Let me clarify since this thread has resurrected itself.
In the northern climates where I live, almost 100% of the heat during winter is either natural gas or propane. It's either fan forced or hot water.
In each case, the amount of electricity consumed by a typical furnace is well under 15 amps. Like a few hundred watts for all but the biggest furnaces.
When the power fails during the coldest part of the year the most critical thing to keep running is the furnace. You can have frozen pipes and other cold related damage in a relatively short time. The amount of time is irrelevant but think multiple hours not days.
We all have flashlights, the fridge isn't a big issue (natural freezer outdoors, and usually free ice) and so on. But the furnace having power is critical.
The quickest fastest way to get that furnace back on is to fire up a generator or some other suitable power source and then hook the generator up to it.
The problem is that people rarely think ahead, so they're trying to come up with a quick solution, and most of them don't really understand wiring. Because, by code, the furnace may not be connected with a plug and socket the homeowner has no option but to open up an electrical box and try to figure out how to hook his generator up. With the not uncommon enough result of the generator trying to power the neighborhood.
The solution is dirt cheap. Instead of requiring a hardwired connection, move to a standard 120V 15A plug and socket connection. Based on other requirements in the code such as for a disconnecting means near the furnace which this would replace as well, the cost is likely to be zero.
Its not uncommon to see this done even though it is against code. Whether it will pass inspection depends on the attitude of the inspector.