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.

 

Anyone have any advice? I guess I can't go wrong with 2" copper.

 

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.

 

Use 3/4.

What size circ pump do you have now. ?

 

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

 

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.

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.

That's a good idea. You have several joints with the telltale green staining. That is caused by leakage.

 

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.....

 

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

 

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.

 

Edit: I thought the thread I replied too might be confusing...

 

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?

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

 

Yes..

But If it were my system I would remove the zone valves and set it up to have individual pumps ...

 

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.

 

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