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Low limit on new oil boilers? (Not old school yankless)

GW
GW Member Posts: 4,538
What's the modern opinion on low limit? Does the added fuel needed to keep the boiler warm offset the crossing dew point issues and small wait time to get the boiler hot enough? What's the lowest number you all use for low limit?

Thanks, Gary
Gary Wilson
Wilson Services, Inc
Northampton, MA
[email protected]

Comments

  • Aaron_in_Maine
    Aaron_in_Maine Member Posts: 315
    I like using zone valves and getting my boilers with the Hydrostat control and wiring the circulator though the Hydrostat. It will hold off the circulator until the boiler gets to 125 but it won't maintain a temp around the clock.
    Aaron Hamilton Heating
    [email protected] yahoo.com
    (207)229-7717
    OuterCapeOilguy
  • Paul48
    Paul48 Member Posts: 4,469
    edited October 2015
    I've seen what circulating 125* water through my gravity conversion did. If I didn't catch it, it would have rotted my boiler out in a hurry. I use 150* as a minimum. That stops the circ at 140.
  • Aaron_in_Maine
    Aaron_in_Maine Member Posts: 315
    I am talking about a normal baseboard system. I wouldn't put a oil boiler on a gravity conversion if I had to though I would put a four way mixing valve on it. I prefer a condensing gas on that type of install.
    Aaron Hamilton Heating
    [email protected] yahoo.com
    (207)229-7717
    Robert O'Brien
  • Paul48
    Paul48 Member Posts: 4,469
    The answer is...it depends on the system. How much more advantage does a 4-way mixing valve give you, over a triple aquastat ? You may prefer condensing gas, but your potential customers may not have that in their budget.
  • Paul48
    Paul48 Member Posts: 4,469
    Hat.........The differential, at anything other than 10* still stays at 10* under. So a 25* differential would be 10 under and 15 over.
  • Marz
    Marz Member Posts: 90
    I need to check something. It was told that the adj diff on the 8124 is an additive diff rather than subtractive. I will research and get back
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,451
    Someone installed a new L8124 on a Buderus? Get rid of that thing and use an AquaSmart or Hydrostat. AquaSmart has a subtractive fully adjustable HL Diff. Expanding the diff will help with short cycling, I would start at 30* diff and go up from there if needed
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  • Paul48
    Paul48 Member Posts: 4,469
    Hat......Using the LL on a call for heat, there is no way for temp to go above LL setpoint.
  • Paul48
    Paul48 Member Posts: 4,469
    Hat...I disagree that the LL/ Circulator control functions that way. The diff operates the circ on a call for heat. Conventionally, on a call for heat, the boiler fires and will not shut off unless the hi-limit is met, or the stat is satisfied. The hi-limit is recommended at least 20* above the LL. On a call for heat with diff at 20*, the boiler fires and circ comes on. When the temp drops 10* below the LL the circ shuts off, and boiler continues to fire until 10* over LL, then the circ starts again. This is with the boiler attempting to reach hi-limit.
  • Paul48
    Paul48 Member Posts: 4,469
    Oh OK....because if you let the 8124 control the circs, it would only allow you a 10* DT. You've got it figured out.
  • GW
    GW Member Posts: 4,538
    Thanks for the comments, I guess my question is more " keeping the boiler warm/hot".

    Does the Hydrostat, Aquasmart, or L8124 have a way to keep heat in the boiler, or are all of these cold start controls?

    If you can keep heat, is it advantages, and what temp?

    Thanks, Gary
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,451
    GW said:

    Thanks for the comments, I guess my question is more " keeping the boiler warm/hot".



    Does the Hydrostat, Aquasmart, or L8124 have a way to keep heat in the boiler, or are all of these cold start controls?



    If you can keep heat, is it advantages, and what temp?



