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Need a dishwasher that will work with tankless heater

Posted by dks35 (My Page) on
Wed, Jul 18, 12 at 0:54

we will need to install a dishwasher that will for sure work with our Takagi tankless water heater. The heater is great, but requires 0.6-0.7 gal/min flowrate to start the burner. I heard that some of the modern "water efficient" dishwashers do not draw much water to begin with and the flowrate at which they fill could be below the minimal flowrate of tankless heater. It seems like with these "green trends" you can either save energy, or water, but not both? Anyhow, Miele representative told us that their dishwashers connect to cold water lines and will heat the water in the tub to needed temperature regardless of incoming water temp. Are there other manufacturers that use the same system? I'd think that Bosch be similar - a sales person at Pacific Sales store told us Bosch will heat the water to required temperature, but when I called Bosch customer support, they said - you must connect to hot water line and incoming water temp must be 120F, otherwise it won't work/clean. Bosch has changed models and model numbers (yet again) and I wonder if this confusion is from people in the sales are not being up to date with current models of Bosch? This same requirement of 120F for incoming water temp is also true for KA dishwashers per their customer support. So - if we can't really afford Miele, what would be our best option besides having to run tap water during dishwasher cycles (water efficiency - out the window!!!). Thank you!


Follow-Up Postings:

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RE: Need a dishwasher that will work with tankless heater

The only method for assured water heating is if the unit does not limit the heating by time ... that is, the cycle progress is delayed until the target temperature is reached. Unfortunately, that kind of detailed information isn't always forthcoming from the manufacturer. Majority of U.S. brands/models have limitations. Some units may have assured heating on a specific heavy or "pot scrubber" cycle or if a sanitizing rinse or high-temp wash option is selected ... but not on normal or light wash cycles.

Foreign brands / models sold on the U.S. market may or may not be "dumbed-down" regards to on-board water heating. Miele and Asko may be OK. Bosch apparently isn't.

Fisher & Paykel DishDrawers have assured heating for both the main wash and final rinse to specific target temps per all choices of cycle selection, thus they can work on a cold connection. DishDrawers do have a different usability profile than traditional dishwashers and opinion ranges from loathe to love.


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RE: Need a dishwasher that will work with tankless heater

thank you dadoes. F&P two drawer DW have a bad reputation and as you say - opinions range from hate to love. I don't want to experiment and contribute to this statistics :)
The best solution might be to save some money and go with Miele. I saw ASKO dishwashers on displays in several stores but have not heard much about them. I did not particularly like the "MADE IN SWEDEN" label right on the front of it - why? As if we are dumb to miss this fact? I do drive a Volvo though and love it, but come on.


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RE: Need a dishwasher that will work with tankless heater

The Bosch will heat cold water it's just that the cycle will take longer. In the trainings I attended we were taught the Bosch heats water at about 2�F per minute and it does not time out before the correct temp is reached.
THe trainings were taught by service so I trust what they say.


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RE: Need a dishwasher that will work with tankless heater

DKS35, based on my DishDrawer being 9 years old and no trouble thus far, my guess is that 99% of the trouble complaints comes from consumer misuse and installation issues ... but that's just my "one person's experience."

I've been using it with a tankless water heater for the past 7.5 years.

I meant by the term usability that it doesn't mesh with everyone's "dishwasher lifestyle" regards to not fitting some types of large/bulky items that need the full tank height of a "standard" dishwasher.


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RE: Need a dishwasher that will work with tankless heater

jakvis and dadoes - thank you for input.
let me clarify this - jakvis, you are sure all current models of Bosch will heat their water, and heater is not on a timer? because this is the question that just doesn't sit square with Bosch Customer Support, as if they were taught to just "parrot" the words - hot water, hot water, hot water. I am not particularly sensitive to the length of the cycle - the water coming into dishwasher may be warm, and definitely won't be stone cold, because the water heater is performing very well. So if it takes a little longer - so be it, rather than having the heater time out and do the washing with lukewarm water. It is just it takes time and some volume to replace the cold water in the pipes and the flowrate may not be high enough to activate water heater properly. We live in Los Angeles, so our water is around 60-70 depending on the season.
Dadoes - is your dishwasher from Bosch? Do you know if your tankless minimum flowrate is about 0.6-0.7 gpm for activation?
thanks!


