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Old 01-14-2012, 08:13 PM   #1
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questions about plumbing hot water tank


My other thread has me thinking about plumbing parts surrounding a hot water tank...

If you think about the simplest setup it would be a cold line going into the tank, and a hot line exiting the tank. I know there is also a T/P relief valve, but that's a part of the tank itself so for the moment I'll exclude that.

But there are some times other things surrounding the tank and I was hoping someone could help me understand when they are needed and how they are used....

- Thermal Expansion Tank -- What is this needed with a typical tank water heater? Is it usually installed on the cold (inlet) line or the hot (outlet) line? When you install it, do you mount it so that it's physically above the water line or below the line? Or does it not matter?

- Back Flow Valve -- In the diagrams I've seen, you have the cold line from the meter flow through a back flow valve, there is a thermal expansion tank T'd in, which continues into the cold inlet of the tank... What is a back flow valve required on the inlet of a tank water heater?

- "Heat Traps", etc -- Sometimes I hear of something called a "heat trap" in reference to a water heater... the idea is to have a vertical length of pipe that dead ends above the water heater...

- Mixing Valve -- Is it typical to have a mixing valve after a tank water heater? I'm guessing that since most people run their tanks in the 120-140*F range they aren't necessary?

- Flexible water lines -- Are those considered bad? I feel like I've read that they are against code in some areas, yet I'm certain that I've seen them sold and that many years ago I've helped friend's fathers install water heaters using them....

The last two rentals we lived in didn't have any of this stuff.. they just had a hot water tank with cold inlet going in and a hot outlet going out... it was really basic in that regard... I'm trying to figure out if those were mickey mouse jobs, or maybe these extra pieces are only for specific situations?

Last two questions--
- Water heater stands... that's only for gas fired and when it exists in a garage space where fumes might collect, is that right? Meaning if I were putting an electric water tank in my basement, I wouldn't need a stand right? I mean, I could get one if I wanted to keep the tank up off the ground in case of a small flood, but I suppose I could also use some cement blocks for that right?

- Straps... I live in MA, we don't have earthquakes, etc... but is it common to install those water tank straps in all places these days?

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Old 01-14-2012, 08:27 PM   #2
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Are you talking about a water heater?

Gas or electric?

To many words to read---

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Old 01-14-2012, 08:31 PM   #3
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What exactly are you planning on doing--what do you have now?---You are hoping someone will write an entire book explaining hydro dynamics---

Tell us what you are doing,please.
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Old 01-14-2012, 08:41 PM   #4
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Quote:
Originally Posted by bubbler View Post
My other thread has me thinking about plumbing parts surrounding a hot water tank...

If you think about the simplest setup it would be a cold line going into the tank, and a hot line exiting the tank. I know there is also a T/P relief valve, but that's a part of the tank itself so for the moment I'll exclude that.

But there are some times other things surrounding the tank and I was hoping someone could help me understand when they are needed and how they are used....

- Thermal Expansion Tank -- What is this needed with a typical tank water heater? Is it usually installed on the cold (inlet) line or the hot (outlet) line? When you install it, do you mount it so that it's physically above the water line or below the line? Or does it not matter?
Installed in the hot water line, sitting in an upright position, if at all.

- Back Flow Valve -- In the diagrams I've seen, you have the cold line from the meter flow through a back flow valve, there is a thermal expansion tank T'd in, which continues into the cold inlet of the tank... What is a back flow valve required on the inlet of a tank water heater?
Never have seen one on a water heater.

- "Heat Traps", etc -- Sometimes I hear of something called a "heat trap" in reference to a water heater... the idea is to have a vertical length of pipe that dead ends above the water heater...
Never heard of one and have never even seen one used.

- Mixing Valve -- Is it typical to have a mixing valve after a tank water heater? I'm guessing that since most people run their tanks in the 120-140*F range they aren't necessary?
One more thing to fail, If you have a newer shower control valve ones built in to it. If you have an elderly or handicaped person living in the house it would be a good idea.

- Flexible water lines -- Are those considered bad? I feel like I've read that they are against code in some areas, yet I'm certain that I've seen them sold and that many years ago I've helped friend's fathers install water heaters using them....
I use them all the time because almost never is the new tank exactly the same as the old one so it's easyer to hook up.

The last two rentals we lived in didn't have any of this stuff.. they just had a hot water tank with cold inlet going in and a hot outlet going out... it was really basic in that regard... I'm trying to figure out if those were mickey mouse jobs, or maybe these extra pieces are only for specific situations?

Last two questions--
- Water heater stands... that's only for gas fired and when it exists in a garage space where fumes might collect, is that right? Meaning if I were putting an electric water tank in my basement, I wouldn't need a stand right? I mean, I could get one if I wanted to keep the tank up off the ground in case of a small flood, but I suppose I could also use some cement blocks for that right?
Stands are code for a gas heater, The bottom of the tank if left in direct contact with concrete will rust.

- Straps... I live in MA, we don't have earthquakes, etc... but is it common to install those water tank straps in all places these days?
Code in CA not a bad idea any place if it's a gas heater or in a garage where someone may hit it.
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Old 01-14-2012, 08:47 PM   #5
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Originally Posted by oh'mike View Post
What exactly are you planning on doing--what do you have now?---You are hoping someone will write an entire book explaining hydro dynamics---

Tell us what you are doing,please.
I'm trying to learn about the components that might be installed with a typical tank water heater... electric or gas, tho I'd be doing electric.

