hot water tank/furnace

I have an electric 40 gallon hot water tank in the basement. Beside it a furnace (boiler type). I was told by the furnace service rep that I could use the furnace to heat my hot water. It was simply a matter of installing a coil and some plumbing. It would certainly save money on hydro but add the cost to oil. Also the furnace would run all year around. At the moment it is turned off during the summer months. I wonder if this would be an energy saving, whether or not the furnace could provide enought hot water for a family of three.
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Depends on;
a) Mainly; the cost of your electricity. How much electricity will you save? What $ saving? b) That your furnace running for short periods of time to only heat water throughout the summer will use slightly more oil than at present; however only working occasionally it will not be very efficient. How much more oil will it use? What $ cost. c) It will preclude shutting off the furnace so that it can be maintained, sweeping the chimney etc during the summer. This may be a small disadvantage if the electric dollar saving versus the cost additional oil is large? d) Will the additional dollars invested in installing a heating coil and its plumbing amortized over a reasonable period of time be small enough to justify the cost saving by not using electricity. Will the new installation be more/less complex or maintenance prone? e) Since you already have the electric tank, best to leave it in place until it eventually has to be replaced; because, even if the furnace fails, runs out of oil or there is an electricity supply failure which causes the furnace not to run (most furnaces need electricity to pump and ignite the oil?) you could have a tank full of nice hot water to fill hot water bottles and have the family retire to bed until the power comes on again?
So; 1) Do a comparative cost study. 2) Jot down the intangible advantages/disadvantages of either leaving it as is or changing, that you can't exactly put a dollar sign on. 3) Make a decision. 4) Live with results of decision. 5) Review you decision after an interval up dating the various dollar amounts involved.
Further comment; using electricity to heat water is virtually 100% efficient; all the electricity you pay for is turned into heat inside the electric hot water tank. When oil is burnt some combustion heat is 'lost' through chimney/flue/vent etc. So not all 100% of the energy content of oil is used to make heat, also a furnace is really only most efficient at working temperature since it requires a short time to heat up and to cool down each time. the electrical parts of the furnace will use slightly more electricity if it has to run during the summer to heat water, although it's probably so small an amount it can be ignored. Terry.
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