Posted By NRT.Rob on 28 May 2012 04:30 PM
Extruded plates will beat the pants off of nearly any lightweight plate out there... no lightweight can do a tubing groove with as good of a contact. it's as big of a difference as no plates vs lightweight plates again.

Warmboard aluminum will outperform concrete as well with identical flooring assemblies above... it's near 100% coverage and on top, no extra insulation. I bet with the labor savings it's probably similar in cost too, and faster response. I'm not saying concrete is BAD, I'm just saying, it's hardly the only game in town and you're jumping through some pretty silly hoops to make it work on what is at least partially superstition based on your responses. If you're doing a slab on grade home, obviously put it in concrete. If you need some weird custom framing detail, maybe not.

extruded plates also hold pipe so it can't move, so the "thermal stresses" are moot. no argument that plates in a joist bay won't be as good as concrete on top of a subfloor, of course. but I design very little but very low temperature systems, and we use both plateless and plated radiant on a regular basis when it makes sense to do so. which is a lot of the time, when you run the numbers. I have at least a couple dozen plateless systems out there at 110-115 degree design temps because the loads allowed for it. My shop, on the other hand, is 90 degree max warmboard with wood on top.

Currently my main floor is tubing in between 2x2s @ 12"oc and in gypcrete and I too run 90F max and I have bamboo T&G on top. BSMT is a couple of old cast rads and so is the 2nd fl. No heat needed on the 3rd but my Fujitsu is there for cooling.

My belief in concrete is not based on superstition but my experience and yes, it does come from the Europeans whom I have studied under and gone to Germany to work with a bit. They did invent the modern radiant heating methods, Warmboard and aluminum plates excepted, and it seems, just about every improvement in hydronic heating.

I have done aluminum plates and warmboard, and i know it can work well, but I prefer the density, sound insulation and fire protection of cement. I feel that I have more freedom of loop layout when I can staple down to a subfloor without concern for the limitations of the plates.

To each they own, I guess.  

the superstition comment was specifically in reference to the water temp and plate stress issues. obviously 'crete works. you're not wrong to use it. just saying there are other options that can be just as good in many cases.

Thicker plates making better contact with the tube makes sense to me. There is nothing that can be added to thinner plates to get better tube contact? Aluminum powder/silicon caulk mix or something?

I have to point out our RHT Heat transfer plates snap on to the pipe, it is an omega shape, that captures the pipe. We also are the only company I know of that manufactures these in both 24" and 48" length.
Dan

we use omega groove plates too, and it's important. and, no matter how omega that groove, it is nothing like a heavy gauge plate grip. you don't hammer pipe into lightweight plates.

lights have their place but they are not equivalent to an extruded, rigid channel.

We use both light and heavy aluminum plates made for radiant floor heating in our design/build work here in Minneapolis/St.Paul, but don't "sell" either.

Love those 48" plates for radiant walls and ceilings but won't design or install sub-floor radiant floor heating without heavy extruded aluminum plates, just like the ones I have under my own oak, bamboo and cork floors here on the farm. In milder climates or with tighter houses the lower performance of light-weight plates may suffice and considering that many "professionals" and amateurs alike still insist on using raw PEX suspended or stapled up to the sub-floor, I am happy for any AL I can get!

You guys, play nice...hhehehehehehee

Posted By NRT.Rob on 29 May 2012 08:52 AM
the superstition comment was specifically in reference to the water temp and plate stress issues. obviously 'crete works. you're not wrong to use it. just saying there are other options that can be just as good in many cases.

Then all I can say is spacing, spacing, spacing. I know a guy in Ireland that uses a 4" spacing with his HPs and is using 28-30C water temps. Really good COP from that but there is no aluminum plate with that spacing (AFAIK)