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Thread: Wide variation in hot water times

  1. #1
    DIY Junior Member jonknite's Avatar
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    Default Wide variation in hot water times

    I recently replaced a standard hot water heater with a tankless system. I get hot water immediately off a sink 4 feet away. It takes about 45 seconds for my master bedroom shower (20-30 feet away). The laundry which is closer than the shower takes 3-4 minutes. The guest shower which is 70 feet away takes a full 5 minutes. I ran a tee off the line about 4 feet from the heater, directly to the laundry room and now it heats in about 30-45 seconds. I can't figure out what is going on. The volume of water in the pipe to the guest bathroom can't take 5 minutes to clear. The original system was set up with a circulating pump that kept hot water flowing through the pipes at all times (not very energy efficient, but saved water). I'm wondering if that has something to do with the issue, perhaps some kind of large loop? I can't trace pipes as there is no schematic and they are embedded in the concrete slab (no basements in the SW). Thoughts anyone?

  2. #2
    DIY Senior Member Smooky's Avatar
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    Cold water is probably getting into the hot water line somewhere. The recirculation loop sounds like a good place to start.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    THere's no comparison between using a recirculation system and one without it! If the pipes are well insulated, it isn't the energy hog you think it is...certainly, it does use more energy, but if your hot water uses are widely separated, you'll waste lots of water (and maybe incur extra sewer charges and if on a septic system, stress it, too) and time waiting for water to arrive.

    THen, even if the recirculation system is not running, with a tank, even if it has a heat trap, will conduct some heat out a bit into the distribution system. WIth a tankless system, it is typically entirely off until the flow rate triggers it to turn on...then, it doesn't get up to temp immediately like a tank of preheated water.

    So, switching systems is a lifestyle change.

    If your tankless system's power (whether gas or electric, and hopefully not electric!) isn't up to specs, the burner may never be reaching the design spec. And, wait until winter when your incoming water temperature dives...you may be in for even more of a surprise! The thing can only raise so much water so many degrees, and when it starts out colder, bad things can happen (assuming you want good flow at a decent temp).

    If you still have some of the recirculation lines there, and not capped off or valves closed, there may be a path between the hot and cold, making things worse.

    As you can tell, while there are situations where tankless is a reasonable choice, I'm not a particular fan of them. Cost too much up front, yearly maintenance required (or you'll regret it as performance drops significantly), and the savings in standby losses aren't all that much if you get good equipment in the first place. THen, there's the convenience issue you're experiencing.

    Keep in mind that it's not just flushing the line to get hot where you want it, you have to potentially heat up the pipe in the process.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4

    Default

    Wow 5 minutes! That could be some kind of record. I think smooky right, the sounds like it might be causing some havoc on things.

    Jadnasha, has a good point about winter, when the ground temp drops, things can get really interesting if the unit wasn't sized right for your home. In some instances you can hook a circulating pump to a tankless such as Rinnai's Ultra. Its a little more effort, but it might worth looking into.

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