Calculators for the energy your home uses: the electricity cost calculator turns an appliance’s watts and hours of use into kWh per day, month, and year (watts × hours ÷ 1,000, the Department of Energy’s formula) and, with the rate from your own bill, into the cost to run it. The solar panel calculator turns a home’s monthly kWh and peak sun hours into the number of panels, the system size in kW, the yearly output, and the roof area the panels cover. The furnace size calculator estimates the heat a home needs from its floor area and climate (a manufacturer’s rule of thumb of 30 to 60 BTU per sq ft) and turns it, or a Manual J heat loss, into the furnace input to look for.
Enter your monthly kWh, peak sun hours, and panel wattage to estimate the solar panels, system size in kW, yearly output, and roof area: at the 2024 U.S. average of 863 kWh a month and 4.5 peak sun hours, that’s about 20 panels of 400 W. Includes a chart by monthly use and sun hours and the PVWatts loss breakdown.
Enter a device’s watts, hours of use, and the rate from your own bill to get kWh and cost per day, month, and year: a 1,500 W space heater run 8 hours a day uses 360 kWh in a 30-day month. Includes a kWh chart by wattage, amps-to-watts conversions, and how to find your rate.
Enter your heated floor area, climate, and furnace AFUE for a rule-of-thumb estimate of the heat your home needs and the furnace input to look for, or enter a Manual J heat loss. Includes a size chart by square footage, input vs. output, and why a Manual J should set the final size.