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shader · Mar 18, 2007, 07:46 AM

Any reason to install, or not to install, a shut off valve in the hot water line at the water heater? Any safety concerns by shutting the hot water at the heater? I’ve seen several installations with shut offs in the hot supply, but the majority are without. Never could get a firm answer on the pros & cons of a hot water shut off… Thanks

coolpj · Mar 18, 2007, 08:31 AM

Well, in my humble opinion, a shut-off valve at the main hot water line (directly at the water heater) is a must for two reasons:

1- For maintenance purposes, and if you need to take the water heater out.
Having shut-off valves before and after the heater would be of practical use, in that case.

2- I you decide to shut off the hot water only and leave the cold water. This valve would come in handy.
For example, if, for any reason, your hot water piping need replacement, or repair, you could use this valve to turn off the hot water and then let it flow again after the repairs are done.

Regards,

Paul

iamgrowler · Mar 18, 2007, 09:03 AM

Originally Posted by shader

Any reason to install, or not to install, a shut off valve in the hot water line at the water heater? Any safety concerns by shutting the hot water at the heater? I’ve seen several installations with shut offs in the hot supply, but the majority are without. Never could get a firm answer on the pros & cons of a hot water shut off… Thanks

You are creating a completely closed system by installing shut-offs on the inlet and the outlet of the H/W Tank.

If you or the next buyer of the home neglects to shut off the gas or electricity to the tank while servicing the plumbing, you have created either a super-heated bomb or a potential super heated swimming pool in the room where the H/W Tank is located.

I've heard a lot of arguments for and against -- But having seen first hand what an isolated H/W Tank can do to a basement recording studio in just a few short hours, I'd recommend against it.

coolpj · Mar 18, 2007, 10:03 AM

Originally Posted by iamgrowler

You are creating a completely closed system by installing shut-offs on the inlet and the outlet of the H/W Tank.

If elecricity or gas is supplied to the WH:
If you closed the shut-off valves... or... if all the fixtures are closed, doesn't that amount to the same thing?

Doesn't every WH disconnect automatically when the set temperature is reached?
And in case this automatic shut off is malfunctioning, isn't there a safety relief valve that opens up, relieving water to the drain?

Regards,

Paul

iamgrowler · Mar 18, 2007, 12:54 PM

If you closed the shut-off valves... or... if all the fixtures are closed, doesn't that amount to the same thing?

It does and it doesn't.

When the entire system is included, there is some room for thermal expansion -- Including back to the main IF the system doesn't have a backflow preventer inline.

BTW, we are now in an era where many municipalities across the US are requiring backflow prevention of the potable water supply -- Making each individual residence in itself a closed system -- Unfortunately, many of these municipalities have failed to make the next logical leap, which is to mandate the installation of an expansion tank.

When it's just the tank closed off, there is no room for thermal expansion -- And if it's a newer tank, say fifteen years or newer, the dialectric nipples in the tank are likely to be one way, which means the expansion tank, if there is one, isn't going to do you a bit of good.

An easy workaround for this shortsighted mandating of closed systems without proper relief would be to require a Reduced Pressure Backflow Preventer, which has a built in double check and relief system -- But nobody really thinks of these things.

Even something as simple as an inline pressure relief valve set to pop off at say 120psi on the cold side of the system and gravity drained to the outside or to an indirect drain would be better than what is currently mandated -- Which is nothing.

Doesn't every WH disconnect automatically when the set temperature is reached?

I'm not sure I understand what you mean.

Are you asking if the gas or electricity shuts off when the temperature is reached?

If so, where do you think the build up in pressure goes during the heating process if the system is closed and confined only to the tank?

And in case this automatic shut off is malfunctioning, isn't there a safety relief valve that opens up, relieving water to the drain?

If this "automatic shut off is malfunctioning", then doesn't it stand to reason that the T&P relief valve might also be subject to malfunction and failure?

You also mention 'relieving the water to the drain'.

I've been in a number of homes where the T&P was never run, or run only to a floor drain.

