Tankless water heater question - Is it bad to keep shutting of the faucet while washing dishes?

Chris Alonzo

I assume that the tankless water heater turns on as soon as it detects water flow and shuts off immediately after it stops. So, if I try to save hot water by always shutting off the faucet between washing each dish, will that be bad for the water heater?

Mad Dog_2

Not really.  You're doing the right thing conserving water.  I wouldn't worry. What kind of Tankless?  Mad 🐕 Dog

EdTheHeaterMan

Each device in that water heater that is involved with turning on the flame ON ands shutting the flame OFF is designed to operate thousand and thousands of times over the life if the heater. Flow switch, gas valve ignition controls and the like will be turning ON an OFF. The more you operate a man made device the closer you get to the total expected cycles to failure. If a switch is expected to last 10,000 cycles and you operate it 1000 times a year, you could expect parts begin to fail in 10 years. If you operate the device 3000 times a year, then you could expect the failures to happen within 4 years or less.

With that explanation, I believe that reducing the number of ON/OFF cycles would make the water heater last longer with less repairs.

That said, those water heater parts are designed to be cycled many many times a day. Use common sense and batch the dishwashing so you can wash / rinse several plates at a time in order to reduce the ON / OFF cycles.

HVACNUT

I don't understand why you would shut off the water unless there's a more efficient way I'm not seeing. I stack dirty  on the right side of the sink, then wash each while stacking clean on the left side. Stopping the water stops progress. 
Then dry and put away. Drip dry and things left in the sink are a pet peeve of mine. I might need therapy. 

Chris Alonzo

HVACNUT said:

I don't understand why you would shut off the water unless there's a more efficient way I'm not seeing. I stack dirty  on the right side of the sink, then wash each while stacking clean on the left side. Stopping the water stops progress. 
Then dry and put away. Drip dry and things left in the sink are a pet peeve of mine. I might need therapy. 

With a standard hot water heater, not using as much hot water is more efficient than leaving it running.

Chris Alonzo

Mad Dog_2 said:

What kind of Tankless?  Mad 🐕 Dog

I am looking to possibly install a Navien NPE-A2 with Recirc kit. They say that it will recirculate the water until it reaches 95F at the end point.

My concern with that is will it make my shower hot enough, or will I still have to wait for the 140F water to arrive?

EBEBRATT-Ed

They make electric dishwashers.

Larry Weingarten

Hi, Are you sure you want 140F at the shower? I'd go for more like 120F as the burn risk is so much lower. Also, you will need to wait for only a few more seconds for the fully hot water to arrive. When 95F shows up, the hotter water is close behind. I prefer demand controlled recirc lines as they are the most energy efficient, both in terms of energy use and water savings. Looking online, it isn't clear to me how the Navien recirc is controlled.

Yours, Larry

Chris Alonzo

I didn't know the exact temperature of the water at the shower. But you answered my question. I see what you are saying that the real hot water is not far behind.

The unit that is installed at the furthest end point seems to be like a thermostatic valve that is set to close the bypass 95F. There must be some kind of logic to turning the pump on and off, like only turn it on if the unit has been off for a while, and turn it off when there is no flow back on the cold water return.

hot_rod

Shower between 95- 105

vhauk

I am sold on Rinnai tankless water heaters. I’ve installed one in each of the last 3 homes I’ve owned. They are so efficient that the exhaust gas in barely above room temperature. Had a Bosch once and won’t make that mistake again. 120 is the correct temperature for showers. I leave my hot water running while washing dishes at around half flow. 

Chris Alonzo

Sounds like a good plan.

I am looking at Rinnai also.

Hot_water_fan

Are you short on space where the heater will go? Space savings are about the only advantage a tankless heater can provide. 

Mad Dog_2

I put in over 100 RinnaiS not a single problem.  Seen many last 12-15 yrs. NYC
Code;

85-110 - Hospitals and handicap folks
120- lav Sinks and showers
140 - 3 compartment Commercial Kitchen Sink.   Mad 🐕 Dog 

hot_rod

Hot_water_fan said:

Are you short on space where the heater will go? Space savings are about the only advantage a tankless heater can provide. 

Endless hot water, no standby loss, and essentially no place for bacteria to live, are some other selling features.

Hot_water_fan

Endless hot water, no standby loss, and essentially no place for bacteria to live, are some other selling features.

