Dual Aquastat Control Strategy?


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Old 11-25-11, 07:00 PM
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Dual Aquastat Control Strategy?

Hi,

First post here. I've been wondering about something for a while and this looks like a good place to try and find an answer. My question is: how does a dual aquastat like the Honeywell L4062B "know" when to employ the high limit strategy? What "event" is determinative? Is it when there is line voltage running through the low limit/circulator side of the control?

Thanks for any feedback.
 
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Old 11-25-11, 07:58 PM
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What "event" is determinative?
In fig 1 and 2 that event is a contact closure coming from the X X terminals of the 832 relay. That X X contact closure is caused by the thermostat calling for heat.

The Low Limit is always active as you know. When that LL switch is shunted by the XX contact closure, the burner will fire up to the High Limit.

Are you asking just out of curiosity, or is there a 'back story'?
 
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Old 11-26-11, 08:23 AM
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The Backstory

Thanks Trooper,

Yes, your keen senses are correct. There is more to my question. I'm the owner of a small apartment building (built in 1964). Heat and DHW are provided by a National-US Radiator (#7-25B) oil fired burner (cast iron and lots of it). The original single control was/is the L4062B. Over the years, as required by newer codes, I've added a LWC, High Limit Safety, and replaced the stack control with a CAD primary. It is a constant circulation system: Click Here for Diagram (hope you can read my chicken scratch!).

The reason for my question is, on my system there is no direct t-stat switch that indicates a call for heat. Instead, as you can see, the circulator runs all the time as long as the outside ambient temp. is below the setting on the Honeywell T675A (65*) AND the boiler water temp. is above the low limit setting (160*).

And that is why I was wondering if/when the circulator in my system is running, if that is how the L4062B "knows" when to use the high limit strategy...?

Another related question I have is: regarding the L4062B, it has a fixed HL differential of 5*. I am wondering if I would be better off with a newer aquastat that would allow me to adjust the HL differential so that I might get longer burns.

Thanks again for the feedback.
 
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Old 11-26-11, 09:16 AM
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My original answer doesn't apply to your setup.

The HL on your control is always 'active'. The LL is only for circulator control.

How does this building NOT overheat? How do you afford the fuel bills?

more in a little while after I study the diagram some more...
 
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Old 11-26-11, 09:28 AM
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More info

Just to add some more info real quick:

- The current burner is a 10-year old Carlin 102CRD which does just fine with a 2.5GPH/60*/SS nozzle @ 100psi.

- The apartments (and a few common areas) each have their own zone valve.

- I quite frankly don't know how I've been affording the fuel bills. Eating nothing but macaroni and cheese for dinner every night helps.

- The low limit maintains water temps. for the Everhot HW tank that makes the DHW.
 

Last edited by Rockledge; 11-26-11 at 09:47 AM. Reason: add more inf
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Old 11-26-11, 09:35 AM
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DHW is provided by this boiler from an internal tankless coil? or is there a storage tank?

Is the hot water supply adequate for the apartments? or do they have to coordinate their showering?

The way your system is set up, that boiler is sitting at 200 24/7, no matter the outdoor temp... and whenever the ODT drops below 65, the circ kicks on and that 200 water runs through all the units... and I imagine there are a lot of open windows at times...

Have you given any thought to replacement of the system?
 
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Old 11-26-11, 09:43 AM
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Trooper,

I just edited my last post to include info on the DHW (Everhot external tankless w/its own aquastat). There is a mixing valve employed in the system, as well.

As for the high boiler temps, again the info I just added might explain some of that. Each apt. has it's own t-stat and zone valve.

Also, during the "shoulder" periods (like now) I usually turn down the HL to around 180* or so.
 
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Old 11-26-11, 09:45 AM
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- The apartments (and a few common areas) each have their own zone valve.
Ohhhh, that changes the picture a bit.

So then there may not be as many open windows.

Without getting into a lot of detail about the piping, I'm going to guess that there must be some way to avoid 'dead heading' the pump when none of the zone valves are open?

For example, a 'bypass' loop, or a 'differential bypass' valve... or quite possibly the zone valves themselves are 3-way diverting type valves.
 
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Old 11-26-11, 09:52 AM
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- The low limit maintains water temps. for the Everhot HW sidewinder tank that makes the DHW.
(Everhot external tankless w/its own aquastat)
I don't see where the LL has any control over the Everhot, other than to cut the circ off in the event that the boiler temp falls too low.

More likely the aquastat on the Everhot is wired into the burner control somehow?
 