My big Q's are: When you need an expansion tank? When do you need a backflow preventer?
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Old 01-14-2012, 09:01 PM   #6
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A back flow preventer is only needed when code requires it--that would be near the water meter.

An expansion tank is required on 50 gallon and larger units in this area---not a bad idea with any size unit.

Most house equipped with aback flow preventer require an expansion tank on all heaters.

I will leave the fine code details for a licensed plumber to answer.
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Old 01-15-2012, 10:28 AM   #7
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Quote:
Originally Posted by oh'mike View Post
What exactly are you planning on doing--what do you have now?---You are hoping someone will write an entire book explaining hydro dynamics---

Tell us what you are doing,please.

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Old 01-15-2012, 12:03 PM   #8
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questions about plumbing hot water tank


Quote:
Originally Posted by bubbler View Post
I'm trying to learn about the components that might be installed with a typical tank water heater... electric or gas, tho I'd be doing electric.

My big Q's are: When you need an expansion tank? When do you need a backflow preventer?
Most of your questions are best answered by using google.
Here's a couple things. A backflow device is independent of a WH. It has to do with the water system of your home as a whole. It's use is determined by the AHJ.
If your water supply has a BF device, PRV, or check valve then you need a exp. tank
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Old 01-15-2012, 07:30 PM   #9
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In my area of California, a back flow preventer is required when there is a chance that ground water or gray water can get pushed back into the water supply. You can use gray water for irragation....and in some cases, you have a tee so that you can water with both gray or potable....in that case, there has to be a back flow preventer.

Additionally, some cities require it when you have an automatic sprinkler system...I guess in some cases, water can get siphoned back into your main water supply.

The Expansion tank is required if there is any device that could block the water between the water heater and the water supply.
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Old 01-16-2012, 09:37 AM   #10
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Codes may require any or all of the items you mention.

Backflow preventer valve -- Importance IMHO is low if you don't have "hard wired" lawn sprinklers. Your water company may or may not require this on the cold water pipe just entering the house (or out at the meter).

Thermal expansion tank -- Importance is high. Each new tankful of water expands a little when heated and will trip the temperature & pressure relief valve if there is a backflow preventer and no expansion tank.

Mixing valve -- Importance is medium. Goes between cold inlet and hot outlet, above the water heater, to reduce scalding when you use the hot water. Not really needed if you set the water temperature to 120 degrees or less.

Dielectric Union -- Importance is low. What looks like a short section of pipe that looks different, one on the inlet and one on the outlet of the water heater. Slows down corrosion where copper water pipes meet the steel nipples at (or tank itself of) the water heater.

Flexible water lines -- Check with your city to see if they are permitted. It is best not to re-use old ones for a new water heater because they can take only a finite amount of flexing before a crack develops somewhere.

Heat Trap Nipples -- Importance is low. Look like dielectric unions and are the first pipe segments attached to the water heater. The purpose is to reduce heat loss from eddies, or tiny water currents going up out of the tank into the pipes and back down into the tank when nobody is using hot water. They behave like partial check valves and can malfunction causing what appears to be a clogged hot water line.

Straps keep the water heater from tipping over during an earthquake. Exactly how it fell and how the burner operates could result in the burner staying on or the gas pipe snapping off and causing a fire. Depending on how they are routed and provided they are rigid metal, the inlet and hot water pipes will keep the water heater from tipping over.
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Old 01-16-2012, 06:03 PM   #11
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Flexible Water lines are code almost everywhere in the United States. There are only a few weird cities here and there that don't allow them (Lincoln, NE). If you're in CA, I think flex on a water heater should be required because of earthquakes. Do you think copper hard piping is going to survive any large earthquake? VERY doubtful.

Just keep in mind that copper flex is a terrible idea. It work hardens immediately after bending and will flatten, kink, or crack if you try to re-bend. Unless of course you have a hydrogen-heated oven and want to re-anneal your copper! LOL.

Honestly, I think the best solution is corrugated stainless steel flex. I put a new water heater in my house a year ago or so and I ended up finding my stainless flex through Falcon Stainless. There are lots of companies out there making SS flex, but Falcon was the only I found with a lifetime warranty, which is why I went with them. Here's their website if you want to check 'em out. www.falconstainless.com.

Hope that helps!

-Rob
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Old 01-16-2012, 06:19 PM   #12
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wow! cold water supply line in, hot water line out. gas line in and vent out.
that is as simple as it gets.
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Old 01-18-2012, 12:55 AM   #13
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I was not being funny. Unless the code has changed, that is what is needed to plumb water heater in my neighborhood.

Last edited by Hardway; 01-18-2012 at 12:58 AM.
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Old 01-18-2012, 07:43 AM   #14
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I was not being funny. Unless the code has changed, that is what is needed to plumb water heater in my neighborhood.
That's what I've seen on most of the installs in this area as well, so I suspect that its all that's required here.

The only thing that I can see maybe being required (or at least a very good idea) is the expansion tank, otherwise you're relying on either being able to push that water back out to the street, or your T/P relief valve opening.

But, it's still good to ask the Q's of the pro's because I'm sure there was a point in time where people were saying "hot and neutral wire, that's all that's required in this area"... but now we have grounds, GFCI's, etc...

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