I am looking to replace the boiler as part of a basement reno. The house was built in 1903 and has cast iron hot water radiators but we've done a fair amount of work to it, added insulation and have all new windows.

The current system is an old boiler from the 50s with hot a water tank. We have big old pipes in the basement which we are removing, which I've been told was because the system originally operated using gravity but has since had pumps added.

I have been given different opinions from different plumbers. One plumber thinks we should stick completely to the atmospheric system with hot water tank and would not put anything else. Another said we could using a wall hung condensing boiler with 4 zones, one for each floor including basement. This would be a little more expensive but means we could relocate the boiler away from the chimney because its side vented.

I'm not really worried about the cost, but want to choose the right setup for our house. Is there any reason to stick with the atmospheric over the higher efficiency condensing boiler?

  • Big old pipes probably means it was a steam system, originally, converted to hot water. That's fairly typical. Gas boiler, presumably?
    – Ecnerwal
    Commented Mar 1, 2021 at 0:08

1 Answer 1


The ONLY argument in favor of the inefficient boiler would be IF it's so basic that it will run with the power out, and thus might help prevent the house from freezing in a long winter power outage (though that would be a limited level with no power for the circulator pumps.)

Otherwise, efficiency favors the condensing boiler. If long winter power outages are a thing in your area, a gas-powered (the same sort your boiler presumably uses, not gasoline) backup generator sufficient to keep the boiler and pumps and fridge and freezer operating would be a solution that does not require throwing a bunch of heat up the chimney, and has more side benefits in the form of the fridge and freezer still working, as well as some lights.

If the chimney is suitable (it may not be) you can get the "not freeze house" and "operates with no power" functions from a wood-stove attached to the chimney for use when the power goes out for a long time in the winter.

  • Thanks for the response, this is helpful. We are in Brooklyn in a neighborhood with underground power cables, so power outages aren't really a thing. The other thing I have been told about condensing boilers is that they are less reliable and can be louder. Any thoughts about that?
    – Charlie
    Commented Mar 1, 2021 at 1:03
  • Condensing boilers will have a fan, typically. May or may not be louder than a naturally aspirated boiler - I've met some of those that were loud enough from flame alone. The fan could fail, but replacement should be straightforward. Does not strike me as great logic for putting an extra 10-15% of heat up the flue.
    – Ecnerwal
    Commented Mar 1, 2021 at 1:20

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