I have installed a Wirsbo staple-up system in my current 120 yr old home. I have been researching for my next project, and came across a question. Wirsbo claims that there is no sense in using a pex diameter larger that 1/2" because you won't get more heat per square foot out of it, yet Radiant Floor Company recommends using a 7/8" pex because it carries twice the fluid, and thus has twice the heat output. (50 BTU's/ft.) Who is right? Am I stupid?

You're not stupid, they are. Did I say that? LOL.

There is very little difference in output between the two. Bigger pipe makes them more money, and makes your installation harder.

We use larger pipe for large commercial installs where longer runs are useful, or snowmelt systems.

it carries more heat. the small print that isn't there and should be is even though it CARRIES more heat (more hot water) it's doesn't TRANSFER much more heat to your floor. it's great if you're trying to get a volume of hot water to a manifold, for example, but for floor loops it's a waste of money and effort for no gain at all.

In short, it's bull. I theorize they are angling for larger pipe to reduce pressure drop on their "open direct" systems so it doesn't choke flow to the domestic fixtures. However no one should be installing open direct systems, so it has no real benefit at all.

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Northeast Radiant Technology, LLC
-=RFH Design, Supply and Consultation=-
RPA certified Radiant Designer
http://www.NRTradiant.com
rob@NRTradiant.com

Another way to look at it is this - Lets say you have a 50,000 btu/hr loss. For easy math, we'll base it on 20* delta T. 5 gpm leaving the boiler at 120* and coming back at 100* is 50,000 btu/hr whether you use 3/8", 1/2", 5/8", or 3/4". Your not changing the amount of tubing your using, or the flow, just the size. Water temps will vary slightly based on the size, and tubing run lengths, but that's about it.

prezakitickly correct!

The pressure drop for 5/8 or 1/2 wreaks havock for balancing issues and sets up the installer for low or no flow under some conditions. Toss in the scalding issues & you'll quickly learn why they avoid the correct sizes for joist-bay installations. We actually prefer 3/8" in joist-bay under-floor applications. Smooth as silk.

No open systems.

Rob,
I'm most interested in your comment that noone should be installing "open-direct" systems. Why not? Many web sites suggest this type of system. What is the alternative? I'll admit that the idea of running your domestic water through thousands of feet of pex doesn't sound like a good idea, but if so, then why so many recommendations for same?
Thanks, Steve

Mr. Yates? I know your face is turning blue,or is it your fingers?:0

Do a search under Legionella and read what Dave Yates has to say. Should answer your question.

Why so many recommendations.......Denial

Gordy


[This message has been edited by Gordon Kaske (edited 02-18-2005).]

Follow the $$$$$

Therin lies the answer.

By omitting a heat exchanger and possibly a few other related components, these companies are knocking several hundred dollars off of their system prices without actually offerring low cost parts, so they maintain their profit margin while also being the bottom line favorite. This sounds great until you see what you are really doing by omitting that very important part of a water heater-fired system.

Open direct systems are dangerous, dangerous enough to be illegal in many areas, and also much more likely to succumb to failure as a result of the constant introduction of new water (read; sediment, minerals, whatever is in your water) which can gum up your valves and pumps.

do the search for legionella on here and you'll see why I say what I say.

------------------
Northeast Radiant Technology, LLC
-=RFH Design, Supply and Consultation=-
RPA certified Radiant Designer
http://www.NRTradiant.com
rob@NRTradiant.com