tankless and a electric water heater together

[nocita1]

Hello , I am wondering if I can put a tankless hot water heater together with a tank heater I must run more than one appliance at once maybe three or four I was wondering if I could put a tankless system in the cold water line above the tank so that incoming water was already heated .this way as the tank is draining ,the water comming in is already hot I must find a way as I am constatly running out of hot water .
If any one has any ideas please let me know

Thank you

[Bruce S]

It'll work, since you will be using the incoming cold water. My worry is about the running out of hot water from the "other" tank.
Is it pretty old? most newer 30 gal and above electric or gas powered tanks have high-demand settings that would at least heat part of the water.

On-demand units can be sized to allow more than one device to be used...

Come back with a bit more info for a more complete answer.
What devices are you using at the same time that uses Sooo much hot water?

Bruce S
 

[nocita1]

It'll work, since you will be using the incoming cold water. My worry is about the running out of hot water from the "other" tank.
Is it pretty old? most newer 30 gal and above electric or gas powered tanks have high-demand settings that would at least heat part of the water.

On-demand units can be sized to allow more than one device to be used...

Come back with a bit more info for a more complete answer.
What devices are you using at the same time that uses Sooo much hot water?

Bruce S
  thanks for the quick reply, I use this system in my hair salon spa. even with two tanks we run out expecillay on a Saturdays. tanks are quite new the demand is just to much. I figured that if the incoming water was already heated the storage tanks would have to work much less to maintain hot water

[nocita1]

thanks for the quick reply, I use this system in my hair salon spa. even with two tanks we run out expecillay on a Saturdays. tanks are quite new the demand is just to much. I figured that if the incoming water was already heated the storage tanks would have to work much less to maintain hot water
 

[ghurd]

I do not know about the efficiency of this idea,
but I think it would be cheaper to preheat the water with another regular hot water heater as a preheater for the other 2.

If the pipes can be accessed between the heaters and the faucets, simply insultaing the pipes will make a remarkable difference in the ratio of Hot to Cold volumes, meaning the hot water will be in the tank longer to be heated.

My parents home has about a 75' run from the heater to one of the baths.  After insulating the hot water pipe, they use a LOT less hot water.
G-

[nocita1]

I hear you. did what your parents did at my house works well. but at he salon even with four tanks we run out. we now use two higher efficiency tanks instead of four but we are out of water before one o'clock on Saturdays .
 can my idea work? if incoming water is forty degrees hotter then you could almost use that on its own, with the tanks more for storage ,and they would heat more so when theres a break in the salon .
 These are only ideas I am trying to get as I need help figuring this out.
Thanks alot for your response

[kensue49]

How many stations?
I would think if you can't get enough hot water once a week you could put 110 volt tankless WH at each station(sink) and use the standard water heaters as pre-heaters.
Costly up front but may save you KwH in the long run and you would have more hot water with better flow.
Kenneth

[Simen]

Sounds to me that an air-water heat pump would suit your needs to pre-heat cold water to around 40-45C...

[nocita1]

Problem here is that even 110 voltsystems require a dedicated breaker . I am in a shopping mall where i can't run wires.
there are 5 sink stations ,4 pedicure stations ,5 manicure stations, and a hydro therapy tub .
 that is why I was hoping to fit the tankless in line. I have the room being that the panel and the tanks are in the same room wiring an water one place all connections so will it work you think.

[ghurd]

An electric takes like 60 to 90 minutes to recover?

You do not say how big the tanks are (or if they are electric or gas).  Total gallons / 1 hour is less than what your average flow is?
And pretty sure that is going to be more than a gallon / minute.
And if the new "two higher efficiency tanks" are 80 gallons, then your flow is crazy high.

No way you will find a plug in tankless unit that can handle that kind of flow.

If you can not run wires, that pretty much limits you to nothing worth a hoot.
But even a small tankless system before each heater would help.
Could maybe parallel 2 tankless units before each heater to get the flow up.

Strange things running through my mind...
Almost seems like it would work better if the 2 existing units were in series than in parallel.
G-
Edit- I see it states electric in the title.

[kensue49]

It may work as a pre-heater if -
1. It has a large enough flow for the heat rise needed.
2. You have the available electrical connection, but a gas tankless system would be better.

You will help your situation but not cure it.
You may still run out of hot water.
The tankless WH internal pipe size and flow to heat rise will be the key to a better out come for you.

Your Hydro Therapy tub is probably the biggest user of hot water so you could dedicate a tankless WH to that usage and use one for
preheating the incoming water.

A tankless system will reduce the water flow to enable it to raise the water temp to your temp setting so check your flow to temp rise on any unit you look at.

