Radiant floor manifold ... above or below the subfloor?

woobagooba

Folks. Situation is an above floor radiant panel system with full basement access below. I am variously reading or being told that the manifold needs to be above the floor, or that it is ok to mount it below. We are very limited in ability to mount the manifold above the subfloor. What are the pro/cons of above versus below mount? Cheers

Dave H_2

Manifold placement is wherever you can get it. My first floor manifolds are in the basement.
The second floor manifold is on the second floor in a closet. It made more sense to mount it up there because I would have eaten up 75' or pex to go back and forth and getting to snake around 8 loops back and forth would have been a nightmare, 1 back and forth was alot easier

EdTheHeaterMan

With the proper piping design, you can mount the manifold anywhere.

"Proper piping design" would use the principles of pumping away from the expansion tank. as outlined in @DanHolohan's book, appropriately titled "Pumping Away and other ..." available in the store on this site.

I would add one additional pipe to the manifold location. A dedicated drain line for purging. then take a clear plastic tube to connect the manifold purge valve to the dedicated drain line so you can see when the air stops and the loop is full of water.. The other end of the dedicated drain line can go anywhere the purged water will not be a problem. A laundry tub, outside to the lawn outside, or to a sump pump in the basement. Just think of it like a garden hose that will always be there in the wall or rafters that has no restrictions or kinks so the purge happens easily when you need it.

Any air that is going to find its way to a manifold or loop will be able to be purged in the initial filling of the system or subsequent service of components. After that, any air that develops during normal operation will be purged by the proper design of the system.

Mr. Ed

GroundUp

Personally, I like to keep the manifolds above the floor when possible for the simple fact that any air that may be introduced can be vented at the manifold. I don't really love mounting manifolds upside down either, but I really hate running a mile of 1/2" pex where it doesn't need to be.

EdTheHeaterMan

GroundUp said:

Personally, I like to keep the manifolds above the floor when possible for the simple fact that any air that may be introduced can be vented at the manifold.

Is that how you picked your handle, Ground Up?

GroundUp

EdTheHeaterMan said:

GroundUp said:

Personally, I like to keep the manifolds above the floor when possible for the simple fact that any air that may be introduced can be vented at the manifold.

Is that how you picked your handle, Ground Up?

Ha, ironically enough, yes. My business is strictly radiant floor heating (I will do other hydronic work but radiant floors is the niche and 95% of it) so I thought it was a cute play on words, effectively heating from the ground up.

ewang

My infloor staple up with plates pex is fed from below - no issues.

hot_rod

Manifolds, especially the type with auto air vents do have the potential to leak, below the floor may be a bit safer.
I have seen some nice installations where the manifolds are mounted below, on their side, so they take very little space. If you can't get them in a joist bay.