I currently have a standard 40 gallon electric water heater on a 30
amp breaker. The panel is 100A service which also services an electric
dryer. I was thinking about getting a tankless water heater to save
space, but after reading some electrical specs on these units, it
seems I would have some issues with the electric.

I have 1 bathroom and 1 kitchen and a washer. From the calculations I
would need at least a 5 gpm unit.
If you look at the specs for the Rheem units, the RT18 needs 2
seperate 40A circuits, with maximum power being 75 amps.

http://globalimageserver.com/fetchDo...2-5934e3043c7d

Obviously my panel cannot support that. I could maybe drop to the RT9
unit that requires 1- 40A breaker, but I'm concerned it might be
undersized at 3 GPM, and also concerned that it uses 38 amps. If my
dryer is on, thats another 26 amps, and my 220V water pump using 5
amps, totaling about 70 amps.
That leaves me with about 30 amps to spare.
So I could either upgrade my panel, or just stick with what I have.
This is for a seasonal home in the summer. Just wondering what
everyone else thinks I should do.

On Wed, 3 Aug 2011 17:05:44 -0700 (PDT), Mikepier
wrote:

I currently have a standard 40 gallon electric water heater on a 30
amp breaker. The panel is 100A service which also services an electric
dryer. I was thinking about getting a tankless water heater to save
space, but after reading some electrical specs on these units, it
seems I would have some issues with the electric.

I have 1 bathroom and 1 kitchen and a washer. From the calculations I
would need at least a 5 gpm unit.
If you look at the specs for the Rheem units, the RT18 needs 2
seperate 40A circuits, with maximum power being 75 amps.

http://globalimageserver.com/fetchDo...2-5934e3043c7d

Obviously my panel cannot support that. I could maybe drop to the RT9
unit that requires 1- 40A breaker, but I'm concerned it might be
undersized at 3 GPM, and also concerned that it uses 38 amps. If my
dryer is on, thats another 26 amps, and my 220V water pump using 5
amps, totaling about 70 amps.
That leaves me with about 30 amps to spare.
So I could either upgrade my panel, or just stick with what I have.
This is for a seasonal home in the summer. Just wondering what
everyone else thinks I should do.

Do you have Natural Gas or Propane in the home?

Guide for a little help...

http://www.tanklesswaterheaterguide.com/

On Wed, 03 Aug 2011 18:18:38 -0700, Oren wrote:

On Wed, 3 Aug 2011 17:05:44 -0700 (PDT), Mikepier
wrote:

I currently have a standard 40 gallon electric water heater on a 30
amp breaker. The panel is 100A service which also services an electric
dryer. I was thinking about getting a tankless water heater to save
space, but after reading some electrical specs on these units, it
seems I would have some issues with the electric.

I have 1 bathroom and 1 kitchen and a washer. From the calculations I
would need at least a 5 gpm unit.
If you look at the specs for the Rheem units, the RT18 needs 2
seperate 40A circuits, with maximum power being 75 amps.

http://globalimageserver.com/fetchDo...2-5934e3043c7d

Obviously my panel cannot support that. I could maybe drop to the RT9
unit that requires 1- 40A breaker, but I'm concerned it might be
undersized at 3 GPM, and also concerned that it uses 38 amps. If my
dryer is on, thats another 26 amps, and my 220V water pump using 5
amps, totaling about 70 amps.
That leaves me with about 30 amps to spare.
So I could either upgrade my panel, or just stick with what I have.
This is for a seasonal home in the summer. Just wondering what
everyone else thinks I should do.

Do you have Natural Gas or Propane in the home?

Guide for a little help...

http://www.tanklesswaterheaterguide.com/
PARTICULARLY in a summer seasonal home you do NOT want a tankless
heater - for SO MANY reasons. Particularly if you have ANY water
issues. They are high maintenance items at the best of times.

As the othe fine person inquired, do you have propane or
natural gas? Either of those is much less expensive for
heat. My sense is that you should leave the 40 gal tank
until it leaks, and then retrofit for a 40 gal gas water
heater.

Considering the cost of the heater, and the upgrade, and the
plumber, you're really spending a boat load of money for
very little storage space. You could buy an outdoor
Rubbermaid storage shed and a padlock, and have a bit of
money left over.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"Mikepier" wrote in message
...
I currently have a standard 40 gallon electric water heater
on a 30
amp breaker. The panel is 100A service which also services
an electric
dryer. I was thinking about getting a tankless water heater
to save
space, but after reading some electrical specs on these
units, it
seems I would have some issues with the electric.

