Not very much.
A couple of lamps, a window fan and a laptop at once? Yes.
An electric blanket? Yes.
A blender? Yes.
A toaster, hot plate or microwave? No.
Coffee maker? No.
An iron? No.
A refrigerator? Not unless it's a tiny one.
An air conditioner? Definitely not.
It will power two 400 watt lamps.
Normally speaking, a 3500 watt generator can typically power appliances such as refrigerator (500-800 watts), laptop (50-100 watts), television (100-400 watts), stereo system (200-400 watts), air conditioner (1,000-2,000 watts), electric stove (1,000-2,500 watts), lights (50-100 watts). It's important to check the specific power requirements of your appliances as they can vary.
If the TV and refrigerator together use (are rated at) less that 340 watts, then the generator will power them until it runs out of gas. It would have to be a very small, efficient refrigerator as they're usually high current devices. The TV would also have to be small and efficient, but that would be easier to find.
1 Joule is 1 Watt-Second. 1 Watt Hour is 3600 Watt-Second or 3600 Joules. 400 Watt-Hours is 1440000 Joules.
800 watt should be fine
Per hour the answer is 400 watt-hours or 0.4 kW-hours (or units).
To calculate a cost in kW/h a time interval has to be stated. How long is the 400 watt heater going to be on in a 24 hour period. You also have to state what you are being charged from the utility power company per kW/h.
A sump pump usually uses 200-400 watts. So 3.5kW is way overkill. That should be about enough to power sump pumps for your entire block.
Four 100 watt light bulbs or anything else that sums to 400 watts.
Watt and degrees centigrade measure two quite different things. You don't convert one to the other.
Try this link ... a clear explanation with worked examples.www.majorpower.com/inverters/battery_sizing_faq.pdf
430 watt bulbs are made to juice a little more light from a standard 400 watt ballast. you get about 3-5000 more lumens. A typical 400 watt HPS produces about 50-55,000 lumens. The 430 will put out about 58,000. Not a lot, but a little extra without any increase in power usage.