Enter home and energy details
Use annual degree days from a reliable local climate source. Estimate coefficients from an energy audit, load calculation, or historical household data.
Formula used
The calculator estimates seasonal thermal loads before converting them into purchased fuel or electricity.
Cooling load: Heat-gain coefficient × Cooling degree days × 24 × Cooling adjustment
Heating purchased energy: Heating load ÷ AFUE factor or COP
Cooling kWh: Cooling load ÷ (SEER2 × 1,000)
Total annual cost: Heating cost + Cooling cost + Maintenance allowance
For gas, propane, and oil, AFUE is converted from a percentage to a decimal. For electric resistance and heat pumps, the efficiency field is treated as COP.
How to use this calculator
- Enter the heated and cooled floor area.
- Use local annual heating and cooling degree days.
- Enter coefficients from an energy audit or model.
- Choose your heating source and provide its efficiency.
- Add current fuel and electricity prices from your bills.
- Adjust usage percentages for thermostat habits and occupancy.
- Calculate, compare scenarios, then export the results if needed.
Example data table
| Input | Example value | Why it matters |
|---|---|---|
| Floor area | 2,000 ft² | Provides context for cost per square foot. |
| Heating degree days | 4,200 | Represents annual cold-weather exposure. |
| Cooling degree days | 1,200 | Represents annual warm-weather exposure. |
| Heating coefficient | 420 BTU/h°F | Estimates total building heat loss. |
| Cooling coefficient | 300 BTU/h°F | Estimates heat gain during cooling season. |
| Cooling SEER2 | 15.2 | Converts cooling load into electricity use. |
Plan home energy costs with better inputs
Understand seasonal energy costs
Heating and cooling bills depend on climate and building quality. Floor area matters, but it never tells the story. Insulation, windows, air leaks, and thermostat settings change seasonal demand. A tight home loses less heat in winter. It also gains less unwanted heat in summer. This calculator turns those conditions into annual energy estimates. It calculates heating fuel, cooling electricity, costs, and broad emissions. Results are planning estimates, not guaranteed utility bills. Weather, occupancy, shading, appliance heat, and utility fees also affect results. Compare the estimate with bills. Adjust inputs until the scenario matches household use.
Heating demand and fuel choice
Heating degree days describe how much cold weather occurs during a year. The heat loss coefficient represents combined heat transfer through walls, attic, windows, floors, and air leaks. The calculator multiplies this coefficient by heating degree days and twenty four hours. That creates an estimated seasonal heating load in British thermal units. Equipment efficiency converts that load into purchased energy. Gas, propane, and oil equipment use AFUE percentages. Heat pumps can exceed one because they move heat. Enter fuel prices using the purchase unit. This matches direct electric systems. Accurate prices improve cost estimates for planning.
Cooling load and electrical use
Cooling degree days describe how outdoor heat affects air conditioning demand. The cooling heat gain coefficient estimates how quickly heat enters homes. Roof color, window shading, humidity, appliances, and occupants add cooling work. The calculator estimates seasonal cooling load from this coefficient and cooling degree days. SEER2 then converts that load into electricity use. Higher ratings usually reduce kilowatt hours in comparable homes. Enter your electricity rate, including delivery charges when possible. The cooling adjustment reflects thermostat settings and operation patterns. Values above one hundred increase the estimate. This reflects reduced conditioned space during summer months.
Reading the results
The result panel separates heating, cooling, maintenance, and total cost. It also provides a monthly average for budgeting. Monthly averages smooth costs across the entire year. The heating fuel quantity helps compare results with deliveries or supplier statements. Cooling electricity appears in kilowatt hours. Carbon estimates use your electricity factor and the selected heating fuel factor. Treat those figures as broad comparisons. Test upgrades by changing one assumption at a time. Lower heat transfer coefficients can represent insulation or air sealing. Higher equipment ratings can represent replacement equipment. Use several scenarios before choosing an upgrade wisely.
Better decisions before upgrades
Use this calculator before choosing insulation, windows, air sealing, or HVAC equipment. Start with a model of the current home. Then create a second scenario for planned improvements. Compare annual cost, monthly cost, energy use, and emissions. Heat pumps may reduce costs when electricity remains reasonably priced. Gas equipment may compare well when gas prices remain lower. Always include maintenance in each comparison. This calculator does not replace a professional load calculation. Proper sizing needs room by room measurements and local design conditions. Discuss final choices with a qualified contractor. Review results when household patterns change.
Frequently asked questions
1. What is a heat-loss coefficient?
It estimates how many BTUs your home loses each hour for every degree of temperature difference. It summarizes envelope performance and air leakage.
2. Where can I find heating and cooling degree days?
Weather services, energy offices, and climate data providers publish degree-day totals. Use the same temperature base consistently, commonly 65°F.
3. Is this a replacement for a Manual J calculation?
No. This tool estimates annual operating costs. Manual J calculations size equipment using room-level details, design temperatures, and local building conditions.
4. Why can heating and cooling coefficients differ?
Summer solar gain, humidity, appliances, occupants, and shading change cooling demand. Winter heat loss follows different building and weather effects.
5. What heating efficiency should I enter for natural gas?
Enter the AFUE percentage shown on the equipment label. A condensing furnace may be near 90 to 98 percent.
6. What COP should I enter for a heat pump?
Use a seasonal average COP. Values around 2.0 to 4.0 are common planning ranges, depending on climate and system type.
7. Does SEER2 include every cooling expense?
No. SEER2 estimates equipment efficiency. Utility fees, duct losses, thermostat use, humidity control, and maintenance may still change final costs.
8. Why add a maintenance allowance?
Energy cost is only part of ownership. Filters, tune-ups, repairs, and service agreements can affect annual household heating and cooling spending.
9. How should I use the adjustment percentages?
Keep both at 100 for a baseline. Increase them for longer operating hours, lower thermostat settings, or unusual loads. Reduce them for partial conditioning.
10. Are the emissions results precise?
No. They are comparison estimates. Electricity emissions vary by utility, season, grid mix, and location. Fuel supply chains also vary.
11. Can I compare retrofit scenarios?
Yes. Save the current inputs, then change one improvement at a time. Compare totals to identify which upgrade produces the strongest estimated benefit.