Proper temp for radiant under subfloor

Dave_61

First of all, I want to thank everyone especially Dave from Denver for the input on my Lochinvar piping woes.
I just had one other question on our radiant loop that is in our master bath. It is stapled underneath the 3/4" plywood subfloor.
On top of the plywood is Denshield gypsum-type backer and then on top of that is 12x12 stone (granite) tiles.
We have run our floor at a temp (from mixing valve near boiler) of 110-115 degrees.
I was told by a plumber that came to look at our piping mess that we could increase the temp to 130 as that would not be the temp that the floor would "see" since there is approximately 50 feet of piping between the mixing valve and where the radiant actually is stapled underneath the subfloor. I had been concerned about raising the temp for fear that we would have problems with mortar and/or tiles cracking, but the room could stand to be a little warmer.
What do you guys think? The radiant tubing is a black rubbery type stuff called Onyx that has an oxygen barrier.

Unknown

You won't have a problem at that temp. Your heat load affects things, but I really doubt you'd be able to overheat the floor with 130deg water in that application.

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hr

Is it not

working well enough at 110-115° Ideally, use the lowest possible supply temperature that warms the floor and heats the space.

Yes, generally the Onix requires 7-10 degree warmer temperature than pex due to the wall thickness.

In a perfect radiant world that floor would have a reset control that adjusted the supply temperature based on indoor temperature and outdoor sensors

If not you can do some manual adjusting as the weather cools or warms.

hot rod

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Dave_61

it must cool quite a bit...

The problem we've had is that the room is not quite warm enough with just the radiant. We need to leave the air registers open.
since there is probably 75 feet of copper/rubber tubing in the loop before it even reaches the subfloor, i figure it probably cools down a fair amt before it gets to its destination.

hr

with the radiant running

how warm does the surface of the tile get? I'd suggest 80- 83° max for comfort sake. IF the floor is getting to that temperature and the room is still cool, then you will need to supplement the radiant, probably.

So the number you need to determine is the floor surface temperature, adjust your supply water temperature till you get the surface to the 80-83°

With rubber staple up, yes, you could need 130 or more. Certainly you want to insulate any piping running to and from that zone, if possible, and especially if it runs through cold spaces ie crawlspaces. Not as critical if that piping runs through conditioned space, as the loss will be lower as the air temperature around the piping increases.

I can't imagine you are loosing more than 3-5° between the boiler and that zone with 75' of piping. But it depends on where the pipe runs.

Now with rubber staple up you will get some striping. As ou scan the floor surface with a temperature gun you will notice the temperature spread between the tubes. Tight spacing will minimize this. Transfer plates make it disapper almost completly

hot rod

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Grumpy_2

Transfer plates for onix?

Hot Rod, where do you find those animals? I would like to use transfer plates on an upcoming Onix job, but haven't been able to locate any.