Aquastat(?) on Forced Hot Water Weil-McClain(about 25 years old)

Discussion in 'Boiler Forum' started by GregoryR, Jul 20, 2011.

  1. GregoryR

    GregoryR New Member

    Messages:
    21
    Location:
    Maine, USA
    Hello,

    I am very glad I found these forums, and really hope somebody can help. I recently compiled some data from my heating bills. The single oil furnace does the domestic hot water, and the hot water for the baseboard heat. All laundry is done in cold. The home is about 1300 sq ft with about 1000 of it heated in the winter. We have one bathroom and two of us total living here full time. Between last October and this April, we used 2 gallons of oil per day(~345 gallons). We use a programmable thermostat to set the heat at 68 when we are awake and home, and 64 during the night.

    I thought 345 gallons was pretty good for a winter. However, in the summer, non heating months, we used ~300 gallons. Only 45 less than the winter?! Granted, there are three people living and showering here in the summer, shouldn't it be less than that?

    I took some pictures of the furnace, and an "Enertol" unit. I could not find any documentation on the Enertrol at all online. I did open the Honeywell temp. control(gray) box and set it to 160 Hi/140 Lo, and there was another small dial, VAR, I believe set at 5. (It was at 180/160, 5)

    The Enertrol box has a left, right switch and and temp sum. I've attached photos. If anybody can help with this, that would be wonderful. Without touching the hot water, it takes 3:47 to maintain the water temp(i.e., no hot water is used, when the furnace triggers on, it takes this time to heat back up). I also noticed the water in the line for the baseboard heat(under floor)(but not at the baseboard) stays piping hot even during the summer.

    Thanks!

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    Last edited: Jul 20, 2011
  2. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,135
    Location:
    Maine
    The Enertrol is an old style analog modulating control that determines boiler temperature by sensing outside temperature. The dial is set at 220 which pretty much overrides the control however for domestic hot water the control has no function anyway. If you want to save money you need to get rid of the tankless coil in the boiler and either go with a gas water heater or an indirect but the boiler looks to be so old that I don't think I would put that kind of money into it. If you really want to save money, tear the old mess out and go with something more efficient and an indirect like a Buderus BE or Logano series or a System 2000
  3. GregoryR

    GregoryR New Member

    Messages:
    21
    Location:
    Maine, USA
    Cool to know a little something about that. So is the water actually heating to 220 and being unused in the summer? The water in the line for the baseboard heat is very hot, hotter than we ever get for dom. hot water.

    I think there is some dom. hot water storage in the boiler itself(or maybe that isn't how it works), as if you turn on the shower, you will get hot water for a little bit, before the boiler turns on. Any suggestions on the VAR/DIFF switch in the Honeywell box? Or the left right switch on the Enertrol? I am tempted to set this to 165.

    Thanks again!


    EDIT:Yes, the black pipe coming out of the top of the unit must be >200 degrees. Just the outside is MUCH hotter than anything we get from the faucet. This is the one that goes through the expansion tank and to the baseboard.
    Last edited: Jul 21, 2011
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,932
    Location:
    New England
    You domestic hot water is made by running a coil through a small vat of hot water in the boiler. Cold in, hot out through the coil. So, to keep the system able to produce that hot water, the whole boiler stays pretty warm all year, all the time. If you drop the temp down too much, the water through the coil can't pick up enough heat. As a result, the boiler is running all year, all the time (well, it cycles - more in the winter, though, but you understand what I mean).

    As stated, the choices are: leave it alone; disable the coil and add in an indirect; disable the coil and add a stand-alone self-powered WH (gas, oil, or electric).

    A new boiler would probably suggest an indirect, although that could be added to the existing unit and much of it could be retained when updating the boiler at a later time.
  5. GregoryR

    GregoryR New Member

    Messages:
    21
    Location:
    Maine, USA

    So the coil would be taken out, and the output attached to a separate tank to store hot water? Would this cause the boiler to turn on less often at all in the summer?

    Also, any ideas on the VAR/DIFF setting on the Honeywell box?

    Thanks!
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,932
    Location:
    New England
    You don't need to take the coil out, just cap off the inlet and outlet. Then, unless you are installing an indirect (which acts like a zone in your heating system), you could turn the boiler off entirely for the summer. With the indirect, you could probably adjust it so it didn't run until the indirect called for heat, and then it wouldn't be constantly hot all the time. If you go with a separate, stand-alone tank (oil, gas, or electric), you could also shut the boiler down for the summer.