Assuming only the hot side was shut off -- Do you think a floor drain is going to keep up with water gushing out of the T&P from anywhere between 35 to 100psi?

coolpj · Mar 18, 2007, 02:30 PM

Growler..
I salute you on your reasoning which is, obviously, backed by extensive experience.

So, to get your point:

Your objection to having shut off valves directly at the water heater is that:
in case the valves are closed and the heating source is still running (electricity or gas), keeping the temperature constantly at the set value (say.. 70 C or 158 F) for a long period, the small amount of piping envolved would eventually expand to the point of rupture, right ?
Plus, any relief mechanism (built into the water heater) would not do much good since, it might malfunction or... it would rush hot water into the drain at high pressure.. which might cause flooding.

So you would propose to:
1- cancel the shut off valves directly at the water heater. This would mean that the heat (therefore the expansion) is absorbed by more piping.
Here I ask: is this enough ??

2- In case the above is not enough, you would propose to incorporate an expansion tank, which would absorb any extra pressure or over-heating in the system (in case there is no back flow to the main)... or... to use the double check plus relief back flow preventer. But this brings us back to the same issue of gushing hot high pressure water to the drain.
And if the Water Heater is not isolated anymore, when would this pressure surge occur?
Does it occur when the tempreature sensor in the water heater malfunctions and the water keeps on heating up?

Again, many thanks growler for clearing things up..

Paul

Originally Posted by iamgrowler

It does and it doesn't.

When the entire system is included, there is some room for thermal expansion -- Including back to the main IF the system doesn't have a backflow preventer inline.

BTW, we are now in an era where many municipalities across the US are requiring backflow prevention of the potable water supply -- Making each individual residence in itself a closed system -- Unfortunately, many of these municipalities have failed to make the next logical leap, which is to mandate the installation of an expansion tank.

When it's just the tank closed off, there is no room for thermal expansion -- And if it's a newer tank, say fifteen years or newer, the dialectric nipples in the tank are likely to be one way, which means the expansion tank, if there is one, isn't going to do you a bit of good.

An easy workaround for this shortsighted mandating of closed systems without proper relief would be to require a Reduced Pressure Backflow Preventer, which has a built in double check and relief system -- But nobody really thinks of these things.

Even something as simple as an inline pressure relief valve set to pop off at say 120psi on the cold side of the system and gravity drained to the outside or to an indirect drain would be better than what is currently mandated -- Which is nothing.

I'm not sure I understand what you mean.

Are you asking if the gas or electricity shuts off when the temperature is reached?

If so, where do you think the build up in pressure goes during the heating process if the system is closed and confined only to the tank?

If this "automatic shut off is malfunctioning", then doesn't it stand to reason that the T&P relief valve might also be subject to malfunction and failure?

You also mention 'relieving the water to the drain'.

I've been in a number of homes where the T&P was never run, or run only to a floor drain.

Assuming only the hot side was shut off -- Do you think a floor drain is going to keep up with water gushing out of the T&P from anywhere between 35 to 100psi?

iamgrowler · Mar 18, 2007, 03:07 PM

Your objection to having shut off valves directly at the water heater is that:
in case the valves are closed and the heating source is still running (electricity or gas), keeping the temperature constantly at the set value (say.. 70 C or 158 F) for a long period, the small amount of piping envolved would eventually expand to the point of rupture, right ?

I object to having two shut-offs installed at the tank -- Not to having a single shut-off installed at the tank on the cold side.

Plus, any relief mechanism (built into the water heater) would not do much good since, it might malfunction or... it would rush hot water into the drain at high pressure.. which might cause flooding.

If everything operates correctly, then you have no worries -- But why create the potential for disaster when you don't have to?

As I mentioned in another thread a few days ago, we live in a very litigious society, a society where lawsuits are more often about going after those with the deepest pockets than they are about going after the actual responsible party.

labman · Mar 18, 2007, 03:24 PM

My vote is for a shut off on both. Where people usually get into trouble is shutting the inlet or main valve off without opening a hot water tap. As far as the hot water tank goes, leaving all the hot water taps in their normal off position is the same as closing a valve on the outlet.

