using tankless water heater with dishwasher and clothes washer

Discussion in 'Tankless Water Heater Forum' started by rafael, Apr 5, 2010.

  1. rafael

    rafael New Member

    Messages:
    18
    Location:
    SF
    I just moved into a house that has a Noritz tankless water heater (model: N-069M). It works fairly well for things like taking a shower, where there's a continuous need for hot water. But it's working less well for things like the dishwasher and washing machine, where the need is intermittent.

    When I'm finished running a load of dishes, I often find that there is soap that is caked on to the dispenser, and I suspect the reason for this is there wasn't hot water, since it often takes 45 seconds or so to get hot water from the unit.

    Has anyone else experienced this problem? If so, how were you able to resolve it?

    Someone told me about something a "tankless metlund," but my understanding is that if I get one, I pretty much defeat the whole idea of having an energy-efficient, on-demand water heater.

    Thoughts?
  2. Dana

    Dana In the trades

    Messages:
    2,793
    Location:
    01609
    Have you timed it? A full 3/4 of a minute is an excessively long time for the unit to light up and stabilize the temp- it's typically 2-4 seconds from start of flow to ignition & temp stabilization with almost any tankless. Even starting with room-temp water in the pipes, at 2gpm flow that's enough to get hot water from the unit at 100 feet of distribution plumbing away. Fully 45 seconds may be an indication that it's having startup problems that should be addressed.

    That said, many water-sipping newer appliances only fill in short bursts of a quart or two at a time. If these bursts are less than 5-10 seconds long, the first couple of seconds of flow is letting cold water through the HW heater during it's ignition cycle, so the distribution plumbing will have segments of both hot & cold water (referred to as the "cold water sandwich"), which means the fill-water at the appliance is tepid, not full-hot.

    A common solution is a recirculation system with a pump that purges the hot water distribution plumbing of cold water when a sensor senses flow, or a switch is pressed to call hot water, like the Metlund D'Mand systems you mention. Some others use timers, or always maintain hot water in the plumbing, but those can waste a lot of energy in standby mode, but the demand-sensing systems like the Metlund don't. Rather than wasting energy by dumping room-temp water or tepid water down the drain until the hot water arrives, the demand systems circulate the water in the distribution line back to the cold-water input to the tankless, so the tankless only needs to raise the temp from 65-90F to 120F instead of from 40-50F to 120F. This is a significant fraction of the total, saving both water and energy. Also, since they purge the entire volume of the intervening plumbing of room temp or tepid water with each cycle it runs the tankless closer to it's steady-state efficiency, which is much more efficient than multiple short-cycling bursts. As long as it's a demand-triggered pump (either button-actuated by the user or a flow sensor), recirculation systems are either neutral, or increasing the net efficiency of the system while guaranteeing that your getting hot, not tepid water. See: http://www.gothotwater.com/D%27MAND/DOE/default.htm

    The system efficiency can be further improved at low cost by insulating the distribution plumbing, preferably with 3/4" wall closed cell foam (not the cheaper 3/8" stuff found at big blue or orange box stores.) By reducing the rate of heat lost from the hot water abandoned in the plumbing, subsequent draws are often still hot enough to be useful (or with a recirc system, hot enough that it inhibits the pump operation). If your plumbing supply outlets don't have it in stock, Grainger often does, or it can be ordered online from any number of vendors (be sure to get the right diameter for your plumbing). Something like 15% of the total energy in a hot water system is wasted in distribution losses in typical homes. Insulating the pipes can bring that down to low-mid single-digits.

    But use a watch to time how long it's REALLY taking hot water to get to the tap to the heater from a cold start. If it's as long as you say it is, there could be some maintenance or installation issues to sort out. Alternatively, measure the volume that would be going down the drain before the first hot water arrives, and estimate the length/size of plumbing between the heater and the tap. It takes about 100' of half-inch plumbing to hold a gallon of water, or 50' of 3/4". If you only have 15-20 feet of line between the heater and the tap it should be well UNDER a gallon of flow before the water is warming significantly at the tap, full temp shortly thereafter.
  3. rafael

    rafael New Member

    Messages:
    18
    Location:
    SF
    Thanks for the extremely informative reply, Dana.

    To answer your question about the time it takes to get hot water, it just took almost exactly 30 seconds to get completely hot water to my bathtub. I then waited 10 minutes and ran the same test in the kitchen where (obviously) the dishwasher is located. It took about 25 seconds to get beyond the cold water sandwich and get fully hot water. While not 45 seconds, this seemed a bit long to me, so I had three separate plumbers come out to take a look. They all said the unit seems to be working fine. They said if there were installation issues, my Noritz unit would deliver error codes to the remote control. As far as I can tell, I'm not getting any.

    I'm a first-time homeowner, so I don't know if my plumbing is 1/2 inch or 3/4 inch. Should I just go up into the craw space and measure the outside diameter of the pipes coming out of the WH? I'm also not sure how to estimate how many feet of line are between the heater and the faucets. Any suggestions there?

