Hot water radiator supply piping size?

Reply

  #1  
Old 08-31-16, 07:04 PM
Member
Thread Starter
Join Date: Aug 2013
Posts: 142
Received 0 Votes on 0 Posts
Hot water radiator supply piping size?

Currently the 5 cast-iron radiators I have on the first floor and the 4 that are on the second floor all come off one zone valve. I'd like to re-pipe the second floor radiators to a second zone valve with separate thermostat to have better control of the temperature up there.

The main supply and return piping in the basement is 2", and the radiators tee off of it in parallel. The 1st floor radiators tee off with 1" piping, the 2nd floor radiators use 3/4" pipe.

To re-pipe the supply+return for the 4 radiators on the second floor to a second zone valve, what size pipe would be sufficient? Currently the piping is steel, I'll probably make the new connections in copper though.
 

Last edited by EvanVanVan; 08-31-16 at 07:22 PM.
Sponsored Links
  #2  
Old 09-07-16, 08:05 AM
Member
Thread Starter
Join Date: Aug 2013
Posts: 142
Received 0 Votes on 0 Posts
Anyone have any advice? I guess I can't go wrong with 2" copper.
 
  #3  
Old 09-07-16, 08:38 AM
Member
Join Date: Jan 2014
Location: USA near Boston, MA
Posts: 696
Received 21 Votes on 17 Posts
Sounds like your system was originally a gravity flow system. Now that systems are pumped the pipe sizes can be much smaller. There is a 3/4 inch pipe from my new boiler to the original 2 inch steel piping that feeds eight cast iron radiators on the first and second floors. I have had no heating problems for 30 years with that arrangement.

I think you can use 3/4 inch pipe (copper, steel, PEX--makes no difference, the size and flow characteristics are the same) for your four second floor radiators. If you are not comfortable with that use 1 inch. Larger will not be necessary.
 
  #4  
Old 09-07-16, 06:53 PM
lawrosa's Avatar
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 17,893
Received 25 Votes on 23 Posts
Use 3/4.

What size circ pump do you have now. ?
 
  #5  
Old 09-07-16, 08:01 PM
Member
Thread Starter
Join Date: Aug 2013
Posts: 142
Received 0 Votes on 0 Posts
Thank you both, I wasn't considering that the pipe size wouldn't have to be any bigger than it's smallest diameter. Upon closer inspection I've got two unused zone valves (3/4" and 1").

I attached a picture for reference, but it's a 1-1/4" circ pump that supplies (3) zone valves. The 1" ZV on the right feeds everything (after the valve it goes up to 1-1/4" copper as you can see.) Then there's the 3/4" zone valve on the left, and the 1" zone valve below it (out of the picture).

Taking a look at it now I'm going to replace those corroded/leaking copper fittings as well...

bigger picture: https://i.imgsafe.org/0c6b4209dc.jpg

Name:  heating system.jpg
Views: 1342
Size:  50.7 KB
 
  #6  
Old 09-10-16, 02:58 PM
Member
Join Date: Oct 2008
Location: USA
Posts: 2,917
Received 7 Votes on 7 Posts
If you have a 2" zone in parallel with 3/4" zone, the flow rates may be unbalanced - the 2" zone will hog most of the flow when both zones are calling for heat. That issue can be avoided by installing a globe valve in the 2" zone to use as a balancing valve that can be throttled.

I wasn't considering that the pipe size wouldn't have to be any bigger than it's smallest diameter
That isn't exactly correct. The flow rate through a loop is not limited by the smallest diameter fitting. Flow is affected by the total pressure drop through the loop, and a shorter section of smaller diameter pipe probably will not be the controlling factor. Your thinking would apply to two sieves of different sizes in series passing granular material - flow of fluids is different.

By the way, do I see a natural gas line that is using galvanized pipe? That is not usually recommended because sulfur in the gas can degrade the zinc coating.

I'm going to replace those corroded/leaking copper fittings as well...
That's a good idea. You have several joints with the telltale green staining. That is caused by leakage.
 
  #7  
Old 09-10-16, 04:39 PM
lawrosa's Avatar
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 17,893
Received 25 Votes on 23 Posts
By the way, do I see a natural gas line that is using galvanized pipe? That is not usually recommended because sulfur in the gas can degrade the zinc coating.
Youll be dead before any coating comes off... In NJ we use galv per local code on outdoor runs all the time... black indoors but if we are running galv then we run it everywhere. in and out.....
 
