Best Of

Ok, the team has spoken! Thank you everyone for your input!

I'm a long time reader of the forum..

@EdTheHeaterMan , yes the old 1970's Burnham America boiler is cycling on/off in short 3 minute-ish cycles as you describe, while the 20yr old Bell&Gossett pump runs a bit longer at maybe 30 min? Your numbers make sense, thanks.

@hot_rod, I currently have 2000sqft + 95' of finned tube over 2 zones (65' 1st floor, 30' 2nd floor). House is comfortable when the heat is running.

I'm planning on combining both zones into a single 95' split zone to get me into condensing temps with a new mod con combi, and avoid a small second floor zone that may cycle.

The Rinnai mod con Combi I'm considering only comes in 60k or 90k for CH, both with199k DHW, both turn down to 15k for CH.

Favoring the 90k unit as I will be adding 1000sqft (+45' finned tube) +1 bath addition next year (a final total of 3000sqft + 135' finned + 2.5bath).