Radiant Heating Programmable Thermostat
JohnD1
| Posted in Energy, Heating & Insulation on
Well, we finally put in the bathroom that was stubbed in 15 years ago. (Why hurry things; at least our daughter gets to use it before she graduates).
We have radiant heat in the floor, and everyone really likes it. But it also heats the room too much. There is no other heat in the room, but the room is well insulated. So, is there a programmable thermostat that has everything?
It needs to control the floor temperature, but I also want it to shut off if the room gets too warm. And, I want the whole thing programmable. Have you ever seen such a thing?
Now, I suppose I could splice in a programmable line voltage programmable thermostat, but having two thermostats would look silly, and would require a very detailed instruction book.
Replies
Radiant floor ... hydronic or electric? What is the floor construction wood/tile or concrete? These make a big difference. We need more information
Overheating can be common w/ a radiant floor if you don't control it. Mostly w/ concrete floors since by the time the slab gets enough heat, it's got too much for the room space temp. Wood floors can be much more responsive (i.e. more quick to react).
Hydronic system: control the temperature of the water so that it just puts in the heat necessary for the load. Now this value varies throughout the season/daily temp, but you can set it based on the time of the season (e.g. early vs. mid winter).
Prog Stat: You can use a standard stat ... not sure why you say you would end up w/ 2 stats in the space. A standard programmable needs to be set to anticipate the setpoint .... if you have a concrete floor, you need to anticipate well in advance both the occupied setpoint and the unoccupied time. It could take say 4-6 hours for the slab to come up to temp. By the same token if you don't shut it off well in advance of the setback time, you can overheat the space.
Fancy computer controls can get you all of this. It can adjust the hot water temp with respect to outside temp (i.e. the load). It can anticipate the space temperature and adjust accordingly ... but it don't come cheap.
if electric heat mat (tres common here) programmable thermostats of-the-shelf run 120 to 250 bucks (cdn) with probe, which can be installed in tile grout after install of tiles (certainly not best install, but if tiles are already in place, with heat mat...)
I apologize for not clarifying things.
The heat is electric (120 volts; about 350 watts). It is a small bathroom.
The floor is standard wood joists with plywood, cement board and ceramic tile.
The installer put in the controller and also put in the temperature sensor (which I am guessing is most likely a thermocouple) into the floor. The controller simply controls the floor temp. I thought he was putting in the programmable version; the packaging even made it seem as if it was that sort of device. Only when I read the instructions did I realize that it was the more basic controller.
As I said initially, I am looking for a "dual" controller. It would control the floor temperature when it runs, but if the room gets too hot it will shut things down.
(BTW: I was going to do this myself. I have installed a lot of ceramic tile. My oldest installation is 15 years old and is in fine shape. But SWMBO said she wanted installed in less than 10 years!)
Who did you get the floor mat from? The company will have the best programmable Tstat for the product. I have two bathrooms with Warmlyours heating mats in them. They both have programmable Tstats in them. One room I have it set to reach a set temp by 6:00AM, so It will read the floor temp and turn on early enough to be up to the set temp by 6A.the floor sensor will also shut it down when it reaches it set temp. The sensor only reads the floor temp, not the air temp. You may have to adjust the temp of the floor to regulate the room air temp. My Tstats ran about $180.
Thanks. Yes, the company that supplied the mats also supplies a programmable thermostat. It is their -2 model. I have the -1 installed, which because of the package wording sounded like a programmable. Pricing is similar to yours.
And, yes, I can regulate the floor temp to control the room air. But as the climate goes into heavy winter, it will probably require tweeking--something I would prefer to avoid.
I've used these controllers in industrial environments for process control. You could set one up with PID (Proportional, Integral, Derivative) autotune and use the existing thermocouple in the floor as a limit control to keep the floor from overheating, and a second thermocouple in free air as the control. They are very precise. I think one with the options you need would be under $200. You would want a no-arc relay and PID with thermocouple inputs.http://www.watlow.com/products/controllers/co_ezzone.cfm
Thanks. Your thinking was where I was sort of headed. But SWMBO is not keen on a second device. And, typically these controllers are not designed to fit in a standard electrical wall box (I tried to open the Watlow site, but my daughter is downloading something and is tying up the bandwidth).I can purchase a programmable line-voltage thermostat for $40. If I need to go that way, I would simply insert it into the line coming from the controller to the floor. (Not to the controller itself; it would lose its memory.)But, as I was saying: SWMBO does not really want a second controller. Plus I would have to reopen the wall to add another box. (I think that is the real reason she doesn't want me to do it; I can take forever to get it fixed/)
Those things are slick, but somewhat expensive, and are more industrial in nature. I mount them in panels, they are not made for regular boxes. You could control the temperature of the room to a tenth of a degree if you wished. They are commonly used for boilers from what I hear.
I have actually played with the things. The fellow across from me was the plant engineer who actually used them. He would get samples from vendors, and after he decided that they did not meet his needs, I would be able to play around.(I was looking to control a railroad signal display, would you believe!)And yes, the wife would NEVER allow an industrial device visible from the bathroom.
Mount the control inside the medicine cabinet!
<Mount the control inside the medicine cabinet!>But then my daughter will be mad because all her stuff has been kicked out! And my son will be mad at the daughter because she has taken over all the counter space he uses for his clutter! And then the cat will be mad at me .... well, just because he is a cat!
Edited 9/9/2009 9:33 pm by JohnD1
Who cares if the cat is mad?
<Who cares if the cat is mad?>
The Cat?
John,
I don't understand why you have to have two t-stats? The company that makes the heating mat can sell you a programmable t-stat. The t-stat will fit in to a single box. They always recommend a double gang box with a mud ring, but a single will hold a t-stat.
<why you have to have two t-stats?>
THERMOSTAT 1: Electric Radiant heating needs to have the floor at a comfortable temperature (86 F default on my particular thermostat)
THERMOSTAT 2: If the floor is left on for too long a period in a well insulated house, there is a good likelihood that the room will get too warm.
(programmable is simply a nice addition)
John, Adjust the floor temp so that it warms the room to a comfortable temp. Mine also defaults at 84 F.
My second floor bathroom stays a very nice temp with the floor at 84. My first floor bath over a cool basement needs more BTU's. I pushed the floor up to 88 F. The room also stays a nice temp. The sensor in the floor turns off the mat and the room never gets too hot. You will have to adjust the floor temp to get get the right room temp.
Thanks Sbds.
I started this thread because the contractor commented that these floors sometimes made the bathroom too warm. But I will simply try your idea and see how it goes. THEN I can change things if needed.
John, Keep in mind all the manufactures of these heating systems always state "they are not for primary heating" . In most cases they do work to heat the room.Danny
Yup! I know that, but for the most part isn't that simply cya?
I mean, after all, if using the heaters to heat the floor at the recommended temperature also heats the room, aren't you heating the room? I guess this gets them off the hook where people jack up the thermostat to try to heat a room where there are really good heat losses.
(Off track, but still CYA related: Our new stove has the same self-cleaning feature as the old one. But now they say to take the shelves out and don't put anything in when cleaning, as it might smoke. Our old one never mentioned that "problem". Again, probably from people complaining about the smoke when they put things in. So, CYA.)