expansion tank on hot water heater
 

In the five homes I've owned over the last 30 years, I have never had an
expansion tank on the hot water heater. My daughter just bought a home (new
construction) and it has one. Did something change? Do I really need one?
It seems to me that any expansion of the water in the tank would just be
pushed out the cold water inlet and pressure wouldn't increase. What am I
missing?

Jmagerl wrote:

In the five homes I've owned over the last 30 years, I have never had an
expansion tank on the hot water heater. My daughter just bought a home (new
construction) and it has one. Did something change? Do I really need one?
It seems to me that any expansion of the water in the tank would just be
pushed out the cold water inlet and pressure wouldn't increase. What am I
missing?



Places with high city water pressure will have a Pressure Reducing
Valve to lower it. By design, these valves block flow to the street
(some exceptions). Also, many localities now require backflow
preventer valves (check valves). All these situations are required
to have an exp tank today.

http://www.stateind.com/expansion/expansion.htm


Jim

In the five homes I've owned over the last 30 years, I have never had an
expansion tank on the hot water heater. My daughter just bought a home (new
construction) and it has one. Did something change? Do I really need one?
It seems to me that any expansion of the water in the tank would just be
pushed out the cold water inlet and pressure wouldn't increase. What am I
missing?

It depends on what's upstream of the cold water inlet.
If there's a checkvalve before there's a pressure tank,
then you ought to have an expansion tank.

Good points. So... since I am on a well the pressure tank will accept the
expansion. Differenrt question: I was in the store the other day looking at
replacing my brothers hot water heater. In the replacement kits, there were
things called "heat traps". THey screwed into the inlet and outlet of the
water heater. What are these? and do they in any way make me need an
expansion tank? (I don't have them on my heater). I'm expecting my heater to
go soon (20+ years old)

"Jmagerl" wrote in message
...
In the five homes I've owned over the last 30 years, I have never had an
expansion tank on the hot water heater. My daughter just bought a home
(new construction) and it has one. Did something change? Do I really need
one? It seems to me that any expansion of the water in the tank would just
be pushed out the cold water inlet and pressure wouldn't increase. What am
I missing?

Jmagerl wrote:
Good points. So... since I am on a well the pressure tank will accept the
expansion. Differenrt question: I was in the store the other day looking at
replacing my brothers hot water heater. In the replacement kits, there were
things called "heat traps". THey screwed into the inlet and outlet of the
water heater. What are these? and do they in any way make me need an
expansion tank? (I don't have them on my heater). I'm expecting my heater to
go soon (20+ years old)


Heat traps are small ball check valves. They prevent hot water
"migration" (small circulating flow) out the Cold and Hot supplies
when no water is being drawn. It is a small energy-saver/.
Chances are you won't need an exp tank on your well; wait and see.

Jim





"Jmagerl" wrote in message
...

In the five homes I've owned over the last 30 years, I have never had an
expansion tank on the hot water heater. My daughter just bought a home
(new construction) and it has one. Did something change? Do I really need
one? It seems to me that any expansion of the water in the tank would just
be pushed out the cold water inlet and pressure wouldn't increase. What am
I missing?

Heat traps are small ball check valves. They prevent hot water
"migration" (small circulating flow) out the Cold and Hot supplies
when no water is being drawn. It is a small energy-saver/.

Why do you need a ball valve? Wouldn't a simple U bend do
the trick?

default wrote:


Heat traps are small ball check valves. They prevent hot water
"migration" (small circulating flow) out the Cold and Hot supplies
when no water is being drawn. It is a small energy-saver/.


Why do you need a ball valve? Wouldn't a simple U bend do
the trick?


These are actually easier to install:
http://www.perfectioncorp.com/water/heattrap.html
since they go straight in-line from the heater threaded bosses.

Jim

I had a hot water heater replaced in January. The instructions said I may need
an expansion tank. Water was leaking from the pressure relief valve. Sure
enough, had to install an expansion tank. No more leaks.

(To send e-mail, remove NOSPAM from address)

Speedy Jim wrote:
default wrote:


Heat traps are small ball check valves. They prevent hot water
"migration" (small circulating flow) out the Cold and Hot supplies
when no water is being drawn. It is a small energy-saver/.



Why do you need a ball valve? Wouldn't a simple U bend do
the trick?

I don't see how it would....Unless they were quite tall and very well
insulated.

Those "heat traps" use lightly loaded check valves to counteract the
small pressure differential caused by the difference in specific gravity
of hot and cold water. What they do is keep the hot water from moving up
and out of the water heater and into the piping and cold water "sinking
down" into the tank from those same pipes during idle periods.

When a hot water faucet is opened, mains pressure easily pushes those
valves open and flow proceeds normally.

Hydronic heating systems sometimes have similar valves to prevent a
similar kind of thermosyphon flow from keeping the heat in the boiler
from reaching the baseboard units when the circulator pump isn't
running, since water will still flow through a stopped centrifugal pump.
They used to be called "gravity valves", and may still be.

Jeff




These are actually easier to install:
http://www.perfectioncorp.com/water/heattrap.html
since they go straight in-line from the heater threaded bosses.

Jim


--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"

wrote:
On Wed, 01 Dec 2004 16:36:08 -0500, Speedy Jim wrote:


default wrote:


Heat traps are small ball check valves. They prevent hot water
"migration" (small circulating flow) out the Cold and Hot supplies
when no water is being drawn. It is a small energy-saver/.


Why do you need a ball valve? Wouldn't a simple U bend do
the trick?


These are actually easier to install:
http://www.perfectioncorp.com/water/heattrap.html
since they go straight in-line from the heater threaded bosses.

Jim



I was wondering the same thing. If these things are ball valves,
where does excessive pressure go in the tank when the water heats? I
have those on my own water heater, but it has never tripped the
pressure release valve, so I dont worry about it. The only thing I
could figure is that they release the pressure at a certain point ????

Mark


Yes. The tiny ball will lift open with very little pressure;
there is just enough force holding them closed to prevent
the thermal siphoning.

Jim

Why do you need a ball valve? Wouldn't a simple U bend do
the trick?

I don't see how it would....Unless they were quite tall and very well
insulated.

The hot water in the tank rises to the top of the U, and stops.
it's not going to to down the far side, because the water
downstream is colder and denser than the water in the top
of the U. you might get some convection between the top
of the U and the heater tank, but that ought to be it.