Tankless WH with a front load washing machine

[Bob from accounting]

Hey everyone!
I have a question about my tankless water heater and how it may perform with a front-loading washing machine. I’ve mentioned before how our tankless system takes a bit longer to deliver hot water at the faucet compared to what I was used to with a traditional tank. While I won’t go into all the details again (to save time), I’ve been thinking about how this affects our washing machine. Since we’ve gotten used to waiting about 60-80 seconds for hot water, I’m starting to wonder about the washing machine’s hot/hot cycles. When the quick valves open and close, I can’t help but think there may not be a sensor that detects if hot water is reaching the machine. So, unless it fills for over a minute, could it be possible that the water isn’t getting as hot as we expect? I’m curious about how modern washing machines work in terms of sensing water temperature. Do they fill based solely on time rather than temperature? If anyone has experience with this, especially with a modern LG front loader and a tankless water heater, I would love to hear your thoughts! Thanks so much!

WH is from 2016, descaled twice a year. No water softener. Water is not terribly hard.
Pex B, with a 50' run from WH to appliance.
Modern LG front loader.
If you want a tankless WH just know you will never wash your hands under warm water again.

 

[Reach4]

If you want a tankless WH just know you will never wash your hands under warm water again.

There are recirculation systems that can work with tankless WHs.

I expect the washing machine fills to a level, but does not discard the cooler starting water. Some WMs have an electric heater built in. Maybe you have that, and are asking if the water starting cooler during the fill messes that up vs the WM measuring the water temperature.

You could run your laundry tub for a minute while the WM is getting ready to draw water.

 

[Sponsor]

 

[bigb56]

We've had a Rinnai for about a dozen years now. The older Rennais do not work with recirc pumps at the heater or recirc loops, I tried everything believe me. What does work is a recirc pump at the last fixture that takes from the hot and pumps into the cold. Sine my house is plumbed with 3 branches, it took 3 of these pumps to get us hot water to every fixture within 1 minute with no wasted water. I used these https://www.amazon.com/dp/B0BC15WJRF?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_2&th=1 which have different options and a thermostat that automatically shuts them down when the hot water arrives at the pump.

Instead of the remote that they come with I wired a 5 minute spring wound wall timer to the outlet where the pump is plugged in. Crank the timer, pump starts, 1 minute later pump shuts down due to thermostat and your hot water has arrived to all the locations between the pump and the water heater. Then wall timer times out preventing the pump from starting again needlessly as the water cools, till the next time you need hot water and crank the timer again.

I didn't like the remote because the shortest option is 1 hour which results in the pump re-starting during that hour even though you are finished using hot water. As long as you continue to use hot water it stays hot anyway, so either way the pump is only needed for a minute at the beginning.

The one under the kitchen sink brings hot water to the kitchen and laundry.

I can tell you that the washer does not know the difference between hot and cold, it just opens the appropriate valve and if the hot valve opens but the water is cold it doesn't know.

The newer Rinnais have optional recirc systems but they may not work with multiple branches like I have.

 

[Bob from accounting]

Thanks for the link, I have used recir pumps at my last location and I loved them. If anyone is reading this, just remember that if you have pex, sometimes they will run home run lines to a manifold. So a recir pump may not work for everyone. Something I am well aware of. But it will work for at least one fixture.
I might buy that one you recommend. I will need to learn more about the timer you are talking about, I had mine just on a time of day set up. So it only popped on a few times a day when we were were home.
I can start with a pump for now. Waste is something to consider but I admit it is really about just having some warm water. All my neighbors with this same Rennais always talk about turning all their water on before they use the bathroom just so there is some warm water.
Just to vent a little more, forgive me.
My whole family turns on the hot water faucet out of habit living with a tank for so long. When they wash their hands or do whatever. So image the whole day, the burner fires up, the tankless unit fires up, gas is used, electricity. And it never reaches the faucet and everyone just uses cold water from the hot water line. So it is annoying to think we use gas and electricuty to heat the first 20 feet of the line and then it cools and then you turn it on again. So it as if we need to train ourselves to never use the hot water side, unless you know you are running it for longer than a 60-80 secs. Wear and tear on something that is usless unless on for a solid 60-80sec. Wash your hands and count to 60 and then imagine you feel warm water, not hot, just warm. LOL. I am all over this circ pump and will look into the logistics. Seems like I might need multiple units. Reach, I will look into running the Wash Tub hot water before starting the laundry , that help too. Hopefully they are on the same hot line. Thanks.