  #8  
Old 09-10-16, 04:48 PM
lawrosa's Avatar
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 17,893
Received 25 Votes on 23 Posts
And its old school thinking that its caused by the NG... One of those things
thats heard or read about so it must be true scenerios

http://www.galvanizeit.org/images/up...ed_Steel_2.pdf
 
  #9  
Old 09-10-16, 04:51 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,493
Received 33 Votes on 25 Posts
Some jurisdictions require galvanized piping, some jurisdictions prohibit galvanized piping and some jurisdictions don't care one way or the other. This is why LOCAL code must always be determined and followed.
 
  #10  
Old 09-10-16, 05:16 PM
Member
Thread Starter
Join Date: Aug 2013
Posts: 142
Received 0 Votes on 0 Posts
Edit: I thought the thread I replied too might be confusing...
 

Last edited by EvanVanVan; 09-10-16 at 05:55 PM.
  #11  
Old 09-10-16, 05:56 PM
Member
Thread Starter
Join Date: Aug 2013
Posts: 142
Received 0 Votes on 0 Posts
gilmorrie: If you have a 2" zone in parallel with 3/4" zone, the flow rates may be unbalanced - the 2" zone will hog most of the flow when both zones are calling for heat. That issue can be avoided by installing a globe valve in the 2" zone to use as a balancing valve that can be throttled.
I mentioned this in my last post but will just clarify it quickly. It's not a 2" zone, it's a 1" zone valve that then connects to 2" main piping in the basement only. You can just see the two 2" x 1-1/4" 90s in the top of the picture, one feeds the radiators towards the front of the house, the other the back. (and can see where the 1" zone valve is increased to 1-1/4" copper right above it). The radiators just tee off the 2" with 1" and 3/4" pipe.

After learning more about heating systems, turns out I have a common two pipe heating system. Along with replacing the globe radiator valves (that was my original project when I started looking at all this), I'm also going to modify the 2" return piping so it's a reverse return which I see can basically balance the system itself.

So now knowing that I have a common two pipe heating system, 3/4" and/or 1" is still sufficient for running a new supply and new return mains in the basement?

lawrosa: In NJ we use galv per local code on outdoor runs all the time...
Yeah, I think the boiler (and that piping) was installed by PSE&G not too long along (10 years?) when my grandmother was alive/owned the house.

edit: well I guess i replied kind
 
  #12  
Old 09-11-16, 06:58 AM
lawrosa's Avatar
Super Moderator
Join Date: Dec 2010
Location: Galivants Ferry SC USA
Posts: 17,893
Received 25 Votes on 23 Posts
So now knowing that I have a common two pipe heating system, 3/4" and/or 1" is still sufficient for running a new supply and new return mains in the basement?

Yes..

But If it were my system I would remove the zone valves and set it up to have individual pumps ...
 
  #13  
Old 09-11-16, 07:52 AM
Member
Thread Starter
Join Date: Aug 2013
Posts: 142
Received 0 Votes on 0 Posts
Yeah I was just reading quite the online debates with pros and cons of each system last night. "Plumbers install pumps, heating guys use zone valves." Technically as a fire sprinkler fitter I guess I should use pumps lol, but for now I'm just trying to make a few minimal changes with hopefully a decent improvement.

I'm also learning it might be more complicated than just throwing a dart at a dartboard and picking a main pipe size... The OP here (http://www.doityourself.com/forum/bo...st1453107.html) has question about pipe size, and NJT really informs him of the complexities doing it properly (http://www.doityourself.com/forum/bo...ml#post1453448).

So maybe it's just change the radiator valves out like I planned, reverse the return but keep it all on one zone and see how I make out this winter...

Edit: side-note: lots of NJ DIYers here.
 
  #14  
Old 09-11-16, 05:22 PM
Member
Join Date: Oct 2008
Location: USA
Posts: 2,917
Received 7 Votes on 7 Posts
Cool

So maybe it's just change the radiator valves out like I planned, reverse the return but keep it all on one zone and see how I make out this winter...
Good plan. There is always next year (during the summer!) if you need to make changes.

Back to the subject of galvanized pipe for natural gas. My gas company currently uses plastic pipe for buried service line to the meter, the outside meter piping is black steel, and the outside pipe from the meter into the house is black steel. But, the buried service has varied over the years - initially (~1953) the buried service was copper. Then they changed it to steel, coated and wrapped. Finally, about two years ago, they replaced mine with plastic.

Inside, local plumbers all use black steel for gas. Maybe, one reason is that it is cheaper than galvanized? I wouldn't fear galvanized pipe rupturing due to sulfur in natural gas - but could the zinc inside the pipe flake off and plug the orifices on gas burners?

I don't know what type of main gas pipe runs under my street. I'll find out after it blows up
 
Reply

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


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: