1.5 inch steel to 1 inch PEX?

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  #1  
Old 07-02-12, 09:44 AM
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1.5 inch steel to 1 inch PEX?

Hi there

I'm currently doing a reno on my 100 year old home that requires rerouting the pipes that feed two of my radiators. The radiators are relatively small in size, and heat two fairly small rooms: a bathroom and a small bedroom. Those rooms have typically been slightly warmer relative to the rest of the house. The system was originally gravity based but now has a circulation pump.

The current pipes are 1.5 inch galvanized steel. Is it possible for me to replace these with 1 inch PEX pipes? My friend is helping me with the project (he knows what he's doing more than I) and had originally recommended PEX but when he found out it was 1.5 inch he recommended transitioning to copper instead.

Thanks very much for any help
 
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Old 07-02-12, 10:36 AM
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What is your concern? The pex is rated for the hot water. The only pain is the fittings to go from 1.5 inch to 1 inch. The fittings are easy to find just type "pex fittings" into your search engine. You might want to find out how much water your radiators need, since you might only need 3/4 pipe", also make sure your pex tubing has the "oxygen barrier" since it is for a burner instead of water pipes. I guarentee the project will take a lot less time with the pex.
 
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Old 07-02-12, 01:54 PM
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Since your going to a pump system you likely only need 3/4", as Bish80 posted.
 
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Old 07-02-12, 03:52 PM
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Thanks for the replies guys. My concern is that the radiators will get less water this way than they should be getting. I'm not very knowledgeable with how these systems work. I'd guess that there could be more resistance with smaller pipes and the water would be more likely to flow through another radiator.

How would I calculate how much water my radiators need?
 
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Old 07-02-12, 05:01 PM
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It's all about BTUs. Each pipe size can only deliver so many BTUs. Three quarter inch pipe can carry about 39,000 BTUs and 1" 71,000 BTU's (http://comfort-calc.net/pictures/Piping_chart.JPG). How are your radiators piped? Are they in series or in parallel? If they are in parallel, then the pipe only needs to carry enough BTUs to one radiator which will be very small. If in series, the pipe needs to carry enough BTUs to the rest of the radiators and that will be a larger number. In order to calculate this, you need to do a manual J heat loss on your home.
 
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Old 07-02-12, 05:58 PM
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Hmm, well the short answer to your question is that I don't know. The rest of the system is in series, but those two rads could be parallel for all I know.

https://www.dropbox.com/s/tqi6a201tc...%20diagram.jpg

Here's a diagram of the system that I made a while ago for a different problem. It's the pipes on the right side of the diagram going up to the 2nd floor. As you can see the rest of the system is in series but I have no idea if those two rads would possibly be set up in parallel instead.

Is there any trick to figuring that out besides tearing out drywall or worse, plaster? Currently my view of the pipes disappears at the ceiling of the 1st floor. I'm rerouting them on the 1st floor and the walls are open there. I could fairly easily take out drywall on the 1st floor ceiling, but on the 2nd floor the walls are plaster.
 
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Old 07-02-12, 06:08 PM
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PS the link to the piping BTU chart isn't working for me
 
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Old 07-02-12, 06:44 PM
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Interesting piping arrangement. The two radiators in question are piped in series, but they are piped in parallel to the rest of the system. That means the hot water from the boiler flows up and through the two rads and then goes back to the boiler to be reheated. Using 3/4" pipe here will not be a problem.

On a separate note, is that living room radiator drawn properly? It is showings its return pipe going back to its supply.
 
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Old 07-02-12, 06:57 PM
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you MUST use oxygen barrier pex.........
 
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Old 07-02-12, 10:33 PM
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Awesome, thanks drooplug. Your answer was confusing to me until I realized that I was mentally reversing series and parallel, so when I said it was parallel, I meant it was series, and vice versa! Also now that you've explained it I can see that clearly those two are in series.

The living room rad is a drawing mistake, the return should definitely go further down to the main return.

Good to hear overall. Any reason I should go with 3/4 over 1"? I kind of want to do 1" just to be on the safe side. And yes, I'll definitely do oxygen barrier.
 
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Old 07-04-12, 06:24 PM
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You need to convert the radiation to sq ft of radiation not a heat loss on the areas so the radiation heats up equally with the others. Then convert it to btu's then size the pipe for that load at a 20f delta-T.
The link Droo was referring to can be entered through the tech menu.
Click this link Technical Menu In the tech menu, the third column click the second topic down. "Btu's, GPM and pipe size chart"
Or you can try this but no guarantees
http://www.comfort-calc.net/pictures/Piping_chart.JPG
 

Last edited by rbeck; 07-04-12 at 06:43 PM.
  #12  
Old 07-05-12, 09:30 AM
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Rbeck, I may need some more help with that. Your post was fairly confusing to me. Can you dumb it down a bit?

Turns out 1 inch is hard to get a hold of, so I'm trying for 3/4 at this point.
 
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