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New Tankless Combi system or replace furnace and leave indirect water tank

Hi All,

I live in the Northeast and currently have a furnace/indirect water tank. My furnace is close to the end of its life and I am looking to get ideas on the replacement with either tankless system or replace existing appliances(not sure how much life is left in the indirect WH). happy to hear anyones suggestions or experiences under either plan. thanks all.

New Tankless Combi system or replace furnace and leave indirect water tank 0 votes

tankless combi unit
New Furnace/indirect water heater


  • When you say furnace, do you mean boiler? If so, does your boiler also heat the house?
    Often wrong, never in doubt.
  • jbutler1969
    jbutler1969 Member Posts: 2
    yes, the furnace heats the house.
    EBEBRATT-Ed Member Posts: 11,996

    If your "furnace" heats water it's not a furnace it's a boiler
  • Jamie Hall
    Jamie Hall Member Posts: 18,931
    Hopefully, as folks have said, it's a boiler, not a furnace.

    If it is, in my humble opinion your best bet is going to be to replace the boiler and keep the indirect (that can be replaced separately, if and when needed).

    A tankless water heater is entirely the wrong appliance to be used for heating purposes, so that's out. There are, however, any number of very good boilers. The number one step, though, is to do an accurate heat loss analysis on the house. You can do pretty well with this calculator: https://www.slantfin.com/slantfin-heat-loss-calculator/, but whoever you hire to do the job should do their own. If they don't want to or can't, you don't want them selecting your new boiler, never mind installing it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England