My home built OWB feeds an 18 X 18 heat exchanger in my oil furnance plenum. When I go on holidays, the OWB is shut down of course and the house is heated by the oil furnace. Because the circulating pump for the OWB is left running, heat effectively flows in reverse and is transfered from the oil furnance, into the heat exchanger and to the OWB. The temp of the OWB reaches about 70 to 80 deg. It is for this reason that I do not use glycol with my system.
My OWB is 160 feet from the house and contains 600 gallons between the boiler and storage tank. My location is central Ontario.
In your case I would think it would help supplement the hot water temp but may not be enough on its own. You will be buying all the needed parts when you build your own OWB anyways so it would cost you very little to try it. Hope my .02 cents helps.