Tankless Electric Water Heater Efficiency

 
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Old 09-17-2015, 08:25 PM   #1
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Tankless Electric Water Heater Efficiency


OK so we have built a garage/pool house for a customer and he wants an inexpensive water heater to heat an outside shower and a utility sink in his new garage. I received the quote from my plumber and he has found a Rheem RTE-9 electric tankless water heater installed for half price of a conventional 20 gallon Rheem electric tank. Only thing is he doesn't normally install tankless electric. So he cant verify the efficiency of the tankless one. It is rated at 3 gallons per minutes and the shower head is rated at 2.5 per minute. Do you think my customer will lose hot water after a few people have showered in the outside shower? I would love to save him some money but do not want to give him an inferior product, The tankless will be around $700 vs one with tank about $1600. He has been the best customer to work for. Easy going, ok with change order prices, and paying on time for every draw
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Old 09-17-2015, 08:40 PM   #2
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Re: Tankless Electric Water Heater Efficiency


The tankless costs less?

Tankless heaters are nearly 100% efficient. They don't run out of hot water, but they may not keep up. It's more than just GPM. You need to know incoming water temp as well. And don't forget their electrical requirements can be enormous.

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Old 09-17-2015, 08:43 PM   #3
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Re: Tankless Electric Water Heater Efficiency


Just looked up the RTE-9. 9KW. Look at the documentation, it can supply 2.5gpm to the shower head only if the ground water is 75 degrees+
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Old 09-17-2015, 08:57 PM   #4
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Re: Tankless Electric Water Heater Efficiency


Hmm thats good to know. 75 degrees huh. Yeah power is no problem, we installed a 100 amp box and the tankless requires a 240 volt 40 amp breaker. As few a times as he will use the water out there I am sure his power bill will not go up considerably. I just cant see heating a hot water heater in an area that isn't climate controlled constantly for just usage on a few minutes a day or every five days or so on. I am just not comfortable with the efficiency of one. Now if it was gas it would be a different story.
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Old 09-17-2015, 11:55 PM   #5
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Re: Tankless Electric Water Heater Efficiency


Your numbers sound backwards. It's a garage. Put a tank in and call it a day.
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Old 09-17-2015, 11:58 PM   #6
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Re: Tankless Electric Water Heater Efficiency


Mines gas, I think it's cheaper than electric.
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Old 09-18-2015, 05:16 AM   #7
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Re: Tankless Electric Water Heater Efficiency


I installed an electric tankless this summer for a bath Reno. It is feeding a bath sink and shower. It was a stiebel eltron and required 2 60 amp breakers and a service upgrade to 200 amps.
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Old 09-18-2015, 05:50 AM   #8
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Re: Tankless Electric Water Heater Efficiency


If the guy needs the space go with tankless. You have the amps. Go for it.

I have propane. Most all jobs I've worked on had gas.

Where are you in Florida?
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Old 09-18-2015, 06:19 AM   #9
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Re: Tankless Electric Water Heater Efficiency


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I installed an electric tankless this summer for a bath Reno. It is feeding a bath sink and shower. It was a stiebel eltron and required 2 60 amp breakers and a service upgrade to 200 amps.
Use the even smaller Stiebel Eltrons several times. Good packaging and connectibility.

Love 'em.
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Old 09-18-2015, 07:04 AM   #10
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Re: Tankless Electric Water Heater Efficiency


You are limited with the 100 amp service. Get the biggest one the panel will handle. And know that shower and sink running together will probably not work well.
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Old 09-18-2015, 07:40 AM   #11
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Re: Tankless Electric Water Heater Efficiency


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I installed an electric tankless this summer for a bath Reno. It is feeding a bath sink and shower. It was a stiebel eltron and required 2 60 amp breakers and a service upgrade to 200 amps.
That sounds more like I've heard here........set up cost...6ga wire too ?
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Old 09-18-2015, 11:28 AM   #12
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Re: Tankless Electric Water Heater Efficiency


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..... I am just not comfortable with the efficiency of one. .....
If by "efficient" you mean the normal definition - that a high percentage of the power consumed by the unit is used to heat the water - then you should be comfortable with the efficiency of an electric unit; there's no flue up which heat can escape.

If you are conflating efficiency and effectiveness - will this thing provide an instant supply of awesomely hot water, well, maybe not. In order to achieve a given output water temperature, tankless water heaters will throttle down the water flow if necessary. You need to look at the specific numbers for the particular tank. Our cold water here is at about 55 degrees F, and that heater might provide only a very weak stream of hot water.

And no, the customer won't "lose hot water" after a few people have showered - the heater will produce that same stream of hot water hour after hour after hour.

If the idea is for people to shower off the chlorine, or to shower before getting in the pool, then a small heater and a very low-flow shower head (like the type you find at the Y) will do the job just fine. If you want to provide people with a spa experience, then you need something more.

Edit: If by "efficient" you mean cost-effective, yes, electric power is more expensive per kwh, in most places, compared to natural gas.
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Old 09-18-2015, 11:53 AM   #13
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Re: Tankless Electric Water Heater Efficiency


I'm not sure the unit you describe will be "big" enough for a shower. It sounds more like a small tankeless for a sink or something. 3 gpm hot water isn't very much depending on the temp you want the hot water at the shower head and the temp of the in-coming water.

Is there any gas available? Even if you need to bury a gas line for a fair distance, I think you will find much better choices with gas tankless. By that I mean, to get the kind of "juice" I think you're gonna need, you are going to need a unit that's going to require some serious power upgrades like the unit Morning Wood installed.
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Old 09-18-2015, 11:17 PM   #14
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Re: Tankless Electric Water Heater Efficiency


A side note regarding electric water heaters; Haven't used one or had to call one out yet but apparently a more efficient way to heat water with electricity (probably in warmer climates) is a heat pump water heater; These aren't tankless.

A heat pump water heater calcs out a lot better (requires less energy) than a normal electric water heater when doing the Title 24 energy calculations that are required here in California.
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Old 09-19-2015, 05:37 AM   #15
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Re: Tankless Electric Water Heater Efficiency


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That sounds more like I've heard here........set up cost...6ga wire too ?

You aren't kidding. I'd say the total cost on the whole thing was over $4k. Service upgrade was $2200-$2500. 2 runs of 6 gauge wire. $900 for the unit. Plumber had to rough it in and connect it. I had to build a special recessed box for it in the wall. It's a summer cottage that get winterized. I really hope the plumber winterizes it correctly because it would suck to freeze it.
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Old 09-19-2015, 09:02 AM   #16
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Re: Tankless Electric Water Heater Efficiency


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If the guy needs the space go with tankless. You have the amps. Go for it.

I have propane. Most all jobs I've worked on had gas.

Where are you in Florida?

Panhandle, bay county.


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