Hi, Lo, and Diff setting

Discussion in 'Boiler Forum' started by Wes, Sep 21, 2009.

  1. Wes

    Wes New Member

    Messages:
    24
    Location:
    Connecticut
    We recently had an addition put on the house and a new heating zone added. We have an oil furnace that supplies heat and hot water. While the plumber was here the last time he decided to "fix" things on the temperature settings.

    Unfortunately, I don't remember what the Honeywell controller was set to before he "fixed" it even though I looked at it just a few months ago.

    Everything used to be fine... NOW, our how water just isn't hot enough. I can have the shower or kitchen sink set to the middle position and the water will be fine. Then in a few minutes it cools off!

    The middle position used to be fine and would stay fine the entire time the water was running.

    Right now it's set to 180/140 with a diff of 15. I think it used to be 130/160 but I don't remember the differense setting.

    Any recommendations?

    thanks
    Wes
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,927
    Location:
    New England
    How is the DHW produced? If it is a heat exchanger in the boiler, it needs to be set warmer. If it is an indirect, it might work, but will cause the system to probably turn on and off more than ideal. The higher you keep the water, the more heat you can get out of it, but you increase the standby losses (and use more oil). Depending on the type of heat you have, 140 might not be warm enough, so there's no easy answer without knowing more details.
  3. Wes

    Wes New Member

    Messages:
    24
    Location:
    Connecticut
    DHW / Seasonal Hi/Lo

    Not sure what you mean or how to tell where the DHW comes from. It comes right from the furnace. Cold goes in, hot pipe comes out to a "mixer" valve where I can adjust the mix of hot/cold.

    I think I solved the problem by setting the differential dial to its minimum setting, which is "10". The hot water is more consistent now.

    I understand that this will cycle the burner more often, but I'm ok with that. That's its job!

    So right now we are at 180/140 with a diff of 10.

    Does it make any sense to ratchet down the HI setting in warmer months? It seems the effect would be negligible in months that the heat is not being activated.


    thanks
    Wes
  4. flamefix

    flamefix New Member

    Messages:
    71
    Location:
    Exeter, England
    I don't really follow your train of thought on this boiler but I can tell you it is not efficient to cycle your boiler on off on off.
  5. Wes

    Wes New Member

    Messages:
    24
    Location:
    Connecticut
    JDNashua was asking where the DHW comes from...


    As for the efficiency, I think you have to balance efficiency with comfort and lifestyle, among other factors. Sure driving at SmartCar would be efficient, but I'm 6'9" and a family of 4. Not very comfy.

    Just like having the hot water flucatuate some much that we have to keep adjusting the shower control. Just not gonna do it for a few extra bucks. That's all I'm saying.
  6. flamefix

    flamefix New Member

    Messages:
    71
    Location:
    Exeter, England
    you're comparing apples with oranges. If the system was working fine before the plumber fiddled with it, get him back to put it right at his expense, why incur additional expense and wear and tear on your boiler just to get steady hot water when you had it before?

    What you're doing is more akin to heating a whole pot of water for single cup.
  7. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    180-200 for the high
    160 for the low
    10 degree differential

    Then have an indirect water heater installed along with an outdoor reset controll and stop throwing your money up the damn chimney. Tankless coils Baaaaahh.

    I had to edit this because it's off on a rant time. Oil and gas are expensive. Way too expensive to waste. Boilers with tankless coils in them are the most inefficient thing you could possibly have in your house. During the off cycle all that stored heat in the boiler needs to go somewhere (remember hot flows to cold?) that somewhere is up the flue, cooling the boiler off and making the burner run again, for nothing. Same with maintaining temperatures as high as 200 degrees for heat. when it's say 50 outside, the boiler does not need to be at 200 so why run it up there? that's what an outdoor reset control is for. To continuously modulate boiler temperature in relation to the actual heat load. You can save hundreds of dollars a year by spending a few dollars now. The investment will pay itself off within a few short years. Time to come into the 21st century.
    Last edited: Sep 30, 2009
  8. Wes

    Wes New Member

    Messages:
    24
    Location:
    Connecticut
    I set it to 180/140/10. Works great. It used to be 160/140/10. No wonder it took a while for the house to warm up.
  9. MAoilTech

    MAoilTech New Member

    Messages:
    25
    Location:
    MA
    Hey Wes
    Normal Range for you aqua-stat should be HI 180 Lo 160 with a diff of 20.
    other words your boiler will run till 180 then shut off when it hits 160 it will turn on again.it will only turn on if A. call for heat or B. for hot water also if you have time sit in front of the boiler keep your eye on the boiler gauge read the temp while its running @ these settings you will see that even when the boiler hits its temp @ 180 and shuts down the boiler temp will go up pass 180 slightly above thats normal it should not hit 200 cuz @ 212 u make steam.now if you have hot water issues check your mixing valve if its bad replace it and if you still have hot water issues then last thing will be your hot water coil the outlet might be plug up with rust ect...this will cuz a weak flow....

    Good luck
  10. Tomkat53

    Tomkat53 New Member

    Messages:
    1
    Location:
    Pennsylvania
    I know this is an old thread, but I just wanted to say "THANK YOU!" for posting this...

    I adjusted my furnace to your recommended settings, and this morning I had the first CONSTANT, and CONSISTENTLY hot "winter-time" shower I've ever had in my home, which I've owned since 1995!

    Now, about the "indirect water heater" and "outdoor reset control"...
    What EXACTLY are they? What do they do? Where can I buy them? (The oil company who delivers oil and services my furnace?)

    Any reply would be appreciated!
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,927
    Location:
    New England
    An indirect WH is essentially a tank, similar to a conventional water heater, that instead gets heated by your boiler pumping water into an internal coil of the indirect (some use an jacket rather than a coil). It is normally set up as a separate priority zone, which means that when it's internal aquastat calls for heat, it becomes the only zone getting heat (this isn't necessarily required, but is fairly common). Because you have the full output of the boiler, you can often get by with a smaller indirect than you would with a conventional gas or electric WH, and, similar to an electric, it is pretty good efficiency wise since it is well insulated and doesn't have a flue in it like a gas WH.

    Whether your oil furnace could use an outdoor reset controller would depend - many can. Unless the boiler is designed to be condensing, you can't lower the operating temperature of the boiler too far, or you'll quickly rust out parts. Essentially, it looks at the outside temperature, the call for heat, and the return temp (at least many do), and figures out if you could run the boiler temp lower. To successfully do this, you may need to make some configuration changes, and it may not pay off until it is time to replace the boiler. Any good HVAC guy should be able to deal with installing an indirect and could advise on an outside reset control. There are some references here if you search, and you can read up on them.
  12. tk03

    tk03 New Member

    Messages:
    56
    Location:
    Harrisburg, pa
    How can we suggest settings without knowing which control he has? The electronic control works differently than the older control like the L8124C. The new control is a subtractive differential and the older control added the differential to low limit - 10f.
    The high limit has nothing to do with hot water. That is a high limit used on a heat demand.
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