Fix or Replace Aquastat.. Add in an ODR?

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Old 01-03-20, 10:53 AM
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Fix or Replace Aquastat.. Add in an ODR?

Hardware: Weil Mclain WTGO-4 boiler converted to gas; has tankless DHW and supplies heat two tube/fin radiator zones and two hydroair zones.

Problem: Current aquastat, Honeywell L8124A runs okay but settings are typically 20degrees lower than actual boiler temp. My biggest concern is it isn't consistently 20degrees off although it is typically around there. This drives me nuts

The Goal: To get the aquastat running right and the whole set up to be efficient (its a summer home that I hate overspending to heat in the new england winter when its vacant).

Option 1) Reseat the probe with some thermal grease on the current aquastat and hope this corrects the temperature. (Cost $10)

Option 2) Fix current aquastat and hook up an outdoor reset. I doubt ODR will gain much here as the boiler always has to maintain 150F for DHW. This option probably isn't worth the expense. (Cost $180)

Option 3) Replace the L8124A with a Hydrostat 3250 . Fairly cheap; hopefully an easy install. And apparently has ability to change hi temp baesd on stat demands. (Cost $150)

Option 4) Replace the L8124A with a Hydrostat 3250 and throw in an ODR because why not; everyone loves to spend money... (Cost $430)

Any votes for one of these options? I get that the cost of any hardware probably wont be recouped very quickly in fuel savings. However, it will bring piece of mind that I setting my temperatures and getting temperatures that can still heat the house and provide DHW while avoiding temperatures that could damage my boiler.
 
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Old 01-03-20, 02:13 PM
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p,
After reading all your current threads personally I think you are overthinking the whole situation. Your return temp is what it is and is determined by the load the boiler has to handle. Every heating unit like your baseboard has a heating value. For instance every foot of baseboard element gives off roughly 600 BTU's of heat. To figure your boiler size you must figure your total heat loss for the house in BTU'S roughly speaking.

Depending how much heat you have on a loop or what you are sending the hot water too will depend on what your return temp is. If you heat 20 ft of baseboard your return temp will be hotter than if you heat 50 ft. Typically you want your hi-lo settings 20 deg. apart so the boiler doesn't short cycle. Bottom line is the return temp is what it is.

The thing I noticed you said was this was oil converted to gas. Oil and gas have different heating values. Gas does not burn as hot as gas and therefor takes longer to recover which might be one reason you are seeing lower boiler temps than your settings. Your aquastat is most likely fine, your boiler just can't keep up.

You said you have a tankless coil which are only installed in oil boilers. They discontinued them in gas boilers years ago when boilers got smaller and had less water because they just could not keep up with the demand because of the cooler temp of the fire. The mistake people make when converting to gas thinking they will save money is they don't consider what the boiler has to heat. That is why you need bigger water heaters with gas and even bigger with electric than you do with oil. It is because of the heating value of each fuel.

Next and this is only my opinion. ODR'S in my opinion are a waste of money that will never be recouped on RESIDENTIAL systems. A house must be properly sized in the beginning to even consider using one. If installing one in a home with an unbalanced system it will only make it more uncomfortable. If some rooms don't have enough heat to begin with at 180 deg it will only be worse at 140.

They work great in commercial buildings and do save a lot of money. That's what they were initially designed for but found that people will spend money on all kinds of gadgets and when they realize they've wasted their money it's too late.

Your HYDRO control is a good control but it's not going to solve your temp problem because you are still heating the same units and using the same fuel.

My suggestion would be to run one unit at a time and check your return temps to see what they are. After running one at a time go to two and so forth before spending money on things that will not change your situation. As you increase the load you will see temps get further apart. There's nothing you can do about that. That problem was created when you switched fuels.

As I said this is just my opinion and hope this helps a little. I am sure there will be at least 1 other opinion when this is posted. At least this will may give you something to think about.
 
