wall radiant question

[mmudd]

I recently installed some wall radiant heat in the finished basement area of my house. Basically I did 2 -7ft high walls 11 ft long using 1/2 pex on 8" centers based on the design shown in the idronics handbook. It works great heating the 600 sq ft and also contributes significant heat for the room above it using low temp water. If you notice on the photo I used 2 different styles of transfer plates on the install. On the top part of the wall , I used extruded alum plates, with the thinking they would be more difficult to pierce with a small nail by an usnsuspecting picture hanger in the future- that could be me

Based on how well wall radiant has worked, I was planning to add more wall heat in my house, and thought about just using the lower 4' of the wall to install the pex tubing (just to limit possible nail pierceing and drwyall finnishing). I would run the pex on 4" centers instead of 8" centers so as to keep total run of pex the approximately the same as though it were an 8' tall wall due to closer spacing of the tubing. I'd keep the pex turn at 8" and avoid kinking by overlapping the loops at the ends.

My question is:
Would the 4" pex spacing, with only 1/2 the amount of drywall exposed to heating, generate approximately the same BTUs as an 8ft high wall with pex 8" on centers. Does the area of the heated drywall (mass) make much difference in the equation if the amount of piping in the wall is the same? I unstand how obstructions (furniture placement etc) can affect performance. I know the tubing expansion by heating causes movement at the pex loops, and because of the overlap they would probably touch each other at the loops in the stud cavity. Assumed that would not cause any problems if I used some tube insualtion at the loops to keep the pex from actually touching. Using only 4 ft of wall would allow me to do 1 piece drywall with no seams, just a chair-rail at 4ft height to allow for where the drywall meets and account for the elevation difference.
Thanks

 

[BoilerMan]

Have you considered using sheet metal strips to cover the exposed pex in the plates? Then you can d the entire 8' w/o worry of picture hangers......

TS

 

[heaterman]

The nice thing about pex in walls or ceilings is you can drive the surface temp significantly higher than you can on a floor. More btu's per sq ft of area.
I like to keep it below 4 to 4-1/2 feet just for the sake of nails and picture hangers. If you go higher the original owner will be aware of it but what about the next guy or the one after him.

 

[mmudd]

Yes, the wide range of temps is an advantage when radiant is not in the floor. I want to keep the temps as low as possible. I have been running 120 degree water when weather is extremely cold, and can use 110- 115 degree water in spring fall. I have a mix valve that supposedly goes from 90 to 170, but I really have not had to adjust much. I want to keep future wall radiant below 4 ft , and hoped by doubling up on pipe, I can still run lower temp water and get good performance. Those extruded transfer plates like I used on higher section of the wall would be tough to get a small nail thru, but are kind of pricey and a little harder to install, since you are putting them on reverse how you would under a floor.ave to get the pipe in before you can install. The transfer plates I got from Tom sullivan were really nice , easy to install, 6 inches wide (vs 4") and cheaper, so I prefer using them.