Fuel is the limit
A standby generator will run continuously until it runs out of fuel or needs service — there's no built-in time limit. On natural gas, fuel is effectively unlimited: the utility keeps delivering, and residential gas service almost never fails during electric outages. Multi-week runtime on natural gas is realistic. On propane, your tank is the clock: a 500-gallon tank (400 usable gallons) at half load gives roughly a week of continuous running; at full load, roughly half that.
Oil and maintenance during long runs
Engines consume a little oil as they run, and long outages mean checking it. Most manufacturers recommend checking oil every 24 hours during continuous operation and changing it after roughly 100–200 hours of runtime (about 4–8 days). Air-cooled residential units are designed for this — they're built to run for days — but they do need that oil check. After any outage longer than a couple of days, schedule a service visit: oil change, filter check, and a once-over.
Heat and rest
Air-cooled generators shed heat through their enclosure fans, and they're rated for continuous operation in hot weather — including a Maryland August. You don't need to "rest" the generator by shutting it down periodically; in fact, cycling it off and on causes more wear than steady running. Let it run.
Planning for the long outage
The 2012 derecho taught Southern Maryland what a multi-day outage feels like. If long outages are your worry: natural gas removes the fuel question entirely; on propane, size the tank for a week-plus and keep it full from June through September; and know your oil-check routine before you need it. We'll walk you through all of it at installation — and our maintenance plans include post-outage service.