A decent mod-con boiler is not cheap to install. It does have the ability to (if setup right) provide more comfortable heat than an old on/off boiler control system. The rated efficiencies will actually vary a fair amount depending on how well they are chosen to match the load and how well the overall system is designed. But, with today's NG prices fairly low, it may not cost that much in efficiency to use an old one verses the install cost of a new one. If there are rebates, that can quickly change the equation. But, in a mild climate and not horrendous electric rates, heat pumps can hold their own, at least in heat output. A boiler may provide better comfort though. Some just do not like the air blowing, and radiation tends to be more even than forced air. A boiler does produce more hot water/faster than an electric WH and at lower costs, so you need to factor that into your overall energy use equation. But, an indirect tank will also cost more than an electric. It will last longer.