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Heating retrofit


I live in the NE. I just moved into an old house built around 1950. The house has a tankless gas water boiler for heating and domestic hot water. Boiler is old Burnham holiday of over 50 years old with 150,000 BTU input and 120,000 output. House has 2 floors with around 1,800 square ft and has very poor insulation We have two zone heat : one per floor. I have 2 questions:

1- the water in the shower gets freezing when the hot water is used elsewhere in the house. We can't use washing machines, dishwasher or even wash our hands without making the other person freeze in the shower. What is the problem and what could be the solution?

2- I would like to retrofit this old boiler and I'm looking into going with more efficient gas boilers or maybe mod con boiler. Currently I have baseboard heat with 180 degrees water supply. I've been reading a lot about how mod con works best with lower water temperature. I'm afraid if I go with mod con and lower the temp of the water supply in the baseboard I will not get enough heat as quick  as I'm used to it and will sacrifice the comfort in the house which for me is the main priority for heating. I have done a heat loss on my own and found out that my heat loss is 45,000 BTU. I have measured my exisitng baseboard length and I have 100 linear ft for the entire house which I believe (based on some info I found online of 550btu/lf/hr per baseboard) I should be just about right and I'm not over sized (55,000 BTU). My question should I go with high efficiency mod con or mid range effciency with cast iron heat exchanger. 

I would appreciate if someone can honestly answer this.

Thank you


  • Ironman
    Ironman Member Posts: 6,973

    I'd go with a mod/con. They come with outdoor reset which adjusts the water temp to match the load. This results in greater comfort and efficiency. But, a word of caution: you don't use setback with this kind of boiler. That would actually make it less efficient and sacrifice comfort for nothing.

    The installer is 98% of the equation. It's imperative that you get a competent one.

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    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
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