New build in Ft Worth TX. Plumber wants to use Rheem propane tankless system. I like what I have read about Takagi. What system is better? Single story, well system and 42 days a year of temps. at or below 36 degrees F. In addition we are considering a "full" encapsulation foam insulation which would create the need for a fresh air exchanger, I am assuming that tankless systems benefit from direct venting. Please chime in. JD