Hi,
Could I have some input on the best way to heat my domestic hot water.

My house is 1907, 8000 plus sq', and changed into 4 apartments (as many of these large old houses were). We are restoring the house from the foundation up (but retaining the apt's.) and are doing all of the plumbing systems at this point. The heat is supplied by a Weil McLain cast iron boiler (new) 216,000 btu that feeds the original cast radiators. The system works wonderfully well, no issues with heat. The house is not insulated but will be when we are done, so I'm sure the heat loss for the building will be less. The boiler should be working less as a result I would think. The boiler stops being asked for heat around May 1st each year and doesn't usually fire up until Oct.

During this never-ending restoration (I tell my wife we are in year 2 of a 10 year project, I've been telling her this for some time) the plumber who replaced the boiler and whose main work involves larger buildings with a great deal of control in their heating systems suggested using an indirect HWT with the boiler. He also suggested having the boiler run on a year round basis was better for it rather than sitting dormant for the non-heating portion of the year. A different plumber doing the work at this stage said to just carry on the way we have now (2-50 gal gas-fired HWT's).

The advantages of the indirect tank seem to be no gas plumbing, no exhaust venting, less maintenance, longer life (most are stainless steel), and one larger tank compared to two smaller ones (more free space in the boiler room). Economically it seems to make sense, the cost of the indirect tank is more than the cost of two gas HWT's, but not by that much.

All these issues aside does the annual cost of natural gas work in favour of the indirect HWT system? Cheaper hot water during the heating season when the boiler is running regularly plus the cost of the boiler being run during the non-heating season for hot water only verses the cost of gas running 2-50 gal HWT's year round. Would a condensing boiler be better (more economical) to deal with the hot water requirements during the non-heating season than the cast iron one?

I realize there are differing opinions and not one correct answer in a lot of this stuff, but is there a more correct answer in this case?

Thanks very much,
Michael