My boiler settings

Leonard

Wondering what temp I should set my aquastat hi/low and differential settings at ?
Also wondering what "differential" setting on it refers to.
( #'s from under aquastat cover L8124A,C L8151A)

Few months ago had cool shower, I compensated by upping the aquastat temps. Now I tracked down problem to leaking DHW mixing valve and fixed it, but didn't mark the original settings.

I also notice the temp/pressure gauge on top of boiler reads about 25 degs higher when burner shuts off than the aquastat high setting. Sounds like one of them is off.

Have force hot water heating with tankless DHW ( copper coil in water jacket), 1 zone , cast iron base boards running perimeter of house ( ~12inch high x 2 thick, cast fins on backside), monoflow system (boiler supplies far end of loop and water returns along both sides of loop). I only heat 1-st floor, 1-st floor alone is 1,500 SF. 2nd floor is unfinished and not heated, cellar is ~ 67 warmed by heat leakage off pipes.

59 year old oil fired boiler , National Sunray IV , boiler # 5-19A/O/OP , rated 128k BTU/hr 1.6 gal/hr
Original oil burner National -US model NB2-K2, firing rate .85-2.0 gal/hr , nossle is either ~1.26 or 1.35 gal/hr

Boiler is on cellar floor, chimney extends from cellar floor thru 1-st & 2nd floor , and another ~ 5ft thru peaked roof, plus another ~ 3 ft over roof.

Len
Mechanical Engineer

Jamie Hall

The flip answer is -- as low as you can set it and still keep the house warm (and the shower). The ideal setting is one where on the coldest nights the circulator runs pretty much all the time.

Leonard

On the L8124 aquastat I assume the hi /low settings are the boiler temperature set points that burner switches off/on at, right ? But what does the "differential" setting do? I suspect it switches circulator.
Current settings are low=140, hi =160, diff =10

Have PLENTY of hot dhw for shower, have to slightly open mixing valve to cool it down, even at ~ 3 gal/min. House heat is ok, more sluggish to respond to room thermostat changes than when hi setting was 45 degs higher, but that's expected.

My L8124 is made by Honeywell, replaced in ~ 1977.
Maybe it's temp settings are off from the factory. Even with no DHW flow when burner shuts off boiler top triple meter is reading ~ 25 degs higher than aquastat hi setting. I suspect top meter is accurate, since when it read ~ 210 deg on shut off I could hear a few bubbles ( likely steam) trickling up pipe from boiler outlet.
IT looks mostly like this. https://www.bing.com/images/search?view=detailV2&ccid=NqK8Rm63&id=4D36AE3220D2491B285B8F37C73E4787C33E59DB&q=L8124&simid=607993428578010478&selectedIndex=18&ajaxhist=0

Leonard

I assume my L8124 aquastat hi/low settings are the on/off settings for burner firing, right? What does the differential setting control, the circulator??

Current aquastat settings hi=160, low=140, diff =10
I believe actual hi/low temps are 25 deg higher, via triple meter on top of boiler. More on that later.

I have PLENTY of hot DHW for shower (~ 3 gal/minute). Baseboard heating seems ok, but more sluggish to respond to room thermostat changes than when aquastat hi was 45 deg higher, but that seems reasonable (now ~4-5hrs to respond to 4-5 deg change) . Also rooms feel cooler but thermometer says it's about the same temp.

When burner shuts off temp at boiler top triple meter is ~ 25 degs higher than aquastat hi setting, with no DHW flow. I believe triple meter is accurate as previously with hi set at 185 when burner shut off it read ~ 210-215 deg and I heard a couple bubbles. ( likely steam) trickle up pipe from boiler outlet. Boiler triple meter said ~ 3-7 psi. Boiler is rated to make hot water or steam, but is used only for hot water.

Leonard

Ok, lets see if I understand differential right.
Lets ASSUME hi is set to 180, low set to 140 and diff set to 15

1) When room thermostat calls for heat does this mean the boiler temp cycles between 180 and 170 (non-adjustable 10 deg differential) ??

