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Another question on Tankless coil or indirect.

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tlucca
tlucca Member Posts: 3
Hi, we live on Long Island in NY and are debating going from a tankless coil hot water system connected to a Peerless WBV burner, over to an indirect system for heating. I hear that it depends on how warm the climate is. Being in NY, we have cold winters and hot summers. How do I know whether I should switch to indirect heat? I live in a 2400 sq. ft house with 2 adults and three kids. We currently have a tankless coil rated at 5 gpm. Would switching to indirect really save us money? I just worry about my kids or my wife running out of hot water. Love to hear your thoughts on this. The tankless coil has been working great, but it is losing some efficiency. Might have to get it cleaned or replaced. Thanks in advance!!

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  • DJD775
    DJD775 Member Posts: 252
    edited February 2023
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    If the tankless coil is working for you stay with it. In my personal experience the savings from switching to an indirect are minimal at best and you will never recoup the initial investment. I personally have an indirect and setup properly they will supply more than enough hot water for a family.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,166
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    A 5 GPM coil in a small boiler will only give you 5 GPM in short bursts. the small BTU boiler can only make so much hot water. It all comes down to the basic equation 1 BTU is the amount of energy needed to raise the temperature or 1 pound of water 1 degree.. Now if you have a large boiler then the 5 GPM coil will be able to produce 5 GPM of hot water forever. (or until the oil tank runs out). Now if you have one of those fancy schmancy showers with 8 different body spray jets. and each jet uses .5 GPM and the shower head is a rainfall type that uses 3 GPM and your kids want to turn them all on full for 20 minutes (My teenager was on of those) then you do not have enough hot water to get that done.

    If you really wanted to get that done, then you might need two 100 gallon tanks of hot water for that. But let's get serious. Your 5 GPM coil should be flushed with a cleaning solution at least every third year. No one ever does that or recommends that. What usually happens is the coil gets clogged up over time to the point where you can even get 2 GPM for a standard energy saving shower head. Then a plumber will tell you to get an electric or gas water heater, and abandon the tankless coil.

    If your tankless coil is at that point, then you need to spend at least the amount of money someone will charge you to replace that tankless coil. If that is the case, then the cost difference of that job or the indirect water heater is what you need to consider. The indirect is less expensive to operate, but not enough to justify the complete job.

    But the difference between the minimum you need to do to get what you have working and the better job might be. So what is the condition of your existing tankless coil, how old is it and when was it last flushed with coil cleaner and was the flush vinegar based or acid based? If your coil is working fine and you have a boiler with a minimum of 190,000 BTU input @ 80% efficiency or has a NET I=B=R rating of at least 150,300 BTUh then you dont need to spend anything on the upgrade, because your system is fine as is.

    If you have a smaller boiler that the 190K or the coil is in need of replacing, or the existing boiler is less than 80% efficient, then you need to think about other options.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    hot_rod
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,166
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    The summertime savings on the indirect is greater then the winter time savings. The idea is that the boiler is connected to a chimney and the boiler must maintain at least 150° or 160°. This means that when ever the burner is not operating the chimney is acting like a vacuum cleaner and pulling basement air (or boiler room air) that you may have paid extra to air condition, will be getting sucked thru the burner air inlet and taking heat with it up the chimney. The boiler temperature will drop down in 3 to 4 hours and the burner will run for 6 to 10 minutes to recover. This happens even if you don't use any hot water.

    Now with an indirect tank that is well insulated, you can take that same burner and run the boiler to heat the tank. Once that tank is full of hot water, the boiler can drop in temperature and go completely cold. In 3 to 4 hours the burner will not need to start up to keep the boiler warm. That is because the hot water tank is not connected to the chimney. And if it is well insulated, the water temperature drop, if no one uses any hot water, may take up to 20 hours before it goes down enough to make the burner come on to recover. So there will be a savings, but will it be substantial? It all depends on your situation. With the right water tank, it may even last thru 2 boilers. Some of those stainless steel indirect tanks have lifetime warranties.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • hot_rod
    hot_rod Member Posts: 22,472
    edited February 2023
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    Using the example of a 150k net, the boiler runs every 4 hours for 10 minutes, how many gallons of oil per month just to keep the boiler hot, even with no dhw use at all?
    Then at current oil prices how much per month?
    The decision to go with an indirect may be determined by how long you plan on living there and the amount of oil difference between the indirect standby loss, compared to the hot boiler standby.


