Montana State University

MSU Extension Forestry

Estimate Space Heating Demand and Effective Costs

Author: Martin Twer
Update: 10/27/2014

For a pre-populated example case study see here.

STEP 1 - Summarize your Energy Data

Look at your utility bills to find the total energy charge for a given time period (e.g. month, quarter, semi-annual, annual) for the fuel used for home heating.
For example, if you heat your home with natural gas, and your utility bill shows two fuels - e.g. electricity and natural gas - use the charge shown for natural gas only.

Depending on the fuel type used for heating, select the "units" here:

Fuel Units Fuel Cost Cost/Fuel Unit Fuel Units for Space Heating Cost for Space Heating
January $
February $
March $
April $
May $
June $
July $
August $
September $
October $
November $
December $

Find the lowest value in the Fuel Units column. This should be a summer month, when no or very little energy is required for space heating, and establishes a "base load" from water heating, cooking, etc.
Enter this value here


STEP 2 - Calculate the Unit Cost of your current Fuel

To determine the per-unit-cost of your fuel, enter the amount (in USD) you were charged, and the amount of fuel used for a given time period.
The cost of fuel (per unit of fuel) is generally expressed as: $/gallon for heating oil, $/therm (or ccf) for natural gas, $/kWh for electricity, $/gallon for propane, $/ton for coal.

Example: Assuming 53 mmBTU (Million BTU) (15,533 kWh) as average annual heating demand, estimates for a household could be

Amount of Fuel used Amount charged Fuel Type
477 gallons $1,860 #2 Heating Oil
15,850 kWh $1,744 Electricity
683 gallons $2,050 Propane
625 therms $590 Natural Gas

Amount of Fuel used Amount charged Cost per Fuel Unit
$ $

STEP 3 - Calculate the Costs per Million BTU (British thermal units)

What fuel are you currently using to heat your home?

LPG/Propane (gallons)
Natural Gas (therms)
Electricity (kWh)
Wood Pellets (tons)
Firewood, 20% MC (cords)
Corn (kernels) (tons)
#2 Heating Oil (gallons)
Kerosene (gallons)
Coal, Bituminous (tons)

Fuel Heat Content per Unit Cost per Million BTU

STEP 4 - Estimate your actual Energy Demand and effective Costs for Space Heating

What is the estimated overall efficiency of your heating appliance?

Air-source Heat Pump (1.55 COP)
Ground-source (Geothermal) Heat Pump (3.3 COP)
Electric Baseboard (100%)
Condensing Boiler/Furnace (95% AFUE)
ENERGY STAR qualified Boiler/Furnace (85% AFUE)
Standard Boiler/Furnace (75% AFUE)
(Vented) Room Heater (80% AFUE)
EPA-certified Catalytic Wood Stove (72% AFUE)
EPA-certified Non-Catalytic Wood Stove (65% AFUE)
EPA Phase 2 Hydronic Heater (75% AFUE)
Conventional Hydronic Heater (45% AFUE)
Conventional Wood Stove (54% AFUE)
Fireplace (20% AFUE)

Primary Energy Use Conversion Efficiency Heating Energy Demand
mmBTU % mmBTU

The amount of energy used for space heating in the specified time period is approximately
mmBTU, at an effective cost of $ per mmBTU.