I have 1 bathroom and 1 kitchen and a washer. From the
calculations I
would need at least a 5 gpm unit.
If you look at the specs for the Rheem units, the RT18 needs
2
seperate 40A circuits, with maximum power being 75 amps.

http://globalimageserver.com/fetchDo...2-5934e3043c7d

Obviously my panel cannot support that. I could maybe drop
to the RT9
unit that requires 1- 40A breaker, but I'm concerned it
might be
undersized at 3 GPM, and also concerned that it uses 38
amps. If my
dryer is on, thats another 26 amps, and my 220V water pump
using 5
amps, totaling about 70 amps.
That leaves me with about 30 amps to spare.
So I could either upgrade my panel, or just stick with what
I have.
This is for a seasonal home in the summer. Just wondering
what
everyone else thinks I should do.

"Stormin Mormon" wrote in message
...
As the othe fine person inquired, do you have propane or
natural gas? Either of those is much less expensive for
heat. My sense is that you should leave the 40 gal tank
until it leaks, and then retrofit for a 40 gal gas water
heater.

Considering the cost of the heater, and the upgrade, and the
plumber, you're really spending a boat load of money for
very little storage space. You could buy an outdoor
Rubbermaid storage shed and a padlock, and have a bit of
money left over.

--
Christopher A. Young
Learn more about Jesus
www.lds.org


Agree that the current service capacity rules out
electric tankless. The other option would be gas,
but if space savings is the main attraction, agree with
the above, that it's an expensive way to get a very
small space.
And depending on how a gas unit gets vented,
where it is, running gas pipes to it, etc, you may not
have any usable space anyway.





.


"Mikepier" wrote in message
...
I currently have a standard 40 gallon electric water heater
on a 30
amp breaker. The panel is 100A service which also services
an electric
dryer. I was thinking about getting a tankless water heater
to save
space, but after reading some electrical specs on these
units, it
seems I would have some issues with the electric.

I have 1 bathroom and 1 kitchen and a washer. From the
calculations I
would need at least a 5 gpm unit.
If you look at the specs for the Rheem units, the RT18 needs
2
seperate 40A circuits, with maximum power being 75 amps.

http://globalimageserver.com/fetchDo...2-5934e3043c7d

Obviously my panel cannot support that. I could maybe drop
to the RT9
unit that requires 1- 40A breaker, but I'm concerned it
might be
undersized at 3 GPM, and also concerned that it uses 38
amps. If my
dryer is on, thats another 26 amps, and my 220V water pump
using 5
amps, totaling about 70 amps.
That leaves me with about 30 amps to spare.
So I could either upgrade my panel, or just stick with what
I have.
This is for a seasonal home in the summer. Just wondering
what
everyone else thinks I should do.

Large cost, small gain. Overall, a pain in the gas. And only
for a couple months a year. Not much return.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"." wrote in message
...

"Stormin Mormon" wrote
in message
...
As the othe fine person inquired, do you have propane or
natural gas? Either of those is much less expensive for
heat. My sense is that you should leave the 40 gal tank
until it leaks, and then retrofit for a 40 gal gas water
heater.

Considering the cost of the heater, and the upgrade, and
the
plumber, you're really spending a boat load of money for
very little storage space. You could buy an outdoor
Rubbermaid storage shed and a padlock, and have a bit of
money left over.

--
Christopher A. Young
Learn more about Jesus
www.lds.org


Agree that the current service capacity rules out
electric tankless. The other option would be gas,
but if space savings is the main attraction, agree with
the above, that it's an expensive way to get a very
small space.
And depending on how a gas unit gets vented,
where it is, running gas pipes to it, etc, you may not
have any usable space anyway.

On 8/3/2011 8:05 PM, Mikepier wrote:
I currently have a standard 40 gallon electric water heater on a 30
amp breaker. The panel is 100A service which also services an electric
dryer. I was thinking about getting a tankless water heater to save
space, but after reading some electrical specs on these units, it
seems I would have some issues with the electric.

I have 1 bathroom and 1 kitchen and a washer. From the calculations I
would need at least a 5 gpm unit.
If you look at the specs for the Rheem units, the RT18 needs 2
seperate 40A circuits, with maximum power being 75 amps.

http://globalimageserver.com/fetchDo...2-5934e3043c7d

Obviously my panel cannot support that. I could maybe drop to the RT9
unit that requires 1- 40A breaker, but I'm concerned it might be
undersized at 3 GPM, and also concerned that it uses 38 amps. If my
dryer is on, thats another 26 amps, and my 220V water pump using 5
amps, totaling about 70 amps.
That leaves me with about 30 amps to spare.
So I could either upgrade my panel, or just stick with what I have.
This is for a seasonal home in the summer. Just wondering what
everyone else thinks I should do.


