What Type of PEX did you use, and who designed it?

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shagbark

New Member
Hearth Supporter
Sep 29, 2008
7
south central, ky
Hello Boiler Room,
My basement dig out was finished today, footers tommorrow! Next week I need/must have some pex to install before slab can be poured. Please point me in the right direction! Thanks in advance.
 
I would use 7/8 OD
Pex with oxygen barrier if you have a boiler that can be hurt from oxygen.... if your house system is separated from boiler then oxygen barrier is not needed....

http://www.radiantec.com/systems-sources/systems.php

http://www.radiantcompany.com/ can help you set up a system. They can tell you what size pipe and pumps....
I would look into a system with 1 more powerful pump and solenoid valves to zone rather than having 1 pump per zone. Something to look into.

In concrete I laid down a vapor barrier (plastic) then 2" foam then wire mesh that was basically 6" squares and I tied my pex on 6" centers. My pex is 1/2 and I think it would of been better to use 7/8 OD pipe

If your project is complex with lots of zones you may need help setting up the system

Some rules are: 300 foot runs are the longest - so one part of my house has 3 - 300 ft runs in the concrete all 1 zone
if you have 150' run and find out you need to add another run in that zone it also needs to be 150 other
wise the shorter run will have more water running through it than the longer run and that will effect heat output...
I was reading that you could have longer runs with more powerful pump. something to look into..
 
Don't forget to pressure test it with air before and during the pour. So you will need fittings to go on the ends of the pex tubes. (maybe available at the local L*wes) Where the pex comes out of the slab, you will probably want to put some long sweep 90 pvc conduit to run the tubes through. This keeps the troweling machine from abrading the pex when you are finishing the slab. Definitely use O2 barrier pex to keep your options open in the future. (usually not available locally) I used 5/8 tubing which is an oddball size. I think 1/2 or 3/4 would have been OK. Smaller the diameter, the harder your pump has to work. The bigger the diameter, the harder it is to bend the pex at the ends. It's a tradeoff. You might want to insulate under the slab... at least around the perimeter.
 
nic89 said:
I would use 7/8 OD
Pex with oxygen barrier if you have a boiler that can be hurt from oxygen.... if your house system is separated from boiler then oxygen barrier is not needed....

http://www.radiantec.com/systems-sources/systems.php

http://www.radiantcompany.com/ can help you set up a system. They can tell you what size pipe and pumps....
I would look into a system with 1 more powerful pump and solenoid valves to zone rather than having 1 pump per zone. Something to look into.

In concrete I laid down a vapor barrier (plastic) then 2" foam then wire mesh that was basically 6" squares and I tied my pex on 6" centers. My pex is 1/2 and I think it would of been better to use 7/8 OD pipe

If your project is complex with lots of zones you may need help setting up the system

Some rules are: 300 foot runs are the longest - so one part of my house has 3 - 300 ft runs in the concrete all 1 zone
if you have 150' run and find out you need to add another run in that zone it also needs to be 150 other
wise the shorter run will have more water running through it than the longer run and that will effect heat output...
I was reading that you could have longer runs with more powerful pump. something to look into..


Whoa there padna'....Not trying to belittle your experience or recommendations but let me interject a few comments here before this poor guy gets himself in trouble.

First of all, the companies you mentioned are probably responsible for more failed attempts at radiant heating than ANY other companies in the USA. Just go over to the Wall at www.heatinghelp.com and mention the name.....then duck and cover. I'm sick of companies like that giving radiant heat a bad name because they gave a poor or ill advised recommendation.

Second, do a heat loss for the structure to find out what you actually need for heat ouput. Nothing you can do will paint a clearer picture of what size tube, control method, pump size, loop length etc, etc. When you know the btu requirements you can make informed and intelligent decisions about the entire system. If I learned one thing early on in my heating career it was to do your own homework. Don't rely on some guy that just wants to sell you "stuff". If you are going to undertake the installation personally, you owe it to yourself to understand the ins and outs of what you're doing. Don't do it if you don't understand why. You'll be glad you did.

