Recently I had a cast iron boiler fail, it was not pretty and replacing it was not going to be easy. After doing some research, decided to go he route of a direct fired, 90% eff unit. There are many brands out there to choose from and these units are much smaller than you can imagine. The Weil-McLain ultra is a very high quality unit, but is also priced that way. In my case, it was outside of my customers range, so research went on. Looked into the Trinity line and found it to be a good quality, many options, and priced at less than 1/2 the Ultra. I made a mistake many years ago with a similar type made by Smith. Ended up replacing it 10 years later, so many questions were asked about the Trinity. Over all, I was impressed, so we put that one in. Parts are easy to find, over all quality was better than I could imagine. Pending on model, it can do DHW tanks. Built in outdoor reset and WiFi access for reporting troubles. NTI gets 5 stars for this, something you may want to look into. If you want to stick with cast iron, Weil-McLain, Burnham, and Crown would be the top brands out there. Geothermal has limitations, as you need just the right field to keep a good temperature. A friend of mine has a high ground water level and is on 50 acres, he was a great candidate for Geothermal and the solar Aray to run it. He rarely has an electric bill. Good Luck on what you decide.