What’s the difference between a high efficiency boiler and a high efficiency system?

There are so many wall mounted boilers and on-demand (tankless) water heaters on the market today, how do you choose?

What do you do when you have two or three quality products that are so similar you just don’t know which one to choose?

Is there a room in your house that is always hot or feels drafty at certain times of the year or in certain weather conditions?