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Thread: Aquastat settings with indirect water heater

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    DIY Junior Member paul m's Avatar
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    Default Aquastat settings with indirect water heater

    My furnace heats my house with infloor heating also my DHW. The furnace used to have a coil for the DHW now it has been removed and I have a 80 gallon indirect water heater tank combined with my solar heat. So now the boiler is controller with an aquastat in the water tank. How should the boiler control settings be changed now that the water in the furnace doesn't heat the domestic water coil like it used to. I don't really want the boiler to maintain its water temp when it's not needed.
    Thanks.

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    In the trades Dana's Avatar
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    If you turn down the aquastat on the indirect to below oom temp it'll never call for heat- done deal.

    If the aquastat on the tank doesn't go that low you may need to wire a switch in series with it to disable it when you want the tank to be truly off, in which case you leave the setting alone, and just flip the switch to break the connection.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    It depends on what boiler controller you have. As you are probably aware, with an internal coil, it is designed to keep the internal tank hot 24/7. That probably isn't necessary any more with the indirect which acts like a big buffer (the boiler doesn't need to stay on since you now have that tank), but it depends on the boiler. It may be as simple as turning a knob or setting some switches. Some boilers don't like cold starts..it somewhat depends on how fast it can respond and the type of material it is made of and whether it would be damaged by condensation.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member paul m's Avatar
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    Yes. That's exactly what I want. I don't want the boiler to be coming on to only heat itself - only if the storage tank calls for it, or the house thermostat. What if the setting on the tank was on 120F and the "Lo" setting on the boiler was on 100F. That way the boiler would just keep itself warm to avoid condensation. Is it true the Lo settiing is for the dhw coil with temp swings controlled by the diff control and the Hi setting is the max temp for the boiler if the house thermostat wants heat.
    Thanks for your help.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Note, the condensation I'm referring to is the result of the heat exchanger and the burner. If the return water is too cold, you'll get condensation of the moisture from the burning gasses. Since these tend to be somewhat acidic, if your boiler isn't designed for that, you can quickly eat through parts. So, you really need to investigate that boiler's characteristics to see how best to handle your new situation. Often, the same boiler is sold with and without that internal coil. The controller could be the same, but just have switch or jumper settings to configure it for the specificed application. All yo umay have to do is reconfigure.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member paul m's Avatar
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    Default Boiler material

    It's a NewYork Thermal boiler about 9 years old.
    How would you find out what it's made of and if it would be damaged from corrosion if left to cool down between demand for heat?

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    In the trades Dana's Avatar
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    Quote Originally Posted by paul m View Post
    It's a NewYork Thermal boiler about 9 years old.
    How would you find out what it's made of and if it would be damaged from corrosion if left to cool down between demand for heat?
    If it's an older oil fueled boiler it's cast-iron or steel, and shouldn't be run lower than 140F on the return water for extended periods, but it's probably cold-start tolerant. NTI's newer oil-fired boilers are designed internally to run at the edge of condensation without damage, and automatically mix return water with boiler output to protect it when it's at that edge, tolerating incoming water temps as low as 90F. Your's may/may-not be one of those.

    I don't recall that NTI had any gas-fired cast iron boilers with internal coils as of a decade ago (they might have.) If it's the Trinity series it's a condensing version designed for low temp, and efficiency will improve with return temps of 120F or less.

    Got a model name/number?

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