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rdtuna
Registered Users
Posts:4
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| 03/15/2006 11:22 PM |
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I will be installing over the floor 1/2"tubing with aluminum plates. If I will go with 8" per center I will end up installing 350' of pipe. I heard that the loop can be 300' max.
Is it better to install 350' going every 8", or install it let's say every 10" (that way the loop will be less than 300' lengh)
Another question: is it worth buying more expensive tubing (like wrisbo or rehau) when you can get no brand pipe with O2 barrier almost for half that price.
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NRT.Rob
Registered Users
Posts:386
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| 03/16/2006 10:16 AM |
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Depends on the brand. Some of the no-brands are pretty brittle and don't handle kinking well. We like PEX-A, personally. Then if you kink, you can heat the pipe and let it reform.
Tubing loop length maxes depend on your load, whether you're using glycol, and your pump. Stick to the 8" o.c. and go with two loops if no one has done a real load calc.
-=Northeast Radiant Technology, LLC=-
www.NRTradiant.com |
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-=Northeast Radiant Technology=-
NRTradiant.com |
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onlyinamerica
Registered Users
Posts:16
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| 03/16/2006 4:50 PM |
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I agree with Rob, Pex-A is the best stuff. From one of the manufacturers they suggest that if it's not too bad a kink to unkink it and leave it alone only if it's on a straight run. He didn't suggest reheating it. AFter you kink a few you'll get a feel for what's a bad kink versus a unacceptable kink. [:D]
onlyinamerica |
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Unregistered
Registered Users
Posts:2321
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| 03/17/2006 10:16 AM |
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My understanding of the 300' rule is that, under most gph situations, the heat will have been sucked out of the water during the time it takes to travel 300'. If I remember right, return water would have been in the system about 3 minutes at 1gph. If your loops go back and forth across the room, the return side of the room will not heat up properly.
If your pattern is a spiral, with supply and return next to each other, the problem is reduced, although you may effectively have warm tubes on 16" centers with cooler temp return runs between them. This pattern may also help because the initial warm line runs all the way around the perimeter of the room, usually where it is most needed.
With some planning of the tubes, you may be able to reduce the length. Couches, counters, and coffee tables don't need heat under them.
Mark Fleming
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NRT.Rob
Registered Users
Posts:386
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| 03/17/2006 10:59 AM |
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Whoa Mark! Couches and coffee tables most certainly do want heat! Counters, sure, skip them. But couches and cofee tables are open underneath.. you get output.. and they tend to move with time.
Max length is determined by Load, which dictates the flow you need at a certain design temperature drop across the loop (usually ten degrees). If you have a low load, less heat transfers out of the pipe and less flow is needed to match that delta T. I've seen a lot of 300' loops than only need .5 gpm to hit a ten degree temp drop at a given load, which is no problem at all. I've also seen many that need 1.5 gpm at which point your pressure loss on a loop that big is prohibitive without upsizing a pump. In that case, shorter loops would be better.
300' is not a rule of any kind. It's an approximation that is often used when no one is doing the math. As such, it *usually* works out. But many times, a better way could be done (smaller pumps, for example) if such a rule of thumb were not the guiding design principle. I would say if no one is doing the math, stick to 250' in most cases. You're pretty safe there.
-=Northeast Radiant Technology, LLC=-
www.NRTradiant.com |
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-=Northeast Radiant Technology=-
NRTradiant.com |
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