Wall Thermostat- what anticipator setting to use -have room temp overshoot

Leonard

Round Wall NRC mercury thermostat, furnace and house are ~ 61 years old. Working fine just have room temp overshoot. Actual room temp is ~ 5 degs higher than set point in winter , and lot more in late spring when it's 60 degs outside.

Winter overshoot is not really an issue, I lower set point to compensate for it. Just wondering if correct anticipator setting would make temp more even, though I don't notice any temp fluctuations.

About 50 years ago as a kid I played with anticipator setting and thru it way off, didn't regulate house temp well. Back then I forgot original setting, so I moved it to 0.4 and never changed it to this day.

Looking for a suggestion on where to initially set it, to save me some trail and error.

House has original 1 ft high cast iron baseboards, FHW, ~ 190 deg boiler temp, oil fired. Ceilings are 8 or 8.5 feet tall. I'm in southern New Hampshire. Typical outside temps are 15 to 30 deg in winter, but can drop to -5 deg ~ every few years

STEVEusaPA

Put a meter on it in that reads in tenths of an amp 0-1.5 on R-W. Or a clamp on if it can read tenths, or wrap the thermostat wire around it 10 times.
Could also be that the anticipator is damaged.

HVACNUT

You posted under oil heat and say it's a furnace.
If the thermostat is wired directly to the burner primary, the primary should have its amp draw stamped on it somewhere.

But maybe that's not the issue. Extended fan run time after the thermostat satisfies and the burner shuts off could also be the culprit. Or temp rise across the HX in general.

mattmia2

As @STEVEusaPA said, the numbers on the anticipator are the current draw of the control circuit, you should set it to match the current draw of the control then tweak it from there if the cycles are too long or short. In a mechanical t-stat like that, the anticipator is a resistor that heats the element during the call for heat to make it end the call before the room temp reaches the setpoint to anticipate the heat that will still be in the system when the call ends.

STEVEusaPA

Could also be the stat is out of calibration...anyone have one of those little wrenches...lol
Marking on the primary is usually good enough as @HVACNUT said, but doesn't take into account long thermostat wire run (more resistance says Mr. Ohms).

Jamie Hall

Is it a mercury thermostat? The older ones are... and if it is, they are very sensitive to being off level. There are leveling ears on the backing plate which you can check.

hot_rod

can you lower the SWT from 190, that may help overshoot also.

Leonard

I have Keithly AC ampmeter , I'll check amps. wire length is short maybe 20ft looks like normal gauge thermostat wire I've seen on other buildings

FHW , so no fans, 1ft high x ~ 2.5 inch CI baseboard of 1958 design, smooth front and top , fins on back ~ touching wall. Passive convection air flow, no fan.

I'm a Mechanical engineer , not a heating guy, but have Freon car cert., and work on my furnace

I need 190 boiler temp for shower. When circulator runs shower gets cold. Exhaust heat exchanger needs to be cleaned again, ash. Been a few years, Have not gotten around to it

I acid cleaned copper coil in water jacket about 10 years ago,used muratic acid ( HCL ~35%) . I suspect it's not fouled again yet. City water, major city in southern NH

Jamie Hall

Another silly question. If this is really an overshoot problem -- that is, the room temperature swings widely -- and not a calibration problem -- that is, the room temperature holds within a few degrees, but is higher than the thermostat is set for -- then it is possible that the anticipator is burned out or shorted. They don't, often, but it's not unheard of.

mattmia2

A CI radiator full of 190 degree water contains a lot of heat which it is going to give off after the call ends. you might need to set it for a little but lower current than the actual measurement to give it shorter cycles.

You could also set up dhw priority so it turns the circulator off when there is a dhw call.

You should be having a good oil burner tech clean the boiler and check the combustion on the oil burner annually.

I'm assuming the DHW is a tankless coil.

Leonard

Tank less coil in water jacket. Old aquastat model L8124A , GUESSING it has no dhw priority capability. Aquastat has low , hi, and diff settings, no idea what diff is about (now diff=10, min setting)

Guessing exhaust passagways just need a cleaning, cool DHW is usually not a problem, just started ~ this winter..

