Controlling radiant floors (what thermostat to use?)
 

I'm very close to putting the pex tubing down in my office. So, I am looking at options on how to control the heat to the floors.

In my sunroom I have radiant heated floors that the previous owners installed. They just used a normal thermostat. This is run to some control box (probably with a relay in it) that turns the pump on and off. This was the only room done up with hydronic radiant floors.

In my kitchen I have electric heated floors. The thermostat that controls these floors uses a temperature probe in the floor to control the actual floor's temperature. This is a neat idea, but I kind of fail to see how it relates to room temperature. I really don't use it enough to get a feel for if this method is any good. It is nice in the fact that you can make sure your floor never gets too hot.

What other ways are there to control the floor temperature?

I have two ways of controlling my floor heating installs.

One is the probe type t-stat which you set for an appropriate temp such as 25C (77F) for example and the tank or boiler sends the water out through a thermostatic mix valve. The boiler temp is then separate from the floor temp, to some extent.

The second is to have a 3 or 4 way mix valve based on an outdoor reset control and no internal t-stat. This is the way I run my own house, drives the wife nuts. Most people want some control but in the end if it is comfy, they soon forget about it.

Put a tube in your floor that will allow you to "snake" a probe in. At that point, you can use any thermostat that uses a wire sensor. I use a section of scrap PEX and I plug the far end.

If you are pouring concrete to encase your PEX snake, this will measure average slab temperature well. If using metal spreaders, pour just a "dollop" of concrete (dessert plate sized in diameter) around the part of the pipe that the probe will be in in. Have some concrete below and above pipe so it is enclosed in a thermal mass.

This thermal mass allows the floor to be better regulated and not have it turn off and turn on quickly. It is the equivalent of the "anticipator" in thermostats.

Steve

Thanks for the ideas guys.

And, I'm bumping for more ideas. If it makes any difference, I will be using solar hot water for space heating.

I guess I am looking for some more info here. What are the pros/cons of each method?

Another way to do it is to measure the return temp on the manifold (properly insulated) and with proper dT on the control you can monitor the floor quite well. I have done this when other tradesmen forget to put in the sensor tube.

Continuous Pumps vs. Intermittant Pumps...
 

I have heard that there are different philosophies regarding radiant floors and how water is pumped into the floors...

As I understand it, in the US, pumps turn on when there is a need for it.

In Europe, where radiant heating predominates, pumps are run continuously, and I would guess, changes are made to the buffer tank temp.

Does anyone have any more information on these strategies?

-AC

Probably more efficient to leave the pump running and modulate the boiler or heat pump as needed. But switching or throttling pumps allows you to zone the system.

Yes, Europeans tend to leave the pumps running. I have a Viessmann boiler with a pump built in and to get the proper temp measuring of the fluid, the pump must run continuously. There is a lot of use of the Grundfos ALPHA or Wilo Stratus pumps which are ECM and tend to run 5-8w even though they can replace a 100w circ.

Zoning is more often done by zone valves and a bypass.