Expansion tanks are becoming more common, and may be a good idea even without a back flow preventer. That way you can cut the cold water off without needing to open a hot water tap.

As water heats and cools, it expands and contracts. Hot water tanks don't. Something's got to give. If you are lucky, it will be the relief valve. Of course, once it opens, it has a good chance of getting dirt in it and having to be cleaned or replaced.

iamgrowler · Mar 18, 2007, 04:58 PM

As far as the hot water tank goes, leaving all the hot water taps in their normal off position is the same as closing a valve on the outlet.

No, it isn't.

The hot water piping itself will absorb a great deal of the expansion (remember the numerous threads in this forum about creaking, groaning and popping pipes?).

If too much pressure is built up within the system, it will seek the path of least resistance for relief -- Which is usually through the rubber washer in a lavatory faucet, a worn shower valve or the tanks T&P.

If you isolate the piping portion of the hot water system from the tank, you have eliminated two potential avenues for thermal relief -- Leaving only the T&P, the threaded nipple sockets and the welds of the tank to absorb the thermal expansion.

coolpj · Mar 18, 2007, 05:22 PM

Where would be the ideal location for the expansion tank?
Any point on the hot water piping ?

iamgrowler · Mar 18, 2007, 05:32 PM

Originally Posted by coolpj

where would be the ideal location for the expansion tank?
any point on the hot water piping ?

Actually, it goes on the cold water side.

I know that isn't going to make much sense, but in a well engineered, properly sized system, thermal expansion bounces back and forth between the hot and the cold water piping.

I generally thread a 3/4" brass tee onto the cold water nipple of the tank, thread the expansion tank into the top of the tee and then put a short brass nipple into the side outlet of the tee and connect the supply line to this.

labman · Mar 18, 2007, 06:24 PM

Originally Posted by iamgrowler

No, it isn't.

The hot water piping itself will absorb a great deal of the expansion (remember the numerous threads in this forum about creaking, groaning and popping pipes?).

It is true everything has a certain amount elasticity and its volume does increase and decrease with pressure changes. The biggest factor in the expansion and contraction of pipes is their changes in temperature. I am on a well. Every time I turn the cold water on, the pressure drops until the pump kicks in. The pressure then rises to the pump cut off. Those pressure fluctuations never seem to produce the creaking and groaning running the hot water may. The noise also occurs after you shut the water off and the system has a chance equalize. While the pipes cool off.

I never remember compressed air lines making that kind of noise either.

iamgrowler · Mar 18, 2007, 07:06 PM

Originally Posted by labman

It is true everything has a certain amount elasticity and its volume does increase and decrease with pressure changes. The biggest factor in the expansion and contraction of pipes is their changes in temperature. I am on a well. Every time I turn the cold water on, the pressure drops until the pump kicks in. The pressure then rises to the pump cut off. Those pressure fluctuations never seem to produce the creaking and groaning running the hot water may. The noise also occurs after you shut the water off and the system has a chance equalize. while the pipes cool off.

I never remember compressed air lines making that kind of noise either.

I'm not so sure any of that directly addressed the points I made in response to your earlier post, Labman.

OTOH, it was *VERY* entertaining.:D

Thanks.

labman · Mar 18, 2007, 08:27 PM

OK, water pipes may stretch a little as pressure goes up, but no way to accommodate the increase in volume of water if you shut off the inlet of a hot water tank. Pipes don't seem to move much in response to changes in pressure. So having the additional piping available isn't going help much.

iamgrowler · Mar 19, 2007, 05:23 AM

OK, water pipes may stretch a little as pressure goes up, but no way to accommodate the increase in volume of water if you shut off the inlet of a hot water tank.

Just out of curiosity, how much pressure differential do you think we're talking about here, Labman?

Also -- How did the volume of water in the system change if the system is closed?

Pipes don't seem to move much in response to changes in pressure. So having the additional piping available isn't going help much.

And yet loops for the express purpose of accommodating movement due to pressure and thermal differential are installed, per code and manufacturer specs, in piping systems every single day, Labman.