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Old 11-26-11, 09:56 AM
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I'm not sure exactly about the terminology, but yes there is a bypass piped into the system. If none of the zones are calling for heat, the hot water can still circulate around in the main loop.

No, the Everhot aquastat is only for the separate DHW circulator. Also, the DHW system has its own piping in and out of the boiler.
 
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Old 11-26-11, 10:17 AM
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No, the Everhot aquastat is only for the separate DHW circulator. Also, the DHW system has its own piping in and out of the boiler.
The circulator is on the domestic side? A 'hot water recirc' system?

I've gotta step out for a few hours, let me think about your system and maybe come back with some recommendations...
 
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Old 11-26-11, 10:30 AM
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Originally Posted by NJ Trooper View Post
The circulator is on the domestic side? A 'hot water recirc' system?

I've gotta step out for a few hours, let me think about your system and maybe come back with some recommendations...
Sorry if I mislead you. I'm not sure %100 sure about terms and how to best describe things.

There are two separate circulators. One for heating which is shown in the linked diagram. There is another circulator that sends hot boiler water through the coils inside the Everhot tank to make the HW and then returned directly to the boiler. More or less like an indirect HW tank setup using a circulator, but with it's own piping directly in and out of the boiler.

I need to run out as well and at least take a stab at the leaves. I appreciate all of your time and feedback.

P.S. Hope you had a great Thanksgiving!
 
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Old 11-26-11, 03:01 PM
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Originally Posted by NJ Trooper View Post
The way your system is set up, that boiler is sitting at 200 24/7, no matter the outdoor temp... and whenever the ODT drops below 65, the circ kicks on...

Have you given any thought to replacement of the system?
This is what I suspected and the reason for my original post/question. The design is such that the boiler itself is only controlled by the HL. I was hoping to confirm this and you have. Thanks a bunch.

In short, instead of the LL setting keeping the boiler firing in the warmer months (for DHW), it's the HL setting that does it on my system. It seems that the design leaves it up the boiler operator to re-adjust the HL setting to match the seasons (essentially treating the HL like a LL during the non-heating portion of the year).

Which brings me back to the other question I asked before: is there another aquastat control that I can use to improve upon this system? Like for example, even if I could simply adjust the HL differential to more than 5*, I'd be able to extend the burner "on" and "off" times, I would think. Do you agree?

As for replacing the current system, I think about it every day! And 20 times a day when I get my oil delivery tickets I actually had a "capital improvement savings account" that was targeted for a new heating system. But unfortunately that money had to be spent on a new fire alarm system (per new code requirements) and it will take many more moons before I can replenish the account and seriously consider replacing the "old girl". So right now I am doing everything I can to hang in there and improve the efficiency of what I have. I suppose the good news is that the boiler has been well-maintained over the years.
 
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Old 11-26-11, 06:12 PM
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The boiler must be controlled by a triple aqua stat with L1, L2, TT ,C1,C2,B1,B2 terminals. L1 is to power aqua stat, TT is for end switch from zone valves ,C1 to send power to circulatory and B1 to send power to burner.The sequence of operation should be,on a call for heat from a thermostat the zone valve opens and the end switch is closed, the TT are then crossed and the aqua stat sends power to the burner as long as the boiler water temperature is below the high setting. Ci does not receive power until the boiler water is above the low setting,this is to prevent the boiler condensing.Settings are usually low 140f, high either 160f or 180f.The aqua stat on the indirect should have a TT terminal and a C1 for its pump and on a call to heat up the tank the TT crosses theTT of the boiler aquastat and power from boiler C1 is sent to the D.H.W. pump.Some systems have priority for D.H.W. and the heat circulatory pump is shut off during a call to heat up the indirect tank.
 
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Old 11-26-11, 06:40 PM
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Yes, that is the way that modern systems can (not must) work.

This is an older system in a multi-unit apt house. There are quite likely no endswitches on the zone valves, so forget about that, without some major system renovations.

The DHW is not set up to call the boiler to fire... it's just a pump on a separate loop off the boiler. Yes, it could be set up with some additional controls and re-wiring, but there doesn't seem to be much point in that... because the boiler is warm start anyway... just start the pump when hot water calls.

Being a monster of a boiler, it would make little sense to cold start the boiler, in my opinion. It would simply take too long to come up from a cold start in order to heat the building.

But, it CERTAINLY does not need to be sitting at 200 the entire heating season!

I'm looking at a way to use a triple a'stat with some 'creative' wiring right now.
 