Right now more interested in Anticipator setting
Room temp feels uniform over the day, just wanted to optimize it. Only got interested since anticipator setting was 1/2 discussed on a non-heating site. The experts are here.

I know about nothing about setting anticipator, thats why I ask here.
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Some test data:

I looked at thermostat (TS), it is original to house. Appears that a variable power resistor (anticipator) is wired in series with mercury switch. So if it anticipator burned out TS would not signal for heat. Anticipator wire looks heavy enough to not burn out.

Aquastat Aquastat model L8124A outputs 29.4 VAC when TS not calling for heat.

With TS calling for heat, TS current is:
200 mA AC @ anticipator = .4
191 mA AC @ anticipator = .9


Wire from TS to furnace is .038 inch diameter so ~ 18 AWG
That wire is 21 feet long (1 way), I calculate ~ .26 ohms round trip, sounds ok.

With TS wire disconnected from Aquastat,
DC Resistance of TS and wire to TS is:
0.8 ohm @ anticipator = .4
.7 or .5-.6 ohm @ anticipator = .9 (measured then moved anticipator)

mattmia2

The anticipator should be set to about .2, maybe a little less with your high mass radiators and high water temp

HVACNUT

> @Leonard said:
> ----------------------------------------------------
> Some test data:
>
> I looked at thermostat (TS), it is original to house. Appears that a variable power resistor (anticipator) is wired in series with mercury switch. So if it anticipator burned out TS would not signal for heat. Anticipator wire looks heavy enough to not burn out.
>
> Aquastat Aquastat model L8124A outputs 29.4 VAC when TS not calling for heat.
>
> With TS calling for heat, TS current is:
> 200 mA AC @ anticipator = .4
> 191 mA AC @ anticipator = .9
>
>
> Wire from TS to furnace is .038 inch diameter so ~ 18 AWG
> That wire is 21 feet long (1 way), I calculate ~ .26 ohms round trip, sounds ok.
>
> With TS wire disconnected from Aquastat,
> DC Resistance of TS and wire to TS is:
> 0.8 ohm @ anticipator = .4
> .7 or .5-.6 ohm @ anticipator = .9 (measured then moved anticipator)

Choo choo!

Is this your data or did N.I.S.T come in for analysis?

Is there a time lapse record of say, an average of 10 cycles to see the time/temp rise after the thermostat satisfies?

The anticipator setting is stamped, or a sticker on the L8124A on top or bottom of the housing near the edge. Assuming there are no other coils in the circuit, that should do it.

Boiler, not furnace.

Why not just upgrade the thermostat? Yes, digital is an upgrade over mercury.

mattmia2

You quoted where he measured the current as .2 amp, the answer is in your quote.

Jamie Hall

Ah, folks... let me go back a step here. @Leonard , you mention that the room temperature is fairly uniform over the day, but isn't what you have set the thermostat for.

Is that thermostat accurately level? Even half a bubble off can throw it 5 degrees one way or the other. There might be a slight misadjustment in the thermostat itself, too. There's no harm to twisting the base (go easy! doesn't take much) enough so that the thermostat tips at the temperature the little pointer thingy points to...

EdTheHeaterMan

L8124 control is a priority for domestic hot water (DHW) control. If the high limit is set at 190° and the low limit is set at 160° with a differential of 10°, the circulator will operate on a call for heat as long as the boiler temperature at the aquastat is above 150° below that, the circulator (C1) terminal current is interrupted. (Circulator stops). Once the boiler temperature reaches 160° the (C1) terminal is energized again (circulator operates.)

You have DHW priority!

If there are other zones with other thermostats connected without using the ZC and ZR terminals from the L8124... there is where your insufficient hot water is happening. If you have only one thermostat and only one circulator, this does not apply to you

If you have more than one thermostat and more than one circulator, there are some simple energy-saving things you can do to with a minimal amount of wiring redesign.