You can easily "do the math" and determine EXACTLY what the temperature
rise is when you run 40 amps at 240 volts through a water heater.

All that really matters is the temperature of the cold water coming in
and the flow rate.

If you are "marginal" you can help by reducing the flow rate and if your
cold water coming from outside is "too cold" you might want to help it
along by running it around the basement. It's important to "temper" the
cold water to the shower mixing valve since the warmer that water is,
the less "hot" water you will need for a comfortable shower.

I can give you a "data" point. We have a conventional electric water
heater. Even when I "run out" of hot water, if I run 100% hot water
into the shower, it's tolerable. Bottom line is that it depends on
just how hot you want your shower.

You first task is to: 1) measure the temperature of the cold water;
and 2) "do the math" and determine the temperature rise at various flow
rates; & 3) decide whether it's "gud enuf."

The only "justification" for a demand type hot water heater is to "save
energy" by not keeping 30/40 gallons of hot water sitting around &
heating up the basement. You can "save" much of that energy by adding
insulation to the heater, installing that gadget that prevent
circulation of the hot water above the heater (I think it's just a
"leaky" check valve), and if your circumstances permit, just shutting
down the water heater when you don't need it.

Frankly, the cost of a new panel or the equipment and wiring costs of a
"demand" WH will take years to recover.

I currently have a standard 40 gallon electric water heater on a 30
amp breaker. The panel is 100A service which also services an electric
dryer. I was thinking about getting a tankless water heater to save
space, but after reading some electrical specs on these units, it
seems I would have some issues with the electric.

I have 1 bathroom and 1 kitchen and a washer. From the calculations I
would need at least a 5 gpm unit.
If you look at the specs for the Rheem units, the RT18 needs 2
seperate 40A circuits, with maximum power being 75 amps.

http://globalimageserver.com/fetchDo...2-5934e3043c7d

Obviously my panel cannot support that. I could maybe drop to the RT9
unit that requires 1- 40A breaker, but I'm concerned it might be
undersized at 3 GPM, and also concerned that it uses 38 amps. If my
dryer is on, thats another 26 amps, and my 220V water pump using 5
amps, totaling about 70 amps.
That leaves me with about 30 amps to spare.
So I could either upgrade my panel, or just stick with what I have.
This is for a seasonal home in the summer. Just wondering what
everyone else thinks I should do.


*I would look into a solar water heater or something to boost the
temperature of the water going into your current water heater.

"John Gilmer" wrote in message
net...
On 8/3/2011 8:05 PM, Mikepier wrote:
I currently have a standard 40 gallon electric water heater on a 30
amp breaker. The panel is 100A service which also services an electric
dryer. I was thinking about getting a tankless water heater to save
space, but after reading some electrical specs on these units, it
seems I would have some issues with the electric.

I have 1 bathroom and 1 kitchen and a washer. From the calculations I
would need at least a 5 gpm unit.
If you look at the specs for the Rheem units, the RT18 needs 2
seperate 40A circuits, with maximum power being 75 amps.

http://globalimageserver.com/fetchDo...2-5934e3043c7d

Obviously my panel cannot support that. I could maybe drop to the RT9
unit that requires 1- 40A breaker, but I'm concerned it might be
undersized at 3 GPM, and also concerned that it uses 38 amps. If my
dryer is on, thats another 26 amps, and my 220V water pump using 5
amps, totaling about 70 amps.
That leaves me with about 30 amps to spare.
So I could either upgrade my panel, or just stick with what I have.
This is for a seasonal home in the summer. Just wondering what
everyone else thinks I should do.


You can easily "do the math" and determine EXACTLY what the temperature
rise is when you run 40 amps at 240 volts through a water heater.

All that really matters is the temperature of the cold water coming in and
the flow rate.

If you are "marginal" you can help by reducing the flow rate and if your
cold water coming from outside is "too cold" you might want to help it
along by running it around the basement. It's important to "temper" the
cold water to the shower mixing valve since the warmer that water is, the
less "hot" water you will need for a comfortable shower.

I can give you a "data" point. We have a conventional electric water
heater. Even when I "run out" of hot water, if I run 100% hot water into
the shower, it's tolerable. Bottom line is that it depends on just how
hot you want your shower.

You first task is to: 1) measure the temperature of the cold water; and
2) "do the math" and determine the temperature rise at various flow
rates; & 3) decide whether it's "gud enuf."