    To make hot water with the coil, the aquastat needs to keep the small tank fairly hot. If the min/max are too close together, and the load is low, it will short-cycle and this is very inefficient. The only good thing is that in the summer, the incoming cold water isn't as frigid as it is in the winter, so you may be able to get by by dropping the min (turn-on) temp. Since that imersion tank isn't all that big (generally), regardless, it doesn't take too long for it to recover.

    Someone more in tune with the specifics can probably give you more details on how best to set the thing. But, if you want to save some money, you'd probably want to disable the tankless coil and get another means of heating the domestic hot water supply.
  7. GregoryR

    GregoryR New Member

    Messages:
    21
    Location:
    Maine, USA
    Thanks to everybody who replied. As a result, I am keeping the setting on 160/140, and have turned the max temp on the Enertrol from 220 to 185, and the water in the shower is still hot.

    Still wondering about the DIFF switch inside the Honeywell box currently set to 5. Also, Any ideas on this knob I have?

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  8. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,135
    Location:
    Maine
    Normally the aquastat is set a 180-200 for the high and 140-160 for the low.

    The high controls the Maximum temperature that the boiler will achieve with the thermostat calling

    The low is an internal thermostat that maintains the boiler at set temperature so that there will be domestic hot water available.

    The differential is the difference between set temperature and any override and it's there to keep the burner from cycling. So with the differential set at 5 the burner will cycle between 155 and 165. Normally it is set to 10

    That dial is a by-pass timer that kicks the Enertrol out of the control loop so that you can have hot water. The Enertrol is wired in series with the high limit. someone probably set the Enertrol at 220 so they would not have to mess with the timer.

    You are currently making hot water in probably the most expensive way possible as you are maintaining the boiler at temperature year around and during the off cycle a lot of that heat in boiler is going up the chimney until the boiler cools and then the burner runs again whether you need hot water or not. Very inneficient. A 40 gallon electric water heater would be cheaper to operate.
    Last edited: Jul 23, 2011
  9. GregoryR

    GregoryR New Member

    Messages:
    21
    Location:
    Maine, USA
    So true. I might actually be able to pay for a HWH itself for less than the cost of 100 gallons of #2. I think I should call my current oil company and get an estimate for a few on demand propane systems, and call another for the cost of installing an electric HWH.

    Thanks so much for bearing with me!
  10. tk03

    tk03 New Member

    Messages:
    56
    Location:
    Harrisburg, pa
    Just a few notes here. First off it looks like the slide switch is standard not mode. That means no ODR function. The setting of 220 changes the curve when modulating the boiler water temperature which is not happening in the standard mode. The 220 setting while in standard does nothing as you would than be operating off the boiler aquastat due to lower setting. These usually came with a timer if installed on a boiler with a DHW coil. You have a manual timer which tells me the Enertrol ordered was for a boiler without a coil and than ooops, and added the manual timer to compensate.
    My guess is this is in standard due to not working anymore.
    The boiler aquastat settings need to be set so the boiler supplies enough hot water. The differential should be set at 20f. This maintaining side of this control has a built in differential of 10f. The water boiler temp drops 10f and starts the burner, and runs until the boiler water temp raises 20f (diff) and shuts down the boiler providing there is no call for heat. Basically it works like this, low water temp - 10 + diff setting. When there is a demand for heat the diff setting is no longer active, just used for maintaining water temperature.
    To reiterate the coil is the most expensive way to heat hot water but if you eliminate by cutting off the pipes do not cap it. You will build pressure and possible create an unsafe condition.
  11. GregoryR

    GregoryR New Member

    Messages:
    21
    Location:
    Maine, USA
    Sooo. They came to my home to get details for the estimate and said there was no place to put the tank. We live in house(eg no landlord) and there is plenty of room in a back yard. I was a tad suspicious.


    They're doing a quote for an indirect instead, but the installer was not sure how much it would cost or how much money/oil I'd save. Any ideas? We use about 300gals in the summer to heat water for 3 people(clothes done in cold).
  12. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,135
    Location:
    Maine
    well it looks like you have a Weil McLain P66 series boiler which means that it is a good 20 years old, however, if the burner is properly serviced and adjusted that old girl does pretty well as far as efficiency is concerned. If the boiler is in good condition then an indirect would indeed be a very good way to go but, it's going to cost you a bit over 2 grand what with the tank, piping, valves, circulator and controls so you have to make a decision as to whether the boiler is worth that investment. On the other hand though, if the boiler does crap out in the near future the indirect would be useable on the new boiler. Where in Maine are you? Oh and a differential setting of 20 is way more range than you need, 10 should do it.
  13. chapchap70

    chapchap70 New Member

    Messages:
    3
    Location:
    Long Island, NY
    Question: How do you figure you are using 300 gallons of oil in the summer? If you have a small old Weil McLain boiler (I could not tell the size from the pictures), I do not think it would be firing at a rate higher than 0.85 gallons per hour. I doubt your boiler fires for much more than an hour per day in the summer even with a tankless coil. Are you estimating usage by when you have gotten deliveries?