    Like I said, I was concerned about the amount of time it was taking to get fully hot water to the faucets, so after learning how many people incorrectly install tankless water heaters, I was concerned that maybe the previous owner didn't have the job done properly. I had 2 plumbers and a general contractor who is listed on the Noritz website take a look. They said the amount of time wasn't unusual, and they didn't think there were any installation issues. Does that sound right to you? If not, any suggestions for getting a more accurate diagnosis?

    Assuming there are, in fact, no installtion issues, I'm very interested in exploring the recirculation system option and the possibility of insulating the distribution plumbing. My house is extremely small. Will that be a problem for either of these options? I'm also not sure if this is something that I can do on my own and how much something like this might cost. Any suggestions for how I go about learning more?

    Thanks again for taking the time to give me such a long and thoughtful reply.
  4. Scott D. Plumber

    Scott D. Plumber In the Trades

    Messages:
    67
    I agree w/Dana. Your problem is "lag time" causedby you haveing to get rid of the water in the piping that has cooled off before the hot water gets there. A D'mand system installed in the right location foryour house should eliminate this. Also, you may be able to "prime" the hot water by turning on a hot water spigot near the washer, wait until it gets hot adn then start the washer. Yes, that wastes water. Again, back to the demand system. My guess is you would have this same issue with any kind of water heater.

    It takes the Noritz about 4 seconds rto get up and going to set point. Plus as Dana said, whatever is laying in your pipes.

    The Metlund D'mand system will only cost about $1/year to opperate since it only runs about 10-20 seconds at a time.
  5. Dana

    Dana In the trades

    Messages:
    2,793
    Location:
    01609
    Measure the volume it takes to get the hot water to the tap, and the vertical & horizontal distance between the heater & the tap in feet. 30 seconds at 2gpm is a gallon, which is ~50 feet of 3/4" plumbing. But if it's flowing at 5gpm that's 2.5 gallons- which would take over 100' of 3/4" pipe. If the tankless is on the far side of the house and 2 floors below the bathtub a gallon or two would be about what you might expect. If it's taking 3 gallons of water or the tankless is only 12 feet away, there may be something wrong. If there's a tap within earshot of the tankless you can usually open the tap and time how long it takes to light up, which should be a handful of seconds at most.

    They'll only spit codes if there's something egregiously wrong with the installation,there could be something more subtle, but if the factory certified pros have eyeballed & blessed it, it's probably fine.

    google "closed cell pipe insulation", and you'll find the goods. Where the pipes are easily accessible it's an easy DIY project. Try to go for R4 or higher goods on the supply line from the pump to the tap. The return line on the recirculation loop need not be insulated. If you're hiring a contractor to do the whole shebang, have them include installing R4 pipe insulation on as part of the spec.
  6. rafael

    rafael New Member

    Messages:
    18
    Location:
    SF
    Scott and Dana,

    Thanks again for taking the time. It means a lot.

    It's a small condo, so the tankless WH isn't very far from any of the faucets. It's in a crawl space in the attic, about 10-15 feet from the kitchen sink, although I have no idea if the pipes take an indirect route that may cause the plumbing distance to be much longer.

    Only one of the three people who looked at the model was listed on the Noritz website, and he was a general contractor. The other two seemed quite knowledgeable, but one never knows. I sure wish I could find someone I am absolutely confident *knows* how Noritz models are supposed to work. They didn't think 30 seconds was a problem, but based on what I'm hearing here, it sounds like you do (based on the fact the WH is so close to the faucets).

    I'm definitely interested in the foam and possibly the recirc, but it seems premature to consider those until I'm fully satisfied the WH is working properly. Does anyone know a plumber in the San Francisco area who absolutely knows Noritz models inside and out? Any other suggestions?
  7. Scott D. Plumber

    Scott D. Plumber In the Trades

    Messages:
    67
    THere is a company out there called Advanced water heaters or something like that. THey are the Noritz "Poster Child" company and from what I have heard there is none better. Look them up on the Noritz Site.
  8. rafael

    rafael New Member

    Messages:
    18
    Location:
    SF
    No one like that on http://noritz.com/homeowners/services/find_an_installer/

    You don't have additional information, by any chance, do you?

    Also, it appears I don't have a dedicated gas line feeding into my Noritz WH. Does anyone know if a dedicated line is required?
  9. Scott D. Plumber

    Scott D. Plumber In the Trades

    Messages:
    67
    Give Noritz a call monday to help you find Advanced. A dedicated line may or may not be required. Depends on what else is one the line, length of run, pressure etc. Normally around here a dedicated line on a retrofit is a "given".
  10. RinconVTR

    RinconVTR New Member

    Messages:
    43
    Location:
    Wisconsin
    I found and confirmed the same problem with H/E washers with tankless water heaters. Many H/E washers pulse water as it fills and senses the load, then fill very little water. LG confirmed their washers do not function with tankless water heaters, and they do not recommend it. Dishwashers could have the same issue, but fill more consistently and some actually heat the water internally if its not to the proper temp.

    While dishwashing has multiple solutions, The only options for H/E washers are recirculation of hot water to the tankless heater which reduces efficiency because the heater will run more often OR stick with a tank water heater.
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