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RE: Need a dishwasher that will work with tankless heater

In the Bosch service training we are taught that the Bosch D/W (old & new) will heat ice water to the proper temp. The Install manuals for all manufacturers say the water supply should be at 120F. The Bosch trainer showed us that while this was good in the past it is really not that good with th new enzyme detergents. The enzymes start dying off as the water temp rises above 130 and the bosch heats the water too fast at 2+ degrees per minute for the enzymes to have much of a chance if you start out with 120F water. He told us to forget what we learned for the last 50 years about running your hot water at the sink before starting your d/w if it's a Bosch.
I have a Bosch and I stopped running the hot water before hand and I use the Finish Tabs. Our results are great and we don't prerinse the dishes. we jus knock off the big stuff.


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RE: Need a dishwasher that will work with tankless heater

DKS35,

Not Bosch. As I stated in the previous post, my dishwasher is an F&P DishDrawer DD603, 9 years old. I scrape dishes, do not prerinse, and do not run the faucet before starting. Per my observation, it heats at about 1.2F per minute. Each fill is 0.8 gals.

My tankless water heater is an electric unit. The specifications state that 0.4 GPM flow rate is required to activate. Once activated, it'll stay on at 0.3 GPM. All of that doesn't matter. Due to the plumbing distance from the water heater to the kitchen, it takes at least two fills (probably a little more) to get the supply line purged and heated water flowing in the dishwasher. Plus, I keep the tankless setpoint at 102F which is the perfect temp for showering ... the dishwasher always heats so the low temp has no effect on it. The tankless is in my utility room, easily accessible to adjust the temp if needed and I do raise it temporarily if hotter water is desired for washing clothes.


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RE: Need a dishwasher that will work with tankless heater

A different solution might be to put a small 5gl water heater under the sink for DW usage.


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RE: Need a dishwasher that will work with tankless heater

thank you all for your replies. i feel much more comfortable now. Jakvis - Bosch might be it then. Smaller storage tank for under the sink is also being considered - i was just hoping for an easier solution to our situation.


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RE: Need a dishwasher that will work with tankless heater

In Europe and elsewhere, dishwashers customarily are attached solely to a cold water feed because the dishwashers run on 240v/15a power and thus have internal water heaters that can heat the water 2-1/2x quicker than 120v US-market dishwashers.

I would think a problem with feeding cold water to a dishwasher is that glasses sometimes break when they're splashed with cold water when they're hot.


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RE: Need a dishwasher that will work with tankless heater

I would think a problem with feeding cold water to a dishwasher is that glasses sometimes break when they're splashed with cold water when they're hot.
I one incident of glass breakage in a dishwasher, a 1992 KitchenAid. Hasn't yet happened in my DishDrawer running on a "cold" connection.


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RE: Need a dishwasher that will work with tankless heater

My in-laws have a Bosch DW with a tankless water heater. Dishes come out piping hot and stupid clean.


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RE: Need a dishwasher that will work with tankless heater

@ Lee676 - Many European d/w's that hook to cold water have a tank mounted on the side wall that preheats the rinse water while the dishwasher is running. The heat of the water inside the dishwasher makes the wall hot and this preheats the rinse water so no cold water is entering the tub and it's also very energy efficent.


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RE: Need a dishwasher that will work with tankless heater

I have a tankless water heater, and have Fisher-Paykel dishdrawers in my kitchen. I installed the DDs in 2005, so have 7 years of experience with this set.....and have never had a problem with the dish drawers. My last house, in Virginia, had F&P DDs in the kitchen when I bought the house (the previous owner was a huge appliance dealer for central Virginia, and this is what he put into his custom-built home -- I don't know how old these DDs were when I bought the house...they definitely weren't new). I lived in that house for 5 years, and never had a problem with the F&P DDs, so it was a no brainer when I moved to Utah, to install this brand in my remodeled kitchen. So, I have a total of 12 years experience with 2 sets of F&P DDs, and have no complaints.

A bit over a year ago, I installed a Navien 240A tankless water heater, that has a built in buffer tank and circulating pump so that I never have the "cold water sandwich". This tankless water heater will put out hot water with as little a draw a .1 or .2 gal/minute. So, I really wasn't concerned about the ability of the dish drawers to get hot water.

Had I been concerned, the wonderful feature of F&P DDs that heats the water in the dish drawer itself overcomes any problem one might have with hot water access. This feature is just one of many reasons why I have been so impressed with the F&P DD products --- 2 different sets, in 2 different houses.

I've been a member of GW since 2004, and have read a lot of posts about F&P DDs...It's always seemed to me that the happy owners signficantly outnumber the unhappy owners. And most of the problems with the unhappy owners were caused because the DDs were improperly installed (because the installer wasn't familiar with these New Zealand products, and didn't read the installation instructions) and/or because the owner didn't read the "how to load" instructions. Many of the unhappy owners returned to the forum to report they were pleased with their DDs once they'd been properly installed, or they understood how to load the drawers.


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