...on that old boiler, it might be worthwhile.

As far as the heat anticipator question.... I don't think you have a problem with the heat anticipator, I believe you have a calibration issue as mentioned by @HVACNUT & @STEVEusaPA & @Jamie Hall

ChrisJ

What "freon cert" do you have @Leonard ?

HVACNUT

I knew I would get at least one disagree 😭. Crawl out of the cave people.

STEVEusaPA

HVACNUT said:

I knew I would get at least one disagree 😭. Crawl out of the cave people.

lol. I wish it would tell us who...I understand why they don't.

ratio

Since I'm very agreeable & never wrong, I just assume someone fat-fingered it on a phone.

Canucker

> @STEVEusaPA said:
> (Quote)
> lol. I wish it would tell us who...I understand why they don't.

I found that most of the time it was an inadvertent pressing on the disagree button while scrolling on mobile. The button sits where a right handed person's thumb touches the screen. Flip it with the agree button and you'll probably have a lot more agrees instead

HVACNUT

> @STEVEusaPA said:
> (Quote)
> lol. I wish it would tell us who...I understand why they don't.

Whoever it was came to their senses and took it away. 😍 I'm back in the Black. Hate being in the Red.

Yes we understand why they're anonymous. I dont watch the MMA or wrestling stuff, but it would be like that, only in cyberspace.

Leonard

Guess I have an accuracy issue not a overshoot issue (when cold outside). I only notice heavy over shoots ( set-=70, actual=80+) when it's warm ~ 60 deg outside. But that's likley because excess hot water energy in long CI baseboards than needed to heat room when warm outside.

Previously I assumed since I had bad overshoot in spring, I might have a small bit of overshoot going on in winter too. I needed basic info on anticitator settings, WHICH way (higher/lower # )shuts off thermostat earlier. My span is 0.4 to 1.0

I'll have to watch spread between set point and actual room temp more closely. I suspect it's pretty constant.
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Test data is actual numbers I measured, I'm a mechanical engineer.
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My freon cert. is likely a basic one. Local wholesale car parts supplier ran a ~free seminar and test to get the cert. That way supplier could sell us Freon (R-12 back then) . But I had already bought ~ 150 # of it at K-mart before regulation @ ~ $1 a can. ( ~ 12-14oz)

Made a lot of beer money back in the 80's refilling cars after work, work had 1000 people, I put my ad on bulletin board.
Apt didn't have A/C so I went to local well A/C cooled Kmart building to cool off, chatted up customer looking at R-12 display, sold them my refilling services. I had the pro dual gauges.

Bought the gauges in July 1981 after sweating in car that was low on R-12. I called around and no one could refill it till cool Sept and it would be $100. Bought pro gauges, hoses, fittings, can tapper, etc that week for less $ and I was in business.

I knew thermodynamics and how to analyze a heat cycle (power plant water cycle) , but no idea on how personal A/Cs heat cycle is set up. So I went to library and read about them and figured it out, I also asked a few questions from HVAC guy at work. Wasn't hard,

ChrisJ

Automotive would be a 609 cert.

To do residential AC work you need a 608 II or 608 Universal. A 609 does not cover these.



I'm only mentioning it because you said you had a cert to work on it. As long as you're not touching the air conditioning it's moot.

For your problem I'd start by getting a Honeywell Prestige and some wireless indoor sensors.


https://www.supplyhouse.com/Honeywell-YTHX9421R5101WW-Prestige-IAQ-Kit-with-RedLINK-Includes-White-Thermostat-EIM-Wireless-Outdoor-Sensor-2-Duct-Sensors


https://www.supplyhouse.com/Honeywell-C7189R1004-RedLINK-Enabled-Wireless-Indoor-Air-Sensor


I run 3 indoor sensors + the thermostat and it averages them.

Leonard

Would 609 cert. cover working on freon system of home window A/C..... ie ~ 5-30K BTU/hr ? I'm guessing no..

