I recently installed a Takagi Flash-Jr tankless water heater.
Although it is working better than I ever expected, I'm now getting
pretty significant water hammer when my toilets finish filling, and
there is a good amount of discharge from the pressure valve.

After doing some research, it looks like I'll need to put an expansion
tank on the cold water inlet to the tankless heater, but I've also
seen suggestions to install a backflow preventer, and a vacuum
breaker.

My questions...

1. How do I size the expansion tank? HD has a variety of models from
Watts - DET-15 DET-30, ET-15, etc. I live in a condo, 1/2" supply.

2. Do I need a vacuum breaker/backflow preventer?

3. Do any/all of these items have to be mounted higher than the water
heater?

Thanks all...

Jerry Napoliano wrote:

I recently installed a Takagi Flash-Jr tankless water heater.
Although it is working better than I ever expected, I'm now getting
pretty significant water hammer when my toilets finish filling, and
there is a good amount of discharge from the pressure valve.

After doing some research, it looks like I'll need to put an expansion
tank on the cold water inlet to the tankless heater, but I've also
seen suggestions to install a backflow preventer, and a vacuum
breaker.

My questions...

1. How do I size the expansion tank? HD has a variety of models from
Watts - DET-15 DET-30, ET-15, etc. I live in a condo, 1/2" supply.

Either the DET-5 (smallest) or the DET-15 will work.
The size of tank is dictated by the volume of water
being heated, in this case there is very little volume.

2. Do I need a vacuum breaker/backflow preventer?

No. There apparently already is some check/backflow valve,
which is preventing flow back out to the street.


3. Do any/all of these items have to be mounted higher than the water
heater?

No, just TEE the exp tank off the Cold inlet;
it can hang downward.
Jim

Thanks all...

What is your normal pressure? I can't see see the after-heating driving it
up all that much, so I suspect you are starting out too high.
Have you checked it?

No, I actually haven't. I have a pressure gauge, but no place to
screw it into. Suggestions? Install a fitting?

Thanks to Speedy Jim, too for the quick answers..

On Wed, 29 Sep 2004 23:29:26 GMT, "toller" wrote:

What is your normal pressure? I can't see see the after-heating driving it
up all that much, so I suspect you are starting out too high.
Have you checked it?

Jerry Napoliano wrote:

No, I actually haven't. I have a pressure gauge, but no place to
screw it into. Suggestions? Install a fitting?


Put the TEE in for the exp tank. You can get a TEE with
a 3/4 female pipe thread on the side outlet. The tank
will screw right in.
Before you put the tank in, screw a gauge in there.
Jim

"Jerry Napoliano" wrote in message
...
No, I actually haven't. I have a pressure gauge, but no place to
screw it into. Suggestions? Install a fitting?

I have put mine on the drain of the water heater, but maybe you don't have a
drain.
In that case an outdoor faucet is fine.