Can PEX be used for old cast iron radiators?

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Old 07-25-11, 08:59 PM
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Can PEX be used for old cast iron radiators?

Hello,

I had some water issues in my basement this spring which forced me to take out some walls in my basement. The only one left to take out is the wall my boiler is hanging on. My plan is to remove most of the old steel pipes hanging from the ceiling and update them so i don't have to heat so much water (some radiators have been removed). When I move my boiler I was wondering if I could could have it feed a manifold and from there run 3/4" or 1" PEX to my old cast iron radiators. This seems easier and cheaper to me, but maybe I'm wrong. My main concern was that the PEX can't handle the heat. Wirsbo hePEX claims to be good for 200 at 80 psi and 180 at 100 psi. My boiler runs at 180 and 20 psi. To me this means it should be safe. Any thoughts would be great.
 
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Old 07-26-11, 06:55 AM
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You need to use Oxygen Barrier PEX. It prevents air from infiltrating and causing corrosion on your heating system.
 
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Old 07-26-11, 08:25 AM
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You did not mention what type of boiler you have but since it is wall hung I will assume it is a mod/con.
A couple of things come to mind here.
1. Removing the large pipes will not reduce the heating bill. It works as a flywheel to boiler operation.
2. If you have cast iron radiation why are you running 180f water temp?
3. Pex will expand and get sloppy looking.
4. Can you do it? Yes, your pressure is well below the rating and the temp is 180 or could even be less.
5. Are you running the outdoor reset?
 
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Old 07-26-11, 09:04 AM
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My boiler is a buderus gb142-24 with outdoor reset. It is set at 180 degrees by the installer.
 
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Old 07-26-11, 12:46 PM
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That is a mod/con boiler. I would bet a dime to a donut that you don't require 180f water temp. We still don't know if there is outdoor reset wired in which was included with the boiler.
Get the heatloss from the contractor and a radiation measurement in sq ft and we can calculate the proper setting for the ODR if it is connected. This will help maximize your savings. The lower the water temp the cheaper the operation plus we know the pex will not be a problem.
 
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Old 07-26-11, 03:01 PM
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It is a sin to run that boiler with that radiation at a straight 180F.

Your contractor is costing you a lot of money in lost efficiency.

Get or do a heatloss and implement an outdoor reset curve based on the heat loss. As rbeck said, all those big pipes provide a buffer volume for the boiler to work against, which when combined with a good outdoor reset, will allow it to modulate down and cycle infrequently. Slow and steady, like cruise control in a car, is the best thing for these boilers. And if the water temps are low enough, it will condense like crazy and bump up your efficiency even more.
 
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Old 07-26-11, 04:33 PM
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I think maybe at this point it might be a good thing to walk Ice through checking out the system settings to see if in fact the ODR _IS_ implemented...

Ice, what model is the ODR on your system? Tell us about all the controls that you see... models, numbers, anything you can find that will help us ID what you have.
 
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Old 07-26-11, 05:52 PM
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You said you removed some of the rads. Put em back if you still have them and they aren't in the way. You also don't want to mix another type of emitter like fin tube baseboard on the same zone as cast iron radiators. They behave differently when heating and will affect the comfort of your home if you have both on the same zone.
 
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Old 07-27-11, 07:20 PM
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The outdoor reset is an AM-10 module that was already installed on the unit. I never really knew anything about it until now. so the way it sounds, my boiler isn't always running at 180 degrees, that is just the max my boiler will heat to, but the AM-10 module is actually adjusting the how the water should be depending on the outside temp? I live in MN, so maybe it runs at 180 degrees quite a bit in the coldest months.
 
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Old 07-27-11, 07:24 PM
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And about the radiators that were removed. I never actually removed them, they were gone before I bought the house to add another bathroom to the main floor. In place of it they had an electric wall heater installed for that bathroom. And there was nothing done to help heat the remaining space, so that room gets a little chilly in the winter, so I just keep the door closed.
 
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Old 07-27-11, 07:50 PM
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why did he set the outdoor reset to 180?? most heating days wouldn't require more than about 140. what type of heating system do you have? monoflo? seperate zones?
 
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Old 07-27-11, 08:32 PM
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I don't know why it was set to 180, that's just the way it was when I bought the place. I have all my radiators tied in 1 loop.
 
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Old 07-28-11, 08:58 AM
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It was default from the factory at 180 so it was left there I assume. To know how to set the outdoor reset curve you need heat loss' and radiation count. Than you can calculate proper min and max water temperature.
 
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