Tankless Water Heater

[davidgarrett]

Does anyone have any experience with the power requirements and installation of a tankless water heater?

 

[Dennis Alwon]

What do you want to know? You do not need 125% since it is not considered continuous use-- art 422.13

 

[Gregg Harris]

Do you have a specific question?

 

[masterinbama]

In certain situations I have actually talked customers out of going with an all electric tankless water heater. If they have natural gas available I will push them towards a gas fired model.

 

[augie47]

In certain situations I have actually talked customers out of going with an all electric tankless water heater. If they have natural gas available I will push them towards a gas fired model.

I have done the same ( unless it's one of the smaller (3 kw ) single point ones.)
Most of the folks I have encountered were not happy with their whole-house systems. The ones that were satisfied installed one of the behemoth ones using (3) 60 amp circuits.

 

[masterinbama]

I have done the same ( unless it's one of the smaller (3 kw ) single point ones.)
Most of the folks I have encountered were not happy with their whole-house systems. The ones that were satisfied installed one of the behemoth ones using (3) 60 amp circuits.

That's why I do that. Even though I had no input on the sizing plumbing etc. the customer will still blame the electrician along with the plumber when the unit doesn't perform to their expectations

 

[Little Bill]

Had a customer that bought an old house that had a 40A tankless already installed. The house really had no place for a tanked heater. She wanted to replace the unit with a larger one until I explained to her she would have to have a service upgrade because of the electrical demands of the larger unit.

Since she had gas available, I suggested she go with a gas model.
She decided to stay with the smaller electric unit for a while. Later she told me it was a game to take a shower while other hot water was being used. Had to play with the handles to get the right flow, then it would go cold sometimes anyway.

Whole house units (electric) are not for areas with a cold climate or have very cold ground water.

I don't know of a single plumber that recommends the electric units!

 

[RustyShackleford]

Probably a thread hijack, but ... I needed a new water heater (for myself) and researched them a lot. I came to the conclusion that tankless are almost a scam. Yes, they save the standby losses (of the tank full of hot water). But these losses are as low as 5% for the newer electric models (with 2" R16 insulation), and the losses in hot water piping (the hot water that's left in the pipes after you turn the faucet off) is generally more like 15-20%. Meanwhile, you have much higher purchase and installation costs - money that you could put towards photovoltaic solar (which is rapidly dropping in price), and maintenance and repair headaches.

Of course, as in the OP, tankless are indispensable where there are space limitations or where there's a legitimate need for endless hot water.

 

[GoldDigger]

... or where there's a legitimate need for endless hot water.

Do you consider teenage children a legitimate need?
One other advantage of some tankless is that since you have almost unlimited capacity you can set the thermostat for a lower temperature (I use 120F) instead of having to keep the tank hotter to deal with recovery issues.
For a tank heater, reducing the thermostat to the lowest tolerable value further reduces losses. And if you are using electric heat, modern washers and dishwashers can heat just the water they need to a higher temperature with no cost penalty. And finally if you have a sprawling house two or more tankless can result in reduced piping losses. (Probably not enough to make up for the cost, but it could add additional value in quick response.)
One more consideration: If you are on a TOU plan, you need to schedule your biggest hot water uses for off-peak hours since there is no storage. That is usually easy enough to do for bathing and washing.

 

[jimC.]

With the tankless it really comes down to flow rate. Most residences require more than one unit, and a change in the way they use their water. Some of the newer systems have a small tank 3-5 gallons, which is important if they have a return line (which most houses seem to have). They're a nice item for the plumbers to sell, don't imagine I would be a customer though.

 

[RustyShackleford]

Do you consider teenage children a legitimate need?

Hah ! Yes, I've heard that can tend to negate any possible energy savings, since unlimited showers are possible.

 

[kwired]

The amount of energy needed to keep up depends on two things.

1. amount of temperature rise needed

2. amount of flow desired.



In colder climate areas, heat losses from a tank water heater are not total loss. This heat takes a little load off the heating system.

 

[RustyShackleford]

In colder climate areas, heat losses from a tank water heater are not total loss. This heat takes a little load off the heating system.

For typical relative COP of the HVAC and the water heater - the former generally 2 or 3, the latter frequently 1 - it's still a loss. And of course there is extra loss in the summer, as cooling load is added.

 

[norcal]

Do you consider teenage children a legitimate need?

Get a 10 gallon electric WH, it will teach them conservation really quick.:lol:

 

[broadgage]

These units are almost unknown in the UK, I installed one recently.
To heat water at a reasonable flow rate needs a great deal of power, 10KW is about enough for handwashing or a not very good shower, but at least 20KW is required for filling a bath or a large sink at a reasonable rate or a good shower.
Most UK domestic electrical services are 100 amps or less, single phase, which effectively rules out a tankless water heater.

The home in which I recently installed one had three phase service at 100 amps.

The owner was not entirely satisfied with the hot water supply.

 

[gadfly56]

I have done the same ( unless it's one of the smaller (3 kw ) single point ones.)
Most of the folks I have encountered were not happy with their whole-house systems. The ones that were satisfied installed one of the behemoth ones using (3) 60 amp circuits.

Once upon a time I was a facilities manager and an internal customer came to me asking about heating the infeed to a DI unit. It seems that he could get a significant improvement in throughput by raising the inlet temperature from about 54F (IIRC) to 70F. Based on his flowrates, the power required was rediculous.

I've looked at replacing my current 50 gallon HWH (gas-fired) which seems to be developing a leak or two. I wouldn't dream of going electric. After the Sandy outage, I'm thinking I won't go tankless either, and I'll be looking for a unit with a standing pilot. By day three of the outage, only the fact that we had HOT running water made it bearable.

 

[kwired]

Once upon a time I was a facilities manager and an internal customer came to me asking about heating the infeed to a DI unit. It seems that he could get a significant improvement in throughput by raising the inlet temperature from about 54F (IIRC) to 70F. Based on his flowrates, the power required was rediculous.

I've looked at replacing my current 50 gallon HWH (gas-fired) which seems to be developing a leak or two. I wouldn't dream of going electric. After the Sandy outage, I'm thinking I won't go tankless either, and I'll be looking for a unit with a standing pilot. By day three of the outage, only the fact that we had HOT running water made it bearable.

But you have municipal supplied water. Having to pump your own water would mean you would have been happy even sooner just to have water. Been there a couple times, in fact just this past weekend, no power outage but well motor quit working. Why does things like that always happen on a weekend or holiday?