You'll need about 4500 BTUs which will take about 1300 watts to generate. While resistance heaters are 100% efficient, they aren't the cheapest way (heat pumps are more than 100% efficient, and gas/oil while less efficient uses a cheaper form of energy in most situations).

4500 BTUs is the upper limit for portable space heaters, but well within the limits of a small permanent heater. Almost all of these run on 240. From a safety point of view, a permanent heater is a better idea.

The word "quickly" complicates matters. Sizing of baseboard heaters is typically done for slower rise times-- in the assumption that temperature setbacks, if any, are minor. 10-12 watts per square foot is typical. More watts per square foot equals faster rise time.
While baseboard heaters are available up to 300 watts per foot of heater length, they are rarely in inventory and 250 watts per foot are more often available. 240 volts is best for permanently installed baseboard units.

This post was edited by bus_driver on Tue, Mar 5, 13 at 14:59

..and the differnce between an 8 foot regular wire in 240 V for maybe $75 and a similar 6' wire in hydronic for $198...

Also, what wil this add to my bill..again raising temp from 63/64 to 70 or so a few nights a week....I assume I should not leave the stat set at 70 but only set it when we are down there....

I suggest that you use the Internet and educate yourself about how to calculate the expected costs-- might do you good and help you too. If electricity is the power source for both, the higher priced heater will benefit only the manufacturer and the seller-- and the state sales tax collector.

thanks!

So if I need 1300 watt board....does it matter the length so long as its rated at 1300 w...most say 1500 watts btw....

Does this sound right:
Cost = (#Watts / 1000) * kw$perhour * Hours run.

I think my electric is .08 per hour. The question becomes how long would the 1300W heater (or 1500W) have to run to raise the temp form 64 to 70 and maintain it for several hours....I'd expect it run non stop till it 70 but then come on and off...

Correct, what you really need to know is the BTU/hr the thing puts out. Fortunately with an electric resistance heater (as these are), there's a direct correspondence between the wattage of the heater and the output. As pointed out, the 1300 watts you need is pretty much the top end of what you can legitimately get out of a portable (plug in heater).

Yes, the heater will run only as much as it takes to get the room up to the set temperature. The one advantage of these electric baseboards is they typically respond pretty fast (they get hot as soon as they turn on). There's also no real disadvantage of putting one a bit oversized in. It will just shut off faster even though it's consuming more power as it is running. This is in stark contrast to a heat pump or even conventional furnaces that lose efficiency when you run them oversized.