Is it a volumne of Freon issue? Or more of a technical issue .....ie like thou shall not use tubing tappers because the O-ring leaks long term

ChrisJ

> @Leonard said:
> Would 609 cert. cover working on freon system of home window A/C..... ie ~ 5-30K BTU/hr ? I'm guessing no..
>
> Is it a volumne of Freon issue? Or more of a technical issue .....ie like thou shall not use tubing tappers because the O-ring leaks long term

No. Small appliances is 608 I.

609 only covers automotive.

The first issue is you keep saying freon.

mattmia2

technically you are supposed to own recovery equipment if you are doing work with the certificate.

Is my recollection correct that the 608 would include automotive work but not the other way around?

see the comment about making sure the subbase is level. Since it tips the mercury switch to turn on/off, it is critical that it be level to be accurate.

the lower the setting of the anticipator the shorter the cycle. there is usually an arrow that says "longer" on the scale that points in the direction of higher current settings.

HVACNUT

> @ChrisJ said:
>
> The first issue is you keep saying freon.
>
>

Everybody knows the correct term is Freezone. 🤪

Leonard

ChrisJ said:

The first issue is you keep saying freon.

I'm a bit older, in 70s and 80's when I played with R12, R22 I thought they said Freon, but that was a while ago.

Ok, point taken, I looked it up .....Freon is just a tradename for refrigerants R-12, R-13B1, R-22, R-410A, R-502, and R-503 manufactured by The Chemours Company. But it is generaly used to describe CFC and HCFC...weikepedia

In test lab at work the gyro test chambers went to -65 deg. Maybe used ~ R410?? and/or R605?? i forget the gas#.
---------------------------------------

Other Cert is just more of a curiosity.

I've found if a WINDOW A/C refrigerant tubing needs to be opened it's too much expense and work for me to bother with. There are PLENTY of free A/C on the curb that only need condenser fin cleaning to blow ice cold again.

Here in cool NH the pumps don't wear out, condensor fins get plugged with dust, and evaporator gets moldy (Clorox and Tide fixes that)
----------------------
EDITED: took out off topic stuff

Leonard

Is there another cert # to work on larger HVAC , I've got a commercial building with 2 HVAC on roof.

I don't have BTU# or gas R#, but for size they weigh ~ 1000# and 1500# . I had to calculate bending stress in rafters that held them.

ChrisJ

Leonard said:

Is there another cert # to work on larger HVAC , I've got a building with 2 HVAC on roof.

I don't have BTU# or gas R#, but for size they weigh ~ 1000# and 1500# . I had to calculate bending stress in rafters that held them.

Google is your friend.

https://www.epa.gov/section608/section-608-technician-certification-0

Jamie Hall

Leonard said:

Is there another cert # to work on larger HVAC , I've got a commercial building with 2 HVAC on roof.

I don't have BTU# or gas R#, but for size they weigh ~ 1000# and 1500# . I had to calculate bending stress in rafters that held them.

Flat roof or pitched, @Leonard ? If it's flat, or nearly so, I do hope you also calculated deflection... excessive deflection can cause ponding, which in turn causes all kinds of mischief.

And in any case, I hope you also calculated shear. It usually isn't limiting with wood members, but now and then...

Leonard

Flat roof, 20ft span, 2x12 wood rafter, think stamp on original was douglas fir, 45 #/SF snow load. Added full length 2x12 sister rafters. Roof drain was right next to it.

1-st tenant was Chinease restaurant and CHEAP CHEAP CHEAP CHEAP you would NOT believe. Had to have our lawyer almost take him to court to force him to fix it, even then we had to pay 1/2 or he would have lawyer fight ( lost business). City wasn't interested as it already "passed", like HELL it did. I calculated bending stress, looked high.

I'm a mechanical engineer so i can calculate bending, shear and deflection , but I'm not a cival eng, so didn't know wood strengths. BUT I got an education, our lawyer said had to hire a cival eng with PE license to PROVE to tenant's lawyer it was unsafe.

After chatting engineer to engineer the old PE said he has calculated shear on long rafters so many times and it comes out nothing that he almost doesn't bother anymore, unless loading is something out of the ordinary. PE said it needed sister rafter because of high bending stress..

