I've had 2 estimates for installation of a Burnham gas boiler. One was for the above model number 204NCL-GE12, the other was for a (Series 3?) Model #305 140,000 btus I need a boiler with at least 109,000 btus. I have a masonry chimney. I prefer to get one with 80+% efficiency. Can you tell me which is the better boiler, and the best for my needs? Thank you. Nancy Gordon