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boiler bypass

jareedojareedo Member Posts: 10
I'm thinking about switching a customers burnham boiler to a cold start to save him fuel through the summer. I was thinking why couldnt I put a bypass in with a zone valve and a aquastat to open up when needed to maintain a minimum 140 degree temp. Has anyone tried this?


  • Paul PolletsPaul Pollets Member Posts: 3,017
    Thermic Valve

    Here's the way to do it without having to install a 4 way mixing valve, motor actuator and control. I like to install a thermometer on the outlet to the boiler return to assure the temps in the return entering the boiler are over 140 within 5 min. of the cold start.
  • heatpro02920heatpro02920 Member Posts: 991

    I am curious as to what something like this would cost? I know we are not supposed to talk prices but I know I would have to charge a decent amount to do something like this since the time it takes may vary, and it could lead to some call backs, just draining back and repiping has to be a few hours?

    How much oil will he save? would it be a better idea to do a few other simple things to save the customer energy, like changing the control or a heat manager, an odr, outside combustion air, ect?

    I am just curious, I would have no idea how to estimate what the customer would save and most customers will ask that question before considering an expensive upgrade... I also don't know anything about your customers boiler, does it already have pre purge control, clean cut pump, ect? Is this a tankless or indirect?

    If saving hot water bills in the non heating season is a priority, depending what state you are in rite now there are a lot of rebates for hybrid tanks that cover a huge part of the cost, and that will give him a faster ROI....
  • EricPetersonEricPeterson Member Posts: 32
    The diagram shows a single pump

    which is pumping towards the boiler.

    In practice do your installs have a single pump as in the diagram?

    How about for Gravity/Large Volume Hot Water Systems as in this diagram:


    Do these installs actually need two pumps, or will one suffice?

  • BillBill Member Posts: 48
    Boiler bypass or System bypass

    The ESBE TV has been replaced by the VTC, with full modulation of both supply ports resulting in more accurate temperature control
  • EricPetersonEricPeterson Member Posts: 32
    1 or 2 pumps?

    Same question for new valve. Don't see why one pump would not suffice.

  • EricPetersonEricPeterson Member Posts: 32
    System bypass vs boiler bypass

    Looks like with one pump this would be a system bypass.

    With two pumps it would provide both boiler bypass and system bypass, as water would flow through both loops when the return temperature was low.
  • SWEISWEI Member Posts: 7,356
    Two pumps

    are required with a 3-way valve, whether thermic or motorized.  A 4-way motorized valve can often work with a single pump, as long as the boiler HX presents sufficiently low restriction.
  • JasonJason Member Posts: 293
    edited March 2014
    What type of system?

    Do you need boiler protection?

    Maybe not. We only need to get to average water temperature in boiler of 140f within a reasonable amount of time.

    How much is boiler over sized? Notice I did not ask if boiler is oversized. Most existing boilers are easily 50% to 100% oversized. If boiler is oversized your concerns are lessened.

    What type of radiation?

    How many heating zones?

    I would forget the idea of the zone valve in a boiler bypass. You stated a boiler bypass and your comments are leaning toward a system bypass. A boiler bypass will bypass water around the boiler back to the system. This is the proper bypass. Due to lower water volume boilers the bypass changed from the system bypass when the boilers had larger water volume. Commercial cadet iron boilers still can use system bypasses.

    A system bypass will pull hot waster from the supply to the return.

    A boiler bypass will use cool return to hot supply. More beneficial. Keeps system flow rates higher, reduces flow through the boiler so water can get warmer faster. Boiler bypass valve is usually wide open all the time. You reduce flow in the boiler with a valve on either supply or return and the boiler.
  • EricPetersonEricPeterson Member Posts: 32
    Speaking for myself

    yes I need protection - at least according to the boiler I/O Manual (Burnham ES2), and the specifics of my installation ("larger" boiler water volume, 3 zones, large water volume / converted gravity system, freestanding radiators, setback thermostats).

    I don't know what is a "reasonable amount of time", but I expect it would routinely be exceeded in my situation.

    In my situation, I cannot see any help from a boiler bypass. A system bypass is the proper bypass in my setup, as it moderates the temperature of the return water to the boiler.

    System bypass has been working well for four heating seasons so far. My plan is to replace this with an ESBE 3-way valve for even better protection.

    I am not a contractor, but a homeowner who does his own work. I am an engineer, and am generally resistant to accepting things on faith, instead need to know the explanation and reason behind them.

  • WeezboWeezbo Member Posts: 6,232
    theres something you may like

    to look into , one is boiler reset the other system reset..

    and warm weather shut down .

    then you might not find that there is much of a cost advantage in not going with the boiler having one way of seeing things and the field another and both of them speaking the same language.

    the ability of when to agree then , is not really an either or situation .

    and , might be a function , i hope that helps .
  • JasonJason Member Posts: 293
    Look at the I&O

    The manufacturer wants a boiler bypass why would you disagree with that? You are putting too much emphasis on return water temperature as many do. To quote Gil Carlson who invented the boiler bypass. Thermal stress and flue gas condensation is a result of extremely cold water entering the boiler or cool water at a high flow rate" The return temperature is not as important as the flow. We should be trying to get the average water temperature of the boiler above condensing temp. When the boilers switched to low water volume the bypass switched to a boiler bypass. System bypasses are for higher water volume.

    I agree that with an old gravity hot water system you definitely need boiler protection.

    How about p/s and using a delta T pump for the boiler secondary piping set to 30 - 40 delta-T.
  • EricPetersonEricPeterson Member Posts: 32
    The manufacturer says

    "Thermal shock: Install a boiler bypass, system bypass, or primary-secondary loop when needed to avoid returning large volumes of cold water directly to a hot boiler."

    "Condensation: Adhere to the boiler’s specific minimum return water and supply water temperature requirements. Install a boiler bypass, system bypass, or primary-secondary loop when needed to

    maintain water temperatures and flows within the specified limits."

    Boiler holds 5 gallons, and the stated minimum flow is "None".

    Because I have three zones, and one zone is very small, the average water temperature is not that straightforward. The one small zone could be at 170, when one of the other two large zones opens up, dumping much cooler water into the boiler. That is one of the reasons system bypass seems a better design for my situation.

    The ESBE valve by its very nature seems to me to provide a system bypass.

  • EricPetersonEricPeterson Member Posts: 32
    I see what you mean though

    concerning flow into the boiler.

    The slower the flow of cooler water into the boiler, the less of an issue it becomes.

    And a boiler bypass slows the flow. So that helps with the thermal shock.

    As for condensation, the minimum return temperature from the I&O manual is 110 F.

    However nowhere is it stated what is a reasonable amount of time to reach that temperature.

    I think boiler bypass works best when the system is simple.

    In my system the problem is compounded by the large water volume, the three zones plus the use of setbacks at night. I think boiler bypass would be fine if only one of those was in place. However with all three I think system bypass is the best solution.

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