Non-ideal tankless application

Discussion in 'Tankless Water Heater Forum' started by Runs with bison, Feb 15, 2014.

  1. Runs with bison

    Runs with bison Member

    Messages:
    897
    Location:
    Midwest
    I've done a relocation since my last time on the forum. While waiting for my home to sell, I've been in a smaller, older, much more expensive rental (lucky me) in a warm climate. Among this home's many problems is the water distribution in general, and the hot water in particular.

    From what I can find the original piping is galvanized iron, underground, uninsulated. Uggghhhhh! If any lines sit idle for a few days I get brown water from them. First thing I did when we moved in was to pull aerators, shower heads and such and flush the lines as best I could full flow.

    The hoped for bright spot was that the home has a Rinnai tankless water heater. Unfortunately, this is more of a mixed bag than I had anticipated. It has operated flawlessly so far, the blame is not with the execution of the unit itself. However, there are some limitations imposed by the installation and design limitations of a tankless. As best I can tell when they did some rework of the home, they ran new blue plastic line from where the old water tank likely resided to the new unit. This adds about 30-40 ft of new line each way. Now, if the water heater was on the same end of the home with the primary users (showers and kitchen) that wouldn't matter. But no, it is on the wrong end, opposite the water supply line. And all of the lines from there are uninsulated and either buried or hidden. Some of the buried lines (kitchen) I can trace with bare feet while running the hot water. The lines are oversized to begin with and take forever to heat up since they have to heat the ground first.

    The Rinnai controller tops out at 120 F, but that doesn't give actual hot water anywhere in the home. Instead, if I run full hot long enough in the kitchen or master shower it will reach maybe 110 F being generous. No reason to run any cold mix. It really isn't sufficient for dishes, and to keep the line warm the hot tap is left on during dishwasher fill and throughout any handwashing (after about 5 minutes just to warm up.)

    To be fair, this would be nearly hopeless for a standard 50 gallon hot water tank since it would soon run out of water, except for one thing: I would move that tank's temp control to 140-150 F so that I could get some actual hot water, and in about half the time, and without needing to run continuously. And of course then I would use my ultra low flow shower heads too, like I was doing in my previous home.

    Getting hot water to loads that require it in the HE clothes washer also requires wasting a lot of hot water, since there is the need to run hot water from a nearby tap continuously until the pulsing wash fill is complete...else the water heater will cut in and out and the water in the washer won't even be warm.

    I haven't done a rigorous breakdown of the gas use by the water heater, but rough checks indicate it is several times what we were using in our previous home. Despite that the water heating itself is clearly more thermally efficient, because gas use should be even worse with us wasting about two to three gallons of lukewarm water for every gallon of almost hot water we get. And the water wasted by this home in a dry climate is epic as well...largely because of the hot water distribution problems.

    If I owned the place I would do several things with the home's water distribution:
    1. Replace all of the water lines. They are s**t.
    2. New runs would all be insulated (hot and cold) and would not be in the ground. (I only insulated the hot lines in my previous home, and they weren't buried.)
    3. Place water heater on the opposite end of the home, where it belongs.
    4. Install a water heater with a higher temp limit (Rinnai appears to have a 150 F controller for some sort of commercial version of this same model...it would get a midnight retrofit with that controller if I owned the thing.) That way I could fine tune the temp control to give 120 delivered rather than 120 at the unit which isn't close to being sufficient. 130-140 would probably work wonders. That's the lovely thing about a tank: sure I burned an extra 3 therms a month for the tank (I measured this several times, that is not an estimate), but I could get the water temps I needed to perform any task in the home by simply turning a knob a little.

    And don't ask me about the idiotic choice of toilets (only a few years old.) I'll save that for later. Man, I miss my Toto's.
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