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Old 11-26-11, 07:05 PM
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When i come across a boiler that does not need to be on stand by i disconnect the blue wire of the Honey well triple aqua stat and the boiler is now a cold start.It saves a lot of fuel, how much fuel could be saved if every boiler was a cold start?
 
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Old 11-26-11, 07:31 PM
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That's not the point here... our answers need to be relevant to the system that the asker has... please don't divert the discussion.
 
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Old 11-26-11, 07:38 PM
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Rock, are the zone valves located in the individual units, or in the boiler room?

What make/model are the valves?

BTW, your system resembles most closely the wiring shown in Fig 4 of the 4062 brochure you posted. Just replace the 'circ relay' with the T675 and it's electrically the same.
 
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Old 11-26-11, 07:44 PM
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Trooper nailed it with his previous post. I wish I could have stated it that concisely myself to begin with. That is exactly how the system is set up. There are no end switches used on the zone valves.

Thanks for chiming in saves. I've thought about reconfiguring the boiler control(s) to make it a cold start, but with its age and design I'd rather not take a chance of any leakage or other issues. The big mama has gotten quite used to being warm all of the time.

But something I haven't ruled out is to maybe upgrade the DHW system and make it separate and distinct from the boiler. The building has a large, interior double flue chimney and only one flue is being used. The other flue was used for - believe it or not - a natural gas-fired trash incinerator (for only about 3-4 years before it was permanently decommissioned for obvious reasons). With an existing NG line in and a spare flue, I believe I have some options. I would be able to afford this sort of upgrade sooner than upgrading the whole H/HW system together. And it would only require me to shut down and restart the big mama once per year, at the beginning and end of the non-heating season.
 

Last edited by Rockledge; 11-26-11 at 07:52 PM. Reason: typos
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Old 11-26-11, 07:51 PM
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Originally Posted by NJ Trooper View Post
Rock, are the zone valves located in the individual units, or in the boiler room?

What make/model are the valves?
The zone valves (Taco 571, IIRC) are in each unit. The end switches are not used.

There is a separate transformer in each unit, as well.
 
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Old 11-26-11, 08:13 PM
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I've had a few ideas I'm toying with...

A couple comments about the current settings first:

I doubt that you need 200 to heat the building, and would think that you could run the circ control down to 140.

Have you tried 180 in the winter, and droppng to 160 in the summer?

Have you tried dropping the circ control to 140?

Have you ever actually witnessed the circulator cutting off because the boiler dropped to 160?

Two ideas:

1. Replace the 4062 with a triple a'stat such as an 8124 or a 7224.

There doesn't seem to be any real benefit to this approach, as in order to wire it to your system the T T on the a'stat would have to be jumpered.

This would allow the circulator to be wired to C1 / C2 , and it would respond to the 'circulator control', i.e. would shut down if the boiler dropped below LL setpoint.

The B1 / B2 terminals would wire to the OB primary, via the aux HL and LWCO.

The burner would still bounce off the HL as before with the LL never taking control other than to cut the circ off if the boiler cooled.

The only advantage to this is that the 7224, if used, does have an adjustable HL differential, up to 30.

2. Fit an ODR module to the existing system, keeping everything else as-is.

The heating curve could be set up to start at say 140 at the bottom end, and up to 180 or so on the high end. This would obviate the need to adjust the controls summer/fall/winter/spring...

I haven't looked yet to see what would be involved in using something like the Tekmar 256 / 260...

Honeywell does make an ODR module that plugs into the 7224 a'stat, and it can be configured to over-ride the heating curve and fire to high limit on a DHW call.

3. Find a replacement control with a wider differential... as you suggested earlier. I'm not sure there is such an animal, but will look.
 
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Old 11-26-11, 08:14 PM
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The zone valves (Taco 571, IIRC) are in each unit. The end switches are not used.
What would it take to wire the endswitches down to the boiler room?

I ask because this would make the 7224 a much more attractive option.

You could, instead of jumpering the TT on the a'stat, wire the endswitches to the TT.

This would let the boiler fall back to 140 (or so) when in 'standby' and bump up to either the HL when called, or if the ODR module is used, up to the heating curve temp.

Additionally, you could also configure the DHW to call the a'stat to fire to HL.
 
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Old 11-26-11, 08:16 PM
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I would replace the zone valves with ones with end switches and install a cube relay on the indirect to start the burner and pump using power from C1 of the boiler aqua stat,as another burner introduces more cost and inefficiency.This is only my way of thinking of course.By the way if your boiler leaks when it is cold it leaks when it hot only the water evaporates.If it leaks it a good idea to fix them.
 
