A couple of issues come to mind after reviewing this again.
Is the 8 days consecutive? or are you referring to 4 weekends? The reason I ask is that, with a real tight building, some of the heat sizing hinges on how fast you want it to heat up. If you are going to heat the building once, for eight day, then you could afford to be a little shy on heater size and fire it up the day before. Doing this four weekends a month is a little different, as you have to "preheat" the building four times.
The other issue, with electric, beyond the fact that it is (generally) the most expensive way to heat, is that code limits heating elements/circuits to a max of 60 amps and this means a 48 amp draw max (80% of 60 amp). Larger heaters simply have more than one feed.
Are you planning on having weekend country music productions in there?
ie. lots of lights, other power draw? or is it a simple get away where you will run the compressor a little and have basic fluorescent lighting, and not a lot more?
My uneducated, uncalculated, gut feeling from what little we know, is that you are probably going to need at least 150k btu to do the job, and a little more if you want FAST heat up and recovery from an open door, etc.
My thinking is you will need about 4 10K watt heaters to begin to make it work, that would be 136K btu and four 60 amp circuits, thus four runs of #6 to the panel and about 168 amps (four 10K watt, 240v heaters at 42 amp draw each). Thats a bunch of wire, and half of your electric capacity.
Buying new, you are looking at $2000 or more (as much as $3500 depending on your shopping skills), plus the installation costs. The GOOD news is, the heaters will last practically forever, and not need any maintenance. You won't be worrying about cracked burner cans, cleaning out combustion chambers, collecting used oil from people, dealing with water and other **** people will sneak in the oil and refuse to admit to. You won't have to have a propane bottle rent charge, or remember to call and have it refilled, or buy one and shop for a good price.
Its works both ways. I have electric (heat pump) heat in my house, because I am not fooling with firewood, or anything else (I do have a fireplace I've not used since I moved in over 15 years ago), I want to set the thermostat and be done with it.
The shop on the other hand, I am not willing to spend any more than I absolutely have to, to make it warm out there.
I spent $5,000 to buy a new waste/used oil fueled furnace heater and then installed it myself. My operating cost is electricity to run the internal fan, combustion fan, ignition, and the ceiling fans and the air compressor (intermittently and not very often). I spend more time that I would like sometimes, gathering up used oil, and I have enough people giving me oil (I work as a mechanic with a bunch of mechanics) that I simply let them know to bring it in to work and I'll take it. I get a gallon or two here and there, and sometimes ten or twelve gallons at a time. So for me, its just some time spent pouring it in the heater and disposing of plastic jugs, and such.
This might be a good situation to use the radiant tube heaters in such as discussed in
THIS THREAD, and simply be willing to deal with the propane.
Charles
