I currently need to replace my boiler/ tankless dhw system and I am looking for some advice from professionals. A little info to help with any questions about my requirements. I live about 20 miles inland from the seacoast area of New Hampshire so winters are cold but not not very often below zero, maybe only 10 days a year. My house is about a 1600 sf cape, 25 years old and a factory built Epoch with six inch exterior walls and heavy gauge vinyl siding with a full wrap of tyvek underneath. Well insulated all around. My current heating/ dhw system is a heatmaker plus 100 in 84 out and has served me well despite its reputation. The lower coil has started leaking over and it over pressurizes and blows off and sometimes goes off on high limit.
I have gotten quotes from good local contractors and have 3 apparently good choices in brands. All full modulating, condensing wall hung units. A Rinnai E110C with attached dhw, a Triangle Tube Prestige solo 110 with a Superstor Ultra stainless steel indirect fired SSU-45 for dhw and a Viessmann Vitodens 100-W with combi plus kit for dhw. After reading all the brochures and specs and doing a little online searching I think that I like the Viessmann the best. The Rinnai has a copper nickel secondary plate exchanger which worries me in a condensing unit due to corrosion. I like the Triangle Tubes heat exchanger design but would really like to not have the big water tank. I just wanted some input and thoughts about pros and cons before making the final decision.