Pex radiant heat system cement board with click vinyl

primitivepete44

Finding out most click vinyl flooring and the like have a max temp rating of 80-85 degrees... thinking installing 1/4 or 1/2 inch cement board directly over the sleepers and transfer plates and pex will help keep higher water Temps dispersed enough to keep from having issues with the flooring....any experience or thoughts anyone????

primitivepete44

hot_rod

There are some solid core vinyl products that can run higher temperature.

But you should not need to go over 82F for a comfortable radiant hard surface anyways, it starts to be uncomfortably above 82f for bare feet. 80F surface should be plenty hot.

If you know the room load, it is what dictates the floor temperature at design day. Tightening to 6 or 8" on center tube spacing would help run lower temperature also, if you have a high load room.

You could put a floor sensor over one of the aluminum transfer strips. Use a radiant thermostat with a floor sensor limit function. I like this tekmar brand. Many of the wifi stats can have a sensor added also.

primitivepete44

thanks, my tubing is all laid in mostly at 12 inches between the 1/2 inch pex runs already....a few returns are closer than that but not many. I was thinking that the water temp would end up being around 100 degrees out of the propane boiler to get the floor up to the 80 degree mark. The issue I am thinking is without some type of cement board directly on top of the tubing to difuse or disperse the heat that the flooring will suffer from that excessive water temp in the tube.....does that make any sense?

hot_rod

It cannot hurt. How thick of a CB are you considering? It may lower the plate temperature a few degrees and also spread that temperature. Is it enough to reach the goal, hard to say without some testing.

To get an average floor temperature of say 80 degrees, the beginning of the loop would need to be warmer than that by 5 degrees, maybe more. The end of the loop 5 or so cooler. Typically those high temperature conditions only happen on a few design days.

If you performed a heatload calc and a design, those numbers would be spelled out for you.

The floor sensor would be your insurance policy so you don’t ever have to find out. Even if an outdoor reset control called for high temperature, the sensor would shut down that zone.

I did see one high temperature rubber tube system put yellow stripes in the vinyl flooring. I suspect it was running well over 100 on the bottom of the tiles. It also caused the adhesive to soften and smell. I think you want to avoid all those potentials?

primitivepete44

Well, either 1/4 or 1/2 inch c.b. ...difference of 1.50$ between the two.  The
Quarter inch would be lighter in weight obviously and heat up faster while the half inch would be a bit slower but retain the heat longer.  Might be an even swap. Height is not an issue as there is only one in- swing entry door. Weight should not be either as the floors are pretty well braced up. I had purchased some inexpensive wood click flooring for the upstairs originally as we we going with baseboard up there...but am going to return it for the more expensive and better mineral core click vinyl we planned on using on the first floor. I'm  sure you'd get a laugh out of the build and design methods I've incorporated in this house. Would have gone easier if there was a contractor who did gypcrete in this state. Most are putting their radiant heat in a slab...which is what the original plan was. Thanks

HomerJSmith

CB has a R-Value that is very low, which means that the heat energy will pass thru it easily. I would think that CB would result in banding and not disperse the heat energy, widely. I don't know how you are planning on constructing the flooring sys.

High heat is where the tubes are and low heat is between the tubes. Some how you have to move heat energy from the high heat areas to the low heat areas to have an even dispersion of heat energy across the flr.

primitivepete44

The picture above shows how it is so far...one inch pine boards,then 5/8 osb, a layer of reflective foil, then the sleeper boards of 3/4 inch osb, the heat transfer panels with the 1/2 Inch pex tubing set 12 inches apart. Not worried so much about the heat getting thru as much as damaging the vinyl flooring from direct contact with the tubing. That's why I'm contemplating using a cement  board product. Maybe a thinner plywood product.

MikeAmann

I like your idea of using cement board.
But there are big differences in the brands.
I would avoid Durock and Wonderboard.
Those are full of voids and I dare you to carry a sheet out of the store and make it to your vehicle without it crumbling. HardieBacker is consistently solid through and through and a superior product, IMO. And it now comes in a waterproof version. Comes in both 1/4" and 1/2" thicknesses.
https://www.homedepot.com/p/James-Hardie-HardieBacker-with-HydroDefense-Technology-3-ft-x-5-ft-x-0-42-in-Waterproof-Cement-Backer-Board-9000556/311573721
https://www.homedepot.com/p/James-Hardie-HardieBacker-0-25-in-x-3-ft-x-5-ft-Cement-Backerboard-220022/100183556
Here is a reply to a question on the site: Thank you for your inquiry. Durock Cement Board is a tilebacker board for use with tile, thin brick and stucco. It is non combustible but it is not a heat shield. It will transfer heat and should not be exposed to temperatures exceeding 200 degrees Fahrenheit. Hope this helps.