    Thanks, Gary

    Hydrostat and AquaSmart have a LL that can be disabled and so does Honeywell 7224. 8124 is an old style electro-mechanical control and does not. LL is actually 2 functions, it maintains boiler temp and provides a reverse control for circulator. C1 isn't energized unless boiler is above LL setting, commonly used with tankless coil oil boilers. If you have a boiler that can be run cold start, why not?
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  • Paul48
    Paul48 Member Posts: 4,469
    I know the 8124 is a triple aquastat and will maintain heat. Unless there's a domestic coil in the boiler, there's no real advantage. Disconnecting the blue wire from the LL makes it a cold-start, but still provides circ switching, if you use it in a high volume system.
    Gary....I see you're in Northampton. That's a nice area. We've been getting off 91 there and heading up 9W. My buddy has a cabin above North Adams in VT. There's a concrete marker by the side of the dirt road, that has VT on one side, and MA on the other.
  • GW
    GW Member Posts: 4,538
    Robert, that's my question, is it overtly wasteful to keep the boiler with just enough temp above dew point, won't the boiler stay very clean?
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • GW
    GW Member Posts: 4,538
    null
    Yes, you're going right through the center of town up rt 9? You're about 3 min from my shop. Yes it's a great town, lots of people doing stuff to their homes.
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • Paul48
    Paul48 Member Posts: 4,469
    Icesailor always argued that maintained boilers stayed much cleaner than cold-start boilers. It becomes increasingly harder to convince folks of that if the price of oil starts getting up to $4/gal. Geez....I wonder why that is? :smile: People will argue that, years ago, all the boilers were cold-start. Years ago, the boilers were built to withstand a nuclear blast, too.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,451
    GW said:

    Robert, that's my question, is it overtly wasteful to keep the boiler with just enough temp above dew point, won't the boiler stay very clean?

    Idle loss is a huge factor in the inefficiency of oil boilers. Triple pass boilers can be easily cold started on baseboard systems, on higher mass systems you need to protect the boiler obviously. But maintaining temp isn't the best way to do it, a bypass or P/S would be superior. With an indirect, how many times does the boiler really start at ambient or close to it?
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    Bob Bona_4Zman
  • GW
    GW Member Posts: 4,538
    Apparently my phone won't let me hit the quote button.

    So is there a difference of opinion or a closed case? Any opinions on how much run time it would take to keep a boiler at 140 full time?

    Certainly it tales some time for a boiler to get to 140 (an exercise in math), so it's not a complete waste of fuel by any means.

    Thanks, Gary
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • Paul48
    Paul48 Member Posts: 4,469
    Yes, but then there's the majority of the heating season, when the boiler may run once or twice, for a total of 40 minutes in 24 hrs for heating.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,451
    GW said:

    Apparently my phone won't let me hit the quote button.



    So is there a difference of opinion or a closed case? Any opinions on how much run time it would take to keep a boiler at 140 full time?



    Certainly it tales some time for a boiler to get to 140 (an exercise in math), so it's not a complete waste of fuel by any means.



    Thanks, Gary

    Are we talking about a heat only boiler or with indirect? Pin or triple pass? Cold start pin boiler is usually a disaster. Do you get rid of the cold start or the pin boiler?
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  • GW
    GW Member Posts: 4,538
    I'm talking G115

    I've never had the time nor the curiosity to try to study the subject. We are doing another boiler job today. I will pay attention to how long it takes from cold start to 1:40.
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • OuterCapeOilguy
    OuterCapeOilguy Member Posts: 30
    For what it's worth, I heat my home with a W/M Gold installed 11/2009, fired with a Carlin EZ-1 with pre/postpurge (60200 primary) @140 psi; 3 heat zones (2 baseboard, 1 fan convectors) and an indirect. I'm using a Hydrostat set up for cold start, 180º h.l., with the 125º circulator delay functioning. In 12/2011 I cleaned & tuned; -0.022" draft, 363º net stack, 11.88% co2. The last cleaning (in 10/2014), after nearly 3 years, netted some off-white powder on the pins, the cast iron above the fire was clean except for a small amount of scale. I left it with -0.021 draft, 371º net stack, 11.95% co2. The other day I took a peek through the inspection hole; a little white powder and clean cast iron again. I should point out that I live alone; unless I have visitors, no one is using dhw during the day all summer long, so it cools off sometimes to 96-98º before the dhw fires it on standby heat loss.
  • GW
    GW Member Posts: 4,538
    It's a hydro air and an indirect, so it's needs the hot stuff.

    Nozzle settings are oem. .55 gal
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]