I know the Rinnai very well. You are correct on the hot water output of the 110. Yes, there is some delay in hot water but mostly that depends upon location of the equipment, location of faucets and hot water piping lay-out. The 110 does have a very robust outdoor reset control. As well it comes with the low loss header. The LLH provides the primary secondary piping. It has a heavy stainless steel HX. It can be vented side wall and the clearance to a door or window is 12". It can vent with either the concentric poly propylene pipe or with 3" PVC. The adapters are provided. The 110 as you know is a Combi boiler and has a 3 way valve internal to the unit that senses hot water flow and diverts the boiler output to the DHW. That is called DHW priority.

I am definitely biased to the Rinnai. They have a much stronger support base as a company. The first time I fired a 110 up I had a bunch of the Boston Gas Utility folks with me. On a first time start-up, with an audience, I was nervous. I turned it on and waited for its pre-purge and self check and waited and waited. I couldn't hear anything. I didn't think it was running. Finally one of the guys grabbed one of the pipes and let go in a hurry as it was hot. I then looked up into the left side view port and saw the flame on the ceramic burner. Relief! Very quiet in operation.

I can't offer advice on the specific device but I can say I replaced my ancient Sunnyday with a 85% AFUE oil boiler (Solaia/BASI) and cut my oil consumption 35%. Gas not available in my area. Getting rid of that dinosaur and switching to gas should save your dad a ton of money.

Thanks for the encouragement. I guess that a big chunk of your 35% is due to the end of a constantly-hot boiler 24/7/365. I do have some concerns about possible condensation in that part of dad's basement since it will be much cooler. We've decided that there is really no point in worrying much about it until we see a problem,

I had a plumber install a Rinnai E110C in my house(built in 1915,I live in Massachusetts) in September of 2014. So far I am very happy with it. The time it takes to get water my shower upstairs(about a 30 foot run from the boiler) is about 10 seconds in the summer and maybe 15 seconds in the winter. Ground water temp in my area is about 52 degrees. However there were a few issues that I experienced. First, I had a concentric intake/exhaust pipe installed out the side of the house. When it would rain, water(the rain) would get into the intake portion of the tube(the outer pipe) and make its way back into the boiler casing and splash around and condense at the bottom of the unit. This is something you don't want to happen as the electronics are housed here. The pipe outside the house was positioned in the corner of where two porches on the house meet and when we would have a rainstorm this was a turbulent side of the house. I eventually had the plumber reroute the intake/exhaust to a two pipe(separate pipes and at an added cost of $800.00 to me) system and on a flat wall in a different direction. Problem solved.

My Rinnai E110C is positioned where the oil tank was. I had put speedi dry down where the tank was and right under the two pipes for hot water heating and return at various times There were moisture spots about 5 or 6 inches in diameter. Putting my hand on the pipes leading into the low loss header, my hand was wet with moisture - condensation. The low loss header itself is insulated with stiff Styrofoam. Just today I put insulation on those pipes and hopefully that will solve the problem.