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Old 01-03-20, 08:06 PM
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You mention this is a summer home in the NE. So I assume there is no HW demand during the winter months. If this is the case and you want to change the aquastat for hopefully more accurate temps do so. You may want to change the aquastat well at the same time as it may have a sediment buildup on the external walls.
If you change the control or not you will have two options after that.
1. When you leave the home for the winter turn the low limit way down to 100F if possible. The boiler will maintain much lower temps saving fuel and still run to 180F on a heat demand. When you return, reset the low temp setting higher to make enough hot water while you are there. When you leave turn it back down.
2. Do the same as number 1 including turning the low limit down when you leave and add ODR. I love ODR as it has several benefits. The fuel savings is the first. If set up properly it will maximize fuel savings. Unfortunately, many contractors would rather disconnect the ODR than take the time to reset the parameters for a better operation. We have added ODr to many existing boilers and saved homeowners money. To improve ODR operation, even more, it pays to know how much oversized the boiler is and what the actual heat loss is on the home. Measure the amount of baseboard and really determine the actual water temperature you can operate at. Secondly, ODR improves the comfort in the home if you are there in the winter months.
 
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Old 01-04-20, 08:45 AM
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Outdoor reset study in 1984 found that the average savings was between 10 to 20% that was run by Minnesota Energy Office. A major factor in favor of outdoor reset is energy savings. For every 4°F the boiler water is reduced, there is a 1% energy savings. By varying furnace water temperature according to outdoor temperature oil consumption is lowered.
A good overview of modern Out-Door-Reset features can be found on Tekmar Quick Setup pages 15 to 17. http://tekmarcontrols.com/images/_li...e/256_d_07.pdf The 21 menu items with adjustable settings are a major contrast with simple temperature and delta-T settings on most aquastats. Some of pbct2019 issues could be dealt with by those menu items.

A top OCR is $158 Tekmar 256. The $228 Taco PC 200 is repackaged Tekmar 256 in green case . Other brands charge $430 or more in pbct2019 Option #4.

https://www.supplyhouse.com/Tekmar-2...iler-4150000-p

https://www.supplyhouse.com/Taco-PC7...SABEgJUVvD_BwE

Adding OCR to systems is simple. OCR has 2 switch contacts that close to activate burner and two contacts for 24 volt AC power. Honeywell, Taco and other vendors try to tie customers in their other system products by using special connectors. Taco PC 200 has special 4 prong plug rather than screw contacts on the Tekmar 256.

The Hydrostat 3250 is an old “work around” that is not nearly as effective as modern OCR's. Beckett and Taco had other "work around" products before OCR's.

I am cost conscious and buy whatever works best for lowest price. The Best Buy is $158 Tekmar 256.
 

Last edited by doughess; 01-04-20 at 10:14 AM.
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Old 01-04-20, 11:24 AM
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Thanks, Spott. You are spot on in that I am overthinking things. This is what happens when an engineering gets too much time off from work and starts tinkering and trying to optimize a system he is still learning about.

The previous owner did the oil to gas conversion and I have no idea how their discussions went with the contractor. I have little faith in the contractors they used, since they wired two of the four zones incorrectly during the install. Regarding your point about the aquastat, I believe I am observing the opposite of what you mentioned. My boiler temps (confirmed by weber grill probe, infrared thermo, and analog dial on boiler) are hotter than my settings on the aquastat. My research suggested this is poor probe contact or bad stat… thoughts?

This winter, I have been using a 150F lo and 180F high on the boiler stat. These settings have worked well for comfort and lower gas bill. But, I now noticed some condensate on my boiler flue (no clue if its new or I never noticed it before). So I ran the system under full load (all zones calling) and I found return temps of 120F on the return pipe (even though boiler analog read 150F+). I got worried these temps were causing condensation on the exchanger, so I upped temps to 190hi/160lo.

