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New Boiler Sizing, Requirements, and Brand Questions

Jaykhjr Member Posts: 10
Hi All,

So this coming spring I want to replace my 1960's boiler with a new model. I am currently looking at a Bosch Greenstar 117k or 89k BTU output.

My home is 2200 sq ft with 10' ceilings. 7 total radiators. mostly black iron pipe running through the house. Single Zone

Current boiler is huge. 200k btu input, 165k output.

My plan is to install and plumb the new boiler myself, then pay a licensed professional in my area to come out, fire it up, and tune it. I have a few questions I am hoping you can help me with.

1. My current boiler has a large holding tank above it, do I need to plan to install a new one?
2. Bosch seems to be a good brand, do you have other recommendations? why?
3. I know I need a regulator on the water supply, blow off valve on the boiler, and a circulating pump in addition to the new boiler. What else do I need?
4. All of the calculators I have used for finding the heat loss tell me in the neighborhood of 96-100k btu... and the nearest Bosch sizes are 117k or 89k. Do I undersize or oversize?
5. The current system vents out the chimney, Can I use the existing hole to run my PVC exhaust through, or should I vent it out through the foundation wall?

I am sure I am missing something. I am trying to learn. and before someone says it, yes I am also considering letting a professional do the complete job, but I like to learn when I can, I'm pretty handy, and have experience with plumbing... just not much HVAC.

Thanks guys!


  • ethicalpaul
    ethicalpaul Member Posts: 5,617
    I'm in your same situation, but smaller. I'm not sure why no one responded to you. Did you have any luck in your search?
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • KC_Jones
    KC_Jones Member Posts: 5,706
    I will be a broken record on here, you should reevaluate your heat loss numbers. I very seriously doubt your load is that high, I'd speculate on the very high end 77k.

    What did you use to calculate the heat loss of the house? Slant fin has a decent app for calculating the load.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
    rick in Alaska