Fortunately our dishwasher has a built in heater so it doesn't use much hot water. We also use space heaters and they are pretty darned good at what they do. Still we average 4-5 gal a day to heat the house in winter and I dont' see anyway around that.
You're thinking in a 20th century pre-peak oil mode.
The energy you use to heat your dishwasher water comes from ELECTRICITY which may not have seen the price increases that the immediate oil market has seen - but it's coming.
Normally, most utilities go on about a three year cycle for electric rate adjustments with the state PUC. The new rates are usually figured so that the return on investment runs about 11 percent a year averaged out over the three years. The utilities generally have a better idea where fuel prices are going than you and I, and they figure it so that the first year the utility makes money beyond the 11 percent, the second year, they break even at 11 percent return, and the third year they lose money.
Thus, right now you're seeing electric rates that were probably predicated on oil prices of perhaps 60 to 80 dollars a barrel. Shortly, the electric rates will be adjusted, and you'll find yourself paying electric rates a third to half again what you're paying now.
Now there is an advantage to allowing your dishwasher to heat it's own water. There is no "standby loss" for a dishwasher and the water is heated as it is used. Technically it's possible to run a dishwasher on COLD water except dishwashers rinse using the water from the hot tap and don't preheat the rinse.
Meanwhile your own electric (or gas, or oil) hot water heater stays comfortably down in the basement and there is a stand by loss which just about equals your monthly dollar hit in hot water. In essence you're paying for your personal hot water twice. Once for the actual hot water and once again for the convenience to keep it hot and ready and waiting for you.
Of course there are the so called "instananeous" electric and gas hot water heaters. No standby loss. BIG energy demand when in service. Usually problematical with maintaining temperature; or at least consistancy. They frequently have problems with lime build up and are noted for a shorter life than the old fashioned tank heater.
As to electric space heater, these allow you to keep your room "average temperature" somewhat lower than might be comfortable. Perhaps even as low as your house thermostat can go maybe even into the mid 50 degrees. You can then use the electric heater to "spot heat" a comfortable space or room for you to be in. Of course the electricity has it's own price, which is generally a bit more than simply burning the home heating oil. But the key is to use it as spot heating. Heat only the space you intend to be in and turn it off when you're not using it.
Remember the old copper dish heaters? These were so called "radiant heaters" and were particularly adaptable to spot heating. The more modern "quartz heaters" were of this ilk too. However, the oil filled radiator types (they look like a sheet metal steam radiator except you plug them in) are more for heating an entire room (or for putting your wet boots on top to dry out.) Not so good for spot heating.
There is no easy solution to home heating. And it gets harder if you eshew oil.
My dad for a while had a "Riteway" furnace in his house and he would burn 7 cords of wood a year (back in the days when the town forest guy would give you the wood for free) and later burned 2 to 3 tons of coal a winter. Like the others though, once the price of oil moderated, he took out the Riteway and installed a oil fired hot air furnace. I wish he still had the Riteway as it was a pretty dependable heater.
I also see "pellet" stoves and corn stoves in more demand. Already, the manufacturers of pellets and stoves are having problems meeting market demand. A good buy for a pellet stove (or any stove for that matter) can he had on most local Craigslists. Expect to pay up to a grand for a used pellet stove, or nearly two grand for a new one.
If I had it to do now, I would explore the coal stove possibilities. Anthracite coal prices have not changed that much and an anthracite coal stove can be had for as little as a hundred dollars on Craigslist.
This coal stove is available in the Cow Hampshire Craigslist for $150.
Best,
Joe