    If you have a triple acting aquastat (Honeywell 8124 or equivalent) with a hi limit setting, a low limit setting, and a differential setting, my understanding is that the hi setting is the hi limit safety control; NOT the operating control. I have our hi limit set at 190, the low limit at 150 and the differential at 20 degrees to keep the on and off times longer. The minimum differential setting on the 8124 is 10 degrees.

    The low limit and differential operate the boiler. Many if not most heating people do not understand how this works. If the low limit is set at 150 degrees and the differential is at 20 degrees, the control should turn the burner on at 140 degrees and turn it off at 160. If the differential is set at 10 degrees, the burner would fire at 140 and shut off at 150. The burner should always turn on 10 degrees lower than the limit setting no matter what the differential is set at. The gauge and control are not exactly the same for various reasons. For example, even though my low limit setting is set for 150 degrees, my burner fires when the gauge reads about 135 degrees and shuts off when it reaches 155 degrees on the gauge. Depending on the load, the boiler temperature may continue to rise after the burner shuts off because the iron and firebox continue to exchange residual heat.

    This should be sufficient to take showers in the summer but the boiler water might not be hot enough to heat a house on cold days in the winter with ~150 degree water. We have a tankless coil also. I am not familiar with the Enertrol but it seems similar to the Beckett Heat Manager. I do not think the Enertrol is being sold anymore.

    About the electric water heater; I don't know what your electric rates are in Maine but at ~25 cents per KWH on Long Island, we still don't even consider it because of price. I don't think you get the same recovery rate with electric as you do with a tankless coil in a oil fired boiler. I would not put an electric water heater outside if that is what you were thinking.

    By the way, ~650 gallons of oil per years seems good for Maine with your boiler. My guess is your usage breaks down to around 500 winter and 150 summer.
    Last edited: Jul 31, 2011
  14. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,135
    Location:
    Maine
    actually on a call for heat the boiler will very often run to the high limit setting.

    The coil in a Weil Mclain P366 or 466 is only rated at 2.5 gpm continuous draw and if there is any scaleing ( and after 20 years or so you can bet there is ) that figure changes considerably.

    I have never run into any technicians that didn't understand how the differential works.
  15. GregoryR

    GregoryR New Member

    Messages:
    21
    Location:
    Maine, USA
    Sounds like it wouldn't be quite worth it(2k), and thanks for the advice. We are in central Oxford County.



    I made a spreadsheet based on orders for oil. We only order when the gauge has been on empty for about 5-7 days. I've attached it for you. Current differential is at 15. Electricity is 18 cents/kwh delivered here. The tank they were referring to was a propane tank they claimed could not be installed anywhere.


    We have about 35ppm of dissolved solids in our water, but I am sure it has built up as you say. We generally have plenty of HW and would only need to consider something for saving oil or money.
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    Last edited: Aug 1, 2011
  16. chapchap70

    chapchap70 New Member

    Messages:
    3
    Location:
    Long Island, NY

    Maybe I'm not a technician because I also deliver. I had a hard time understanding this and maybe I still don't. The guy that trained me said the low setting turns the burner on and the high setting turns the burner off. I know that is wrong. I turned on the heat leaving the settings alone and the burner seemed to turn off at the low end of the high (10 degrees below 190) limit but my aquastat and gauge are not exactly the same. My understanding is that the hi limit differential is fixed at 10 degrees. I hear heating guys trying to explain aquastats to people a lot and see it on forums.


    Looking at the oil delivery spreadsheet, it looks like 300 gallons got used between 3/10 and 10/18 which is over 7 months. Most likely, some of that in March and April was used for heating so it doesn't seem that abnormal. Maybe you can try lowering the low setting of your aquastat to 140 or 150 if you haven't done so already and see if you still have enough hot water.


