Boiler Short Cycling, Looking to increase efficiency and stop wasting Fuel Oil

pauljr

Just bought a house/office that was built in 2005, boiler installed in 2005
I have 10,000 square feet of finished space with Hot Water Baseboard heat.
The heating equipment is:
Boiler -- weil mclain Ulitimate PFO-7, Beckett Oil Burner 1.20 80A nozzle
Control Is Honeywell L8151A -- (Not used for circulator pump control)
Zone -- 12 Heating zones, 1 hot Water zone, 2 TACO SR504 and 1 TACO 506
Hot water is indirect 60 gallon superstor and set for Priority on the TACO 506 control

Issue:
I have noticed since moving in that the Boiler seems to run a lot for short duration.
Typically 3 minutes, sometimes as little as 30 seconds.
I believe this short cycling is wasting a lot of oil.

I discussed this with the service tech. same person who installed the boiler when house was built.
I find the boiler runs even when there is no calls for heat of hot water.
He said this operation is normal for this type of boiler and the boiler cannot be "cold started". He stated cold start boilers have problems and I will not have hot water if a cold started this boiler.

I have done some research and the L8151A was setup for Low Limit of 140 and high limit of 180 with a 10 differential. In my quest to reduce this short cycling behavior I changed Low Limit to its lowest point 110, and set differential to 20 (highest). This has helped some but the boiler still runs a lot even without calls for heats.

Since the circulators are controlled by the TACO controls when a call for heat is made the pump for that zone starts immediately, and the boiler is then controlled by the high limits of the L8151A.

Therefore I do not see why I cannot change this boiler to cold start.
Why do I need to keep the boiler hot?

The house that I moved from had a System 2000 boiler installed in 1989 with 30 gallon indirect tank this is a cold start system and I never had an issue for over 30 years. Never ran out of hot water, I serviced it myself for the last 10, I always found it easy to clean.

Based on my observations, I believe I am using approximately 300 gallons of oil a year maintaining this boiler in a warm start condition. The basement utility storage room where this boiler is located to 900 square feet and it typically is over 80 degrees in that room. I working on insulating all the exposed hot water pipes but I think the majority of the heat is from the top of the boiler. The stack of this boiler is always HOT, I am considering installing a Stack damper to stop the flow of heat up the chimney when the system is not running.

Since I am only controlling the boiler with the L8151A, I think this control is one of the issues.

I just need a very basic boiler high temp controller, any recommendations??

Would a stack damper save me some energy?
Is a stack damper worth it? or does it add more problems?

Would an upgrade to a triple pass boiler be worth it??

My oil/propane company is pushing new propane boilers since they are 96% efficient, I keep thinking yes BUT propane has less BTU's then oil and cost about the same per gallon.

I would appreciate any comments/advice, to gain the most efficiency for the least amount of $$




Thank you

EdTheHeaterMan

I agree with the cold start option. The near boiler piping may not be advantageous to making DHW quickly if that zone is piped off of the space heating manifold. Summertime operation may add un-needed 180° water to the entire manifold piping. If the indirect was piped direct from the boiler to the DHW tank on its own circuit separate from the space heating manifold then a large section of the piping will never get warm (or hot) when the DHW calls for heat. This is probably why the original installer decided to use a "maintain minimum heat" control logic. If you count the pre-purge timing and warm up of all those gallons of water in a boiler and large manifold from a cold start, you may get close to the DHW tank storage capacity before the recovery starts to catch up to the hot water demand.

If you try the cold start burner logic without redesigning the near boiler DHW zone piping, and you are satisfied with the results, then you are done. If you run out of DHW then a repipe would be in order. either way a cold start will ultimately yield some savings..

If there are no wires connected to ZC or ZR, then that is all you need to do!

STEVEusaPA

I can't see all your near boiler piping, but you can do a few things to help mitigate.
The true only way to eliminate short cycling for this situation would be a buffer tank with some re-piping.
You could switch to cold start but you must protect the boiler from cold water return temperature. That can be done best with a 3 way, or 4 way valve.
Second best, if the boiler has it's own loop with its own circulator (Primary/Secondary set up), you can change the aquastat to a modern one that has a feature like 'Circulator hold off', which will help prevent colder return water temperature from condensing the boiler.
You may also be able to combine some of the smaller zones to prevent short cycling.
You could also save some electrical cost with more efficient circulators.

