Hi,

I have a zone with 2 loops by 210' 1/2 pex-al-pex. For supply/return line to the zone I want to use the same pipe. It's easier to run than a copper, and I have pipe leftovers anyway. In terms of water flow, it's probably not a good idea: the supply/return line will become the bottleneck. To match the diameter of 2x1/2 I have to use 3/4 pipe. However:
- don't want to buy extra roll of 3/4 pex just for supply
- with 1/2 supply line, the water in the line will move twice faster than in the zone itself. So, less heat loss along the way.

What do you think?

Thanks

quote:

- with 1/2 supply line, the water in the line will move twice faster than in the zone itself. So, less heat loss along the way.

No.

Do you know the load of the room? That dictates how much flow you actually need.

How long will the supply/returns be? You could have just ran each loop from the mechanical room to the zone as long as your loops were 300' or so, no longer than 350' each.

quote:

Originally posted by RPA guest:
Do you know the load of the room?

Around 5,000 Btu/hr.

quote:

How long will the supply/returns be? You could have just ran each loop from the mechanical room ...

Hmm, you know, I'll do that. Sounds really good to me. Supply/returns will be around just 20'.

quote:

Originally posted by RPA guest:
... as long as your loops were 300' or so, no longer than 350' each.

I belive this statement is not quite correct.

The loop is limited to 300'. If I run it back to the mechanical room with extra 100' pex, it make the loop 500' long. So what? First and last 100' of the pipe is not a "loop", it's a "supply/return line". So it should be just fine.

Really loop is limited to 300' to keep the water temp even along the loop. So, we want even water temp only on the part of pex that considered as as "heating loop".

No. I'll explain it (try to), but you should check out Robert Bean's seminar today. He will expain it much better I'm sure.

300' 1/2" for pex has nothing at all to do with even temperatures. It has to do with pressure drop and keeping your pumps small.
1/2" pex rule of thumb is 250'-350' max, 300' being in the middle. You could do 400' if you wanted to use a bigger pump, but that pump costs about 3 times what the smaller pump costs, and costs more to run and more to replace.

Your load is 5000 btu, so you either need .5 gpm total (.25 per loop) at a 20* DT, or .75 gpm at a 15* DT, or 1.0 gpm at a 10* DT.

At 1 gpm (.5 per loop) your head loss is pretty low (less than 2'), but your load is pretty small. Now you need to factor in the pressure drop for your supply/return lines.

1 gpm through 40' of 1/2" pex is actually pretty low also. In your case, it will work, but this is by no means whatsoever the norm. You have to look at every job.

Dear RPA Guest,

Can I read/lean more details about such (was a typo here - "suck" instead of "such") calculations anywhere on the Internet? URL, please.

This message has been edited. Last edited by: Tarpan,

I don't understand why you think they suck?

500 x gpm x DT = BTU. Can't dispute that.

Pressure drop through 1/2" pex at .5 gpm is (approximately) .008' per foot of pipe.

210' x .008 = 1.68', right?

Please explain.

Unless you meant "such" calculations?

quote:

Originally posted by RPA guest:
Unless you meant "such" calculations?

I'm sorry. It's just a typo.
Yes, I meant "such".

I did not mean in any way to upset you. Please consider it just as a funny typo.

Ah you didn't upset me, just confused me. I'll try and find a link to some formulas.

http://www.capcosupply.com/Hydronic%20Handbook%2004/22%...e%20Drop%20Chart.pdf

Thats a pex pressure drop chart. It's a little higher than the one I was using earlier, but close.

http://www.capcosupply.com/hydromanual/page23.pdf

Zoning rules of thumb.

http://www.capcosupply.com/old%20hydromanual.htm

All kinds of junk there.