I am in the process of remodelling my home. As I do I am going to remove old galvanized heating pipe and replace it with pex. It is a fhw heating system that has copper piped baseboard heat. The old heat ipe is indeed soldered to the galvanized and you can see the rusting or breakdown where the copper meets the galvanized tubing. Other homes in the area have it and they have had it replaced as it was rotting from the inside out. Anyway, my question is, what size pex do I use. I has assumed 3/4 since that's what exists, but someone told me I had to go 1" if I were mating it to 3/4 copper baseboard. Any help would be appreciated. One other small question, when I drain the zone do I have to shut the water supply off to the main boiler or can I isolate just the zone I am working on. There are 2 zones and its summer so I'm not concerned about the heat bneing off. One zone is all copper serving just one room that was an addition to the original; house, the other is a split loop that served all the original ranch. I intend on removing the split and heating just the bedrooms with this zone and using the other zone for the daytime living quarters. House is 1400 sf. Thanks

Hi Kasey54:

You cannot use regular water pex for this... you know that... right?

In my area we are using FOSTAPEX piping (Has O2 barrier... see image of 1/2" fostapex) and we would use 3/4" fostapex for each zone unless you are on a monoflo system that includes a loop with a feed and return going to each piece of baseboard... then you would step it up to a 1" fostapex as far as you could until you needed to install monoflo tee fittings!

Fostapex is also more form-stable than regular pex allowing a cleaner looking job as it can be hung and will maintain reasonable bending/shaping.

I'm betting you have a regular individual loop for each zone and therefore recommend using the 3/4" fostapex tubing.

Check out this link for more info.:

http://www.viega.net/cps/rde/xbcr/en-us/TD-PFFP-1207_FostaPEX.pdf

Works for us just fine!

In terms of shutdown of water, if you can isolate the zone without shutting off the boiler water feed then you can do that without issue... just be sure it is isolated on both feed and return. Drain from a boiler drain and open a vent upstairs to start draining if possible.

MARK

Thanks mark, yes I know about the 02 barrier. I would love to use the fostapex. I recently put in some water pipes, bought a crimp tool and used the standard crimp rings. I should have researched earlier, now I have a tool, but I don't think that will work with the press sleeves required for fostapex, is that right? I'll have to check my boiler, pretty sure the feed line comes right off the boiler, no shut off, and feeds two zones with what I think they call flow valves(they have an arrow on them.) I will recheck and see if there is a shutoff in between. The return line has a shut off, drain valve and shutoff just before the circulating pump, so I would drain the zone there as they are all baseboards with no drains upstairs. Would the flow valve prevent the second zone from draining back into the system? I'll recheck the whole thing and see if I can post pics. The zone I'm working on is a split zone and I am removing the split as it will only service 2 bedrooms. Thanks

Yeah...

You would need to purchase the VIEGA pex tools to use viega pex (fostapex).

Most likely the valves with arrows are flow control valves as you suggested... they should actually hold, but if one is stuck or is not working properly it will create a real issue for you when soldering, etc.. It's probably best to drain the system and then just refill and purge air out later.

Check upstairs for COIN VENTS or any other threaded vent and remove at least one of these to start things draining correctly. If no vents then you will definitely need to drain the entire system to let air in to displace the water to drain out of the pipes... no question!

Pop back as you go along...

MARK