2) When room thermostat does NOT call for heat does the boiler temp cycle between 130 and 155 ?? (does adjustable diff only apply on high side, ei fixed -10 deg on low side and what ever diff is set to on high side)

My Honey well L8124 aquastat from 1977 looks like this , except for one Z terminal on bottom is moved slightly
https://15254b2dcaab7f5478ab-24461f391e20b7336331d5789078af53.ssl.cf1.rackcdn.com/heatinghelp.vanillaforums.com/posts/6000/Honeywell-L8124C.jpg

Paul48

On a call for heat the only thing that will shut the burner off is the thermostat being satisfied or the hi-limit has been reached. If the hi-limit is reached, the burner shuts down and waits for the boiler to cool 10*(fixed), then the burner fires again. On a call for heat, the lo-limit is effectively bypassed, as far as the burner is concerned via the relay contacts. Not the circulator, as it's control remains dependent on the lo-limit. It will always switch functions at 10* below lo-limit setting. So, in your example of 140 with a 15 degree differential......at 130*the lo-limit switches off the circulator, and turns on the burner(already bypassed). When the boiler gets back to 145*, the lo-limit switches the circulator back on, turns burner off( which it can't, still bypassed). The circulator control is acting as boiler protection. So return temperatures don't cause condensation.

Leonard

Sounds like the aquastat acts as two boiler temp controlers in one box.

-- hi temp range one that acts when room thermostat calls for heat.
--low temp range one that acts when there is no call for heat.
(basically maintains minimum temp for the tankless DHW coil in boiler)
-- plus a lower temp ( 130) circulator shut off circuit.

In my example, with room thermostat continuously calling for heat, sounds like circulator will always run, except when boiler temp drops below 130, but circulator comes back on when boiler reachs 145, right ?

Paul48

Right......On a call for heat, the lo-limit control the circ around it's setting.......20* diff= 10 under, 10 over.....25*diff= 10 under, 15 over.......make sense? On no call for heat, the lo-limit controls the burner....a setting of 140* with a 15* diff would turn the burner on at 130*, and off at 145*.
Look at fig.3....the 1k1 and 1k2 are the relay contacts in the aquastat. https://customer.honeywell.com/resources/techlit/TechLitDocuments/95-0000s/95-6571.pdf

Leonard

Thank you , now I see 1k is coil of thermostat relay, contacts are 1k1, 1k2.
Schematic wasn't in engineering format I'm used to, looks more ladder diagram format.

Was little confused on differential , but picture in manual link shows that very well on page 7

Manual also helps me understand how to add controls for 2nd zone.

Paul48

Zoning a monoflow system is a bit more complicated. Confirm your plans here, before you start changing things. It'll save time, in the long run.

Leonard

Zone 2... infrequent heating of uninsulated 1.5 car garage, peaked roof, southern NH. Haven't thought it thru too much but figure a separate run and return from boiler to a heat exchanger in semi-conditioned celler ( cellar is 60 deg min, warmed by heat leakage) , then separate antifreeze loop to garage, water to air blower in garge . I have couple water/air blowers from another property.

Would be nice to tap existing mono flow piping to save pipe costs, it's 60 years old , ~1.5 inch copper pipe for mono-loop. Maybe 30-40 ft from boiler to garage. In past figured ~$500 for 1.5 inch copper pipe, ouch. Any ideas how to minimize extra $$ piping to the heat exchanger. Sounds like your thinking solinoid vavles to save a circulator and one feed pipe run from boiler.

Paul48

You're going to convert the whole system to antifreeze? Otherwise you need to separate the garage out of the main system with a heat exchanger. I'd leave the monoflow alone, except for running the loop between supply and return manifolds. Off the same manifolds, you run your new zone(s) with PEX, circ and 2 zone valves.

Leonard

I plan on water/water heat exchanger. Want to minimize use of of antifreeze. Convenience of not having to run antifreeze in house loop. Makes draining and working on main house loop easier. Plus I think main loop with many baseboards holds a lot of gallons of water, $$$ antifreeze.

Don't have manifolds, just inlet and outlet of boiler. currently one zone system. Sounds like your taking about 2 Tee fitting and maybe 2 one-way valves so don't have flow from one zone into other.

Figure on getting a used heat exchanger or making a tube in tube copper one.

Paul48

You need to know the capabilities of the HX vs. the output of the Modine heater.