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Preheating an indirect with a coil

I didnt see it first hand , but it was explained to me by my boss - We are replacing a Weil Mclain 588 water boiler that is supplying heat and hot water to 2 apartment buildings , around 40 apartments . The old boiler is preheating 2 existing Phase 3 indirects with hot water though 2 internal coils , I believe . The new boiler is a Peerless LC 8 section , and we are using the 2 coil ports for added hot water capacity .

What would be the best way to pipe in the 2 coils in the new boiler to preheat the 2 indirects without having a big pressure drop on the hot side ?

Would teeing in all the hot outlets of the coils and indirects in one spot , and going into a commercial sized auto mixer tbe the most optimum ?

What about using bronze circs to run the hot water through the coils somehow , maybe tee a loop though the coil into the cold and hot of the indirects , with a circ , checkvalve and aquastat in line ?

As you can tell , I am trying to avoid having to run the water through the coil and then through the indirect - I believe there might be a severe pressure drop doing it that way .

Thanks for any help you can give me , Ron


  • Bill NTSG
    Bill NTSG Member Posts: 321

    the pressure drop won't be the worst thing in the world. Ever see how small the hole is in a flow restrictor.[the thing that comes in the bag with your Peerless boilers that you throw away] I used to use a stop & waste to slow the water down at the coil inlet. That way the oil guys wouldn't cut it out later like they do to the flow restrictors and the tempering valves. I use ball valves for everything , but that was one of the few places I slipped in a S&W valve. I would just go through the coil into the indirect, don't get too complicated. My boss lets customers talk us into all kinds of options with the tankless feeding the oil,gas,or electric water heater. Too many valves. Yesterday I cleaned a boiler that was off all summer with the 50° water running through the coil on the way to the water heater. Yick. In residential you are not saving money this way. In your commercial application you may be supplementing the hot water. Some how it seems there is never enough money to size the right sized heater to begin with.
  • eleft_4
    eleft_4 Member Posts: 509
    This works


    Two tees in the heater cold feed line with a ball valve between them.
    A line to each tee from the boiler coil and adjust the valve to temper the water to about 80*. No strain on the boiler or the phase 111. No noticeable pres. drop.

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