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,166
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    I used the 150K net because that is the amount of energy needed to maintain 5 GPM @ 60° rise is 150,300 by the math. But your point is well taken @hot_rod . If you have a Riello burner with the air inlet door that closes then the boiler may stay warm longer and the burner may only run for 6 minutes ever 6 hours. But I had a customer that experienced the 10 minute every 4 hours. He save a lot of gallons when I replaced the boiler and indirect. The oil dealer was not happy, but I told him the alternative was the plumber was going to install Gas heat. So less oil is better than NO OIL.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • tlucca
    tlucca Member Posts: 3
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    Thank you for the responses. I took a pic of my current boiler, Peerless brand. Its about 14 years old.
    the coil has never been flushed. Right now on long island the outside temp can be between 20F and 60F in the winter, but probably average is around 35 deg. I guess it depends on how high I put my aquastat.
    Right now I have the high setting on 180 and the low on 150 with a diff. of 15 degrees. That usually keeps a shower warm enough to take. If I go lower with those temps the shower gets luke warm pretty quick. Im hoping just to keep my current tankless coil, but we plan on staying here at least another 10 years. Who would typically flush the coil? I contacted two companies that clean/tune up the burner and niether of them do it. Would a plumber be the best person to do this? I have talked to a lot of people and they say I should just go indirect, but it is pretty expensive to install. Thank you again for the wonderful advice!!!

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,166
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    Looks like the 1.5 GPH nozzle will get you 5 GPM on the water heater. But that is the maximum capacity to get 5 GPM non stop from that coil for hours on end. If you are operating at the 1.25 or the 1.00 firing rate then you will get 5 GPM from the coil on short usage line 3 minutes or less. But the 15 minute shower with the lower firing rate will yield you 4 GPM or lower. If the shower head is rated at 2 GPM then you can operate two showers at a time and still have enough DHW. It is all in the math.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • tlucca
    tlucca Member Posts: 3
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    Thank you Ed. How do I know what firing rate my heater is operating on? does it depend on the size of the nozzle? Is this something that can be changed on the fly?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,835
    edited February 2023
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    @tlucca

    If it was me and you can get by with the tankless as you have been why not just replace the coil? After not being cleaned for 14 years ....is it worth cleaning? Could be money down the drain. Check out TFI-Everhot for a replacement coil

    The tankless coil is an easy replacement.......if the bolts come out use neverseize on the bolts and threads.

    A picture of the tankless coil will help us decide. Is it clean looking or a lot of rusted bolts and leaking gasket?
    DJD775
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,166
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    tlucca said:

    Thank you Ed. How do I know what firing rate my heater is operating on? does it depend on the size of the nozzle? Is this something that can be changed on the fly?

    The firing rate is based on the nozzle that the last service person installed. It could be any number of nozzles within that range. as far as changing it on the fly... Not recommended. Anyone that will change a nozzle on a oil burner SLOULD also make the final adjustment with combustion testing tools and gauges. Those that say they can tell by looking at the flame are just lazy or improperly trained.

    As far as getting the coil flushed, you might need a plumber for the first one. Your tankless coil must be set up with the proper valves for flushing, and 14 years old is not too old for an acid flush.


    Here are the directions for Sizzle

    HOT WATER COILS:
    1) Close the cold water feed valve to the tank or coil.
    2) Break the nearest union on the cold water feed line to the unit.
    3) Connect a standpipe into the cold water feed line to unit. Inlet must be at least 6” higher than hot
    water outlet line.
    4) Break nearest union on hot water outlet line.
    5) Make a solution of 1 quart Sizzle and 2 parts water and add to standpipe until solution runs out the
    hot water outlet. Hot water outlet should be at least 1” higher than coils.
    6) Leave solution in unit until foaming stops. Unit is clean if adding more Sizzle solution does not
    produce more foaming.
    7) Thoroughly back flush to remove residue and remaining acid solution by removing the standpipe
    and inserting water hose into hot water outlet of unit. Back flush through and out cold water inlet
    for at least 5 minutes after all foam or residue is removed.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    hot_rod
  • DJD775
    DJD775 Member Posts: 252
    edited February 2023
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    @tlucca

    If you don't have one already it is a good idea to have a baseline for oil usage throughout the year and during the non-heating season only. I like to get an oil delivery when the heating season ends and then fill up at the beginning of the heating season to see approximately what I used during the off season. With the oil usage numbers you can make a more informed decision on any potential savings when deciding to add or upgrade equipment.