    With a gallon of heating oil having the BTU content of about 40.5 kwh, the equivalent price of electricity at 18 cents per kwh is about $7.29 per gallon. At 40% efficiency for the tankless coil, water heating costs might be similar to electric but the boiler should maintain 110 or 120 degrees in the summer anyway so you might as well use it for hot water. With the electric water heater recovery rates at between 20 and 25 gallons per hour, you might not have enough hot water to take the third 2.5 gallons per minute 10 minute shower in a row with a 40 gallon tank.
    Last edited: Aug 2, 2011
  17. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,135
    Location:
    Maine
    Why should the boiler maintain 110 - 12- degrees in the summer? Oh, because you think it will leak? The Weil McLain P series boilers use rubber O rings between the sections. If anything is leaking when the boiler is cold it needs to be repaired. Maintaining temperature is a huge waste of money.

    Yes, the high limit on most Honeywell aquastats has a fixed 10 degree differential. You need to have some differential or the burner would short cycle. During a peak heat demand the boiler will and should bounce off the high limit frequently.

    The low limit maintains boiler temperature for domestic hot water and has nothing to do with a call for heat except that the heating circulator will not operate until low limit has been reached. In other words if the low is set to 160, the heating circulator will not run until the boiler hits 160. This keeps cold return water from cooling the domestic coil and giving you a blast of cold water in the shower.

    If this was my boiler I would:

    1- have it thouroughly cleaned, inspected and the burner professionally set up and combustion tested
    2- have a Super-Stor or similar indirect water heater installed
    3- get rid of the old Enertrol analog re-set controller and install either an Intellicon, Taco PC700 or Tekmar re-set controller.

    Payback should be around 5 years.
    Last edited: Aug 3, 2011
  18. Dana

    Dana In the trades

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    2,812
    Location:
    01609
    What Tom said.

    In addition- the low limit also protects the boiler from operating in a destructive condensing mode, where exhuast gases condense corrosive liquids inside the boiler (or flue). For most oil boilers 140F is the low limit before it can become self-destructive- maintaining it at 110F all summer isn't doing your boiler any favors, since it guarantees that all burns are condensing.

    Whether an outdoor reset approach buys you anything depends a bit on the amount of radiation/baseboard you have. In many cases (especially in homes that have undergone air-sealing and insulation & window improvements) the radiation is overbuilt to where it can deliver design-day heat just fine at 140F, but you can't run an oil boiler there anyway, so outdoor reset would be essentially useless. The Intellicon HW+ takes a different approach, maximizing the temperature hysteresis on the boiler/system's thermal mass when there's a significant heat load, but purging that temp down to the boiler-minimum when there is a new call for heat before firing up the burner, and intelligently anticipating the thermostat being satisifed based on the recent burn history, shutting down the burner ahead of time to be able to "park" the boiler at a lower than maximum temp between burns for lower standby loss. It tends to maximize the lengths of burns (no short-cycling losses) while minimizing standby idle losses. The more radiation you have and the larger the boiler oversizing factor, the better this works relative to an outdoor reset approach.

    Depending on where you expect oil prices go over the next decade, it might be worth thinking about mini-split heat pumps as supplemental heat too. At 15F they all run a coefficint of performance (COP) around 2.5, and at 30F & up they're 3.0+. A 2x oversized 85% efficiency boiler runs about 75-80% efficincy as-used, so for that 138000BTU/gallon only 110000 BTUs are delivered to the house (best case), which is the equivalent of 32kwh as resistance heat, not 40.5, so at 18cent electricity you're really looking at being equivlant to ~$5.76/gallon oil. But with a mini-split assuming a seasonal average of even 2.5 (which it would get, in Long Island), every kwh of power in results in 2.5kwh of heat out, so that's equivalant $5.76/2.5= $2.30/gallon oil burned in a pretty-good old school boiler with some updated controls. A 2-ton (24000BTU/hr) mini-split is less than $5K, installed.

    Mini splits works better in homes with open floor plans, since it's a point-source heat, but multi-splits add about $1200-1500/head to the base price. If it can support the entire load most of the time, setting up the boiler's thermostat a couple degrees lower, than the mini-split it won't kick on until the mini-split can't keep up, which would usually be when the outdoor temps are lowest, and the COP the lowest (they're all under 2 at 5F and below). In situations where they can work the savings can be substantial, even at 18cent electricity- remember, the COP is 3+ at 30F, and over 4 at 45F, which are temps where the boiler's net efficiency is falling off rapidly due to low duty cycle on the burner. During the shoulder seasons the heat pump can take your oil consumption down to water-heating-only levels. This guy's experience is probably better than some, but it's not rare.
  19. GregoryR

    GregoryR New Member

    Messages:
    21
    Location:
    Maine, USA
    I know you were responding to somebody else, but just FYI this was turned off for a whole week this June and the only leak was from the...ahh..copper pipe on the side? If you know what I mean?