EdTheHeaterMan

STEVEusaPA said:

I can't see all your near boiler piping, but you can do a few things to help mitigate.
The true only way to eliminate short cycling for this situation would be a buffer tank with some re-piping.
You could switch to cold start but you must protect the boiler from cold water return temperature. That can be done best with a 3 way, or 4 way valve.
Second best, if the boiler has it's own loop with its own circulator (Primary/Secondary set up), you can change the aquastat to a modern one that has a feature like 'Circulator hold off', which will help prevent colder return water temperature from condensing the boiler.
You may also be able to combine some of the smaller zones to prevent short cycling.
You could also save some electrical cost with more efficient circulators.

Agree with Steve. If your boiler is not piped this way,

you may have a case to ask for the original installer to repipe if they did not follow the manufacturers instructions. If it is piped this way, then you have the necessary piping to accomplish Steve's idea of adding a buffer tank or just trying it with the piping "as is" Perhaps the original installer will work with you to get your system to operate a little more efficiently.

Does the original installer also provide your fuel? Just saying... there is motivation to make your system more or less efficient. If they want to keep you as an oil customer, tell them you want a lower operating cost by redesigning the boiler to operate as a cold start. The way the manufacturer's instructions recommend! Or you can find someone that will do that for you. Talk to the oil company top man. The owner (or the district manager if it is one of the big players). Loosing 200 gallons a year is better than loosing a 2000 gallon customer.

pauljr

Thank you both for your comments.
I agree the DHW tank is to far from the boiler. One of the first things I noticed last summer was my first floor baseboards were warm when i had the A/C running. The check valves are obviously not closing tight and hot water just wants to rise up. The DHW being on the very end of the manifold means the entire manifold is hot 24/7. I mitigated that situation last summer by shutting off all the manual ball valves. The installer did put valves every where, I can manual isolate every zone and every circ pump.

The boiler is already getting slammed with cold return, which I was concerned about but does not seem to be an issue. Sine the L8151 controller does NOT control the circ pumps and the pumps are completely controlled by the TACO relay boxes the minute a Tstat calls for heat the circ pump kick ON.
With 12 Heating zones I only really using 4 zones, the other 8 I have the Tstat set at 45 degrees (lowest setting)and I know those zones do call for heat, therefore I sure that 45-50 degree water is heating that 120+ degree boiler.

Also last summer, I had to take a trip and I shut the boiler down for 4 weeks, no issues upon restart.

I think my first items will be to unplugged the blue wire on the L8151a to make the boiler cold start.
( read somewhere else that would convert the control) THANK YOU for the confirmation.
Second insulate all the manifold piping.
Third (and most expensive) would be to repipe DHW tank closer to the boiler, and install a balancing valve to add some warm water to the boiler return. (warm up the cold water return)

The piping was done by my neighbor across the street, he is a plumber who work for the builder that built this house. He plumb all the houses on the street. The boiler was installed by the oil company. This is a small town and the oil company does not touch plumbing, and the plumber does not touch the boiler except to attach the feed and return pipes. I can try talking to him but I doubt he will even consider helping me out.

If I spending $$ to repipe the DHW, would a new triple pass boiler save me enough money to make it worth while??

EBEBRATT-Ed

No a new boiler will not pay for itself. I question the size of this boiler. You say it has a 1.20 nozzle which is 168,000 btu/hour but your boiler name plate says 276,000 heating capacity . I am going to look it up cause that does not make sense


If they oversized the boiler that will contribute to short cycling.

I agree with @STEVEusaPA & @EdTheHeaterMan comments about piping changes and return water temp protection & maybe a buffer tank

Jon_blaney

If you are going to repipe the indirect tank, how about adding a hybrid water heater in series. Heat pump in summer and shoulder seasons, indirect for winter. That is a lot of boiler to fire up on the 4th of July to take a shower.

pauljr

According to the book the Min. nozzle is 1.05 with 130 MBH and max. nozzle is 2.35 with 276 MBH.
I do know when more then 4 zones call for heat at the same time the boiler runs a long time, However typically its only 1 or 2 zones at a time.

