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Oil boiler, can you turn off domestic function?

Shadowdoc Member Posts: 32
I have an old Rheem cast iron boiler that was installed in my house in 1964. It’s supplies both hot water for baseboard heat as well as domestic hot water. Old 1904 Four square home ~1980 sq feet.

Is it possible to run the boiler just for the baseboard heat and not use it for the domestic hot water?

It seems to burn a lot of oil just maintaining the temperature for the domestic hot water in the house. I would rather install a separate hot water heater for the domestic portion.


  • STEVEusaPA
    STEVEusaPA Member Posts: 5,672
    If this were newer equipment, properly installed (heat traps), pipes insulated, I would say not to do it. Modern 3 pass boiler, and an indirect, or an EK would be pretty efficient, and a good way to go.
    But with your old boiler you probably have a large amount of water in that boiler, and if you don't have large domestic usage, you're probably better off with the water heater.
    You could even pipe in the water heater as it's own zone for storage, or using some valves, hook it up so in the summer you use the water heater, in the winter the boiler.
    Keep in mind, with an electric, you're not going to get the hot and maybe plentiful amount of hot water you probably have now with the boiler.
    You'll have to adjust your triple aquastat (if you have one), or reconfigure some controls if you have all separate controls (high limit, low limit, low limit reverse.
    Best of course would be a heat loss, proper sized modern equipment and like I mentioned at the top-Modern 3 pass boiler with indirect, or an EK, with or without an indirect for storage.
  • Shadowdoc
    Shadowdoc Member Posts: 32
    That’s a great idea. Didn’t think of that. I can pipe in a water heater that will be solely used in the summer for domestic and then run the boiler in the winter since it’ll be on for heat. A couple of valves would do the trick.

    Thanks for the insight.
    HVACNUT Member Posts: 4,560
    IMO, it's time to talk about upgrading to a high efficiency system. At that age, with other age related problems lurking, I wouldn't put any money into a 54 year old residential boiler.
    Like @STEVEusaPA wrote, most 3 pass boilers with a matching burner, or an EK Frontier or Resolute will save plenty if sized and installed right.
    If you think it's an option to upgrade, feel free to get info here. These guys are wicked smart. No $$ talk though.
  • Shadowdoc
    Shadowdoc Member Posts: 32
    I Think you’re probably right. Time
    To upgrade.

    1980 sq ft Four Square built in circa 1910. 6 small bedrooms, 1 bath upstairs, currently on 2 loops. 4 equal sized rooms down with 1 bath also on 2 loops. 2 zones, 4 loops total. Not much has changed except more insulation in attic. Plaster lathe construction with hollow walls. Catskills NY.

    For info and nostalgia :-), I attached what I have now, which was installed back in ~1963.

    The big question is.....What would be the best system to replace it with?
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,672
    Nice stuff!
    At least check the 'Find a Contractor' to see if someone from the Wall is in your area.
    1. Consider building envelope upgrades first. They could make a huge difference on your heat loss, and boiler sizing.
    2. Have a proper heat loss performed.
    3. Don't oversize the equipment, especially for domestic hot water. If you look at the original proposal, 1 157k btu boiler is probably 3 times the size boiler you require. It has old school thinking about being big enough for additions, etc. This wastes a lot of energy and money.
    4. The installer is the most important part. If they don't do 1, 2, and 3, don't use them.