Radiant Floor Heat Problem in Bathroom

wanttolearn

Hi-

I have radiant floor heat in only a single area of my entire house, in the master bathroom.  This room has it own thermostat that regulates the radiant floor heat.  I moved into the house last year, so I have no idea when it was installed and how.

I set the thermostat at a constant 72 degrees all the time.  The problem that I have is that while the system seems to work ok on moderate temp days, on days when the temperature drops below 30 degrees outside, the system is not producing enough heat, and the temp in the room never reaches 72 (it mostly hovers around 70 on these cold days).

I have gone to the boiler room downstairs and there are two flexible tubes that I believe serve this radiant floor heat.  One of the tubes is red and one of the tubes is blue.  The tubes appear to be connected directly to my boiler.  There is also something that looks like a temperature knob, but it is already turned to the maximum temperature.

Two symptoms I should tell you about that I have noticed:

When I touch the red flex tube with my hand, it is defintely warm, but it is not burning hot like some of the copper tubing coming out of the boiler is.  I can easily close my fist around the red tube with no discomfort.  Is this an indication that the water passing up this tube is not hot enough?  should this tube be very hot or just moderately so?

Secondly, I noticed that not all of the bathroom floor gets evenly hot. One half of the floor gets noticably warm, the other half gets only very mildly warm.  None of the floor gets really hot, not even on the coldest of days.  Is this also an indication that the hot water serving th system is not warm enough?  Or does it just mean that the system is defective?

Any help would be appreciated, as 70 degrees is just too cold for a bathroom on a freezing winter day!  also I am concerned that the system is running all the time to reach the target temp, and that this is causing my heating bills to escalate.

Thanks. 

Brad White

Up against the edge

I think you are finding the intersection of your space heat loss and your available radiant floor area at that temperature.



Given the uneven heating, you may have a flow restriction or possibly (as I gather), your radiant floor area is "slaved" to the main house zone and so responds only to the main house needs, not the bathroom need. That zone should have its own circulator and it will be a small one.  When slaved to the main house, if the main house temperature is satisfied, your bathroom is left abandoned. Unloved. Alone.



The "feel" of pex is no nearly so warm as copper; it is hard to tell temperature through pex by the hand, although a relative difference between warm and cold is obvious.



The floor should not be "hot", but should be "neutral to warm", meaning not over 85 degrees.  80 to 82 is ideal, but for a bathroom, one can tolerate higher temperatures, 85, sometimes 90 but no more. (Spend more time in the bathroom and 90 degree floors will make the room feel stifling.)



To recap: Put the radiant floor on a dedicated circulator with a mixing valve to control the temperature. A Taco iValve is a good place to start, even the setpoint type, but they also have an outdoor reset type. Give the room its own thermostat. This will fire the boiler to meet this and will increase your heating costs, but what in life is free except love?  OK, love can be expensive too. Analogies? They are free here and worth every penny.

wanttolearn

Further Info

I just went back to the boiler room, and there is a separate Taco ciculator for the radiant heat zone.  Like I mentioned in my original post, there is also a knob that regulates temperature, but it is already turned to the maximum (setting 2).

so clearly the radiant heat has its own zone, circulator, and thermostat.

i also took a temperature gun and just took the temp of the floor in the bathroom.  The warm half of the floor was at 86 degrees, the cold half was at 78 degrees.  Based on what you were writing in your post, the floor is warming up adequately.

So why is the room only at 70 degrees when the thermostat is set at 72?

it is 38 degrees outside today, so its not even a particularly cold day.

any further guesses as to why the room does not reach the target temperature?

Jean-David Beyer

This may be a false alarm, but...

"One of the tubes is red and one of the tubes is blue."



I am not a heating professional, but it is my understanding that red pex tubing if for hot domestic water, and blue is for cold. These do not have an oxygen barrier. Water for heating systems should have an oxygen barrier. Oxygen and air are harmful to many hydronic heating system components.

Brad White

Arteries and Veins

Good Point JDB!



I did not pick up on that.  Possibility of no oxygen barrier.

Brad White

Good So Far

You obviously have a manual valve arrangement, but check to see if the radiant zone fires the boiler in addition to operating the pump. That circuit, if it is dependent on the main house zone calling, would start/stop the circulator based on need but not fire the boiler. You would get what you get when the circulator runs.



If the main house is satisfied, will the bathroom zone also fire the boiler?



