Using 1/2\" pex for B/B

Bob Forand

Does anyone know how much Baseboard can be used when connected with 1/2" pex ? What I am thinking is using Rehau radiant manifolds which are capable of 2GPM per outlet, with zone actuators, connected to baseboard. If I am thinking correctly 2GPM would equal 20,000 BTU, when divided by 600 BTU per foot, I would be able to get roughly 35 feet of board. Am I correct in my thinking ?

Steve_35

You're better off with 3/4\" PEX

Gonna have lots of resistance w/2gpm and 1/2" PEX.

Jim_65

It depends...

> Gonna have lots of resistance w/2gpm and 1/2"

> PEX.



What is your design Delta T?

At 20* DT you can successfully carry 2.5 gpm with 5/8" Pex. I would calculate your total zone heat loss/Btu's and then determine what is the appropriate tubing size and what makes the most sense in this application.

Jim_65

It depends...

What is your design Delta T?

At 20* DT you can successfully carry 2.5 gpm with 5/8" Pex. I would calculate your total zone heat loss/Btu's and then determine what is the appropriate tubing size and what makes the most sense in this application.

Ragu_5

I Like You Guys!

You make me think!

My B&G chart shows 1/2" copper at a maximum flow rate of 1 1/2 gpm, with a max. BTU of 15,000. I don't know how this relates to 1/2" Pex.

Around here, the smart guys try not to use regular pex to feed baseboard, but if they do, it's 5/8 or 3/4 and they drop the water temp to a max. of 170.

Most of us have switched to 5/8 or 3/4 Pex/Aluma/Pex to flexibly feed baseboard applications. You can keep the water temps up to where you need them.

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Jim_65

Exactly

I apologize for not suggesting Pex-Al-Pex for distribution purposes. This is the pefect application for it.

I base my supply water calcs off of Max 170*. This will of course lower the original post of 600 Btu's per lineal ft. but this is a more logical way to approach designs for me. Again, it would depend on the brand baseboard you are utilizing as to output.

I know that Dan has a helpful chart in one of his books that shows the recommended flow rates for copper and steel pipe. Or as ME puts it you can see how many Ft. per Sec. on the B&G Pizza Wheel of Death...:-)

S Ebels

We use a lot of 5/8\"

Just finished a house using BB fed with 5/8" Fosta-Pex. Viega makes fittings, both straight and ells, to go directly from 3/4" BB to 5/8" FP. The Fosta-Pex is GREAT STUFF for BB installs because you can form it to whatever curve you need and it has an expansion ratio that's a fraction of regular pex. It makes no noise at all. Using 5/8" instead of 1/2 or 3/4 gives you an excellent comprimise between capacity and flexibility of the tube. 1/2" won't carry a lot of BB and 3/4", in pex or FostaPex gets hard to handle.

Edit:BTW Fosta-Pex, unlike other multicor products that I know of, uses the same fittings as regular pex. You just use a tool to peel the outer jacket and the same fitting fits both types.

Ragu_5

\"Pizza Wheel Of Death\"...

Jim, you cracked me up! I've never heard that before. Thank you, ME. Is it also available in pepperoni?

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Jim_65

Mark

and his Eathertonisms...I am waiting to hear what his new ones will be now that he is back from Germany.

Take care Ragu.

Steve_35

I'm hearing a lot about Fosta PEX.

Who makes it? Is it PAP?

If it's PAP why are you liking it better than other brands?

Thanks for the info

Contractor

Fosta vs PAP

Pitman,

the difference b/w Fosta-Pex (name comes from Fo = Form and Sta = Stable) is that the FostaPex uses a full layer of Pex tubing wrapped in an Al layer (its essentially pexcel tubing wrapped in al). This gives Fostapex its durability and resistance to kinking and even though it doesnt have an outdoor rating it does have unlimited UV protection. and with the prep tool which is a tool that you put over the end and spin it a couple of times to shave off the layer of Al, Fostapex uses the same tools and fittings as Viegas other tubings. one fitting system.

PAP has a very thin layer of pex then the Al then another very thin layer of pex which can be damaged more easily so than a full layer of pex or a layer of Al in which the fostapex has. both hold their shape very well and have a expansion rate similar to copper. just one in my mind is more durable than the other.

Jed_2

That's It, Guest

Fostapex uses a full inner layer of pex(c), aluminum, and a thinner outer layer. The thicker inner layer gives this stuff incredible resistance to kinking. Fo=form,Sta=stability.

Bob, regardless of the flow ratings of the Rehau manifold, baseboard should be limited to 25' or less, or a maximum of 1½ gpm through the circuit with ½". Many zones these days fall within this range. Viega Fostapex comes in ½", 5/8",3/4", and 1". Viega's Press fittings are Bronze, and don't have a siginificant pressure loss. My Contractor Customers do it all the time. You should use PAP in any event, not PEX.

Jed