Replacing old innefficiant boiler with Rinnai i120 condensing boiler

barnstormerjack

Hi, and thanks for the add to the group. the old boiler was located in my garage, with 1 inch insulated pex underground to house 15 ft away. Three zone valves in crawl space. Its a ranch style house with a great room in the back with 16 ft ceilings ,we added an addition to the house about 20 years ago, and the house was built in the 50's . Amazingly, with only one pump, it heated the place just fine at 130 degrees water temp! it is 2200 sq ft, 3 bdrooms, and not great insulation in the main two zone areas of the house. In plumbing the Rinnai boiler, reading the pumping away book, I believe as many slant fin registers ( covering most all the walls) we will still be ok with just one pump going into the house , and also the pump Rinnai requires on the intake side of the close tees on their system. My plumber is also in agreement, and told me to post and see what others would recommend. In planning and being an apprentice , im learning lot even at my old age!

Ironman

I’d recommend that you use a heating only boiler with an indirect water heater instead of a combi. Longer life span, less short cycling, less issues.

Depending on your locale, a 2200 square foot house probably only needs 45-50k btus on the coldest night of the year; half that when it’s 35-40* outside. A 120k btu boiler would short cycle a whole lot, especially with low mass emitters connected to it. But you need the 120k btus to get 3gpm domestic heated instantaneously. This is the problem with combi boilers.

hot_rod

The I120C steps up to 199k for DHW and should give you. 5 gpm at a 70 degree rise, I believe, and a 15k turndown for heating which will help with short cycling under low load conditions

Measure how many feet of actual fin tube you have to get some idea on condensing operation.

Follow the piping shown in the manual. If they recommend a low loss header, sep or or PS piping go with that