I am an electrician and I posted info about vehicle mounted generators which is not really your issue. The bigger the generator for portable use means it is more hungry for gasoline. If you plan to be around when it is running you could load spare, meaning turn off the frigde for 4 hours and turn on lights etc. Turn off the lights and on goes the furnace. If you only have say 5 gallons in stock that is only maybe good for 8 hours at 5000 watt load. My thoughts are 3500 watts but load spare. A good quality 3500 watt will last a long time. Do not connect into the house unless done CORRECT.Cord connected is simple and safe.
Craig Clayton
I have three sources of power:
A 4400/5000 watt unit that I bought from Harbor Freight in 1996 for $279. That was before the Y2K fervor. It will run 1.5 hours on 1 gallon of gasoline.
A 1000/1200 watt 2-cycle interruptor governed portable that I bought at Coastal Farm for $149 about 5 years ago. It will run 4.5 hours on a gallon of mixed gas, and is very quiet.
A 2000 watt inverter hooked to a pair of deep cycle batteries charged by a lawnmower motor and a truck alternator. It makes no noise at all when the motor isn't running.
Load managing is simple. First, I don't even get a generator out until the second day of the outage. A few wall hung oil lamps and candle sconces, a battery powered radio (DX-440), and a LED clip-on reading light for books is all I need for the first 24-48 hours. The wood stove keeps the house warm, and low head gravity feed water refills the toilet and provides drinking water.
After 48 hours, I'm tired of sponge baths, so I fire up the 4400 watt generator to heat a tank of water and run the pump for a hot shower.
The little 1000 watt generator will run the TV and a satellite dish, or a computer and DSL modem, plus a light bulb or two. It will also run a freezer or refrigerator.
The inverter provides demand power when I don't need any. I can turn on a light bulb in the middle of the night. The inverter only uses about 100 mw at idle, so leaving it on all night won't drain the batteries. When I'm charging the batteries with the motor, it will also handle both a refrigerator and freezer at the same time.
Worst case scenario, I have a FSC travel trailer with propane furnace, twin 30 lb. tanks, and twin deep cycle batteries that I keep on a float charger. The little 1000 watt generator is my camp generator, and will handle the 30 amp charger plus lights just fine.
I think people over-pay for generators, buying too much generator for the amount of fuel they store, and too much capacity. A cheap B&S engine will run fine for years if you drain all the fuel and fog the cylinders before you store it. It's not like you put hundreds of hours on an emergency generator. Running it 2 or 3 hours a day, I have put maybe 20 hours on my 4400 watt generator in the last 13 years. At that rate it will last longer than I will.