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Internal coil question

lchmb Member Posts: 2,997
I have seen a few over the year's piped in reverse (based on marking's on the coil). I generally ask the homeowner if the hot water is acceptable and have never had a complaint. Would be interesting to pipe one, test it then reverse it to see if it makes a noticable difference...


  • We've been having a debate

    on if it makes any difference in output if you reverse the piping on a coil - hot pipe on the inlet , cold on the outlet . Some coils don't come marked at all , some come with peelable stickers marking hot and cold , some come stamped with the letters .

    I've heard that the aquastat would respond faster when the inlet is the inner coil wrapping . Looking at the Burnham RSA coil , the inlet feeds the outer wrappings first . On the Peerless line the inlet is the inner wrappings . The aquastat well is situated in the middle of the coils , but both coil brands extend into the boiler farther than the well goes .

    Anyone think there's a dcrease in output if the coil tappings are reversed ? Thanks in advance .
  • J.C.A._3
    J.C.A._3 Member Posts: 2,981

    How much difference can it make? The water is going in one side, traveling through the same amount of pipe, through the same temperature water. I suppose having the immerssion well closer to the cold inlet has a quicker response but that's all I can think of.

    How about if you turn the coil so the cold goes into the bottom and comes out the top rather than side by side? Other than maybe having to have a longer well adapter to fit the fittings going into the coil behind the control, there won't be too much difference.(Hint here....Buderus has a special long insertion well for their horizontal indirect tanks, and if it won't be in contact with the back of a short coil, could be a nice addition for a more uniform response...). Thinking out loud again, but wouldn't it be nice to just install an indirect with every boiler? I know your space limits all too well from your postings so this isn't always an option eh? Chris
  • I think there's a decrease

    Coldest water to coldest part of the coil; hottest water at the hottest part of the coil.

    Once the water in the domestic side starts to get warmed, and you run it against water that ISN'T the hottest water, it stops gaining in temp, but the time in the coil doesn't change.

    I don't believe that the time not gaining (much) heat is offset by the time in the superhot water in the beginning of the pass through the coil.

    If you overdraw the domestic side of the coil (vs. it's rating), I think the aquastat will be slow to respond, and I don't feel confident that having the well cool off early is worth the trade off.

    I'd pipe it as designed, whether the coil is big enough (actually, it's the firing rate that would be too small for the domestic draw, at 50,000 BTUH per gpm of draw on the coil; not the coil itself), or not.

  • J.C.A._3
    J.C.A._3 Member Posts: 2,981
    Hey Noel,

    Are flow restrictors part of the tankless codes on the Island Of Long? In the state of confusion,(Ma.) they are supposed to be installed into the feed /cold line going into the coil, and restricted to 2 and1/2 GPM.

    A nice way around this was developed by Watts with their P-3 MULTI ORIFICE FLOW RESTRICTOR. I seem to remember them adjustable from 2.5 gpm up to either 3.5 or 4 gpm. The big kicker is that the Fire Dept. does the oil inspections and wouldn't even notice if it was set at a higher than the code requirement of 2.5 gpm, and with the required mixing devices. Chris
  • Firedragon_4
    Firedragon_4 Member Posts: 1,436
    You're right Noel

    and we cover this in our Hot Water Handbook. Cold water travels through the center of a round bundle first, outer wrap last.

    With an external tankless, converter or horizontal tankless it's not that important, just that the flow be bottom to top.

    With a round front type tankless better to get it right or lose a few gallons on recovery, now that's important, FACT!

    BTW and JMO, but the front tankless should not be used at all. This is due to pressure drop and the amount of coil exposed to water, you will always get better performance from a loose wound coil over a tight wound coil as the coil gets dirty.
  • They are a must, if it's to work properly

    I have no clue which inspectors know about this, though.

    As long as YOU know, I'm good with it.

  • kevin coppinger_4
    kevin coppinger_4 Member Posts: 2,124
    I asked this....

    question one of HTP regarding a SSC-50. The flange rings come on the coil one way but if you look at the install manual it is reversed....called they say it does not matter. strange. kpc

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  • Firedragon_4
    Firedragon_4 Member Posts: 1,436
    Big difference between

    a tankless and an indirect, FACT!
  • No code here

    as far as I know . And we never use one on a new install . We hardly ever hear of hot water running out using a coil . Although I do have a coil in my Peerless I gotta start adjusting the handle if I'm in there more than 10 minutes . I think I got the low limit and diff set too low and wide for a quick response for the coil .
  • Which brings up the question

    why would a manufacturer make the supply through the coil the outer wrap ? It was a Burnham RSA coil , but I don't think it was made by them . I'll check Monday on which wrap the V8 series starts with , as well as the Peerless and Weil , and who makes them .
  • Sssshhhhh !!!

    One thing I do not want to do every day is a boiler AND indirect ! Somehow sooner or later they'll try to push us to get finished with just 2 men in one day . It's a good thing for me there simply aint no room in these homes to add an extra tank . This question came up because we did a boiler changeout and for aesthetics we moved the aquabooster closer to the new boiler ( not even a thank you from the homeowner ) . We repiped the tank with the flow going the wrong way through the coil . For some reason the homeowner had his plumber over there and noticed the sticker on the coil ( I knew I shoulda accidentally " burnt " that tag off ) . We had to go back and reverse the flow .
  • Lchmb

    We do pipe them reversed on occasion and I haven't heard of a complaint ( and we most certainly would hear about it , our clientele are not shy ) . My thinking is that it only takes a a few seconds for the flow of water to get through a coil . Unless theres something on the inner part of the coil that grabs the water when it flows a certain way , I can't see much of a difference what's the inlet and outlet .

    Here's another question - would having a primary pump running keep the boiler water hot around the coil longer than no circulation of boiler water at all ?
  • J.C.A._3
    J.C.A._3 Member Posts: 2,981
    I think...

    The SSC is a booster, stailess steel tank. In that case, you'd be storing a pile O' hot water and the flow through the coil would probably make less of a difference.Chris
This discussion has been closed.