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# manifold size for my radiant floor

Member Posts: 7
Would a 3/4" manifold with three 300 foot loops or about a total of 750 square feet have enough gpm. I would be making it myself any suggestions. Thanks

• Member Posts: 4,393
Did you do.....

a heat loss? What are the loops?... 1/2 pex/? 3/4" pex? 5/8" ? In Slab? Staple up? kpc
• Member Posts: 7
1/2"

1/2" pex under a 2" mud job
• Member Posts: 3,086
Heat Loss

What's the heat loss? When you say 300' does that include the leader lengths to and from where the manifold will be?
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Member Posts: 7
the manifold will be piped 10' from the boiler

i was thinking of making my own manifold with temperture gages and balancing valves.

One 300' loop will take care of the kitchen/dining room that is next to the boiler room and

the two additional loops would take care of the bath, living room and bedroom. I will be mounting the manifolds in the boiler room
• Member Posts: 3,086
edited November 2011
Still

Doesn't anwser the question as to the heat loss. With this post I'm now wondering how you are determining that all the rooms need the same water temp and what is telling you how to balance. I'm also wondering about thermostat placement. You mention nothing about zoning.

What I meant by leader lengths is the length of loop tubing that exits and enters the floor from and to the manifold. Is that calculated into your 300'.
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Member Posts: 9,546
edited November 2011
Starts with a Heatloss

Room by room.  The heat loss dictates the flow rate (GPM), and the water temps needed to heat the space.

But in a nut shell 1/2" pex CAN carry 15000 BTUS at 1.5 GPM 20* DT. Half that at a 10* DT.

If you are going to run 3 loops off of the same manifold then you should make it the size that can deliver enough max BTUs of the 3 loops combined so 45000 btus. 3/4" copper pipe can deliver 43000 BTUs at 4.3 GPM. 1" can deliver 88000 BTUs at 8.8 GPM. This would be at 20* DT. Again half those carrying capacities for a 10* DT. That is also for type M copper. Type L drops those numbers.

The problem with the 3/4" pipe size is potential GPM delivery. IF YOU NEED the full 15000 btus in each loop that would require a flow rate of 1.5 gpm each, for a total of 4.5 gpm. The 3/4" maxes out at 4.3 gpm.

Again these are max flow rates to avoid velocity noise, and pipe erosion. Chances are you will not need near that. The only way to tell is through a heatloss. With out it everything is a guess.

Also unless you have short supply leaders to the loops they may be a little long for 1/2' pex. Long loops require bigger pumps because there is more friction losses to over come.

Gordy
• Member Posts: 3,086
edited November 2011
He Should Be Running

a 10 degree delta-t based on his application. I hate it when I see a I'll just run tubing to equal the square footage. It tells me no heat loss, no looking at solar or any internal heat gain. It also tells me low budget or internet shopper.

No personal dig to the poster just fits the hundreds of similar profiles I've come across.
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Member Posts: 9,546
Agree Chris

Floor treatments also.
This discussion has been closed.