Space Heating Demand and Effective Costs - Example
EXAMPLE CASE STUDY
Jane Smith heats her house with natural gas. Her heating appliance is a condensing furnace rated at 95% AFUE (annual fuel utilization efficiency).
STEP 1 - Summarize your Energy Data
She looks through her monthly utility bills to find out the amount of fuel used and
what she paid for it. Common units for natural gas are "therms" or "ccf" (hundred
Her lowest monthly use of natural gas was in August, at 5 therms. Assuming that at this time of the year no natural gas is needed to heat the home, this amount is an estimate of what is used every single month of the year for other heating applications like water heating, cooking, etc.
Depending on the fuel type used for heating, select the "units" here:
STEP 2 - Calculate the Unit Cost of your current Fuel
After calculating, she can see in the "TOTALS" line that she used 431 therms and paid $388 for space heating that year. She enters these amounts here, and clicks "Calculate".
STEP 3 - Calculate the Costs per Million BTU (British thermal units)
She selects "Natural Gas (therms)", and the cell "Fuel Heat Content per Unit" is populated
with the value "100,000" as one therm of natural gas contains that many BTU's.
She finds that she pays $9.00 per Million BTU.
STEP 4 - Estimate your actual Energy Demand and effective Costs for Space Heating
She selects "Condensing Boiler/Furnace (95% AFUE)". Her "Primary Energy Use" (from STEP 2) is 43.1 Million BTU. Since her furnace converts only 95% of the energy contained in the fuel into useable heat, the actual Heat Energy delivered to the home is 40.9 Million BTU at an effective cost of $9.48 per Million BTU.