If, as you say, you cannot keep up, then the circulator would be running all of the time and not shut off. Is this the case? That actually is good because constant circulation is a good way to equalize temperatures.



But that kind of a gradient,  86 to 78 degrees, is rather wide for a system with constant circulation. Might you have a crimp in your tubing? 

Is the floor underneath insulated? If so, by how much? If not, that is going to lose half or more downward. Is this above heated space?



Do you know the approximate heat loss and how much area is actually radiated? As mentioned, you may be up against available area doing all it can (with whatever defects, we do not know), and falling short by two degrees on a mild day.



By how much does it under-perform on a mild day?

CMadatMe

Design

Most radiant systems are not designed for a setpoint of 72. Generally water temp is based off a setpoint of 65, 68 or 70 degrees. This means that the water temp going through the floor is designed only to make the setpoint it was designed around. You can put the thermostat to 90 makes no difference.



JB picked up on the fact there is blue  tubing. He is correct this is a sign that a non oxygen barrier tubing was used. Without knowing the heat loss of the room, loop lengths and the radiant application used its a tough troubleshoot to figure why the temp differences. The use of the non barrier pex may be effecting the ability of the circulator to move water. If you can, shut down every loop. Open them one at a time and run the circ. What is the temp differece between the water supply out of the manifold loop and it's return. Once you open and close each loop and then open all of them. Find the loop giving you problems. It may not be balanced correctly. Finding this would just eliminate the difference in the temps across the floor may not necessarily get you to 72 though. You would have to raise the water temp in the mixing valve to accomplish that. If you have a floor surface with a 86 degree water temp that is not a good thing. General floor surface temps would be in the 73-80 degree range and nothing more.

Jean-David Beyer

Balancing hydronic systems.

I am finding this very difficult. My radiant zone is 1/2 inch copper tubing in a concrete slab at grade. There are 5 rooms there and 5 ball valves in the supply to the slab. A 1-inch pipe comes out of the slab. The temperature into the slab is between 75F and 120F depending on the outside temperature.



I assume one valve is for each of the rooms; 5 valves, 5 rooms. But I do not even know that for sure. I have an infra-red thermometer (Black and Decker  TLD100). With all 5 valves full open, I do get enough heat at all times. But one room is usually too hot (has two computers, one of which averages 400  watts), so it needs less heat than average). My bedroom is hotter than I prefer (runs 72F when I would prefer 69F. And so on.



The trouble is that it takes 6 hours or so to get a change after I change the thermostat setting or close a valve most of the way, and I fear to turn one of those valves all the way off because I do not wish to risk freezing that part of the tubing. Turning one of those valves about 1/2 way off does not make much difference; I should probably get the fancy balancing valves, but I doubt I will do that. It seems to me that before I get serious about balancing those things, I should at least know what valve goes to each room.



My first strategy was to guess how the tubing in the floor was, assuming no tube crossed over any other tube. I do not know that that is true. Another assumption is that each valve controls exactly one room. My first guess makes a neat diagram, but it does not correspond to what happens. I tried again and made a diagram, also neat, but a little strange. But that is not right either. The trouble is that I can test only on seriously cold days when the system is running the zone's circulator almost the entire day. So far this winter, I have figured out which valve goes to two of the rooms. And I cannot figure a way to account for those and yet have no tube crossing another in the slab.



I wish it did not take almost 24 hours of a very cold day to check one valve. I wish I knew that my two assumptions were correct. I really hope that there is exactly one valve per room. It is possible to pipe the system so pipes do not cross one another in the slab, but so far, that does not seem to be how it is. I do not suppose there is any code about this, or was in 1950 when this was built. Of course, there is no plan of the tubing layout in the documentation of my house.

wanttolearn

follow up question

Hi-

thanks for the responses. 

To the User who recommended that I try to identify the loop that is giving me problems, I am not sure what he means by that.  As far as I can tell, there is only one loop for this whole room.  The hot water goes up from the boiler in the red tube, passes through the floor of the bathroom, and then passes back down via the blue tube through the boiler.

If there are more loops, how do I access them, because I do not see any other piping from the boiler going to this bathroom.

Thanks again for all your help.

CMadatMe

Loops

IF the bathroom is only one loop my questions would be then. What is the water temp leaving the red tubing and what is the water temp coming back to the blue tubing?

Gordy

IF

 The bathroom is one loop. Then why shall I ask is the red tubing turning blue when it comes back to the boiler.  Spliced?? Other wise if two loops there should be two red ends, and two blue ends. Does not compute.