I just had two 1500W/220V baseboard heaters installed on my back sun room. Each unit has a thermostat dial which we will be turning down at night and back up in the morning (we plan to at least). So they will be running a good portion of the day when the weather gets colder (this week it’s supposed to have overnight lows under 20F). I’ve found some formulas but I don’t know how to plug in the correct values. My utility reports electrical cost of 5.87¢ KWH. I don’t know how to do the conversion.
Assuming they’re running at full load (rather than being staged on a bit at a time), 1500 Watts is 1.5 kW each. Multiply 1.5 kW by the number of hours you operate the unit to obtain your energy usage in kWh. If you’re running both units, multiply this by two. Now multiply that by your cost in $/kWh to obtain the cost.
I hate it when details are that obvious. “kWH” == thousand watts per hour. Duh.
Ok, does this reflect the difference between running 1500W 110V heaters versus the 220V units that are installed? I got 220V units because they are supposed to be cheaper to run.
No, watts is watts. The total energy usage will be the same, but the current draw of the 220 V units will be half that of the 110 V units. This is the reason 220 V is preferred for high-power appliances, not operating cost.
Shouldn’t you have checked into this BEFORE you installed the heaters?
To do a little math for you:
If you are running both 12 hrs per day (say 8am to 8pm), you should expect your bill to increase by about $63 per month.
Not too shabby I suppose for a piping hot sun room in the winter. Of course if it’s on a thermostat it probably won’t be running at full capacity all day long. Thus you should save some money.
Would knowing how much it would cost have made him warmer? 
Also double check w/ your electric company, I asked that question and got 2 answers, one the price per kwh, and the other inclusive of delivery fees and taxes, which is quite a bit higher.
Anyway if price is an issue and all electric resistance heaters are 100% efficent and expensive, I would look into other ways to heat that space.
The work is done and the room is warm, there’s definitely no going back. I was really just curious as to the impact on my utility bill. The way natural gas is going, it might be easier to sit in the sun room with the new heaters then the rest of the house.
Another thing you can do is learn to read your power meter if you don’t know how. Go read it once or twice a week, and record your results. You can then figure out if you are using tons of power before you get that $500 power bill.