Temperature differential with new Navien install with recirculating line

Discussion in 'Tankless Water Heater Forum' started by niftyc, Feb 10, 2013.

  1. niftyc

    niftyc New Member

    Messages:
    2
    Location:
    Ann Arbor, MI
    Hello, I bought a decrepit historic farmhouse and I am trying to bring it back to life. We are camping in it. It had no hot water, no kitchen, and no bathrooms. We are doing the work in phases and this weekend is the first time we are able to shower in our first brand new bathroom (yay! exciting!).

    Our plumber installed a Navien NR 240-A tankless hot water heater to serve an eventual 3 bathrooms. After doing some calculations, he decided that one tankless located in the basement would be able to serve the whole house. However, it is quite a long pipe run to the first bathroom from the basement (bath: 2nd floor, other end of house) so he recommended a recirculating line, which we did.

    So this weekend is the first time we got to try our first finished bathroom (yay! exciting!) and... the hot water never gets hot up there. It gets warm, but never hot. The tankless was set to 125. I increased it in 5 degree increments to 140, the "consumer" maximum. This produces extremely hot water in the kitchen adjacent to the hot water heater, but the water at the first bathroom is still not very hot.

    I'd suppose since we live in a cold climate (current outdoor temp = 5 degrees F) the hot water is losing heat over the long pipe run. Clearly our plumber is aware of the long pipe run -- he suggested the recirculation because of it. But the issue isn't recirculation if the pipes can't retain the heat. I'm going to have a conversation with him on Monday but I wondered if some pros on this forum would be willing to give me advice on how I should feel about this situation.

    I feel wronged. Our plumber got to design this system from scratch and do whatever he wanted. If he had said "and you'll need to insulate these pipes for an extra $XXX" we would have paid it as we trusted him. If he had said "we need a kryptonite pump" I would probably have said yes. What do I know about designing plumbing? Nothing. But now we've closed all the walls and the contractors have left and this stuff is supposed to work. Whatever conversation we have on Monday I have a feeling that I am not going to like the outcome. This system he designed should be working right now. However, I've never done a big job like this before. Is there a different perspective I should take?

    Another option is to increase the hot water temperature further on the Navien. There is a "PRO" setting with a lot of warnings: "THE PRO KEY CAN ONLY BE USED BY FACTORY TRAINED INSTALLERS" that will allow me to raise the temperature further -- but this seems like a bad idea as it will only lead to burns in the kitchen. Is that right?

    Thank you for any advice on these two questions. I really appreciate it. After spending so much on the plumbing I am very sad and I'm hoping for some perspective.

    Christian
  2. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
    Does the bathroom just have a shower at this point? Is there a lav? If so, does the water there get hot? If it is just the shower, it could be as simple as the shower valve. Many have and adjustment to control how hot the water can come out at. Just might need adjusting. Could be other things as well, but we need to figure out if the bathroom isn't getting hot water or if you just aren't getting hot water out of the fixture(s).

    I doubt the problem is heat loss. The pipes should be in interior walls (especially in a cold area). Even if they were outisde, water at 140F flowing at a couple GPM has quite a bit of energy and it would be difficult to cool it off much with a striaght run of pipe in fairly still air.

    If the lav isn't installed yet, but the valve are there, you could run the water into a bucket and see if if gets hot.

    Other possibilities for hot water not coming out hot would be a crossover in one of the shower valves (maybe in a bathroom that isn't finished yet) allowing cold water to mix with hot.
  3. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,132
    Location:
    NW Ontario, Canada
    Nukeman makes some very good points. Look for possible crossover if unfinished rough-ins have only a test cap and no plug or valve installed.

    If there is heat loss due to the run going through unheated space, that loss should diminish as more of the house is brought up to temp. What is the temp on the recirc line?
  4. niftyc

    niftyc New Member

    Messages:
    2
    Location:
    Ann Arbor, MI
    Wow I really appreciate your help. I did some poking around and found this: http://www.flickr.com/photos/niftyc/8461463299 [​IMG]

    ...inside a newly-installed access panel near the bathroom. And indeed there was what I think is a crossover valve inside the access panel and the estimated setting on it with our input temperatures was 108 degrees. So it was cooling everything down. I figured this out by checking a hot water line that did not appear to go through (or near) the crossover, just as nukeman suggested.

    Hot shower, here I come! I really appreciate your help! Now I can feel better about my bathroom again.
  5. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,132
    Location:
    NW Ontario, Canada
    I'm not sure what I am seeing WRT the lower unit that has four lines in/out of it. My guess is that it is a tub filler/shower rough-in but the octopus of lines is confusing.

    The unit above it with the knob looks like a tempering valve which works by blending some cold into the hot. It is not a crossover.

    A crossover is a non-intentional interconnection between hot and cold that lets hot water get into the cold side and/or cold water into the hot side.
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