Regarding short cycling causing flue condensation, I never noticed it happening. One thing that might be a problem is one of my zones in this house has two fan/fin rads on it rated at about 7,000 btu each (depending on flow and temp). This zone does fire often; could it be this small load zone fires the boiler and lets it reach max temp very quickly causing flue condensation? Would it be worth disconnecting this zones ability to fire the boiler and it run off of low temp 160? Let me know if my logic here is flawed. Sounds like all I might be doing is shifting the problem to occur at a lower temperature?

So I am gathering I should set a hi that is comfortable and effective (180F) and a lo that is 20degrees below that…? If everything is designed right, the boiler should more or less be running during the call for heat. Balancing input with output needed?? And if boiler is sized properly, it should recover from the brief exposure to low return temps and not have condensation.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Rbeck; I see your point. My boiler is a cast iron non-condensing system. Based on talks with the manufacturer, it should be maintained at 150F to maintain seals and prevent condensation. So I don't think approach will work for my setup.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Doughness. Thanks for the comments. I see both sides of the argument for ODR. I think for me, it will come down to how much savings can be had if the hi range I can work with is really just 160F and 200F. Also, as Spott mentioned, comfort may become an issue and will have to be tested. If its 50F at my house, the ODR might think 150 is okay, however, this will lead to my hydroair zones blowing cold enough to be uncomfortable.

Thanks all.
 
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Old 01-04-20, 03:03 PM
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p,
You seem to have 2 concerns here. One, being condensate in the flue and boiler temps different from what your aquastat is set at.

Below I have posted a sight that will explain how your aquastat works. You have a triple action aquastat which is a warm start, meaning it has high & low control settings and maintains constant temp because of your tankless coil. Your aquastat has a low limit adjustable differential which could account for the temps you are getting compared to what you have set. On the sight posted below go to install instructions and scroll down to page 7 and it will explain how the dif. works.

As far as condensate goes, you can have condensate in the boiler which is caused by low water temps and you can have flue condensate which is caused by low exhaust gas temps. They are not the same and are 2 different problems. You seem to be concerned about flue pipe condensate which has nothing to do with your return water temps but the exhaust temp of the flue gases or the temp of the chimney flue and the lack of sufficient boiler exhaust to heat it up. This is also due to the different fuels. Your WGO4 has a 7" flue pipe which is a large pipe for temp of gas exhaust to heat let alone heat the chimney flue also. You need temps above 300 going up the flue and for gas the flue must be properly sized for that reason.

When you install a new gas boiler at least in MA. you must add a new chimney flue liner to match the exhaust pipe of the boiler so the chimney will heat and pull a draft. What you should do is get a temp gauge and measure your exhaust flue pipe temp or have someone come in and do an efficiency test on the boiler and see if there is a problem.

The next time you are there if you could post some pics of the boiler it would be helpful to see what they did.

https://www.supplyhouse.com/Honeywel...79e72e08618b3b

As rbeck said if you are not using your coil in the winter you can turn your low limit down to 100 or 110 if you're nervous. It will not hurt anything because you will still be calling for heat as you do now. It will just not maintain that higher temp which you do not need. You will basically have a cold start boiler which, if you ever change that boiler you will have anyway because with gas there is no option anymore.
 
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Old 01-04-20, 03:22 PM
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Not sure why the manufacturer would say what you said. All cast iron boilers over the last 35 years have been designed for a cold start application even though they may maintain temperature.
They may have been referring to the coil plate gasket, the boiler will be oK.
 
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Old 01-04-20, 03:53 PM
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r,
Not sure what you're referring too but I agree with what you said. Maybe my higher temp remark may have been confusing. I was getting writers cramp. I meant he would not be maintaining the low limit setting of 150 by turning the LL knob down which I believe its what you suggested.
 
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Old 01-04-20, 10:10 PM
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Here are general comments on things in this thread:

OCR fuel savings add up over the years. If only 10% on a $1,000 annual fuel bill that is
1 1/2 year payback... then the rest is money in the bank.

There is a learning curve with OCRs. They can easily be tweaked over the season by pushing three buttons.

rbeck mentioned heat load calculations and nozzle size. I did not consider either in setup.
OCR's are basically closed loop controls adjusting to variable conditions and loads.

