Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 10-15-2008, 02:23 PM   #16
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,055
Share |
Default

Tankless or tank, but not both


Small volume tankless are usually around 10, or 12KW.

beenthere is offline   Reply With Quote
Old 10-15-2008, 02:25 PM   #17
Member
 
Join Date: Sep 2008
Location: Portland, OR
Posts: 1,186
Default

Tankless or tank, but not both


Quote:
Originally Posted by gp_wa View Post
Marvin, you described almost exactly what I have in mind. Except for the part about 1000 gallons of hot water.

The difference is, because my house is all electric, I want a smallish tankless (under 100 amps) that will not keep up with heavy demand if it's fed with ground temp water. Even when solar is not working (at night, on dark cloudy days, etc.) I need to maintain warm water in the tank. I just don't want the tank and the tankless going full blast at the same time, which might occur during the tail end of filling the bath tub.
There is no reason to have a tanked water heater with solar hot water panels. It is counter productive and there is no savings on energy cost if you factor in the cost of the solar hot water system.

For this reason I would go with a tankless that will meet your needs should the sun not shine for a few days at a time.

I know nothing about the electrical demands of a tankless. I only do gas and propane. That information would have to come from someone who is more experienced with those.

I suppose as a backup you could have a switch that would turn on the tanked water heater. If you had the tanked heater set for 125 degrees and the tankless set for 118 degrees the tankless would not come on since the water is already above the threshold of the tankless.

Just an FYI on saving more on energy costs with a tankless. They can be controlled remotely as to temperature settings. When I am filling the Jacuzzi I turn the temperature down to 108 degrees. This way I don't have to heat the water to 120 and the cool it down with some cold water. This a pure energy going to waste.

That information was free and you won't be charged extra for it.....oh wait, this is all free so nevermind.

But moving on here.

If you have a 120 gallon of hot water at 140 degrees and want to fill your 50 gallon tub to 108 degrees you would need roughly 40 gallons of hot and 10 of cold to make that happen (too busy to do the actual math right now).

This would leave you with 80 gallons of 140 degree water in the tank being mixed with 55 degree ground water and give you 120 gallons of about 95 degree water. Still pretty warm.

So a tankless would heat the water from 95 to 108 which would not require a lot of energy or a big tankless to get the job done.

If your demands are higher then there are other options for storage which is hard to beat. When you have solar hot water panels there is nothing like having lots of storage.

The commercial heat exchangers are expensive. You could have a custom one made that would be bigger and just have the heating coil for the solar panels. Then put that in a insulate it real heavy. My guess with 120 gallon commercial tank going for about $1500 you could have one made twice that size for less money.

Just an idea.
__________________
My idea of a perfect day: No where to go and all day to get there.

Last edited by Marvin Gardens; 10-15-2008 at 02:28 PM.
Marvin Gardens is offline   Reply With Quote
Old 10-15-2008, 02:46 PM   #18
DIY
 
Join Date: Aug 2008
Location: Seattle, WA
Posts: 162
Default

Tankless or tank, but not both


Quote:
Originally Posted by Marvin Gardens View Post
There is no reason to have a tanked water heater with solar hot water panels.
I think we're missing each other here...

As long as the solar collector is able to keep the tank temp above ITS set point, the element will never come on. The only reason to have an element in the tank at all, is to guarantee enough heat to make a < 100 amp tankless sufficient, even in the dead of winter, when the solar isn't saving me anything anyhow.

I'm planning to use my existing 50 gal tank with an external heat exchanger and see how that does. If it's not enough, I can always upgrade later.
gp_wa is offline   Reply With Quote
Old 10-15-2008, 02:53 PM   #19
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,055
Default

Tankless or tank, but not both


Quote:
Originally Posted by Marvin Gardens View Post

Just an FYI on saving more on energy costs with a tankless. They can be controlled remotely as to temperature settings. When I am filling the Jacuzzi I turn the temperature down to 108 degrees. This way I don't have to heat the water to 120 and the cool it down with some cold water. This a pure energy going to waste.



If you have a 120 gallon of hot water at 140 degrees and want to fill your 50 gallon tub to 108 degrees you would need roughly 40 gallons of hot and 10 of cold to make that happen (too busy to do the actual math right now).

This would leave you with 80 gallons of 140 degree water in the tank being mixed with 55 degree ground water and give you 120 gallons of about 95 degree water. Still pretty warm.
Actually, it would be about 19.6 gallons of 55 water mixed with 30.4 gallons of 140 to give you 50 gallons of 108 water.
And it would use the same amount of electric weather mixing 30.4 gallons of hot water from a tankless at 140, or a tankless heating the full 50 gallons of water.(Actually, the mixing would use 500 watts less).

The only time that makes a real differrence, is if you are billed for your electric by demand/rate of use.

Tankless only save money because you only heat what you are using.
So you virtually have no standby loss.
beenthere is offline   Reply With Quote
Old 10-15-2008, 03:07 PM   #20
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,055
Default

Tankless or tank, but not both


A 12,000 watt(50 amp at 240 volt) tankless will provide 1.1 GPM at 70 temp rise. That would be at 55 entering water temp raised to 125.

So even if your tank was depleted of warm water, the tankless can provide what you need without he tank having to use electric.
beenthere is offline   Reply With Quote
Old 10-15-2008, 03:13 PM   #21
DIY
 
Join Date: Aug 2008
Location: Seattle, WA
Posts: 162
Default

Tankless or tank, but not both


Quote:
Originally Posted by beenthere View Post
So even if your tank was depleted of warm water, the tankless can provide what you need without he tank having to use electric.
What makes you think I only need 1.5 GPM? That's not much water...

Also keep in mind that a tank should lose less heat at 90* than it will at 130* or 140*, so it's somewhat incorrect to compare the maintenance losses in my scenario to a conventional tank installation.