Third, all of the experienced heating professionals I know use O2 barrier tube for all heating applications regardless of whether it's an "open" system or not. In Europe, where radiant heating is much more "mature" than here in the U.S. barrier tube is mandatory. I have learned to pay attention to the Euro people when they talk about heating because they speak from knowledge and experience, especially the Germans. That being said my two favorite tubing brands are Viega and Rehau. Both are top drawer product. When you're putting it in cement and consider the cost of a tube failure there is no substitute for the best. I've met a lot of people that brag about how they bought 1/2" tube for $.?? a foot only to hear a few years later that their system is abandoned because of a failure of some kind. Tain't worth it man! Buy something with a good warranty and a long (15-20 year) reputation. Read the fine print. A lot of companies warrant the tube but not associated repair costs. Big deal!!!

Now, as to tube size and length, there are a number of schools of thought on temp drop and heat transfer and each argument has it's own merit. I'll just say that the main thing you want to avoid is a system with high head. That means you adhere to these rough guidelines: 1/2" tube = 250-300 feet, 5/8" tube = 350 to 400 feet. 3/4 tube in a residential application is a waste of effort and needless expense along with being a PITA to work with.. The only time we use it is in 500' runs for a snow melt application or for a main.

Lastly, I want to apologize if I come off a tad strong on the radiant heat/ tube stuff. As a heating professional I have run into a lot of jobs that are screwed up and don't work because someone got some bad advice.....or worse yet, tried to do it cheap. I get to come in after the fact and try to straighten out a mess ar worse yet, tell the customer there's no fix for what they have done. They get a bad taste in their mouth about radiant heat and my business suffers because they go around telling all their friends they would "never do that again".
I don't begrudge anyone the opportunity to do it themselves, just do it right or else don't do it at all.

The soapbox is now open.


BTW: Don't neglect edge insulation in that basement!!!!!
 
Just wanted to ditto what heaterman said there.

Radiant, done right, is the best way to heat (in my opinion, anyway). Radiant, done wrong, is a nightmare.

You need to start by determining your heating needs, then move from there to a tubing layout and pipe size selection based upon the runs in the layout.

Joe
 
I think you are getting lots of good advice and warnings worth listening too. I just want to say that if you are willing to do the research and get feedback on your design before you implement it, you can do this yourself. I have been in your situation... project underway, concrete showing up, and needing a radiant plan quick because it snuck up on you. In an ideal world, you would have hired someone with references to have this designed for you (optimally) and the pex would already be on site. If you err on the conservative side of every decision (and understand every decision), it will cost more money for materials (than if you had it professionally designed) but your project can stay on schedule. Don't throw caution to the wind, but there are several factors you can play with later on that can compensate for less-than-optimal decisions now. (pump size, H2O temperatures, balancing valves, etc.) Of course, one really bad decision now (like no insulation anywhere, or 3/8" tubing, or one big 800 foot loop, et. al.) could permanently ruin the whole setup for you later on down the road too.

I would unplug the TV for the next 3 days, read everything you can about radiant design, draw some sketches and post them here and elsewhere to get feedback. Get it all done at least a day before the concrete trucks show up - you don't need to be worrying about this when you are trying to pour concrete! Good luck.
 
I would unplug the TV for the next 3 days

I unplugged my TV 30 years ago and I am still way behind on my projects.

Spend the money on a manifold with more taps than you think you need and run more, shorter loops of 1/2" O2 barrier tubing. It will take less power to pump the same amount of heat into the slab. That will save money every minute the system is running for the rest of your life. You can also balance the flows to different parts of the floor to allow more water where more heat is needed.

Insulate under and around the edge of the slab. Start with what you think you need and then double it. The myth that you'll heat the ground beneath and then it won't take any more heat is just exactly that, myth. The earth will continue to suck out the contents of your wallet all year long.

With this recession going on maybe it's not too late to get some good advice from a radiant designer that has some time on his hands. Their services are not a lot of money compared to the cost of the system and especially compared to the cost of fixing it later. It's not easy getting it just right first time.

My $.01
 
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