Yup... OWB's, boilers, add-ons, forced air furnaces and whatnot all require some source of power to run. Pretty much any wood-fired heating appliance except stand-alone stoves (space heaters) are gonna' need power. The way I have my wood furnace "plumbed" I can use it and some heat will filter up through the return vents, but it ain't very efficient and I need to watch closely for over heating.
Several years ago a February ice storm put us out of power for 10 days. We kept the furnace burning low which kept us from freezing... barely. We melted snow in buckets by the furnace for flushing the toilet, washing up and such. Did most of the cooking outside over a fire, but heated some soup and such on the furnace. About 5 days in, I was able to borrow a small 1200 watt, 120v generator (couldn't buy one within a 1000 miles) so we could run the furnace blower a bit, but it couldn't power the 240v well pump. I ain't no fool, learned my lesson and purchased a 5500/6500 watt, 240v generator after that. I keep it full of stabilized, non-ethanol fuel... drain it and refill with fresh every 12 months, start and run it a bit every 30 days or so. I don't keep a lot of extra fuel on hand for it during the summer, but I try and make sure there's around 3 days fuel (about 15 gallon) all winter. We've had to use it a couple times, the longest was about 16 hours... 5500 watts powers the whole house and well pump just fine as long as you use a bit of common sense, such as don't flush the toilet when using the stove top, turn unnecessary lights off, unplug appliances when not in use (the transformers are always drawing power), etc. It ain't so much that the generator won't handle it... but the fuel lasts a lot longer if you can reduce the load.
"Course, that ain't gonna' help much when Armageddon hits... 'cause there won't be any fuel available anyway.