The only "justification" for a demand type hot water heater is to "save
energy" by not keeping 30/40 gallons of hot water sitting around & heating
up the basement.

There's another justification and that is availibility of an unlimited
amount of hot water, ie there is no tank to run
out.


You can "save" much of that energy by adding
insulation to the heater, installing that gadget that prevent circulation
of the hot water above the heater (I think it's just a "leaky" check
valve), and if your circumstances permit, just shutting down the water
heater when you don't need it.

Frankly, the cost of a new panel or the equipment and wiring costs of a
"demand" WH will take years to recover.

Thanks for all your inputs.

I have well water, so it is fairly cold. I think I'm just going to
stick with what I have for now.

On Aug 10, 9:20*am, Mikepier wrote:
Thanks for all your inputs.

I have well water, so it is fairly cold. I think I'm just going to
stick with what I have for now.

For what it's worth, on our vacation home I installed a 30amp double
pole wall switch in the hall and put the hw tank on it. When we are
not there it gets turned off.

On Aug 10, 9:26*am, jamesgangnc wrote:
On Aug 10, 9:20*am, Mikepier wrote:

Thanks for all your inputs.

I have well water, so it is fairly cold. I think I'm just going to
stick with what I have for now.

For what it's worth, on our vacation home I installed a 30amp double
pole wall switch in the hall and put the hw tank on it. *When we are
not there it gets turned off.

Yes, I aslo turn off the breaker to the water heater when I go away
for a week or 2. I also turn off the well pump.

On Aug 10, 12:08*pm, Mikepier wrote:
On Aug 10, 9:26*am, jamesgangnc wrote:

On Aug 10, 9:20*am, Mikepier wrote:

Thanks for all your inputs.

I have well water, so it is fairly cold. I think I'm just going to
stick with what I have for now.

For what it's worth, on our vacation home I installed a 30amp double
pole wall switch in the hall and put the hw tank on it. *When we are
not there it gets turned off.

Yes, I aslo turn off the breaker to the water heater when I go away
for a week or 2. I also turn off the well pump.

I think standard breakers really are not meant to be used as
switches. You can get breakers that are specifically rated for it. I
found it more convenient to install a real switch next to our
thermostat which we change when we leave too.

GPM tells how large the water pipe that goes through the water heater is, not the actually heating capacity. You have to pay attention to watts. An electric tankless water heater has perfect efficiency so there is a strict maths that tells you how hot it can make the water. What you need to know is how much water flow you are going to require, how hot is good enough for you and you incoming tap water temperature. This explains it much better:
http://toastyreviews.hubpages.com/hu...heater-reviews
If you decided to do tankless, you definitely need to get something bigger than you think you need. There is going to be some heat loss in the pipes etc. so you can never get a too powerful electric tankless water heater. That's why many people say tankless sucks. They get a small device and it doesn't heat enough.
I doubt Rheem RT9 will do any good even for a single person, unless you are in a really hot region. 15 watts is the minimum for tankless electric.

On Thursday, September 18, 2014 12:20:48 AM UTC-4, sol wrote:
GPM tells how large the water pipe that goes through the water heater is, not the actually heating capacity. You have to pay attention to watts. An electric tankless water heater has perfect efficiency so there is a strict maths that tells you how hot it can make the water. What you need to know is how much water flow you are going to require, how hot is good enough for you and you incoming tap water temperature. This explains it much better:

http://toastyreviews.hubpages.com/hu...heater-reviews

If you decided to do tankless, you definitely need to get something bigger than you think you need. There is going to be some heat loss in the pipes etc. so you can never get a too powerful electric tankless water heater. That's why many people say tankless sucks. They get a small device and it doesn't heat enough.

And the flip side is that a big one takes so many amps that it may
require upgrading the panel/service. Factor that in with the much lower
cost of an electric tank type unit and the tankless doesn;t look so
good. Also, many places have time of day metering now. If you can run
the electric tank WH during off peak, at night, etc, it can save a lot
in operating costs.



I doubt Rheem RT9 will do any good even for a single person, unless you are in a really hot region. 15 watts is the minimum for tankless electric.

You left out the K in Kwatts. I can see smaller ones used for special
applications, like if you had just a sink somewhere in a building that's
rarely used. That could be a good application for tankless and a small
one would fit. But I agree that you need a decent size one to do even
one bathroom with shower. Whole house gets worse. If you want tankless,
gas tankless looks much better, but I'm not a fan of those either, for
well known reasons, high initial cost being the main one.