Other issue I found is installers like to drill 3/8 inch dia screw hole up into bottom of rafter ( like 1/2 way deep) to carry under roof loads. I calculated that removes a high % of cross section and load carrying capability of rather when it's done at rafter midspan.

So as next tenant installed stuff I warned him I wanted U bracket instead, and drill horizontal bolt hole thru rafter1/2 way up rafter height( neutral bending axis)

What's your experience with hanging heavy stuff off rafters? big cooking exhaust hoods,etc

Jamie Hall

"What's your experience with hanging heavy stuff off rafters? big cooking exhaust hoods,etc ".

Variable. Particularly for flat roofs -- if they are designed right (hmm... well...) usually the point load from the heavy widget is actually less than the distributed load from snow. But it's well worth checking, and since you already know the equations, @Leonard , it's mostly plug and chug. Douglas fir should be good for around 1300 psi for bending. Just add the point load stress to the distributed load.

Your old engineer is right on shear -- it is vanishingly rare for shear to be controlling in a timber structure -- about the only time it is a concern is on very short beams, or the odd case where for some reason there is a big point load within say 10 depths of the end. Or where somebody has reduced the section and made a tenon too small in post and beam construction! Seen that, been there.

As for people drilling holes in beams... a small through hole in the middle third of the depth is usually not a problem. At least not something to have a heart attack about. Anywhere else -- no. Just don't do it. Your installers should be shot. Your U bracket solution is much better!

I worry about deflection on flat roofs because of ponding. What happens is that if there is a low area, it may collect water. Which is heavy. Which increases the deflection. Which collects more water. Which... you see where I'm going. If you're lucky it leaks. If you're not lucky, and are close to the limit load, you get loud noises.

Leonard

This douglas fir was from ~ 1950 when building was built. Think I saw bending stress for that OLD stuff @ ~ 1700psi, but that was in a general book I saw , not an engineering book. Back then sometimes wood quality was better, and stronger.

Been a long time but I think modern SPF ( spruce/pine/fir) is ~ 1100 and ~1200 for grade I and II. forget which one is which

Specially selected and inspected wood can have higher strengths, heard of acrobatic airplane wood having ~10,000 psi. But that's not normal.

Flip side is steel in old I beams of ~ 20's or 30's was only ~ 22,000 psi, where as now a common C1030 steel is ~ 30,000psi ( as per the PE)

----------------------------------------
Yes short beams can have higher shear stress.

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I wasn't so concerned about deflections, edge of HVAC was on OVERSIZED steel I-beam, drain was 2ft away. Besides I was very busy hammering on them about high bending stress. Snow loads are very high , even 45#/SF is ~3/4 ton on a 20 ft span.

40x 100ft building can have ~ 90 tons on snow on it.
In 80's was a heavy snow storm, whole roof of Hartford Civics Center (Conneticut) fell in. Just few hours after it was FILLED with people watching a hocky game, ALL ~ 5,000 people would have been KILLED. Bad work killing people is what I worry about
https://patch.com/connecticut/hartford/hartford-civic-center-roof-collapsed-40-years-ago


Drilling into bottom of beams......., lot structurally incompetent carpenters out there, I've seen a few. That's why citys want a PE engineeering stamp on plans/designs. I even saw a carpenter's young guy @ ~ 10AM drinking a "soda" bottle but was only sipping it ..... gave bottle a wiff...... brandy.

Saw him doing structural work in a way that was not right, had to tell him how to do it right. Other older guy that worked with him really objected to being told how to do it. Lot of crummy carpenters out there that remind me of a 3 Stoogers TV cartoon.

Jamie Hall

The AITC Timber Construction Manual (now 4th edition) is the goto for engineering timber structures. Like any other such, it isn't cheap... but it's inexpensive.

That Civic Centre collapse was combination of somewhat dubious workmanship -- and a modified construction detail. Interesting and sobering read on the analysis of what and why.

STEVEusaPA

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