Maniblock manifold and expansion tank

[Kaizen]

I've done a bit of plumbing and having an issue finding an answer so hoping someone here knows.
I have a 3/4 line coming in and put a new heatpump water heater and maniblock within ten pipe feet of the entrance after the meter which i am assuming has a backflow preventer making my house isolated.
I cut out the mess of 100 years of copper and ran new pex. I've always had a little pipe banging when the washer runs but now i notice it more as well as the dishwasher. My water heater install says to install an expansion tank on the cold line going into the tank. Now the questions
- Should i just run the standard big boiler size off the shelf at Home depot and check my water pressure/adjust?
- Should I run two smaller ones on hot and cold at the maniblock inlets which are after the hot water inlet?
- Can i use the 1/2 Maniblock extra port/s to run up to an expansion tank? In theory it would see the whole system but not sure if having on a bigger pipe size makes a difference?

 

[mike93lx]

The expansion tank is for your water heater, not to deal with water hammer.

Install the expansion tank on the cold at the water heater and try hammer arrestors elsewhere.

 

[Kaizen]

The expansion tank is for your water heater, not to deal with water hammer.

Install the expansion tank on the cold at the water heater and try hammer arrestors elsewhere.

Thanks will do. I thought they both did the same thing

 

[larry4406]

As the old copper was rigid compared to the new pex noodle, any chance the pex is now banging against structure when a water solenoid valve shuts off (dishwasher, washer machine, etc)?

Our plumbers use these style with integral arrestors at washing machine and ice makers. Last image is similar to what they install under the kitchen sink cabinet for the dishwasher supply.

 

[rlitman]

...- Should i just run the standard big boiler size off the shelf at Home depot and check my water pressure/adjust?...

Boiler expansion tanks aren't made for potable water (they have a steel ****** that's exposed to the recirculating deoxygenated water), and are set with too loo a pressure. You want a much smaller tank made for DHW use. And if you have a heat trap ****** on the water heater, you'll need one on the HOT side. Since your water lines on the cold side don't change in temperature all that much, even with a check valve on your service, there's not much point in one for just the cold side.

While expansion tanks and water hammer arrestors have similar construction, one does not substitute for another, and placing an expansion tank on your manifold will do little to stop hammer. PEX on a manifold can have a bigger hammer issue than a network of copper pipes, simply because the home-runs of PEX without any fittings act like a perfect conductor for hammer.

 

[fitter30]

Just need one on the cold side that is where most of the expansion happens. Sizing the tank

Expansion Tank Sizing Calculator (Potable)

Expansion Tank Sizing Calculator (Potable)

www.watts.com

 

[Kaizen]

Boiler expansion tanks aren't made for potable water (they have a steel ****** that's exposed to the recirculating deoxygenated water), and are set with too loo a pressure. You want a much smaller tank made for DHW use. And if you have a heat trap ****** on the water heater, you'll need one on the HOT side. Since your water lines on the cold side don't change in temperature all that much, even with a check valve on your service, there's not much point in one for just the cold side.

While expansion tanks and water hammer arrestors have similar construction, one does not substitute for another, and placing an expansion tank on your manifold will do little to stop hammer. PEX on a manifold can have a bigger hammer issue than a network of copper pipes, simply because the home-runs of PEX without any fittings act like a perfect conductor for hammer.

Thanks for stopping me from drinking rust. GJ saves me again

 

[Kaizen]

As the old copper was rigid compared to the new pex noodle, any chance the pex is now banging against structure when a water solenoid valve shuts off (dishwasher, washer machine, etc)?

Our plumbers use these style with integral arrestors at washing machine and ice makers. Last image is similar to what they install under the kitchen sink cabinet for the dishwasher supply.

definitley. I didnt care much about the copper as it was the thick stuff from 60 years ago. But with the pex i can easily see it rubbing and causing a leak so i'm taking these steps now. I've added a ton of clips to secure it every few feet so i'll see how that goes with the hammer arrestors.

 

[PWC Repair]

Thanks for stopping me from drinking rust. GJ saves me again

What's wrong with drinking rust? The body needs iron LOL!

 

[Codyboy]

What's wrong with drinking rust? The body needs iron LOL!

Hell yeah.
I purposely look for old RR tracks that are not used much, if at all.
When my body feels like it needs some iron supplement I'll pull over (try not to do it near a busy crossing due to getting weird looks from passersby's and there may not be a safe place to park) and give it a few licks.
It's pretty satisfying.