The situation I do not understand (and I ran downstairs to look) is I heard the boiler fire up and it ran about 30 seconds and shut off. I hear this a lot and I am trying to figure out why. I ran downstairs and no Tstats including DHW were calling for heat, no circ pumps running and the boiler temperature was 170. Seems to high for being turned on by low temp control, and I was down there fast so it could not have cooled down from 180 high shutoff. 30 Seconds run time is a waste of fuel.

pauljr

What type of hybrid water heater would you recommend. In my old house I had 4 solar hot water panels and they worked GREAT!!! Unfortunately the design of this place solar would be VERY difficult.

pauljr

Just thinking the easiest hybrid water heater for me to install, would be a propane or Oil fired heater. Could easily install either one, plumb in series, and shutdown the oil boiler all summer.

EdTheHeaterMan

@pauljr, Try the Control Wiring Hack I mentioned above. It won't cost you anything, it is perfectly safe because that wire connector is insulated (But you can add a piece of electrical tape as an added precaution) then any burner operation will be Zone thermostat or DHW thermostat only.

There is a logical explanation to your 30 second burner operation. Consider this. Since all your controls are analogue, there are only switch or relay contacts that turn on circulators and operate the burner.

Lets say zone 3 calls for heat and it is the only zone calling for heat. Since the burner is firing at a rate much greater than zone 3 could possibly need the L8151A reaches 180° rather quickly. Say about 3 or 4 minutes. The burner shuts off by the high limit, as it should. However the call for heat from zone 3 is not satisfied. so the circulator pump continues to operate, as it should. In about 6 0or 8 minutes, zone 3 operation caused the temperature to drop the high limit differential (That is fixed at 10°). So now the water in the boiler at the control sensor bulb is 170° and the oil burner starts up, as it should. Within 20 to 30 seconds, the call for heat from zone 3 is satisfied. The burner shuts off and the circulator shuts off just 30 seconds after the burner just came on, as they should. By looking at the Zone Controls just after the 30 second short cycle you should find boiler temperature near 170° and no call for heat from any thermostat

According to the sequence of operation logic of your analogue control system, this could happen more often than not because you have so many zones. Each of these zones do not communicate with each other nor do the zone controls communicate the boiler temperature to the zone circulators. Your system is basic. To resolve the 30 second short cycle you need to purchase a more expensive "Smart Control System" with microprocessors to more efficiently communicate more parameters to the burner, maybe from a company like Tekmar. The EK System 2000 has something like that incorporated in the master control but I would not try to re-engineer that control to a cast iron boiler.

EdTheHeaterMan

@pauljr Try the cold start hack if that gets you closer to the result you want, you may be finished. If however you want to upgrade the L8158A control to an electronic control with some energy saving features you might like the Honeywell L7224U. It has some microprocessors that can reduce short cycling along with other energy saving features. It actually costs less then the L8151A or the L8124B,C,D... that it replaced.

pauljr

Thank you for your well written explanation, this is what I suspect is going on, just something I could not put into words so clearly. The house I moved here from had a EK System 2000 I had installed back in1989 and that system was still running problem free when I sold the house in June 2021. I am very used to the behavior of that system and this system shocks me as to how basic and wasteful it is. FYI: I am an electrical engineer and work as a Controls specialist for many years. I have designed, built and installed many one of a kind special control system during my life time. But I hate reinventing the wheel when a system already exist. I really like the feature in the system 2000 that continue to circulate the water until it cools down after the Tstat is satisfied. I paid to heat that water is just very wasteful to have that hot water sitting in the pipe.

MikeAmann

If @pauljr does go the cold-start route, then his burner would only be controlled by the HI Limit with it's fixed 10 degree differential. The TACO's are controlling his circulators, so then I assume nothing is connected to C1 C2 in the Honeywell L8151A aquastat. What would really help his situation is a larger diff setting. Is there a simple way to control the burner using the LO Limit instead and set the diff to 25?

pauljr

I just did the hack, (unplugged blue wire) and I will see in the next few days if that helps, especially when the weather gets warmer on Sunday. I just came home after repairing my daughters oil burner simple repair Riello burner, hydraulic jack leaking oil.

Her boiler has same setup as mine (different mfg), L8151A, superstor DWH. I did the hack on her control too. FYI: Small house only 1 zone heat, 1 zone DHW. No balance connection between feed and return.

I like you idea of controlling the burner through the Low temp and adjustable diff. especially with my large boiler. A 10 degree diff is nothing and in less then 2 minutes I hitting high temp. setting.

I am just not sure IF the control can be setup that way. I will take another read on the manual, maybe the C1 C2 circ connections could be used to control the boiler?

MikeAmann

C1 C2 connections operate (the circulator) within the allowable settings. If trying to use this to fire the burner, you would be firing when the water was already hot enough to circulate. You want to fire the burner when the water needs to be reheated.

For now, wait to see if disabling the LO Limit is a step in the right direction.

Now, I believe you are already aware of this, but I will explain it for you:
BOTH the HI limit AND the LO limit are actually hi limits (burner cut-off temp). The HI limit is the one in play in the winter, controlled by your thermostat. In the summer, the thermostat is not in play, and the LO limit is your cut-off temp setting to keep the boiler water warm for DHW needs. So in the summer, the boiler/burner is being controlled by the LO Limit (and it's ADJUSTABLE differential).

pauljr

Agree C1 C2 will not work for the burner, I just reviewed the manual, you cannot control the burner with the low limit circuit without a complete redesign of how this control works. I would need a spare control and spare burner to experiment/test with.

EdTheHeaterMan

MikeAmann said:

If @pauljr does go the cold-start route, then his burner would only be controlled by the HI Limit with it's fixed 10 degree differential. The TACO's are controlling his circulators, so then I assume nothing is connected to C1 C2 in the Honeywell L8151A aquastat. What would really help his situation is a larger diff setting. Is there a simple way to control the burner using the LO Limit instead and set the diff to 25?

You could take the wires from the high limit to the low limit NC contacts

EDIT:
Since the white plastic block only has wires connected to the front of the aquastat, (there are no hidden wiring under the control) then it is easy to use the limit portion of the LOW side of the control and abandon the High Side of the control since C1 and ZC are not needed.


Remove the blue wire connector from the High side. (not the low side) Then swap the two wires at the bottom of the white block. This will put the burner B1 terminal on the LOW side of the aquastat (that has the 25° differential). As an extra safety precaution, disconnect and cap the white wire from the NO contact terminal (also called W in the wiring diagram). This will prevent ZC and C1 from receiving power. Just in case anyone in the future tries to use the control for operating a future circulator.

MikeAmann

Awesome @EdTheHeaterMan
I knew it could be done!

pauljr

Ok, Thank You everyone for the advice.
First I the hack removing the blue wire (B) on the Top Right (low limit side) and that did remove the low limit control. The boiler stop running to maintain the 120 degree Low limit.
I have the high limit set at 180 and when the temp drops down to about 170 it runs for approx 3 minutes and shuts down at the high limit of 180.

Then I did the 2nd change.
I put the blue wire (B) on the Top Right (low limit side) back on where it was.
I removed the black wire (B) on the Top Right.
I then swapped the 2 bottom wires. (red & yellow), I also removed and capped off the white wire.
Now the the low limit temp adjustment sets the high limit which i set at 180
The diff. is set to 25.
BUT the boiler still kick on at about 170.

MikeAmann

Congratulations. What you did IS working correctly.
Now I need to explain how the adjustable DIFF works.
There is still a fixed 10 degree MINUS built in.
The adjustable diff ADDS temp ABOVE your setting.
Sounds complicated, but it's easy. Just follow this:
It's SET POINT minus 10 B.I. diff PLUS the adjustable DIFF.
So if you want 180 as your highest burner cut-off temp, with a 25 degree adjustable diff, you would set the LO Limit dial for 165. Here's the math: 165 - 10 + 25 = 180.
If you set the diff for 20 degrees, then for the same 180 cut-off, then 170 - 10 + 20 = 180. Get it?
Back to the 25 diff example: CFH makes burner run to 180 and it will not fire again until 155 (165 - 10).
You now have a 25 degree spread. This will give you less short-cycling and longer burn times.

pauljr

Ok, that explains the temp difference I saw when I put the burner control on the low limit adjustment.
I saw the boiler temp going over 190 and I turned the adjustment down until it shutdown.
I now have it set halfway between 160 and 170.