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Old 11-27-11, 08:19 AM
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3. Find a replacement control with a wider differential... as you suggested earlier. I'm not sure there is such an animal, but will look.
If you needed a direct replacement for your 4062, the L4081B would be an appropriate choice and does have a 10 HL (fixed) diff vs. the 5 on the 4062, but that's not much gain... but if yours crapped out and you needed a replacement, it would work.

http://customer.honeywell.com/techli...it/60-2105.pdf

Re: ODR

256

http://tekmarcontrols.com/media/literature/256_a_06.pdf

The first diagram would likely work on your system. The "BOILER" terminals could wire to the T T terminals on your OB primary control rather than have to break into the HV wiring.

http://tekmarcontrols.com/media/literature/256_d_06.pdf

There is an adjustable DIFF setting (up to 42) on this control... or you can run the diff in 'auto' and it will decide what is best.

The 256 has no provision for over-riding the heating curve for DHW use. In your system with constant circ, and warm start boiler, this might not be an issue, but it could be possible that if your ODR targeted something like 140 during the shoulder seasons, that you might have issues with domestic hot water recovery time.

260

http://tekmarcontrols.com/media/literature/260_a_06.pdf

The 260 can also be wired for constant heat call, but these diagrams don't show this. You have several options for controlling the boiler for DHW production, and this app note doesn't show all those options.

http://tekmarcontrols.com/media/literature/260_d_06.pdf

The 260 has all the functions of the 256 with added options for DHW.
 
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Old 11-27-11, 08:23 AM
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But something I haven't ruled out is to maybe upgrade the DHW system and make it separate and distinct from the boiler.
Adding another fuel burner is probably not the best choice as has been suggested.

If you were to upgrade the DHW, going to an indirect would be the way... just replace the Everhot with an actual indirect unit. You've already got the pipe loop and pump in place! A few wiring changes and you're in business...

Speaking of the Everhot, what is it's 'storage capacity' ? A few gallons? I should think that for a multi-unit building it would have to be a bit more substantial than that?

I didn't think they were still making these... but apparently they are:

External Tankless Water Heaters
 
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Old 11-27-11, 09:07 AM
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Wow! Lots of suggestions and information to digest! I will take a look at everything that's been mentioned and read it over real good. I especially need to bone up on ODR technology. Good stuff!

I'm running out of the house right now and so I am short for time, but just to answer the questions posed:

1. It would be a rather labor-intensive job to run all the end switches to the boiler room. The building is 3-floors with 5 units per floor. Plus there are 3 other zones re the common areas. Not impossible, but a big project in and of itself.

2. No I have never witnessed the boiler go down to 160* or utilize the LL at all. Hence my curiosity about the LL function on the L4062B.

3. I have never set the HL down to 160* in the summer, but if I keep the same L4062B control, I certainly will go for it in the future. And I will keep the HL at 180* this winter, again assuming the same aquastat. Now that I have a better grip on how the system actually operates, I can act accordingly.

4. The Everhot tank is a #25 "Wide Super" model.


Again, thanks a bunch. Be back later...
 
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Old 11-27-11, 09:42 AM
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I'm 'multi-tasking' right now myself... but will be out of touch myself for the rest of the afternoon.

I emailed Everhot to see if they can get me GPM specs at lower entering water temps, the info isn't on the website. The ones on the website are rated at 200 EWT... and yours is rated for 25 GPM with 200 EWT... dropping to 180 might (or might not) cause DHW supply problems... we'll see what they say about capacity.

Have there ever been complaints of 'not enough hot water' ?

Yeah, #1 seems out of question for now...
 
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Old 11-27-11, 12:44 PM
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There are sporadic complaints about not enough DHW, maybe 2-3 times a year. I've attributed it to extra heavy usage (in other words, I sort of brush it off ).

I hadn't considered the drawbacks to an independently-fired HW Tank, thanks for the heads up. Doing a quick search, it appears that Indirect HW Tanks are recommended quite often on this board. I would also definitely consider this option, since I have personal experience with an indirect (Amtrol Boilermate) in my own home. It's an upgrade from an original internal tankless system that wasn't cutting it anymore. What a difference! And I would think it would be fairly straightforward to incorporate the indirect tank into any new replacement boiler/heating system that I might be lucky enough to afford in the future.
 
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Old 11-27-11, 04:19 PM
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How about the L8024?

