There was some previous posts asking about the portage main optimizer. I have one and would lie to say so far Im very impressed with it. There is very little to no smoke,Its built like a tank and very easy to use. Weighs 3000 lbs. has about 90 ft. of heat exchanger that is easy to access and clean. I think they really did a good job on this boiler . There is one nozzle in the fire box that is about 4 inch thick refractory and looks to be easy to replace. The target area is firebrick that would be easy to change if there ever is a problem. On the newer model they eliminated the bypass door, I called the factory and asked why, they said there was an issue of it not sealing well so they got rid of it, I was concerned about smoke when loading without a bypass but its no problem at all. I would recommend this boiler to anyone looking for an outdoor unit.