Formula Used
U-value from R-value: U = 1 / R
Conduction heat transfer: Q = A × U × ΔT
Infiltration heat transfer: Q = 0.33 × ACH × Volume × ΔT
Thermal energy: kWh = Load W × Hours / 1000
Heat pump electricity: kWh = Thermal kWh / COP
Gas fuel use: Therms = Thermal kWh / Efficiency / 29.3071
Annual EUI: EUI = Monthly equivalent kWh × 12 / Floor area
How to Use This Calculator
Enter the home size, surface areas, insulation values, window values, and weather conditions.
Add air leakage, operating hours, equipment efficiency, utility rates, lighting, appliances, and solar offset.
Press Calculate. The result appears below the header and above the form.
Use CSV for spreadsheet records. Use PDF for a printable summary.
Residential Energy Efficiency Basics
A residential energy efficiency calculator estimates how much energy a house needs to stay comfortable. It connects physics, building data, and utility prices. The main idea is simple. Heat moves through walls, roofs, floors, doors, and windows. Air leakage also moves heat. Better insulation and tighter construction reduce that movement.
Why Heat Loss Matters
Heat loss is not only a winter concern. The same weak points create cooling demand in summer. A large temperature difference increases the load. A bigger surface area also increases the load. A lower resistance value increases the load. That is why attic insulation, window quality, and air sealing often matter more than one appliance upgrade.
How The Calculator Helps
This tool combines conduction, infiltration, equipment efficiency, lighting use, appliance use, solar offset, fuel prices, and emission factors. It reports heating load, cooling load, monthly energy use, estimated cost, carbon output, and an efficiency score. The score is a guide, not an audit certificate. It helps compare upgrade choices before money is spent.
Useful Input Tips
Use measured areas when possible. Enter window area separately, because windows usually lose more heat than insulated walls. Use realistic air changes per hour. Older homes may have high leakage. Newer sealed homes may be lower. Energy bills can help you tune assumptions. If the estimated cost is too low, increase hours, air leakage, or base appliance use.
Upgrade Planning
Start with low risk improvements. Seal gaps around ducts, attic hatches, rim joists, and doors. Add attic insulation if levels are poor. Replace failing weatherstripping. Then compare larger changes. Efficient heat pumps, better windows, solar panels, and smart controls can reduce annual costs. The best choice depends on climate, fuel price, house shape, and current equipment.
Reading The Result
A high heat load means the building shell needs attention. A high cost with moderate load may mean energy prices or equipment efficiency are the issue. A high carbon value points to fuel mix and usage. Review each result together. No single number explains the whole house.
For best results, save several runs. Compare one upgrade at a time. This makes the payback clearer. It also shows which physics factor drives the strongest savings for your home.
FAQs
What does this calculator estimate?
It estimates heating load, cooling load, energy use, monthly cost, emissions, and an efficiency score. It uses surface areas, insulation values, leakage, system efficiency, utility prices, and solar offset.
Is this a certified home energy audit?
No. It is a planning calculator. A certified audit uses inspections, blower door testing, duct checks, equipment testing, and local standards. Use this tool for early estimates and upgrade comparisons.
What is an R-value?
R-value measures resistance to heat flow. A higher value means better insulation. The calculator converts R-value to U-value using U = 1 / R for conduction calculations.
What is a U-value?
U-value measures heat flow through a surface. Lower U-values are better. Windows often use U-values because they lose heat faster than insulated walls or roofs.
Why does air leakage matter?
Leaky air carries heat into or out of the home. This increases heating and cooling demand. Air sealing can reduce comfort problems and monthly energy costs.
How should I estimate air changes per hour?
Use a blower door result when available. Without testing, use lower values for tight modern homes and higher values for older leaky homes. Adjust using past utility bills.
Why is solar offset included?
Solar production reduces net purchased electricity. The calculator subtracts monthly solar kWh from gross electric use before calculating electric cost and electric emissions.
Which upgrades usually help first?
Air sealing, attic insulation, duct sealing, and weatherstripping often help first. Bigger upgrades, like heat pumps or windows, should be compared with cost, climate, and current equipment condition.