On 9/17/2014 11:20 PM, sol wrote:
GPM tells how large the water pipe that goes through the water heater is, not the actually heating capacity. You have to pay attention to watts. An electric tankless water heater has perfect efficiency so there is a strict maths that tells you how hot it can make the water. What you need to know is how much water flow you are going to require, how hot is good enough for you and you incoming tap water temperature. This explains it much better:
http://toastyreviews.hubpages.com/hu...heater-reviews
If you decided to do tankless, you definitely need to get something bigger than you think you need. There is going to be some heat loss in the pipes etc. so you can never get a too powerful electric tankless water heater. That's why many people say tankless sucks. They get a small device and it doesn't heat enough.
I doubt Rheem RT9 will do any good even for a single person, unless you are in a really hot region. 15 watts is the minimum for tankless electric.


Can we agree to make that 15 AMPS, Sol?

Ah, I knew we couldg

for electric tankless figure at minimum 200 amps just to heat water, plus a different panel of 200 amps for everything else. at least a 100 amps but you might as well go 200 amps.

this will require 400 amps total, need new service drop and the power company may need to do upgrades on their side of the meter....

the payback is never...

a friend looked into this, he called it going green.

all in over 15 grand.

On Thursday, September 18, 2014 10:15:34 AM UTC-4, wrote:
On Thu, 18 Sep 2014 07:20:11 -0500, Unquestionably Confused

wrote:



Can we agree to make that 15 AMPS, Sol?



Ah, I knew we couldg



Not unless you are saying a tankless water heater is 3.6kw

Agree. I took that 15 W as a typo where he meant 15 KW. That seems
more likely, IMO.

On Wed, 17 Sep 2014 21:20:48 -0700 (PDT), sol
wrote:

GPM tells how large the water pipe that goes through the water heater is, not the actually heating capacity. You have to pay attention to watts. An electric tankless water heater has perfect efficiency so there is a strict maths that tells you how hot it can make the water. What you need to know is how much water flow you are going to require, how hot is good enough for you and you incoming tap water temperature. This explains it much better:
http://toastyreviews.hubpages.com/hu...heater-reviews
If you decided to do tankless, you definitely need to get something bigger than you think you need. There is going to be some heat loss in the pipes etc. so you can never get a too powerful electric tankless water heater. That's why many people say tankless sucks. They get a small device and it doesn't heat enough.
I doubt Rheem RT9 will do any good even for a single person, unless you are in a really hot region. 15 watts is the minimum for tankless electric.
15 THOUSAND watts - the RT9 is 9000 watts. On 240 volts that is 40
amps!! The big one is 37000 watts - 160 amps!!!!!

On Thu, 18 Sep 2014 10:15:34 -0400, wrote:

On Thu, 18 Sep 2014 07:20:11 -0500, Unquestionably Confused
wrote:

Can we agree to make that 15 AMPS, Sol?

Ah, I knew we couldg

Not unless you are saying a tankless water heater is 3.6kw
The one he wefferenced is 9kw

On 09/17/2014 11:20 PM, sol wrote:

15 watts is the minimum for tankless electric.


Now I'm wondering how long it would take that 15 watt water heater to
heat enough water for a bath.

Probably forever, since it cools off faster than it heats. 0% efficiency.

A 15kw heater (62 amps at 240v) will give you about 45 degrees above

the input water temperature at 3 gallons a minute.


assuming your delt T is in F degrees
I get 19.8 kW

using 3.785 kg per gallon and a specific heat of 4.187 J/g K

it is interesting at $0.15 per kW hour it costs about 5 cents a minute to take a shower.

also a 45 deg F rise is a pretty cold shower, need more like 70 F rise, 50 to 120...no?

Mark

sol wrote:
GPM tells how large the water pipe that goes through the water heater is, not the actually heating capacity. You have to pay attention to watts. An electric tankless water heater has perfect efficiency so there is a strict maths that tells you how hot it can make the water. What you need to know is how much water flow you are going to require, how hot is good enough for you and you incoming tap water temperature. This explains it much better:
http://toastyreviews.hubpages.com/hu...heater-reviews
If you decided to do tankless, you definitely need to get something bigger than you think you need. There is going to be some heat loss in the pipes etc. so you can never get a too powerful electric tankless water heater. That's why many people say tankless sucks. They get a small device and it doesn't heat enough.
I doubt Rheem RT9 will do any good even for a single person, unless you are in a really hot region. 15 watts is the minimum for tankless electric.

Hi,
1 BTU/hr is ~0.3W