MikeAmann

If this modification works satisfactorily for you and you decide to leave it this way, be sure to write a note of what was done and why AND POST IT WHERE IT CAN EASILY BE SEEN. You might not remember in the future, and you don't want to confuse any future service techs.

pauljr

Already labeled the inside of the box with the modification instructions and how to put it back to its original config.
Now I have been monitoring the boiler closely trying to determine if this made a run time difference.
It is now successfully working as a cold start boiler, if no call for heat from any zone the boiler does not turn on, it takes about 3 to 4 hours to drop to 100 degrees (depending on outdoor temp) and then from 100 it is REALY slow to drop.

However, I cannot say the change to 25 diff made much of a difference. If the boiler is warm (above 140) and a call for heat is gets to 180 and shutdown in less then 4 minutes. Before I made the change it was less then 3 minutes.

Only times it runs longer then that is if more then one zone calls for heat or the boiler was cold when the call for het came.
My wife and I have even purposely taken back to back showers with the boiler at or boiler 100 and never run out of hot water. The boiler does turn ON fairly quickly but it catches up fast.

With the price of oil at over $5 a gallon I really thinking about installing an electric heat pump (Hybrid) hot water heater and install it after the superstor, and put a switch on the Tstat connection of the superstor so I can shut it off. The output of the superstore would feed the input of the hybrid. and the hybrid would then feed the house HW. Seems to be the simplest install.

Summer time I could shut off the boiler.

MikeAmann

Yes, it appears that your boiler is really oversized, or your having 12 separate zones does not give much of a heating load to the boiler. If you only had one zone, like me, you would see a more dramatic difference.

Before you go the electric heat pump (Hybrid) hot water heater route, look into the new boiler controls such as the Hydrostat 3250-plus. The money saving features are already built in.

ethicalpaul

The Rheem heat pump water heater I installed costs almost nothing to run (heat pump only mode) and is a great way to not have to heat your house in the summer. Highly recommended 

pauljr

Iwas just looking at the Rheem unit, and the AO Smith. The Rheem seems to have a few features like wifi to monitor the heater with smart phone and a little higher energy saving factor. My electric rates is 23 cents per KWH, Would the Heat pump be cheaper then running the OIL HW zone on the superstor storage tank?

I understand the heat pump needs a warm air/warm environment to draw heat from.
My basement utility room (where boiler is located) seems to stay around 70 degrees and hotter during cold winter days when the boiler is running often.
Seems like ideal space for the heat pump. If it did get too cool in summer I could as a vent to the outside to bring in the warm air.

ethicalpaul

I just posted this on a different thread but here is my usage for a two person family. It doesn't need a lot of heat. 40 degrees is enough but of course warmer is better (source: https://www.energystar.gov/products/water_heaters/high_efficiency_electric_storage_water_heaters/considerations )

I used 35 kWh for last month. So that would be 29 cents per day at your rate. Mine is also next to my (steam) boiler so it's always about 70 in the winter and 65-75 or so other seasons. I run it in "heat pump only" mode which is around 350% efficient compared to the 100% efficiency of resistive electric (not that 100% resistive efficiency means a great way to heat)

You won't need to vent in outside air in the summer. It won't noticeably cool your basement. It does a little of course, but it's not noticeable.

I guess you could keep running a massive boiler all summer to do this instead but I can't imagine why.

EdTheHeaterMan

@pauljr
There is a best way to pipe an auxiliary water heater to operate as a duel fuel with a choice of primary tank to be A or B. The valving is intricate but offers you the chance to use the indirect when the price is right and the Heat Pump tank when it is not.

The cost of each fuel will fluctuate differently over time. If you install based on todays political climate, you will be stuck with that choice for a long time.


In this diagram both tanks are utilized to keep water in the unused tank from becoming stagnant reducing the chance for bacteria to form.



Same thing in reverse by reversing 4 valves at the change of the season or as the price to operate one becomes lower than the other.

You must add a manual switch to the Temperature thermostat circuit in order to take the idle tank off line for fuel usage.

BONUS: If you ever add that super spa shower with 10 body sprays or that 120 gallon whirlpool bath tub, you can power both heating sources and have enough HW to fill the Grand Canyon. (might be an exaggeration)

Jamie Hall

It isn't at all difficult to compare the operating cost for various methods of heating -- in this case, water. Except that you do need the COP of the unit, which is the ratio of effective heat output to electric energy input. Then compare the cost of some handy number of BTUs from one source, such as oil or LP or gas or electricity factored for the COP with whatever other source you are interested in. Useful numbers: one KW of electricity is 3400 BTU. One gallon of oil at 80% efficiency is 112,000 BTU. One therm of natural gas at 80% is 80,000 BTU (and a therm is very nearly a cubic foot, if that's what your meter reads). One gallon of LP at 80% is also about 72,000 BTU.

pauljr

ethicalpaul: Is that energy use profile on the Rheem tank screen, or smart phone interface?

