yeldogt,
Out here in the West, we have milder weather than you guys, and you're right, the grooved plywood systems were designed to avoid thin pours.
Back in the eighties, Maxxon was known as Gyp-Crete Corporation. They started a division named Infloor and developed a line of radiant products that included a zone control system and various other products that were all branded "Infloor". They, were using polybutalene 1/2"OD tubing and were all geared up around that material in that size. The main competitor at the time was Wirzbo, later Upanor. There was a lot of talk about oxygen barrier, constant circulation, European boiler design, etc.
I was working closely with the main west coast distributor, installing systems, doing seminars on boilers and rattling infloor's cage about their proprietary design and the problems I saw with it. Most everything was going into gypsum slabs from the parent company, Gyp-Crete Corporation.
There began to be more tension between Gyp-Crete and Infloor and the distributors, so the distributor began looking for an alternative to pouring the gypsum slabs. This would save money, be simpler, reduce the 12lbs per ft load that had to be allowed for, and change the whole marketing strategy. This is when and why Thermal-Board was developed.
It was presented to architects as a simple method to add radiant. They were handed a simple enough looking package, with design help, lots of colored literature and a hydronic plan. So they began to spec it in their designs. A lot of radiant contractors hated it. The manufacturer played down the fact that it needed plywood over the top to protect the tube, wasn't waterproof and wasn't designed to hold flooring nails.
The labor was about 6-10 times as much as the simple staple down system. The $3.00 per ft pour cost of gypsum became $5.00 per ft for the Warm Board. The elaborate puzzle and methods needed to run the tubing and the supply lines was difficult. Nailing wood flooring down was a problem because the board was not designed to hold nails and the tube was getting hit by careless installers. Carpet pads were stapled down right into the exposed tubing. The material could not be used in showers and would not work near manifolds. Tubing runs were short with the 1/2" OD tube and power had to be run to the manifold locations to operate the proprietary zone control system.
But it did allow the separation of the parent company and the radiant spinoff. It allowed for a "no pour" radiant system.
Since that time, there have been a lot of similar grooved plywood systems developed. Each brings with it some benefits and some drawbacks. It's important for anyone considering the use of these, to really take a hard look at all that is involved. Cost, complexity, limitations, finish flooring materials in bathrooms and other living areas. It's also important to make your own decisions. Over and over I hear contractors or developers, that know nothing about materials or heat transfer or efficiency, try to re-play the same sales pitch that someone gave them.
These materials have their place, but they are definitely have their own set of drawbacks.
So many times, I've been called to "finish up" a Warm Board system where the general contractor just installed it as per design specs, as the house subfloor, and then built the interior walls right over the board. After I either give them a realistic installation cost, or just politely describe what must take place, and then move on, they find someone else that is willing to take it on. Invariably, the homeowners don't really understand what they have gotten themselves into with poor zoning, high cost, delays, etc. But, yes, it works fine if done properly. I just looked at one recently where they were in a big hurry and the board was already down, walls were all done and they were wanting to start the sheetrock that week. They were shopping for the lowest price to finish the radiant, and had never realized what was required to do so. The whole house was going to be on one thermostat, regardless of the function of the rooms, because the grooves went right through the living rooms, bedrooms and baths. The idea of routing new grooves and running supply lines underneath was like speaking a foreign language. "Can we start sheetrocking now" was the answer. Typical with this situation.
I have always done my own designs in consultation with the homeowner or developer. Often they have spent thousands, before I got there, for a specific radiant plan from a designer. I became curious after seeing how we always had to change the designers plan to make it work, so I went to the certain design firm and looked at their method. No consultation with the homeowners was ever done. They just took the plans and dropped on a bunch of serpentine lines that were adjusted to fit. Then a standard hydronics page was added and a manifold location was called out. The whole process takes about five minutes and they charge $2,000. - 3,000. for the work! The combination of my reputation in the field, and my unwillingness to put up with a lot of BS, has allowed me to get away with telling people why they just wasted a lot of design money for a system that is ill suited to their stated goals. And then to do it better.
That's the fun of radiant. There are so many ways to do it and different environments to do it in. So many different house designs and lifestyles. And it works so well in combination with solar.
It's funny too, to be working away on an installation and have another guy come along and say: "That is so easy". "I'm gonna start doing radiant". I alway encourage them. "Yeah, you should", I declare. Then the questions start. How do you size the boiler? How do space the tubing? How are the controls done? Why use PEX? How many thermostats? What's the cost? bla bla bla..............
Just like any other field, if done right it looks simple, but there is a lot more to it than people realize at first glance. I'm always striving for simplicity, without giving up function.
