About GetGridTally.com: Open-Formula Home Energy & HVAC Calculators

GridTally (GetGridTally.com) is an independent project that publishes free home energy calculators, created and maintained by the site owner. It helps homeowners and project planners across the United States, United Kingdom, Canada, and Australia estimate rooftop solar sizing, heat pump operating costs, EV home charger circuits, room-by-room HVAC BTU loads, and backup generator wattage using clear, step-by-step math.

Many online home-energy calculators act as lead-generation forms: they hide their formulas behind a mandatory phone-number or email wall and rely on rough square-footage rules of thumb that can push larger equipment packages than a home actually needs. GetGridTally.com was built around a simple goal: publish transparent thermodynamic and electrical sizing formulas that anyone can run in real time, 100% free of charge, with zero registration or personal contact data required.

How GetGridTally.com Works: Three Core Principles

Because residential electrification projects involve major household purchases ($1,500 to $30,000+) and high-voltage branch circuits, every calculator and guide on GetGridTally.com is built around three straightforward principles:

Core Mathematical Formulas Used in the Calculators

Every interactive calculator on GetGridTally.com shows its underlying equation below the input panel so you can check each assumption against your own utility bill and equipment datasheet:

• Solar Photovoltaic & LFP Battery Sizing (Calculator 01): The solar sizing calculator follows the US Department of Energy (DOE) / NREL PVWatts v8 approach. Instead of assuming 100% ideal lab output, the formula applies an 18% combined real-world system derate factor (0.82 efficiency multiplier) to account for inverter DC-to-AC conversion efficiency (~96%), rooftop module cell temperature losses (-0.35%/°C above 25°C STC), DC/AC wiring voltage drop (~2%), and seasonal soiling/snow losses. It also reflects 2026 incentive rules—noting the December 31, 2025 expiration of the US Section 25D and Section 25C residential tax credits under Public Law 119-21 (IRS Home Energy Tax Credits) and focusing on active state utility rebates, IRA HEEHRA/HOMES point-of-sale rebates where available, and third-party lease/PPA credits. Always check your local utility rate and state energy office for current incentive availability.
• Heat Pump vs. Combustion Furnace Thermodynamic Balance Point (Calculator 02): To compare electric heat pumps against natural gas, propane, or heating oil across four countries without unit confusion, the calculator converts fuel inputs into delivered kilowatt-hours of space heat. Using the physical equivalence of 1 US Therm = 100,000 BTU = 29.307 kWh (and regional factors of 29.3 kWh/therm in the UK, 2.76 m³ natural gas/therm in Canada, and 105.5 MJ/therm in Australia), it divides delivered thermal demand by the heat pump's seasonal Coefficient of Performance (COP) and compares it against combustion fuel consumption multiplied by Annual Fuel Utilization Efficiency (AFUE).
• Level 2 EV Home Charger Circuit & Fuel ROI (Calculator 03): Under NFPA 70 / National Electrical Code (NEC) Article 625.41, electric vehicle supply equipment (EVSE) is treated as a continuous load (operating for 3 hours or more). Branch circuit breakers and conductors are therefore sized at 125% of the EV charger's maximum continuous current rating (for example, a 40A NEMA 14-50 charger uses a 50A two-pole breaker; a 48A hardwired charger uses a 60A breaker; a 24A commuter charger uses a 30A breaker). The fuel cost comparison also includes a 10% AC-to-DC onboard charger conversion loss factor so electric charging costs are realistic.
• HVAC & Ductless Mini-Split BTU Load Sizer (Calculator 04): Simple retail charts multiply floor area by 20 BTU/sq ft and ignore ceiling height and insulation—which often leaves high-ceiling rooms and uninsulated garage workshops undersized. Our zone sizing model starts with a 25 BTU/sq ft baseline and applies multipliers for ceiling height (Ceiling Height ÷ 8.0 ft), wall/attic insulation quality (0.85× spray foam to 1.35× uninsulated garage envelope), window sun exposure (0.90× shaded north to 1.15× south/west glass + kitchen heat gain), and occupant load (+600 BTU/hr per person above two).
• Whole-Home Standby & Inverter Generator Load Sizer (Calculator 05): Generators usually trip offline not from steady running wattage, but from the brief Locked-Rotor Amps (LRA) starting surge needed to spin up inductive motors (central air conditioner compressors and deep submersible well pumps). The calculator adds continuous running wattage to the largest motor starting surge and applies a 15% continuous generator headroom margin alongside multi-day propane (LPG) fuel consumption estimates.

Primary Sources Used for Regional Defaults

The default regional electricity rates, natural gas prices, fuel averages, and government rebate summaries used as starting presets in our calculators are based on public data from the following agencies (since utility tariffs vary by city and provider, always enter the exact rate from your own utility bill):

How to Use GetGridTally.com for Your Home Project

To get the most accurate planning estimate from our calculators before you request local contractor quotes:

1. Find Your All-In Supply + Delivery Rate: Look at your most recent electricity or natural gas bill and divide the total usage charges (excluding fixed monthly customer connection fees) by the total kilowatt-hours (kWh), therms, or cubic meters consumed. Enter that exact number into the calculator rather than relying solely on national averages.
2. Check Your Main Breaker Panel Amperage: Open the metal door of your main electrical panel and read the number stamped on the main two-pole disconnect handle (typically 100A, 150A, or 200A). Knowing this rating helps determine whether a 24A Level 2 EV charger or heat pump circuit can fit on your existing panel without a service upgrade.
3. Print or Save Your Spec Sheet: Use the "+ Save Estimate" or "Print PDF" buttons inside any calculator to compare multiple system sizes side by side and share your baseline assumptions when speaking with licensed local electricians or HVAC installers.

Advertising & Independence Disclosure

GetGridTally.com is funded by programmatic display advertising through Google AdSense. There are no paid product placements from equipment manufacturers or solar sales companies on this site, and outbound reference links inside the calculators point to official public government and regulatory portals (such as NREL, DSIRE, ENERGY STAR, UK Ofgem, GOV.UK, and NRCan). Advertising never influences the calculator formulas, COP balance points, or breaker sizing outputs.

If you notice a utility rate update, a rebate change, or a calculation question, please reach out via our Contact page or email support@getgridtally.com.