Steamhead

MikeAmann said:

Yes, it appears that your boiler is really oversized, or your having 12 separate zones does not give much of a heating load to the boiler. If you only had one zone, like me, you would see a more dramatic difference.

Before you go the electric heat pump (Hybrid) hot water heater route, look into the new boiler controls such as the Hydrostat 3250-plus. The money saving features are already built in.

This, or the Beckett AquaSmart, would be my first choice.

SuperTech

ethicalpaul said:

The Rheem heat pump water heater I installed costs almost nothing to run (heat pump only mode) and is a great way to not have to heat your house in the summer. Highly recommended 

Heating your house? What does that have to do with domestic hot water? I've been in plenty of basements in the summer with boilers that have indirect tanks and even tankless coil boilers and the basements are always cool and comfortable.  Even a steam boiler with an indirect doesn't heat up enough to make steam to keep an indirect tank hot.
I would imagine some serious piping or controls related problems exist if the house is being heated as a result of the boiler running for hot water production.

pauljr

In my 2000 sq ft house in CT, all the pipes in the basement were insulated, and the cellar was never very warm and the boiler held about 3 gallons of water.
When I was looking at houses in NH I noticed in all the houses the pipes in the basement were not insulated. The purchased a 10,000 sq ft house/office built in 2005. I have been slowly insulating the pipes and I think that will make a difference when I am done. Since I have 12 heating zones and 1 HW zone all plumbed to a manifold made with 2" IRON pipe there is a LOT of IRON that getting heated, plus the boiler holds approx 15 gallons of water. The manifolds are about 20 feet long each and the plumber installed the indirect tank at the very end of the 20 foot manifold. I know it should be relocated right next to the boiler but that is a major project.

I read many comments that the boiler is oversized, which is probably is for 90% of the time. Proper sizing for this house I think is a problem. Right now is just my wife and I and we have 2 to 3 zones turned up to 68 degrees, and like I reported the boiler runs about 3 minutes and then shuts down for 5-10 minutes depending on heating requirements.

However, when my kids and grandkids (have not happened yet)come visit and we turn up the other 5 to 6 zones to 68 degrees what happens to the boiler run time. I do not know since we have not tried that yet.

One possibility (which I hate to even think of) is have 2 heating systems, one for the primary 3 zones, that 2 to 3 people living in this large house would typically use, and a second which would kick in when the additional heat is required.

I really not sure what the correct answer is, but I really starting to wonder if using this large boiler to heat the 50 gallon indirect tank is cost effective in the summer.

ethicalpaul

pauljr said:

ethicalpaul: Is that energy use profile on the Rheem tank screen, or smart phone interface?

It’s from their app

ethicalpaul

SuperTech said:

ethicalpaul said:

The Rheem heat pump water heater I installed costs almost nothing to run (heat pump only mode) and is a great way to not have to heat your house in the summer. Highly recommended 

Heating your house? What does that have to do with domestic hot water? I've been in plenty of basements in the summer with boilers that have indirect tanks and even tankless coil boilers and the basements are always cool and comfortable.  Even a steam boiler with an indirect doesn't heat up enough to make steam to keep an indirect tank hot.
I would imagine some serious piping or controls related problems exist if the house is being heated as a result of the boiler running for hot water production.

Those BTU are going somewhere. 

pauljr

Yes, the BTU's are heating the 15 gallons of water inside the boiler, heating the meatal chimney pipe (always HOT) going to the brick chimney, and the 40+ feet of iron piping in the manifold system. 12 zone pumps take room and the manifold is long.
When the boiler runs, (does not matter for heat or HW) all of this gets hot also. No way to stop it from getting hot.
Modifying the aquastat to shutoff the warm start is certainly helping. The boiler is now getting to 100 degrees or less especially on warm days. The way is setup before the boiler never got below 130 and was typically in the 150 to 170 degree range.