Feed to manifold sizing

Gordy_2

to include the fact that my design temp is -10 with an inside design of 72*.

There is a slant fin heatloss program on this site you can download,its in the lower left hand corner on the homepage here,and its free.

Gordy

G Terrill

Hydronic Manifold Feed

Looking for info to help size supply and return to a 5 loop manifold from the circulator located off of the primary loop which is approx. 50 ft away. I assume the size of the pipe needed is a function of the characteristics of what is being supplied but wondered if after doing the calcs, 9 times out of ten a 3/4" or a 1" supply is used. This particular manifold has five loops at 250 ft each 1/2" barrier pex. Is the real way to do this to figure out the frictional losses of the amount of 1/2" tubing as well as number of fittings etc. in the supply line from circ. pump to manifold?
Do most forego the real calc and use a rule of thumb?
Is it common to use pex to run from the circ. pump to the manifold vs. the costlier copper?
Thanks in advance for your input!
Greg T

Norm Harvey

How many BTU's do you need to supply to that manifold?

Gordy_2

Loads

1/2" pex has the ability to carry a maximum of 15000 btus.

So if there is 5 loops that is 75000 btus potentially the manifold can handle, if it needs to.

1" pex can carry 104000 btus, 3/4" pex can carry 54000 btus. These are at 20* delta ts, So you would need to use 1" pex.

But as Norm points out what is the load for the manifold ?
You may not need to run the 1" if your load is under 54000 btus.

Gordy

G Terrill

Maybe I'm confused on this. The heat loss calc done by the boiler wholesaler for my retailer came up with a load for this 1368 sq ft basement area of 3,120 btuh. Design temp is 0 deg. with inside air temp of 65 deg. Doesn't this seem low, even for a walkout basement? Even using a rule of thumb I found of 0.3 btuh/sf/degreeF would put the load at 26,676. Without better info, worst case scenario my loops can offer more than I need therfore allowing me to run a lower temp water and I can feed this manifold with either the 3/4 or 1".

The wholesaler used Wrightsoft (Uponor System) software. They may have made a lot of assumptions because some of my window info for the house is not available yet.

Let me tell you my objective here in learning this. I have studied radiant with on line research and magazine articles for the last 5 years or so. I have placed the tubing in the slab and can handle some of the design and all of the plumbing work but don't want to buy a heat source on line with no backup or warranty. I have received pricing from two mech. contractors that are willing to work with me to supply the heat source but I don't just trust what the contractors tell me, especially when the pricing is all over the board between the two. I'd like to approach this with caution because if they sell me the wrong unit I'm still the one stuck with it.

Thank you to Gordy and Norm for your responses.
Greg T

Gordy_2

My basement heatloss is about 10000btus for 2100 sqft. 600 0f it is semi conditioned crawl space.

Fully in the ground, no exposure,12" cinderblock walls, no insulation.

I don't know what you have, but pretty darn efficient by those numbers.

Gordy

G Terrill

That's my point. I don't think I have reliable information to continue. I will have to start with the right info or will just be taking a shot in the dark with this.
Thanks, GregT

G Terrill

Continuation

I NOW have a correct heat loss calc. so I wanted to move on to the rest of my pipe sizing. Entire house requires 71,000 btu's and my three zones each falls below the capabilities of 3/4" pex to feed the manifolds so I am good there. Now on to the primary:

Boiler will have 1" water inlet and outlet and with a max capacity of 1" copper being 80,000 btu (w/ 8gpm & 20* dT) I think my primary loop can be from 1". First question, am I missing any other info that would make me use a
1 1/4" primary and if so, the boiler 1" in & out becomes the limiting factor on gpm? OR is it a pressure drop but higher flow still gets maintained?

Secondly, and similar in nature, if I add an indirect dhw tank later that also has 1" in & out, does larger pipe to the tank do me any good for faster recovery?

Thanks for bearing with me and for your previous responses.
G Terrill