HEATING A very LARGE HOME?

Water use will depend on how many people are using the water, but of course it will cost more to heat and light a larger home than a smaller one if all else is equal. Exactly how much that will be depends on the electricity rates where you are, what heat source you use, and how the house is built, all kinds of factors. If you insulate it heavily and install solar panels or maybe geothermal heating and all that green stuff, it will cost a lot less to light and heat every month but you'll pay more up front for building that stuff into it. That's the kind of thing you discuss with your architect, your builder, and any other professionals involved in it. But really, if you can afford to build a house that size, you shouldn't have a lot of trouble paying to heat it. Around here, a 7,000 square foot house built with average finishing, not the expensive things like marble flooring, granite counters, expensive bathroom fittings and detailed woodwork, would cost about a million dollars. That's for the building only, not for the land it goes on.