    1. It does get professionally cleaned before each heating season, yes.

    2.Does this save oil? Or just give more hot water?

    3. That sounds reasonable.

    I was looking at two HWH on Sears.com:

    1. http://c.shld.net/assets/eg/116435.pdf

    (It says about 4773 kwH/ year. I believe this is based on a family of four that washes in hot water. Lets say we'd use 4500 kwH)
    That is $810/year.


    2. http://c.shld.net/assets/eg/796445.pdf

    (It says about 1856 kwH/year, so let's say we'd use 1600.)
    That is $288/year! Is this what you guys meant at all my mini pump? http://www.sears.com/shc/s/p_10153_12605_04232100000P?prdNo=14&blockNo=14&blockType=G14




    Thanks again.
  20. Dana

    Dana In the trades

    Messages:
    2,812
    Location:
    01609
    Going with a Super Stor both saves oil, AND gives more hot water. It saves oil by not needing to keep the boiler hot (== high standby losses) and gives more hot water by being able to deliver 100% of the burner's output to the hot water by suppressing calls for heat from the zones during hot water heating burns. Embedded coils in boilers are typically ~30-35% efficiency some more, someless in hot-water-heating only mode, so even a resistance-type cheapo electric HW heater will likely prove cheaper than what you've got. Take the time to understand the results for boiler #12 in tankless (embedded coil) vs. indirect (like a SuperStor) detailed in Appendix 12 of this study:

    http://www.nora-oilheat.org/site20/uploads/FullReportBrookhavenEfficiencyTest.pdf

    By going to an indirect and being able to set the low limit to 130F rather than 160F the water heating efficiency more than doubled! This will vary from boiler to boiler, but the savings are always substantial.

    A mini-split heat pump is a space heating/cooling device, not to be confused with a heat-pump water heater like the GE in your #2 link. During the heating season a heat-pump HW heater is pulling heat out of the house which has to be replaced by the heating system. It'll use about half as much electricity as a resistance-electric tank, but it'll add to the heating bill. A mini-split heat pump is a ductless split air-conditioner with a reversible loop to be able to heat or cool. The interior heads look like this:

    [​IMG]

    The exterior units look like this:

    [​IMG]

    Both the interior air-blower and the exterior compressor have high efficiency variable speed motors, and with no ducts or air handlers the efficiencies are quite high. (Look at the HSPF rating which isn't a perfect way to compare them, but it's better than nothing. An HSPF of 8.5 is good, 10+ is better.) They're most efficient if you "set and forget" rather than try to use a setback strategy, since they're most-efficient at low and mid compressor speeds, so anything gained by the setback is eaten up by the lower efficiency of being maxed out during the recovery period.

    Even though it's 4x the money up front, the payback on a mini-split will be much better than with a heat-pump water heater, and an indirect will give you far more hot water capacity than any type of electric tank. Assuming you can get at least 40% water-heating mode efficiency out of your boiler with a SuperStor you'll get 0.4x 138000= 49200 BTU/gallon out of the boiler, and with a 0.90EF resistance type electric tank you'll average ~0.9 x 3412= 2047BTU/kwh. At 18 cent electricity that's about the same as $4.30 oil with the SuperStore so for the time being it's cheaper to heat hot water with oil (especially since you can probably be bumping on 50% efficiency with the SuperStor.) With the heat pump water heater you'd use half the elecricity but also be getting the other half the heat from 75% efficiency space-heating oil 3/4 of the year, so the ROI is very small. Heat pump water heaters are a much better deal in cooling dominated climates, since it reduces the cooling load of the house.

    By comparison, a mini-split heat pump takes a huge chunk out of the space heating bill if set up to provide the lion's share of the total space heating, since at 18cent electricity it's like burning $2.30 oil in your boiler during the winter, and more like $1.75 oil during the spring & fall, which (last time I checked) is a HUGE discount over current heating oil pricing. In places with cheap electricity and bigger heat loads (such as MN or WI) the payback on a mini-split can be 3 years or less, but a bit longer much of NY/CT/MA where the electricity is 2x the price of what it is in much of the upper midwest.
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