 

[Breplum]

1. With modern HE laundry detergents, hot water is virtually totally unnecessary. Even my grubby plumbing overalls come out completely clean with any of the name brands (think Tide or Kirkland) and cold water. Unless you are cleaning auto shop grease laden coveralls.
2. Navien and Noritz tankless condensing WH with built in pumps do the whole job for recirculating hot water with dedicated recirculation pipe with either pushbutton demand trigger or built in aquastat. And a half baked crap job with a NavCirc or Grundfos bridge if you like hot water when you open the far cold water outlet.
Dedicated return line is the only sane way to go.

 

[Fitter30]

Pex tubing volume cap. Flow rate for lg washer 3-5 gpm holds 7-10 gallons
.5" - .92 gallon @100'
.625 - 1.34 gallon@ 100'
.75 - 1.83 gallon @ 100'
1". - 3.03 gallons @ 100'

 

[bigb56]

When I was wiring new houses I would always run a spare wire from the bath light switch to a recirc pump location. Then whenever the bath light is switched on the pump starts.

 

[Bob from accounting]

There are so many great ideas here! It's good to hear that hot water isn't necessary for laundry; I suppose I should have started looking into that earlier.
One thing I read about is the under-sink bridged circulation pumps used with tankless water heaters. When users turn on the cold water line, they can hear the water heater (WH) fire up and begin to operate. It’s important not to get confused about why there is warm water in the cold line—that's expected.

The main point is that the check valve allows water from the hot line to flow into the cold line when the cold water is turned on. This flow on the bridged side triggers the water heater to turn on when the cold water is being used.

Yes, there will be warm water in the cold line, and I want to clarify that. The concern arises specifically when you turn on the cold water that connects to the under-sink recirculation pump and bridges the lines. You can actually hear the water heater turn on, which seems unfortunate and not intended. It almost feels like there should be a second check valve to prevent this. This may be beyond my expertise, but I would love to hear about anyone's experiences with their water heater activating when they turn on the cold water. Which is only specific to those using an undersink bridged recir pump with a tankless WH. Any other set up would be absent of this. T
Thanks-

 

[bigb56]

I'm not exactly following you, I just went and tried running cold water at 2 of my pump locations and neither one triggered the water heater.

We do get a little warm water in the cold side of the fixture where the pump is located, but only at that fixture, not at any of the upstream fixtures.

 

[Reach4]

One thing I read about is the under-sink bridged circulation pumps used with tankless water heaters. When users turn on the cold water line, they can hear the water heater (WH) fire up and begin to operate.

If you turned on cold-only, the WH should not fire up due to that. If you turned on hot previously, and use the cold pipe as the return, that pipe is charged with warm water.

 

[Bob from accounting]

I'm not exactly following you, I just went and tried running cold water at 2 of my pump locations and neither one triggered the water heater.

We do get a little warm water in the cold side of the fixture where the pump is located, but only at that fixture, not at any of the upstream fixtures.

The simplest way I can think on how they have explain it. The Hot water line is not isolated from the cold water line. The cold water line is however isolated from the Hot water line via a check valve. So when you turn on the cold water line, there is nothing preventing the hot water line from flowing into the cold water line a little bit. When hot water flows from the line, the WH will activate on. This was specific to "Smart Instant Hot Water Recirculating Pump System NSF/ANSI 61 & 372 for Tanked, Tankless Water Heater 3 speed HBS24-12"

 

[bigb56]

The simplest way I can think on how they have explain it. The Hot water line is not isolated from the cold water line. The cold water line is however isolated from the Hot water line via a check valve. So when you turn on the cold water line, there is nothing preventing the hot water line from flowing into the cold water line a little bit. When hot water flows from the line, the WH will activate on. This was specific to "Smart Instant Hot Water Recirculating Pump System NSF/ANSI 61 & 372 for Tanked, Tankless Water Heater 3 speed HBS24-12"

OK I read that review and I recall reading it a couple years ago when I bought my first pump. For whatever reason it doesn't happen with mine. Could be the flow rate isn't enough to activate the WH. The only one I didn't try yet is the shower but I plan to test that tonight.

