It depends on which appliances you want to power. Essential loads (refrigerator, lights, furnace blower, sump pump) typically need 5,000–7,500 watts. Adding central air conditioning can push that to 10,000–20,000 watts or more. Use our Wattage Sizing Calculator for an estimate based on your specific appliances.
Running watts is the continuous power an appliance uses during normal operation. Starting watts (surge watts) is the extra power needed when a motor first starts up — typically 2–3× the running watts. Your generator must handle the highest starting wattage of any single appliance, on top of the running watts of everything else already on. Read our full running vs. starting watts guide.
Portable generators cost less upfront and offer flexibility but require manual startup, fuel refills every 8–12 hours, and typically power only essential circuits. Standby generators start automatically during outages, run on natural gas or propane for extended periods, and usually cover the whole home — but cost significantly more installed. Compare both paths with our Standby vs. Portable Calculator.
Yes. NEC Article 702 requires a transfer switch for any generator connected to your home's electrical system. It prevents dangerous backfeeding of power onto utility lines, which can injure or kill utility line workers. Manual transfer switches cost roughly $300–$800 installed; automatic transfer switches for standby systems run $500–$2,000+. See our full transfer switch guide.
Operating costs depend heavily on fuel type and generator size. Gasoline portables typically run $2–$8 per hour depending on load. Propane and natural gas standby units generally cost less per hour but the equipment and installation cost more upfront. Use our Fuel Cost Calculator for an estimate based on your specific generator and local fuel prices.
Yes, but it requires a properly sized standby generator (typically 15–26 kW or more for an average home with central AC) and professional installation with an automatic transfer switch. Most homeowners choose to back up essential circuits only, which allows a smaller and less expensive unit. Try our Whole-House Sizing Calculator.
A generator loses roughly 3% of its rated output for every 1,000 feet of elevation above sea level, due to thinner air affecting combustion. If you live above 3,000–4,000 feet, size up your generator accordingly. Our Whole-House Sizing Calculator factors this in automatically.
Gasoline is widely available but has a shorter shelf life — best for occasional, short-term use. Propane stores much longer and burns cleaner but provides slightly less power per gallon. Natural gas is the most convenient for standby units connected to a home's existing gas line, since supply is effectively unlimited. Diesel is the most fuel-efficient but generators cost more upfront. See our full fuel cost calculator for a side-by-side comparison.
A Level 2 EV charger can draw as much as 7,200 watts continuously — more than most essential-circuit backup systems are sized for. If you want charging available during an outage, size your generator to specifically include the charger's full load, or plan to pause charging while running other essential loads. Add it as a custom load in our Wattage Sizing Calculator to see the impact on your recommended size.
Portable generators are typically the loudest, especially older or non-inverter models. Standby generators are engineered to run quieter and are usually placed away from windows per manufacturer and code setback requirements. Many HOAs and municipalities have specific rules on generator placement, sound levels, and required permits, so check local requirements before installation regardless of which type you choose.
Some insurers offer discounts for homes with a professionally installed standby system, particularly in outage-prone areas, though policies vary by carrier and region — check with your insurer directly. Many buyers view a standby generator as a desirable feature, but the specific value it adds to a home sale varies by local market.
It depends on your generator's size, expected load level, and how many days of runtime you want between refills. Common residential propane tank sizes are 120, 250, 500, and 1,000 gallons; a 500-gallon tank typically supports several days of runtime at moderate load on a mid-size standby unit. Use our Fuel Cost Calculator with propane selected to estimate consumption for your specific setup.