And to add... 90* is simply the lowest setting on your average tank heater. If 90* is overkill, I can either disable it find a way to regulate it at a lower temperature.
gp_wa is offline   Reply With Quote
Old 10-15-2008, 03:31 PM   #22
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,055
Default

Tankless or tank, but not both


A standard 40 gallon electric water heater, only provides, 1.1 gallons a minute first hour at same temp rise, after that, its depleted.

Its main advantage is that since you have 40 gallons stored, you can tap 4 gallons a minute for 10 minutes. Which makes it seem like you have a lot of hot water available.
But after that 10 minutes, you will be waiting for it to catch back up.
beenthere is offline   Reply With Quote
Old 10-15-2008, 03:39 PM   #23
DIY
 
Join Date: Aug 2008
Location: Seattle, WA
Posts: 162
Default

Tankless or tank, but not both


Quote:
Originally Posted by beenthere View Post
Its main advantage is that since you have 40 gallons stored, you can tap 4 gallons a minute for 10 minutes.
Right. I don't want to install a system that can't provide similar short term performance to the existing tank-only system. Gawd forbid someone might want to wash their hands in the kitchen sink while someone else is taking a shower...
gp_wa is offline   Reply With Quote
Old 10-15-2008, 03:46 PM   #24
Member
 
Join Date: Jul 2007
Posts: 1,590
Default

Tankless or tank, but not both


Quote:
Originally Posted by beenthere View Post
A standard 40 gallon electric water heater, only provides, 1.1 gallons a minute first hour at same temp rise, after that, its depleted.

Its main advantage is that since you have 40 gallons stored, you can tap 4 gallons a minute for 10 minutes. Which makes it seem like you have a lot of hot water available.
But after that 10 minutes, you will be waiting for it to catch back up.
But at 1.1 gallon per minute being heated in real time by a tankless it take 45 minutes to fill that 50 gallon Jacuzzi?

The tanked heater/storage in combo with a tankless will fill it much faster because he can put a lot higher water flow through the tankless since he is only bumping the temp up 18 degrees at most and probably a lot less than that.
jogr is offline   Reply With Quote
Old 10-15-2008, 03:52 PM   #25
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,055
Default

Tankless or tank, but not both


With 90F water in the tank. A 12 KW tankless can provide 2 gallons a minute, at 130F.(a 40F temp rise)

When the tank is depleted(actually, after about 10 to 15 gallons are drawn from the tank) And both the tankless and the tanks element are on. You will be at 16.5KW.
Or, an amp draw of 68.75 at 240 volts.




PS: You might want to check the pressure drop through the tankless.
Opening a second faucet at the same time someone is showering, may drop off the hot water flow in the shower.
beenthere is offline   Reply With Quote
Old 10-15-2008, 03:58 PM   #26
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,055
Default

Tankless or tank, but not both


Quote:
Originally Posted by jogr View Post
But at 1.1 gallon per minute being heated in real time by a tankless it take 45 minutes to fill that 50 gallon Jacuzzi?

The tanked heater/storage in combo with a tankless will fill it much faster because he can put a lot higher water flow through the tankless since he is only bumping the temp up 18 degrees at most and probably a lot less than that.
Actually, closer to 30 minutes. You would be mixing in cold water to bring the water temp down some.
beenthere is offline   Reply With Quote
Old 10-15-2008, 04:01 PM   #27
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,055
Default

Tankless or tank, but not both


If he gets a 20KW tankless, he could fill the 50 gallon tub in 19 minutes, with incoming water temp at 55, and raising it to 108.
beenthere is offline   Reply With Quote
Old 10-15-2008, 04:04 PM   #28
DIY
 
Join Date: Aug 2008
Location: Seattle, WA
Posts: 162
Default

Tankless or tank, but not both


I am considering an 18KW unit, possibly a little higher. That would draw 75 amps at full power. With a 5500 watt in-tank element, I'm up to 98 amps. I'd rather draw 75 than 98 at peak usage. That would enable me to use a 100 amp sub panel and main breaker, and have enough juice for both water heaters (if they don't run simultaneously) and solar pump(s), and hopefully plenty of hot water almost all the time.
gp_wa is offline   Reply With Quote
Old 10-15-2008, 04:23 PM   #29
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,055
Default

Tankless or tank, but not both


There is nothing wrong with over kill.


What size is your current electrical service.

Have you checked to see if it can handle the additional load.
beenthere is offline   Reply With Quote
Old 10-15-2008, 04:33 PM   #30
DIY
 
Join Date: Aug 2008
Location: Seattle, WA
Posts: 162
Default

Tankless or tank, but not both


Quote:
Originally Posted by beenthere View Post
There is nothing wrong with over kill.
That's pretty much my view on things

Quote:
Originally Posted by beenthere View Post
What size is your current electrical service.
200. And remember, all electric house with 9 KW backup heat.

Quote:
Originally Posted by beenthere View Post
Have you checked to see if it can handle the additional load.
I should be OK if I stay under 100 amps. There is always the potential to pop the main if somebody runs a bath while a turkey is roasting and the dryer is running and I'm sticking two pieces of metal together out in the shop while the air compressor runs. I'm not quite sure how you reconcile a load calculation with real world usage.

gp_wa is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Low hot water pressure crebive Plumbing 38 02-26-2013 12:26 AM
Toilet jpark Plumbing 18 01-05-2009 07:12 AM
No water pressure in my pressure tank GordH Plumbing 6 05-18-2008 11:19 AM
Upstairs toilet pipe noise bliss Plumbing 8 01-10-2008 07:55 AM
Tank vs. Tankless Irishman General DIY Discussions 11 08-22-2007 10:09 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.