The pump for the master shower is the only one not at a fixture, I ran about 6 feet of hot and cold PEX from under the house to the tub access where I mounted the pump inside the wall.

edit: I just had my wife crank up the cold water in the shower while I stood next to the WH, it did not start even for a second. So that's all 3 pumps tested.

 

[Fitter30]

OK I read that review and I recall reading it a couple years ago when I bought my first pump. For whatever reason it doesn't happen with mine. Could be the flow rate isn't enough to activate the WH. The only one I didn't try yet is the shower but I plan to test that tonight.

The pump for the master shower is the only one not at a fixture, I ran about 6 feet of hot and cold PEX from under the house to the tub access where I mounted the pump inside the wall.

edit: I just had my wife crank up the cold water in the shower while I stood next to the WH, it did not start even for a second. So that's all 3 pumps tested.

Take a couple of pics of the heater. Pipe size, length and fitting count. Pumps are sized by by three things. Gpm, head, size and type of pipe material. Doesn't matter if how many gpm a pump is rated it's the head that has to overcome. The resistance of the pipe size ,length and fittings.

 

[Fitter30]

Hey everyone!
I have a question about my tankless water heater and how it may perform with a front-loading washing machine. I’ve mentioned before how our tankless system takes a bit longer to deliver hot water at the faucet compared to what I was used to with a traditional tank. While I won’t go into all the details again (to save time), I’ve been thinking about how this affects our washing machine. Since we’ve gotten used to waiting about 60-80 seconds for hot water, I’m starting to wonder about the washing machine’s hot/hot cycles. When the quick valves open and close, I can’t help but think there may not be a sensor that detects if hot water is reaching the machine. So, unless it fills for over a minute, could it be possible that the water isn’t getting as hot as we expect? I’m curious about how modern washing machines work in terms of sensing water temperature. Do they fill based solely on time rather than temperature? If anyone has experience with this, especially with a modern LG front loader and a tankless water heater, I would love to hear your thoughts! Thanks so much!

WH is from 2016, descaled twice a year. No water softener. Water is not terribly hard.
Pex B, with a 50' run from WH to appliance.
Modern LG front loader.
If you want a tankless WH just know you will never wash your hands under warm water again.

Read post 13

 

[Bob from accounting]

When I run a bathroom faucet, which is 40 feet away form the WH, after all the hot water in that line empties, it never gets hot again. After 5-6 minutes of testing, I noted that even if I turn the faucet off and on again after a minute, the WH always remains silent, and the faucet runs cold water. Unlike when the kitchen or laundry faucets which I can hear the WH on and they process water after 60 secs. To be clear, the vanity faucet is running upstairs, and I an standing 2 inches from my downstairs WH listening.
I tested all the vanity faucets, upstairs and down stairs, and none produced hot water after their warm lines emptied, nor could I hear the WH turn on in these three test. It seems that there might be a minimum flow requirement for the WH to activate, and one bathroom faucet may not provide enough flow.
The kitchen faucet and Laundry faucet are also 1/2" pex lines but they do process more flow. Is this min flow hypothesis a possible scenario with some Rinnai tankless water heaters? Or is there another factor here involved I can test.

Here is what I found on google:
Rinnai tankless water heaters require a minimum flow rate of 0.4 to 0.6 gallons per minute (GPM) to ignite and 0.26 GPM to maintain operation. If the flow rate drops below these levels, the unit will shut off, as it senses no need for hot water.

 

[bigb56]

It does sound like there is not enough flow. Try the faucet with the aerator removed. Rennai also says the minimum flow rate can vary slightly depending on set temperature and incoming water temperature.