Best Spot For An Expansion Tank - Plumbing - DIY Home Improvement | DIYChatroom

Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Plumbing


Thread Tools Display Modes
Old 10-28-2010, 10:39 AM   #1
Join Date: Oct 2010
Location: Lancaster, MA USA
Posts: 2
Rewards Points: 10

Best spot for an expansion tank

Good morning everyone,

I've spent the last couple of years fixing up a nice old house that needed a little TLC. It's been a lot of fun. I'd like a little advice on where to site my new expansion tank.

Currently our tankless water heater spits a bit of water out of its pressure release valve whenever a valve on a hot water supply line shuts quickly. (We put in a high efficiency washer that causes this especially frequently.)

We do not currently have an expansion tank anywhere, and after a bit of reading I think I should install one on our cold water supply.

Does it matter where on the cold water supply I install the expansion tank? I think that it does not. Should it be as close to the tankless water heater as possible, or closer to my water meter. (There are a couple of branches from the cold water supply before it reaches my water heater.)


russwilliston is offline   Reply With Quote
Old 10-28-2010, 10:48 AM   #2
Long-Time DIYer
Mike Swearingen's Avatar
Join Date: Mar 2005
Location: On Albemarle Sound In Northeastern NC
Posts: 1,460
Rewards Points: 500

I've always seen them installed on the cold water side very near the water heater. That's where the hot water is expanding back into the cold line from.


Mike Swearingen is offline   Reply With Quote
Old 10-28-2010, 11:44 AM   #3
Join Date: Sep 2010
Location: Massachusetts
Posts: 77
Rewards Points: 75

Not sure what make/model water heater you have, but I know in Rheem/Ruud's tankless water heater manual it states "if the relief valve on the system discharges periodically, a problem exists. Turn off the water heater, unplug the unit, and call for service"

There is no need for an expansion tank on a tankless water heater because there is no hot water being stored.

Your problem could however simply be a faulty relief valve. However, I'm going to guess that it's caused by water hammer within your pipes from the fact closing valve in the clothes washer. This can be corrected with water hammer arrestors. They are some arrestors made specifically to be installed in line on your washing machines hoses. follow the link for an example.

I'm also curious as to what pressure your water service is. I hope this helps.
moopey is offline   Reply With Quote
Old 10-28-2010, 12:46 PM   #4
Join Date: Oct 2010
Location: Lancaster, MA USA
Posts: 2
Rewards Points: 10

Thanks for the advice!

I'll pick up a pressure gauge and check my pressure...I planned to do that anyway to see what size tank I need. I suspect my water pressure is pretty high.

My water heater is a Noritz 841-MC-DV (I see Noritz has changed their numbering, and it's now a NCC199-DV). The plumbers who installed my water heater were pretty thorough and have a good reputation in my town, so I don't doubt that they did the job properly.

I've heard a lot of anecdotes about the same problem though, where the fix was an expansion tank on cold water supply. I'll report back this weekend...
russwilliston is offline   Reply With Quote
Old 10-28-2010, 04:53 PM   #5
Plumb or Die!
Join Date: Oct 2010
Location: BC, Canada
Posts: 321
Rewards Points: 250

I'd say, "Baloney Moopy!" If you heat water, there's expansion, period. If there's any kind of check valve on the water main, you absolutely gotta have one. Especially with a tankless.
plumber666 is offline   Reply With Quote
The Following User Says Thank You to plumber666 For This Useful Post:
the_man (10-28-2010)

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Is a Hot Water Expansion Tank required Needagameplan Plumbing 9 04-27-2010 03:09 PM
Installing a new boiler expansion tank CoachDad HVAC 0 01-06-2010 01:12 PM
Pressure relief leaking and expansion tank full themow HVAC 1 11-25-2009 04:49 PM
Installing new expansion tank ted schumm HVAC 2 07-19-2009 09:49 PM
No Expansion Tank for Water Heater vasanvasan Plumbing 4 12-13-2007 11:16 PM

Top of Page | View New Posts


Search Engine Friendly URLs by vBSEO 3.6.1