Originally Posted by NJ Trooper View Post
I've had a few ideas I'm toying with...

1. Replace the 4062 with a triple a'stat such as an 8124 or a 7224.

There doesn't seem to be any real benefit to this approach, as in order to wire it to your system the T T on the a'stat would have to be jumpered.

This would allow the circulator to be wired to C1 / C2 , and it would respond to the 'circulator control', i.e. would shut down if the boiler dropped below LL setpoint.

The B1 / B2 terminals would wire to the OB primary, via the aux HL and LWCO.

The burner would still bounce off the HL as before with the LL never taking control other than to cut the circ off if the boiler cooled.

The only advantage to this is that the 7224, if used, does have an adjustable HL differential, up to 30...
I just remembered that I saved the old triple aquastat from an oil-fired burner I had in my home that was replaced a few years ago. The old boiler was also a warm start and it had an internal HW coil (as I mentioned, I got rid of the coil and installed an Amtrol indirect - night and day difference).

The triple aquastat is (a Sid Harvey rebuild of) a Honeywell L8024A. There is an adjustable (up to 20*) differential on the HL. Do you think I can somehow utilize it as an improvement over the L4062B? The only specs I can provide for the L8024A are a few pics of the unit with the cover removed. I believe it is the predecessor to the L8124 that you mentioned.

Pic1

Pic2

Pic3

The L8024 is free, and it would be easy to swap in while I consider everything else that's been suggested. What do you think?
 
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Old 11-27-11, 05:18 PM
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There are sporadic complaints about not enough DHW
You may find that they increase if you drop the HL setting down... easy fix if they do, just push it back up. It's worth a try though, you may find that the complaints aren't enough to counter the fuel savings.

indirect (Amtrol Boilermate)
I don't know that I'd recommend a Boilermate in an apartment building though... and whatever you get will need to be generously sized! You might find that you even need TWO indirects... but calculations would need to be done to properly size the WH for the bldg.

Actually Amtrol does have a Commercial model that would probably fit your bill:

http://www.amtrol.com/media/document...BoilerMate.pdf

adjustable (up to 20*) differential on the HL.
I believe that you will find that adjustable DIFF to be on the LL. I don't know of any HW a'stats that had adjustable diff on the HL.

I believe that the 8024 has a 10 fixed diff on the HL, which is 5 more than you've got on the 4062, but probably not worth the trouble.

Also, you would have to jumper the T T on the a'stat to use in your system, and I'm really not keen on the idea of having a relay energized 24/7... a drawback I hadn't mentioned previously.

One other point to keep in mind when swapping controls... the immersion well has to be of the correct type and size in order to accept the control. Yours 'probably' is, but there is always the possibility that it's not and would need changed.
 

Last edited by NJT; 11-27-11 at 06:19 PM.
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Old 11-27-11, 07:21 PM
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I have apartments and use 40 gal. electric hot water tanks piped up to the boiler coil , with pump and controls so that it acts like another zone. The advantages over indirect are : cost, a back up for hot water and it can supply some heat to the boiler in a emergency. I would not run my system with out the zone valve end switches wired up to an out door reset, oil is over a dollar a liter just too expensive.
 
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Old 11-27-11, 07:27 PM
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Originally Posted by NJ Trooper View Post
You may find that they increase if you drop the HL setting down... easy fix if they do, just push it back up. It's worth a try though, you may find that the complaints aren't enough to counter the fuel savings
I'll see what happens. Right now I'm in an experimental frame of mind, so I'm willing to try anything that might help. I'll make the adjustments and observe the consequences. I'll even be a bit more proactive and ask a few tenants how the DHW is holding up, rather than wait for any complaints.

...calculations would need to be done to properly size the WH for the bldg.
Agreed. I wouldn't want to install something that can't do the job. I won't pull the trigger on a new tank until I have a good grip on the HW requirements of the entire building.

I believe that you will find that adjustable DIFF to be on the LL. I don't know of any HW a'stats that had adjustable diff on the HL.

I believe that the 8024 has a 10 fixed diff on the HL, which is 5 more than you've got on the 4062, but probably not worth the trouble.

Also, you would have to jumper the T T on the a'stat to use in your system, and I'm really not keen on the idea of having a relay energized 24/7... a drawback I hadn't mentioned previously.

One other point to keep in mind when swapping controls... the immersion well has to be of the correct type and size in order to accept the control. Yours 'probably' is, but there is always the possibility that it's not and would need changed.
Understood. Thanks.
 
 

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