Tankless water heater, water smell

Discussion in 'Tankless Water Heater Forum' started by Czar787, Dec 17, 2019.

  1. Czar787

    Czar787 New Member

    Joined:
    Dec 17, 2019
    Location:
    Michigan
    Installed new tankless water heater with a complete re pipe job. Swapped out cpvc, and a 50 gallon tank for a Rheem 199,000btu tankless with pex viega manifold, with bluefin pex and bluefin poly fittings. The pex is ran in home run fashion off the manifold. Off the water heater we go to copper for about 5 feet on both cold and hot witch then transitions to pex. There is a recirculatio system installed for this we have 3/4 pex ran around the basement in almost a big You connecting to every hot line with a 3/4x1/2x3/4 T. So now that you have an understanding of the system the hot water side has a pex smell to it, atleast to me I believe it’s a pex smell, one person said maybe a burning smell, the cold side has no smell or odor... has anyone ever experienced this... I believe it has something to do with the tankless heater?
     
    Last edited: Dec 17, 2019
  2. Tim Beck

    Tim Beck New Member

    Joined:
    Aug 6, 2019
    Location:
    Middlebury, IN
    Two things:
    I recently installed a 199k Rheem with recirculation utilizing pex, and I, too, have noticed an unpleasant odor from the water. It seems to be coming from both hot and cold lines, in my situation. I recall that one type of pex (whether pex-a or pex-b escapes my memory) is worse than the other about leaching chemicals from the manufacturing process. I'm hoping that this is the issue and that it will pass with time.

    Second, you may want to take another look at your manifold. It's generally discouraged to use a manifold with recirculation, as water will take the "easiest" path from high to low pressure and drag. Rather than having equal flow through all the return lines, the majority of the heated water can pass through the shortest path only, which may not necessarily be where you want it. You could theoretically have heated water being pumped down your shortest hot line, and returning without providing hot water to the other home runs. Typically, when manifolds are used with recirculation, each home run has its own recirculation pump. I'd say that grabbing a IR thermometer and checking the temps of each home run is an order. If you have good performance, great! If not, it may be wise to re-plumb with a single loop.

    Also, regardless, make sure you have a check valve on your return line on the end furthest from the heater. When a hot water valve is open, water can actually reverse its course down the return line and flow backwards to the valve.

    I've been fighting some cold water sandwich that I believe is the recirculation trying to perform smarter than it actually is. Have you had issues with cold water sandwich?
     
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  4. Czar787

    Czar787 New Member

    Joined:
    Dec 17, 2019
    Location:
    Michigan
    Tim the system I installed for this customer will not have the cold water sandwich issue because although al the main runs are off the manifold the recirculation line is a branch system a 3/4 line runs through the basement almost like a big U. With one end connecting to the pump and one caped. Then starting at the farthest end we have 1/2 lines with check valves for extra insurance connected to hot lines. As the pump runs the 1/2 inch lines pul the water into the 3/4 and with the check valves installed yes are sure no water back feeds back into the hot line.
     
  5. Tim Beck

    Tim Beck New Member

    Joined:
    Aug 6, 2019
    Location:
    Middlebury, IN
    I get what you're saying, and it may be working well in this particular circumstance. But, the flow will not be balanced through all hot runs. It's essentially creating several parallel water lines that likely won't flow equally. The runs with the shortest length and fewest elbows will have the highest flow rate, and the runs with the longest length and most elbows will have the lowest flow rate.

    In theory, a home run system with a single return could flow 100 percent of the recirculation pump's capacity through one run, and no flow through any of the other runs.

    I mostly deal with commercial and industrial sites, where manifold plumbed runs are the normal, and can feed dozens of separate loops. It's perfectly normal, but each loop always has it's own return, and each return always has it's own pump.

    Again, I'm not saying that your system isn't functioning properly, and I'm not trying to insult your intelligence or experience. I merely mean to say that plumbing recirculation in such a manner can be a risk, as functionality of the recirculation could be imbalanced or leave much to be desired.
     
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