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Old 09-28-2008, 12:40 AM   #1
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Pex tubing/heat layout questions


I have a home on a slab. I plan to extend some areas in the future, and abandon the heating pipe in the foundation. I have oil/HW. My questions are: 1. Can I place Pex tube, or copper in the walls along the area where the heat baseboards will be (only exiting the walls for the baseboard runs, of course) ? 2. How/where to properly/efficiently place new baseboards? and 3. How to trace the existing path of the heating/domestic HW plumbing? I want to replace all the old stuff, maybe doing some radiant, and putting some of the baseboards where I want to put them. Thanks in advance!

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Old 09-28-2008, 09:41 AM   #2
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Pex tubing/heat layout questions


Mudpaws, think about it, You don't want water piping buried in the walls of your house. What are you going to do if there is a leek?

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Old 09-28-2008, 12:06 PM   #3
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Pex tubing/heat layout questions


I don't know how else you could run the piping without going through the walls of the house unless you could use the floor bays. But unless the floor joists are running the way you need them to go so you can loop one end of one radiator to the next and you've easy access to them, this is going to be a bit of work. I think PEX would be easiest and likely not to split if it freezes unlike copper would; also, since it is for heat, unlikely these pipes would ever get cold enough (assuming they're on the heated side of the wall insulation).
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Old 09-30-2008, 12:58 PM   #4
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Pex tubing/heat layout questions


Pex radiant heat (and cooling) is really catching on. I use it all the time for radiant floor heating.

You can run pex as you describe instead of electric baseboard heaters. You can even get aluminum plates that attach to the pex and help draw off heat.

There are several things to remember.

If you have any ferrous in the water circuit (like an iron pump) then you have to use barrier pex which is double the cost of regular pex. This keeps pex from absorbing oxygen and causing rust in ferrous metals. If there isn't any ferrous in the circuit then regular pex is fine. If you do use a pump there are brass ones that are expensive.

Pex is only rated up to 200 degrees and 60psi. Any more than that and it will rupture. I know as I have tested it. At 140 degrees it will run at 120psi (if memory serves me well).

You will have to have a pressure bladder, pressure relief valve, pump and air scoop in the system.

If your system is closed (versus open) and in danger of freezing then you will need to have a 50% mixture of propolyne glycol. Pex is unlikely to break when frozen. It can expand to 50% it's size before it breaks. Most often it is the brass connections that break and these can be well insulated to prevent that.

I love radiant heating. It makes the living enviornment more stable and not prone to getting too hot and then too cold. It warms up the infrastructure and keeps it warm to radiate out constant heat. Central air just heats the air and does nothing for the structure.

The big drawback is the lag time before you see any heat. It can take hours to heat a room if the heat has been off for a while.
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Old 10-28-2008, 11:17 PM   #5
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Pex tubing/heat layout questions


Well, if I had a leek, I'd eat it! ha ha .. Seriously though..Thanks for the detailed answer Marvin! I don't have floor bays, except for the upstairs. AS i mentioned, 1st floor is on a slab foundation. Everything would be on the living space side of the house, in other words, heated- not prone to freezing. Perhaps where I don't do the radiant, I could run the tubing along the bottom of the wall studs (attached by, say a u-clamp) and build a custom moulding that hides it and looks good. I don't know if there is a such thing already, but a sort of "compound base moulding" (term I made up, I think) might do the trick. I would need to get a pressure bladder and a I think a brass pump. Right now the circ is a Taco cast iron one. I have the scoop and rel valve.
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Old 10-28-2008, 11:31 PM   #6
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Pex tubing/heat layout questions


Quote:
Originally Posted by mudpaws View Post
Well, if I had a leek, I'd eat it! ha ha .. Seriously though..Thanks for the detailed answer Marvin! I don't have floor bays, except for the upstairs. AS i mentioned, 1st floor is on a slab foundation. Everything would be on the living space side of the house, in other words, heated- not prone to freezing. Perhaps where I don't do the radiant, I could run the tubing along the bottom of the wall studs (attached by, say a u-clamp) and build a custom moulding that hides it and looks good. I don't know if there is a such thing already, but a sort of "compound base moulding" (term I made up, I think) might do the trick. I would need to get a pressure bladder and a I think a brass pump. Right now the circ is a Taco cast iron one. I have the scoop and rel valve.
Sounds like you have it down. To get the most out of the heat make sure you don't just do a big loop. Otherwise buy the end of the loop the water will be cold.

If you have some pipe just passing through a room and don't want to give off the heat make sure you insulate it well.
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Old 11-21-2008, 11:59 PM   #7
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Pex tubing/heat layout questions


oh- another question:

The air scoop must be brass too? I believe my relief valve already is...

Before I do this, it will probably be Fall '09 at least. It's not in the budget this year, and I planned to add onto the house. At that point, I will do the radiant.
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Old 11-25-2008, 11:34 PM   #8
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Pex tubing/heat layout questions


also, can I do a "load calculation" myself? as in plan out how many baseboards and where to best place them?
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Old 11-26-2008, 04:51 AM   #9
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Pex tubing/heat layout questions


Slantfin has a good load calc program, or you can use this one.
http://hvaccomputer.com/talkref.asp
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Old 11-26-2008, 04:59 PM   #10
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Pex tubing/heat layout questions


Keep in mind that baseboard requires a much higher temp water than radiant. So if you currently have baseboard you have a high temp water. If you want radiant heat you will need to bring down the temp of the water that will be used for that.

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