JStephens11
New Member
I just installed a pex radiant heating system in between the joists in my subfloor and I'm having trouble getting sufficient flow at the supply manifold. I have 4, 250ft loops connected to manifolds which are centrally located in my house.
Here is a picture of the 4-port supply manifold assembly I'm using:
It has 4 ports on the supply and return manifold. The supply manifold has an adjustable flow meter, and the return has a balancer. This is to allow you to adjust the flow so that it is equal in each of the four loops.
My furnace has a 3/4" copper supply line. I've reduced this to 1/2" PEX and ran that to the hot side of a 1" mixing valve. (There is a 1/2" x 1" reducer bushing installed on the mixing valve to accept the 1/2" pex)
The outlet of the mixing valve is then reduced from 1" to 1/2" pex, which is then connected to the 1" supply fitting on my supply manifold. (with another 1/2" x 1" reducer bushing)
My supply manifold has flow meters on each of the 4 loops, and I cannot get flow above 0.2gpm out of each of these lines. I need the flow to be around 2gpm.
Do you think this is because of the size of my pex lines? I'm thinking I should purchase 3/4" PEX and run that instead of 1/2" pex, but I do not want to spend the money on these fittings if it is not going to fix my problem. I'm also going to need to buy 100ft of 3/4" pex, when I only need to use about 20ft.
FYI: From everything I've read online, 90% of the time flow problems are because of air trapped in the loops. I spent about an hour and a half yesterday trying to purge the air from the lines, but my flow is so low that I do not think this is possible. What I've been instructed to do is shut the main valve on the return manifold and connect a garden hose to the drain valve on the the return manifold. Then I flow water through 1 loop at a time for 15 minutes out the garden hose to remove the air. When I do this the water is flowing out the hose very slowly...not the steady stream that I'd expect.
Attached is a basic diagram showing my plumbing layout...minus all the little fittings that I described above.
If you have any questions let me know and thanks in advance for your help.
Here is a picture of the 4-port supply manifold assembly I'm using:
It has 4 ports on the supply and return manifold. The supply manifold has an adjustable flow meter, and the return has a balancer. This is to allow you to adjust the flow so that it is equal in each of the four loops.
My furnace has a 3/4" copper supply line. I've reduced this to 1/2" PEX and ran that to the hot side of a 1" mixing valve. (There is a 1/2" x 1" reducer bushing installed on the mixing valve to accept the 1/2" pex)
The outlet of the mixing valve is then reduced from 1" to 1/2" pex, which is then connected to the 1" supply fitting on my supply manifold. (with another 1/2" x 1" reducer bushing)
My supply manifold has flow meters on each of the 4 loops, and I cannot get flow above 0.2gpm out of each of these lines. I need the flow to be around 2gpm.
Do you think this is because of the size of my pex lines? I'm thinking I should purchase 3/4" PEX and run that instead of 1/2" pex, but I do not want to spend the money on these fittings if it is not going to fix my problem. I'm also going to need to buy 100ft of 3/4" pex, when I only need to use about 20ft.
FYI: From everything I've read online, 90% of the time flow problems are because of air trapped in the loops. I spent about an hour and a half yesterday trying to purge the air from the lines, but my flow is so low that I do not think this is possible. What I've been instructed to do is shut the main valve on the return manifold and connect a garden hose to the drain valve on the the return manifold. Then I flow water through 1 loop at a time for 15 minutes out the garden hose to remove the air. When I do this the water is flowing out the hose very slowly...not the steady stream that I'd expect.
Attached is a basic diagram showing my plumbing layout...minus all the little fittings that I described above.
If you have any questions let me know and thanks in advance for your help.