Bob
Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
Vaporstat with a 12oz cut-out and 4oz cut-in
3PSI gauge
• Member Posts: 307
BobC said:

I divide the total BTU's consumed by the degree days to get a number. I did some work on the house this summer and my BTU's/DD number improved by about 33% this winter over last winter.

Bob

Nice work. What were the improvements you made?
• Member Posts: 5,477
edited February 2017
i calculated my results by converting all of my gas and electricity bill s into BTU's and dividing that number by the monthly degree days. I figure any electric used in the house is heat just like the gas I burn in the boiler.

I FINALLY had the walls of this 95 year old house insulated with blown in insulation, enclosed the north facing front porch, and had a 12,000 BTU minisplit heat pump installed on the first floor (14k+ in heating mode).

I can isolate the first floor by closing doors so on days when temperatures stay at 30 or above I can heat the first floor with just the heat pump. i really don't care if the second floor is colder because when I'm up there for any amount of time I'm under a good quilt. The steam does run to bring the house up to 66 from the overnight setback of 63 and when it's going to be below 30 I just let the steam do it's magic. Shielding the north facing front of the house from that nasty NE wind had substantial effect as well. The porch is enclosed but not sealed but I've only seen water freeze on that porch 3 times this winter and we have had some cold weather in the Boston area.

Bob
Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
Vaporstat with a 12oz cut-out and 4oz cut-in
3PSI gauge