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question regarding boiler+hot water heater and chimney liner

zdirt Member Posts: 2
so our boiler needs to be replaced and I'm more than clueless on how this needs to be done. I've spoken with numerous people that confirm I need a new boiler and have had a few quotes and estimates. I also need a chimney liner placed. as per the chimney guy, we can put in a 6in stainless steel liner and with our 28ft chimney, this will be rated at about 214k btu. Our existing water heater is a 74gallon American Water Heater G62-75T75-4NV rated at a max of 75,100 btu. The boiler the boiler guy is suggesting is a Weil McLain CAa 5 cast iron standard efficiency boiler rated at a CSA Input (MBH) 140k. AFUE% 83.5. Net (MBH) 102k. DOE Heating Capacity 117k.

We are running these appliances into the same flue, on perpendicular sides of the chimney. They are less than 5 feet from the chimney itself. It is in an unfinished basement in New England (2500 sqft home). The total max of both boiler and water heater is 215,100 btu, slightly higher than what my chimney guy told me his "chart" said for the chimney liner capacity.

Are these appliances unsafe to put together into this flue? Or do I need to find a different boiler. Per the chimney guy, he can only fit a 6in liner in, nothing larger will go.

Thank you in advance.


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,237
    I'd be more concerned that you need a boiler that big. Did anyone do a heat loss?
    Ironmandelta T1927steamm
  • Ironman
    Ironman Member Posts: 7,169
    Unless you house's envelope is extremely leaky, it shouldn't take 30 btu's per sq. foot to heat your house, possibly much less. That's 75k btus! Why would you want to put in a boiler that's twice that size? Especially when you only need that many btus on the coldest night of the year? At 35 - 40* outside, you only need half that much.

    What type of radiation do you have? Cast iron, baseboards?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • zdirt
    zdirt Member Posts: 2
    I couldn't tell you. They took measurements all about, but I'm not sure. We have an older house, 1957. We have baseboards through the upstairs and radiators downstairs.

    what are the issues with having a boiler too large (aside from cost I'd assume)?

    and if this model is still recommended, would that capacity be too much for my chimney liner/flue?

    Thank you
    EBEBRATT-Ed Member Posts: 13,770
    I would not put in a boiler that large unless you have an accurate heat loss done first that shows you need that size. You need a heat loss calculation. Measuring baseboard heaters or home square footage will not work.

    Your other alternative is to install the boiler and install an indirect water tank and heat it from the boiler. That way the chimney liner will work

    But check boiler size that's most important
  • Ironman
    Ironman Member Posts: 7,169
    I've been doing load calcs for 40 years and I've never seen anything that needed more than 32 btus per sq. foot - including the most leaky old farm house.

    SlantFin has a free app that you can download to calculate your heat loss. Just enter the correct construction data and dimensions and it will do the rest.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • SuperTech
    SuperTech Member Posts: 1,940
    Install an indirect tank and you will have one less issue to worry about. It's a superior, more efficient setup than running a direct fired unit.