# Eletric Tankless Hot Water Heaters - Energy Efficiency



## spur0701 (Feb 7, 2010)

My current hot water heater is about 10 years old and electric with an 80 gal tank (I think)......it's working fine but my wife wants a water softener and the install would be easier if we replaced the old water heater and tank with a tankless one (in that there would then be enough room in the mechanical room for both the tankless water heater and water softener).  Aside from that consideration is it worth it to replace it with a tankless electric one from an energy efficiency standpoint?  The kids have grown up and gone so hot water usage has gone down for showers and we wash clothes with cold......but we do have a big Jacuzzi in the master bath that's used a couple of time a week.


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## seige101 (Feb 7, 2010)

I can't comment on the units them selves other than the power requirements. As an electrician i have installed several (wired) Depending on the size of the unit you get (whole house gpm etc) and the temp of the water you are trying to heat they can have very heavy power requirements. The last one i installed in a new house, we had to install a 200 amp service in this tiny 600 sqft cabin, because the heater had 3 240v 40 amps feeds. Yes you are reading that right, 120 amps in feeds, it sucked down just over 100 amps in full demand situations!

So my point if you don't have the power capacity in your house and would need to upgrade your electrical service make sure to factor that into your installation cost.


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## jebatty (Feb 7, 2010)

Besides electric demands, users of tankless hot water heaters sometimes tend to use more hot water than before, because now it is "endless," and any economies from hot water on demand are lost. Instead, I would recommend staying with an electric hot water heater and super-insulate it, install heat traps on the cold supply and hot out pipes (don't rely on the ones now installed on the tank itself), and insulate all hot water pipes you can get to. We cut our dhw electric bill by 50% by doing those things (we have a 50 + 80 gal electric hot water heaters on off-peak billing). By super-insulate I mean raise it up off the floor at least 4" and insulate underneath, and add at least 6" of fiberglass insulation around the sides and top of the tank. Our hot water tanks were new and foam insulated, and still we realized these savings.


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## PJF1313 (Feb 7, 2010)

I fully agree with Siege - they are power hungry.

  We have a few of them in our out-buildings at work (rest rooms/ concession stands) and the bills have increased substantially - and not just for the use, but the installs as they required upgraded services and dedicated circuits.  

The only other way I can think that they MIGHT be more efficient is LP or Nat Gas - but I don't know if it's available to you or if it will cost you less in the long run.

As for what Jim (jebatty) stated, it is probably the best way.  

Either way you go, do what Jim suggested, *insulate* all the H/W pipes


PJ


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## geoxman (Feb 8, 2010)

Wow! I love mine and it has been in use for a while. I had an old 20 year old gas water heater that was running me about $40 per month, that what our gas bill was in the summer. My unit only has to have a 60 amp breaker and it does the heating just fine. If I were to run the washing machine, dish washer and shower at one time, it could not keep up. If I wanted to run everything I would just piggyback on another unit, but we don't ever run all three at one time. The showers are nice and hot and so is the water coming from the faucet. My unit has an adjustment on it so I can change the temp output in the summer when the incoming water is warmer. I am on budget billing with electric and my bill has increased $15 since install.  We are not using any more hot water than in the past because the tank was 80gl and between 3 people 80gl of water is tough to use. The unit paid for itself in under 10 months and I wish I had done it years ago.


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## SolarAndWood (Jan 15, 2011)

geoxman said:
			
		

> Wow! I love mine and it has been in use for a while. I had an old 20 year old gas water heater that was running me about $40 per month, that what our gas bill was in the summer. My unit only has to have a 60 amp breaker and it does the heating just fine. If I were to run the washing machine, dish washer and shower at one time, it could not keep up. If I wanted to run everything I would just piggyback on another unit, but we don't ever run all three at one time.



How big is yours, 2 gpm?  How does it do with a shower and a sink?  My POS lp water heater with a pilot light that doesn't stay lit in high winds sits right next to the panel.  Easy install and a can of great stuff in the old B vent pipe hole should be a dramatic difference.


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## mr.fixit (Jan 16, 2011)

I have tempra 24 electric tankless for almost 3 years now.It runs on 2 60amp double pole breakers.Works fine but does take longer to get hot water.
Currently its tied into after a 200 gallon storage tank heated with the boiler and homemade solar panel.So this time of the year the tankless very seldom comes on.
But no standby losses with the tankless. The tankless alone will run a shower with a lowflow head and one faucet just fine.
I did use the tankless for a couple months prior to adding the solar and boiler and it did lower my electric bill a small amount.


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## rowerwet (Jan 17, 2011)

the big energy savings with tankless is no heat loss from storage, since there are only two of you and you aren't using the water like your family did before, tankless would save you money from those losses.


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## semipro (Jan 17, 2011)

I've always thought that a perfect application of a tankless water heater would be using it with a solar water pre-heater with the tankless as close to the point of usage as possible. 

I realize the cost of multiple units might add up but I think the ideal scenario would be using a smaller tankless heater located at each point of use area (bath, kitchen, etc.) with solar preheat.


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## SolarAndWood (Jan 17, 2011)

Semipro said:
			
		

> I've always thought that a perfect application of a tankless water heater would be using it with a solar water pre-heater with the tankless as close to the point of usage as possible.
> 
> I realize the cost of multiple units might add up but I think the ideal scenario would be using a smaller tankless heater located at each point of use area (bath, kitchen, etc.) with solar preheat.



Makes a lot of sense to me.  You can get 3 2gpm units for the price of a single 4gpm and you don't have to deal with 120 amps.  I'm tempted to go this route now and just run 2 2 gpms in series until I get the preheat done.  Its a lot less money than the heat pump and wood or solar preheat trumps the efficiency of the heat pump.


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## semipro (Jan 17, 2011)

SolarAndWood said:
			
		

> Semipro said:
> 
> 
> 
> ...



I could look it up but you probably know of the top of your head..  How many amps do the 2.2 gpm unit pull?  I'm assuming its 240v.


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## SolarAndWood (Jan 17, 2011)

They need a 60 amp circuit.


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## pyper (Jan 18, 2011)

If you have a well insulated tank and turn off the heating element, the water will stay hot for a long time. Days.

My conclusion, based on this fact, is that it doesn't take much energy (whatever the source) to keep water in a water heater hot. Most of the energy is used to initially heat the water.

Here's something about the way the gas tankless heaters work. You might want to investigate the electric to see if there is a similar problem. Suppose you're washing dishes. The way many people wash dishes involves turning the hot water on and off numerous times. Well, with my tankless heater, every time you turn the water off, the heater goes out. Otherwise it would boil the water and blow up the pipes. Then when you turn on the water, a little cold goes through the system before it gets the heater turned back on. As a result, you end up with a blast of cold water on the hot side. In order to avoid the cold water, I'd need to leave the hot running for longer periods of time.


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