I’ll give you the second two - but as you know, there are condensing, tank heaters with big burners available . 

Is standby loss significant? It might be $10/year for me. 

Mad Dog_2

The first Rinnai I installed I marveled at how this small appliance cranked out endless, non stop hot water.  If you ran faucets for 5 hours straight it just kept goin....nobtank to empty....Mad Dog 🐕 

vhauk

and wand why heat 30 - 50 gallons of water, until it’s needed?  Installed one on a propane tank in Texas and the usage was cut in half. Took out a 50 gal and got the use of a closet. 

Derheatmeister

At High Altitude with 38 F water coming into the home the endless hot water thing does not always work out very well..Especially if you add Well water and Propane into the Equation.
Recirc lines...Recirc to a storage tank...Multiple units...All this adds more complex moving parts that will need even more services.
We have seen people trying to do the "Green thing" just to achieve even larger Carbon foot print.
Not saying that on demand is bad...Just make sure that it is the right situation for it..

Hot_water_fan

and wand why heat 30 - 50 gallons of water, until it’s needed?  Installed one on a propane tank in Texas and the usage was cut in half. Took out a 50 gal and got the use of a closet. 

Why not? It’s cheap and convenient to keep water ready. Would you rather fill up at the gas station every day or once a month? 

I agree, most tanks are inefficient. That isn’t because they’re tanks, it’s because the burners don’t condense. You can buy efficient tanks. 

You’re correct, saving space is a real benefit of tankless. Shoot, in the south sometimes they’re installed outside! 

vhauk

I never got into the recirculating hot water thing. Worked on one system that I liked just slightly better than the waste oil shop heater. For the average size home one heater seems enough. Are we talking about the same thing? I understood demand water heaters to be point of use. 

Chris Alonzo

vhauk said:

For the average size home one heater seems enough. Are we talking about the same thing? I understood demand water heaters to be point of use. 

One tankless unit is enough for the average household, they have 199,000 BTUs, enough for 3 people to take showers and to run a sink.

If you want to eliminate the wait time without using recirc, you can install units in each endpoint. But it gets pricey.

Larry Weingarten

Hi, If you have the opportunity, putting in the right sized piping can do a tremendous amount to reduce the waste and wait for hot water. Appendix M in the UPC goes down to 3/8". If there is adequate water pressure, this is a good way to get good hot water service without any moving parts.
To push the window a bit, the Plastic Pipe Institute has released a new calculator that goes down to 1/4"! https://www.plasticpipecalculator.com/

Yours, Larry

EdTheHeaterMan

hot_rod said:

Shower between 95- 105

If it get any cooler outside, then Bob prefers to use the bath tub. I personally use the shower as low as 60° outdoor temperature. Any cooler, then I use my indoor shower. We have both indoor and outdoor showers, living near the beach.

We all have our own preferences

EdTheHeaterMan

But I never understood the concept of a tankless water heater with a recirc pump. Isn't the idea of a tankless water heater to not have hot water just laying around in a tank or pipes where it can cool off and waste energy'. If your home is so big that the water pipes need more than 30 seconds to het the hot water to the tap, maybe you should rethink your hot water source location. Like putting the tankless closer to the point of use. Or maybe 2 of them, one at each end of the plumbing system.

I have also found that using the Mana-Block® type system reduces the time needed to get hot water to the end point tap. but charging the plumbing system or adding a buffer tank just defeats the purpose of the concept in my humble opinion. (IMHO)

vhauk

A side note. I had a friend when I lived north of Fairbanks Alaska that had an outdoor shower. He and his girlfriend used it all winter. Ain’t for me. 

Chris Alonzo

I had also contacted Rinnai support about this issue and finally got an answer from them regarding the I-series unit:

"The unit will not activate unless it sees a demand of .4 gpm. Once the water is at temperature, the plate hex will stay warm, and only heat up as the temperature drops while you pulse the domestic hot water."

hot_rod

EdTheHeaterMan said:

hot_rod said:

Shower between 95- 105

If it get any cooler outside, then Bob prefers to use the bath tub. I personally use the shower as low as 60° outdoor temperature. Any cooler, then I use my indoor shower. We have both indoor and outdoor showers, living near the beach.

We all have our own preferences

A trick I learned from my many trips to Ocean City, outdoor shower! Until it starts to get below 32F outside. A little more complicated now that I live in a city.