I will have a five-zone radiant heat system in my home.  As I understand from the installer, there will be five individual thermostats, but I don't think he will install a programmable type.  Is there a recommended programmable thermostat for radiant heat systems?

Generally any programmable thermostat will work fine with radiant systems. Are you also using to control a form ac or chiller? if so I would recommend something by Luxpro, I sell a lot of their model PSP511.

I tried a Honeywell RLV430A with triac . It did not work with the 110 volt switching of a pump. I found out it is only good for resistive load (IE Electric heaters0. would probably be Ok with solenoid valves of your zoned system . The programmable feature is not all that useful if you are heating a significant concrete mass. I wanted to use it to force the ehating to occur daytime only when combustion air is a little warmer. I run a low set point & boost with electrical space heat for the occupied hours because of the slow response.

I would almost always rather see you run a good reset water temperature instead of trying to use setback.

NRT.rob - Are you implying controlling the water temperature? I'm not sure what you mean by reset water temperature versus setback.

All on the forum - Is the control algorithm for a radiant heat thermometer different than for a forced air system? When you think about it, there is a good bit of "dead time" from the point the room temperature starts to drop below its intended setpoint, and the time it begins to rise back to target.

yes, I would rather see dynamic water temperature control, based on at least outdoor temperature, rather than programmed setbacks. UNLESS your max water temperature is very, very low.

Depending on what kind of radiant you are using, and how well your water temperature is matched to it among other things, you might need a thermostat that can "anticipate" better than a typical one.

We replaced 3 of our 8 thermostats with programmable Honeywells from Home Depot (read the back carefully, some aren't compatible with all systems) and it works great. The rooms we want heated at night - our bedroom and our bath - stay toasty at night, and the floor in the great room, kitchen, offices comes on around 5:30 and is completely warm by 6:30. The spare bedroom and little-used bath are just to a constant 65F (which is cold underfoot). We've had to turn down our boiler several times, and it's now running at 120F (making me question why we bought a large EXPENSIVE boiler instead of a water heater). Even at 120F, the floors get hotter than the flooring mfr's recommended 85F max.

After 6 months with the warmboard system, 3 of those in an unusually cold and snoy winter (night temps in the single digits, day temps barely double digits, and about 3' of snow), I'd say I like the system overall. We keep our house around 70F, and use a very small woodstove only at night mostly for ambiance rather than heat. Our monthly electric bill (gas isn't available here) for the two of us in a 2,000sf passive solar house runs about $160 for the cold months.

The real problem with a boiler and passive solar and warmboard is that there is not enough thermal mass to store heat - during the day, in the sun, the system shuts off completely and the sun warms the floors amazingly well. But the floors don't hold the heat (we have tile over Hardiebacker) and as soon as the sun goes down, the boiler kicks on. The floor heats fast with warmboard, but it cools off fast as well.

We're contemplating doing some homebrew design changes that would involve changing the way the water circulates, monitoring "slab" temp as well as ambient and adding some storage.

what kind of boiler do you have? running a regular boiler at 120 will kill it prematurely from condensation.

An electric Slant Fin Monitron - so stack condensation is not a problem. We don't have gas out here, and I mistrust the future price of propane. We might, in fact, have to cut one of the loops out (simply by flipping a cricuit breaker) to cut the temp further.

We live in the mountains in Oregon, on the sunny side at about 5,000'. The daytime temps, in the sun, can vary from 10 degrees in the morning to 80 degrees through the windows (we have an IR thermometer, and with the heat shut completely off, the tiles have hit 105 degrees). That's free energy that we're wasting, because the system only circulates water when the boiler is on. Meaning that the colder, non-south-facing parts of the house could use that heat, but we can't get it there because of the system set-up.

Some of these programmable thermostats come from Europe and are difficult to program. Warmzone posted a video on YouTube on how to program a Danfoss thermostat manufactured by OJ Electronics. I think it has been viewed a couple of hundred times - must be useful for some. Search: 'Warmzone thermostat' on YouTube and you should be able to find it from there.