Replacing Gas Boiler & Heater

Discussion in 'Tankless Water Heater Forum' started by Pete San, Oct 3, 2021.

  1. Pete San

    Pete San New Member

    Joined:
    Oct 3, 2021
    Location:
    Columbia, Missouri
    Hi guys,

    I've tried to fill my brain with a lot research this forum has to offer and I'm finding myself torn with which route to go.

    In the middle of a pretty big renovation to my house that was built in 67. Currently using an Ack-O-Matic Boiler that's stamped with LP, but it's definitely using Natural Gas. I'm pretty sure it's the original boiler based on the condition. The data plate is barely legible so my best guess at input is 130k btu and output is 105k? I tried looking up the unit, but the model number is reluctantly hard to read as well. It's setup for 2 zones; main level upstairs and a basement. Upstairs has about 80' of fin baseboard and about 55' in the basement. I can't really speak on overall efficiency, but it definitely kept the house comfortable during our winter seasons here in Missouri.

    My 1st dilemma has been deciding on having two separate tankless heaters or going with a combi unit. I have 3 full bathrooms and at most 2 would be used at the same time. Dishwasher barely gets used and laundry will be setup in the utility room with the space saved from removing the boiler and heater tank.

    I was almost set on a Navien NCB 240 combi until I read Dana's post about the heat exchanger problems from factory. Assuming I would've still went that route, I feel like it would be way oversized for my system. I was also planning on shortening the length of a baseboard heater in one room upstairs because I am also consolidating from 3 windows to 1.

    I would really prefer a combi system over having two separate units, but I wouldn't mind having two units if both could be utilized for DW during non winter months.
     
  2. fitter30

    fitter30 Well-Known Member

    Joined:
    Feb 2, 2020
    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    First you need to know max gpm dhw ( garden tub or muilti head shower), coldest incoming water temp combi heaters are sized by flow and temperature rise. Heating what water temp are you running? Combi units 95% when return water is 130* or under, above 86% efficient.
     
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  4. Pete San

    Pete San New Member

    Joined:
    Oct 3, 2021
    Location:
    Columbia, Missouri
    At most we'd be running 2 showers, a washing machine, and kitchen sink simultaneously. Flow would be conservatively be around 9gpm. Incoming water temp is 52* so about a 60* rise is required. I honestly have no idea what water temp was running for the boiler, but my gut is telling me 180*. I'm not able to verify that as the boiler crapped out at the tail end of last winter.
     
  5. John Gayewski

    John Gayewski In the Trades

    Joined:
    Aug 7, 2021
    Location:
    Iowa
    DO NOT USE A WATER HEATER FOR SPACE HEATING. A water heater is not meant to do the duty of a boiler. No matter whether you splot the load between two units or more. It /they will wear out lickity split. Water heaters are not continuous duty at loads big enough to heat a house. There your answer.
     
  6. Pete San

    Pete San New Member

    Joined:
    Oct 3, 2021
    Location:
    Columbia, Missouri
    I'm determined to go tankless and utilize a system meant to act as a boiler. I know there are units that modulate and condense for optimum efficiency. It's just a matter of sizing the system properly and making sure it modulates how it should. I've definitely still got a lot of research to do, but my dilemma is going with a tankless combi vs a tankless DWH + tankless boiler
     
  7. John Gayewski

    John Gayewski In the Trades

    Joined:
    Aug 7, 2021
    Location:
    Iowa
    OK. My interpretation of your first statement wasn't whether you were thinking of going with a combi or a condensing boiler, but a combi or a tankless water heater.

    I would go mod con boiler with an indirect.

    But since you want to go tankless for your water heater (I hope you have treated water or like maintenance) I would do that. Combi puts you down for the count when you have issues.
     
  8. Pete San

    Pete San New Member

    Joined:
    Oct 3, 2021
    Location:
    Columbia, Missouri
    No worries! I plan on adding a water softener for the DW
     
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