[kensue49]

Ghurd,
Series the tanks and hang a tankless pre-heater on in coming water and a tankless post heater on the out going water.
Set the pre-heater to raise the water temp from say 50 degrees to 70 degrees and set the post heater to the desired temp, probably set  at 140 degrees now to try and over come the lack of hot water volume needed. Tank one then set at 90 to100 and tank two at 120.
Post tankless water heater set at 120.
It is very wasteful but may meet the needs from 1:00 Saturday until closing time.
Kenneth

[nocita1]

Thanks all of you for your replies. I just figured that by putting a tankless in the cold water line before the water tanks {electric} would heat the water up by 40 degrees ,and then the tanks would not have to heat as much water comes in at 55 degrees .and 50 more from the tankless would make 100. witch is more that the 50 degrees that we used on Saturdays 90 degrees is better than 50

[Bruce S]

Thanks all of you for your replies. I just figured that by putting a tankless in the cold water line before the water tanks {electric} would heat the water up by 40 degrees ,and then the tanks would not have to heat as much water comes in at 55 degrees .and 50 more from the tankless would make 100. witch is more that the 50 degrees that we used on Saturdays 90 degrees is better than 50

Going this route will certainly help on the recovery route. Since you're in a mall type setting I'm thinking it'll be an electric one. Only issue will be the electric wiring to run to the tankless unit, I would personally go for the higher voltage ones say 240 or above. They of course do not heat unless water flow is detected so that will also give the other water heater some work to do.
Flow is another issue most of the ones I've looked at max flow at 3gpm, so this may be a sizable issue for you.

Best of luck

Bruce S
 

[kensue49]

Good Luck and let us know what works.

[nocita1]

Thank all of you for the help. yes it is electric and I'm hoping that when the water in the main tank goes down a little, it is usually replaced with cold. now it will be replaced with hot witch is better than cold city water, as far as the temp goes I hope i'm right

[wingman1776]

I do plumbing for  living if you get a properly sized instant water heater you can get rid of the tank ones and run hot water all day long and not ever run out.

[Bruce S]

I do plumbing for  living if you get a properly sized instant water heater you can get rid of the tank ones and run hot water all day long and not ever run out.

His problem is a unique one, he has a very high-demand office usage that may very well overwhelm a tankless unit. At least the units I'm able to see. I'm sure there are commercial grade units, but the flow rates are still much lower than just a couple of the wash basins they use will go through.

Since he already has the electric ones in place, to me it would be a good in-place bumper to put one in place to help to others.

I could be wrong I'm and no plumber, certainly update us with good commercial units with flow rates. I'm sure he would be delighted to see this work. In his biz hot water is a must.

Cheers
Bruce S

[kensue49]

Perhaps this one -
http://www.e-tankless.com/stiebel-eltron-tempra-36-tankless-water-heater.php
But this maybe over kill...maybe not.
With all the stations it may work.

[wingman1776]

ok what you need to do to size the unit you need it to find out how many gallons  min  you use at peak times and get a unit that will susport it. rember when you are looking check the temp rise compaired to the incoming water temp. if you have it a gas unit would be you best cheapest to operate choise. I recently installed a nortis 11 gpm unit it could run three showers 3 sinks all day long. they run about 1,400.00

[ghurd]

Perhaps this one -
http://www.e-tankless.com/stiebel-eltron-tempra-36-tankless-water-heater.php
But this maybe over kill...maybe not.
With all the stations it may work.

I kind of like the idea of that one.
Looks like it can deal with the hot water flow, even if it might not be able to keep up the temp at peak flow.  Most of the time, all 4 stations are not going full blast 100% duty cycle anyway.
Plus, you can turn it off on the slower days.

I doubt the mall would allow any flue.

I do a lot of plumbing too.
I fixed my own kitchen faucet 5 times one day! 
G-

[WindriderNM]

Sneak a solar system on the roof when know one is looking. LOL
If gas is available a gas tankless may work.
If you can figure out your flow is on Saturdays you can calculate how much power you need to heat that amount of water.
You may not have enough power to meet your demand.
Another idea is to put low flow faucets or flow restricters  on some of your equipment.

[Norm]

Whew!  All that hot water going down the drain ! My Mom's last husband would have loved this! He would have advised
you to install a  heat exchanger  that hot water going thru a heat exchanger before it went down the  drain would
easily preheat the incoming water.

[d34]

The easiest solution and probably the cheapest I can see is to have an electrician rewire the water heaters you have.  Most electric water heaters have 2 elements but only 1 is powered at any given time.  It would take adding an additional supply wire to each water heater so that each element works independently but would easily take care of your problem. 

[12AX7]

The easiest solution and probably the cheapest I can see is to have an electrician rewire the water heaters you have.  Most electric water heaters have 2 elements but only 1 is powered at any given time.  It would take adding an additional supply wire to each water heater so that each element works independently but would easily take care of your problem. 

I'm sure that this can be done,  but not as simple as it sounds.

I had a electric hot water heater several years ago and my memory is a little fuzzy.  I believe that there's only one thermostat and one over temp cutout.  in order to power both elements one would have to add both a second thermostat and an over temp cut out.

I think one would have to cut open the outer shell and "weld" some sort of mounting hardware for both devices. 

Additionally,  I'd suspect that one would be breaking codes somewhere,  probably both plumbing and electrical codes.
The alteration of a appliance and using two power feeds to one device.

[kensue49]

Dual Thermostatic controls-http://www.plumbinghelp.ca/water_heater_thermostat.php

[12AX7]

Dual Thermostatic controls-http://www.plumbinghelp.ca/water_heater_thermostat.php

I believe that the "dual" thermostat controls power to two heating elements but only one element at a time, and not both elements Simultaneously.
The dual element thermostat would not have the current ratings to switch both elements on/off Simultaneously.

[kensue49]

Right, my fast response without thinking. 
You would need two primary thermostats, another equal sized cable from another breaker.
Then it might work if you could balance the thermostats, it would use alot of power.