If original settings do not give adequate heat, raise MIN - The minimum temperature allowed for the boiler target temperature.

OCR settings do not have to be kept the same all season. In warm weather I set low at 145F.
Around 30F outside raise it to 155, near 0 F go to 165F.

As far as return water lowering boiler water temp, I use low temperature circulator cutout set at 135F OFF and 138F ON. (a $10 eBay PID temperature control)

Tekmar 256 has adjustable setting OCC “The system’s warm weather shut down during the occupied (Day) period.” If the outside temperature is above 50F setting, system will not run.

Tekmar 256 has adjustable setting UNOCC “The system’s warm weather shut down during the unoccupied (Night) period.”

rbeck: Secondly, ODR improves the comfort in the home if you are there in the winter months.
While “comfort” is subjective, OCR by slowly adjusting water temp as outside changes results in occupants not sensing changes in heating from day to day. We find the house is just more comfortable.
 
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Old 01-05-20, 12:14 AM
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Thanks, everyone.

Regarding the aquastat, thanks for the info. I have read that manual in and out 10 times already ;-). The number one thing that makes me doubt the proper function of my aquastat is really the hi setting (not necessarily the lo and the differential). If I set the hi to 180F, my boiler will actually get up to 200-210F. If I dial the hi back to 160F, I get my target output of about 180F. During the summer, when the boiler was controlled strictly by the lo setting, I saw about a 20F difference between setting and actual as well. This was with a 10F diff, so the boiler should cut off at target and i guess climb a little higher after burner off from residual heat?

Regarding the flue stack. Unfortunately, Its looking like it will be a few weeks before I am back to take pics. From what I could tell it meets the recommendations of manufacturer but I have no idea if they changed it up after the conversion. It does look like it has a fairly new damper on the stack that's wired to the burner. If my understanding is correct, flue condensate is from (1) too short of a cycle (2) wrong flue design or (3) both. My guess says it could be short cycling of my boiler on the low load zone that fires often. My biggest concern was that condensate their might indicate condensation problems within. Seems like they are independent events, though.

Regarding the lo temp setting when not home. It was suggested to turn it down as low as possible. Maybe I have a misunderstanding here with condensation. Natural gas condenses around 140F. If I turn Lo to 110F and the week is mild temperatures outside, the zones will never call for heat. Then the boil will drop down to 110F and periodically fire to maintain 110F. Won't firing and maintaining 110F cause condensation in the boiler and ruin it? That is the thought process that has led me to maintain 150F all the time. Maybe I am wrong here?

Regarding outdoor reset; a lot to consider here. I know I could do all the math but anyone have rough estimates on gas usage if I heat at 170F for a month vs 180F? Or something along those lines? The temp settings you mention for your system, Doughness, would definitely fail to heat my house based on tests ive done. If I send 150F to my small hydroair zone, it will only blow cold. Since I would need higher temps, I think I will have to do a bit more math to determine the time to payoff the ODR.

Thanks again
 
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Old 01-05-20, 04:07 PM
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The flue gas condensation will only happen if you are running the circulator. If just maintaining temperature there is no flow in the boiler and the boiler will not condense.
With the high temp set to 180f, on a heat demand, the boiler will rise towards the high limit setting of 180F.
 
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Old 01-13-20, 09:02 PM
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rbeck:To improve ODR operation, even more, it pays to know how oversized the boiler is and what the actual heat loss is on the home.
It is not necessary for DIYer to know boiler size or heat load to set up Tekmar ODR. Common settings are high temperature set at 180F and low at 140F.

Knowing my heat load and that boiler fires at 50% of rating played no part in setup. Various system quirks did require some tweaking to optimize performance.

The whole idea of ODR's is automatically adjusting water temperature to changing outdoor temperature and resulting heat load. In one sense it is dumb..... keeps firing burner until set temperature is reached. If someone opens a lot of windows, increasing load, it will just run longer.
 
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