Expansion tank and back flow preventer on an indirect water heater

Rickoo

Hello!

I'm replacing my Peerless boiler tankless coil water heater with an HTP Superstor Ultra 45. My home has no back flow prevention in the water service line. No pressure reducing valve. Just a water meter with ball valves on either side.

The boiler has appropriate back prevention. I'm wondering if I should install an expansion tank and back flow prevention in the domestic cold water line to the indirect. Pretty sure its not required in my situation, but I'm wondering if its a good idea anyway?

Is a simple swing check valve appropriate here?

https://www.supplyhouse.com/Bluefin-SCS075-3-4-Solder-Ends-Swing-Check-Valve-Lead-Free

Any reason why I wouldn't want the expansion tank and back flow prevention?

Thanks!

Jamie Hall

There should be a backflow preventer on boiler heating water makeup water line, at the very least. A single check valve is NOT a backflow preventer.

pecmsg

Install a back flow protection on the water heater or the incoming water line?

Larry Weingarten

Hi, @Rickoo , I don't see what benefit you would get from making this change. You would have a bit more complexity and things to fail. Simple is good.

Yours, Larry

Rickoo

Did you read my post? The boiler HAS A PROPER back flow preventer in its water supply line. I'm talking about the domestic water supply to the indirect. 

Larry Weingarten

Hi, I did read it. Maybe I misunderstood. Still, I don't imagine a benefit to adding this to the domestic water supply. What benefit do you see?

Yours, Larry

Rickoo

Thanks Larry!

My understanding the reason expansion tanks are installed in water heater domestic cold water supply is to prevent expansion of hot water from the water heater from possibly causing the water heater relief valve to drip. Or possibly causing damage to fixtures or appliances due to increased pressure. If the house has a check valve in the main water feed (like in a pressure reducing valve) I believe they are required. I don't have that and the expanded pressure from the tank will generally be absorbed back into the municipal feed line coming into the house.

At least that's the way I understand it. Does this make sense?

Rickoo

This is what I'm speaking about....

Intplm.

I wouldn't bother installing anything that isn't necessary. If you are not experiencing any problems, do not add anything.

If you like, look into what a closed domestic water supply is as apposed to a open system.
You can find this information by down loading the direction on a "domestic cold water expansion tank."

As to your boilers "appropriate" back flow prevention. If you truly do have the proper device installed then you should be covered.

The swing check you showed in your first post is not appropriate in any area that I have worked.

A appropriate "BFP" would be a RPZ-----Reduced pressure zone device.

This type of BFP is considered a high hazard device installed on boilers and is required by most plumbing/heating codes as well as most department of public health agencies.

Larry Weingarten

Hi @Rickoo , We're on the same page. Because you don't have anything in the supply line that prevents backflow, thermal expansion cannot raise water pressure. You can make sure of this by putting a pressure gauge on any hose bibb, or water heater drain valve and see if pressure increases at all when the tank is being heated. I like the gauge that has a red indicator that shows the highest pressure reached. That way to don't have to stare at the gauge for a long time

Yours, Larry

Rickoo

Thanks. This is a new install of an indirect on an existing boiler. I haven't plumbed it yet and was debating the installation of an expansion tank. The link to the swing check valve I posted wasn't intended to prevent contamination in any way. The boiler feed has a Watts 9D-M3. The swing check was to prevent hot water from migrating back into the cold.

hot_rod

Are you on a public water supply? If so there may be a BFD on the meter or elsewhere

if you are on a private well, no need for a BFD

public water suppliers do not want water back after it has entered your property, that is the reason for the BFD requirements

Rickoo

I'm on public water. Just a water meter between the utility and my home. Is it possible for a water meter itself to incorporate back flow prevention? I've never heard of that?

Maybe I'll skip the expansion tank and see if I have issues with thermal expansion. If so, I'll put it in then.

Just trying to do the right thing here.

hot_rod

All the plumbing codes require BFDs of different types. If you have a water meter in a pit outside, it could have a BFD in the yoke.

Hose bibs need BFDs to protect your homes water. Kitchen faucets with spray hoses have protection also, as should any lawn sprinkler system.

So some are intended to protect your plumbing regardless of the city connection. The BFD in or at the meter protects the rest of the water users.
Backflows of various listings are also required on boiler connections to potable water.

Check with your water provider for a clear answer. Many cities require BFD and yearly inspection, as their insurance carriers get involved also.