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

GW

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

Aaron_in_Maine

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.

Paul48

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

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.

Paul48

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

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

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

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

Paul48

Hat......Using the LL on a call for heat, there is no way for temp to go above LL setpoint.

Paul48

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

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

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

Robert O'Brien

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?

Paul48

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

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?

GW

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.

Paul48

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? 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

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?

GW

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

Paul48

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

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?

GW

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.

OuterCapeOilguy

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

It's a hydro air and an indirect, so it's needs the hot stuff.

Nozzle settings are oem. .55 gal