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    Ideal temperature for radiant heat? (35 Posts)

  • Coany Coany @ 5:34 AM
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    Ideal temperature for radiant heat?

    Big Mansion, 7 zones of baseboard and two bathroom radiant zones.
    Both radiant zones circulating 110-120degrees.
    complaint is insufficient heat.He can't feel it/can't tell if its on.
    our service dept disagree weather you SUPPOSED to be able to tell if its on.
     I say with marble floors and bare feet you SHOULD be able to tell if it on.
     Another view is you tell by just feeling its warm in there.

    I adjusted the diverting valve to allow it to circulate 150-160 degree water.
    The customer will get back to us after a few days
    my co-service techs think I've got to return and turn it back down to 120-130.

    what do you think?
    " Do what you can, with what you have, where you are" Teddy Roosevelt
  • Chris Chris @ 7:08 AM
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    Heat Loss

    The anwser to your question is all in the heat loss and radiant design. How is the radiant controlled? Are you just using a thermostatic mixing valve? If so that may be the cause of the whole problem. The customer  is not telling you the room is cold he is telling you the floor is cold. May be too late now but should have used floor sensors. What was the floor surface temp when you shot it with a laser?

    By turning up the water temp you are going to nothing but satisfy the zone quicker and could potentially crack the floor.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
    This post was edited by an admin on April 8, 2010 7:12 AM.
  • Jean-David Beyer Jean-David Beyer @ 7:34 AM
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    I am a homeowner, not a contractor.

    I have radiant heat in the slab downstairs in my house in New Jersey. The boiler has outdoor reset. I have tried to set the reset curve so that the circulators run most of the time. That curve may not be exactly right on cold days because there have not been enough very cold days this past winter to tell.

    In any case, if the thermostat is calling for heat, the boiler supplies 75F water to the floor until the outdoor temperature drops to 56F. Then the water temperature increases as the outdoor temperature drops to 0F, when the water temperature has increased to 120F. This certainly heats the house. If I run water that is "too hot" in the slab, when the thermostat is satisfied, the heat in the slab is so much that the room overshoots by quite a lot (e.g., 5 degrees or so).

    I had been told that one got warm floors with radiant heat, and if it is very cold outside (e.g., 14F) I can feel heat in the floor. But when it is just cold out (e.g., 40F), there is about 88F water in the floor and that feels cold to me. However, that is enough to heat the house. My guess is that the floor will not feel warm to a barefoot person until the floor surface is about body temperature.
    This post was edited by an admin on April 8, 2010 7:37 AM.
  • Coany Coany @ 4:18 PM
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    more info

    Down on the manifold the pipe was running about 115 or so.
    I didn't check the floor itself.
    It was a 50 degree gray spring day, might have been the only two zones calling.
    I was concerned about damaging the floor, 
    but I gambled the thick marble tiles could take it.
    the customer told me he leaves the thermostat in the bathroom high,
     he likes it warm in there.


     so should you be able to tell if its on or not?
    at 115 degrees this customer cannot.
    Comfort is his primary concern, over savings.
    " Do what you can, with what you have, where you are" Teddy Roosevelt
  • NRT_Rob NRT_Rob @ 4:21 PM
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    you have a choice

    you can have short bursts of comfort that is noticeable, with longer bouts of cold floors. this method may cause room temperature swings. this uses higher water temps.

    or you can have more continuous comfort that is NOT noticeable, but the floor doesn't get cold either. room temps are locked in. water temps are low.

    I think #2 is the right way to go. clients should never be sold radiant floors on warm feet. Just comfortable feet. but after the fact, the client can do what they prefer. they can try it both ways.
    NRT.Rob
  • Chris Chris @ 4:37 PM
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    115 on a 50 Degree Day?

    Seems awful high. Is the application staple up with no plates? Staple up with plates? How is the radiantwater mixed? You are probably overheating the room. Meaning the therm is satisfied so the floor stays off for long periods of time thus cooling down. Then your cramming a high water temp you don't need so the room therm again gets satisfied via a short run cycle. This is what happens when we don't modulate water temp to meet the heat loss at different outside temps and the none use of floor sensors when needed.

    The customer it seems to me isn't complaining that the room is cold. It's just the opposite warm room cold floor. You will never make this customer comfortable without a floor sensor to maintain the floor surface temp where you want it and you must be using outdoor reset of some type.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Jean-David Beyer Jean-David Beyer @ 5:15 PM
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    I am tryinig to imagine this setup...

    on a day where it is 50F outside and the indoor thermostat is calling for heat indoors. If my system is typical, I would be putting 80F degree water through the floor. I would not put 115F water into the slab until it got down to 6F outside. Now how are the controls arranged in a house with both Outdoor Reset and a floor sensor? Does the hotter temperature request take precedence? Or are they averaged together? Or what?

    With my old one-zone system, oversized boiler, and amazing near-boiler plumbing, I do not know what the water temperature in the floor slab was, but I would guess it did not get over 140F. I could sure tell when it was heating for a while though. It sometimes got uncomfortably warm, and the asphalt tile on the floors would not stay down.
  • Coany Coany @ 3:31 AM
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    more info

    yes there is an outdoor re-set, but only on the two radiant zones, it has been steadily turned up over the last few winters in response to re-occuring insufficient heat calls.
    The house was extensively remodeled by others in 2004
    these two radiant zones were added then, I don't know if floor plates were used.
     the setpoint is now at 75, which seems pretty high to me.
    the thermostats in the bathrooms don't have actual numbered setting.
    just cool/ normal/ warm range.He keeps it up in the warm range all the time
    There is no floor sensor.
    Can one be added?
    The thermostatic mixing valve is new, customer just paid a hefty bill to replace it.
     It was condemmed by service manager in response to insufficient heat calls.


     my sense from this group is that 115ish on a 50 degree day is already somewhat high.
     but the customer keeps calling back for insufficient heat
    " Do what you can, with what you have, where you are" Teddy Roosevelt
    This post was edited by an admin on April 9, 2010 3:36 AM.
  • Chris Chris @ 7:42 AM
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    Coany

    I'm a little confused. You state that the 2 zone of radiant were out-door reset and then said there was a thermostatic mixing valve. Which one is it?  I still haven't heard that his complaint was room temp. It's the floor temp. I would also suggest you find out if plates were or were not used. This is going to make a big difference is your strategy. Plateless jobs mean long response times.

    You possibly could add a floor sensor. I don't know what is below the room as you would have to go bottom up. If you do add it then your changing that therm. If you use the Wirsbo 511 or 501 would have to be able to power it 24v. I would be interested in knowing the floor surface temp when that thermostat is satisfied and then the floor temp when it finally calls again.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • NRT_Rob NRT_Rob @ 8:58 AM
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    floor temp is insufficient

    because your heat load is low.

    apparently your thermostats and the floor mass are doing a good job "taming" your high water temps. instead they are giving you the average floor temp they need to maintain room temp. which is low, because the load is low.

    With a 75 degree room temp I would expect him to be able to feel the floors with any real heat load. but on a 50 degree day... tiny heat load... maybe not.

    You will never be able to make his feet warm all the time without cooking him out of the house. Radiant is about invisible comfort. Not noticeably warm toes. Not unless it's cold or the house is leaky. If you are maintaining room temperature, you are not "insufficiently heating".

    If he really wants warm feet, he can open a window and make the floor crank up its output. That is what it takes. Or he can shoot for 80 degree room temps.

    this sounds like an expectation management problem, not necessarily a system problem.
    NRT.Rob
  • Jean-David Beyer Jean-David Beyer @ 11:49 AM
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    expectation management problem

    As a non-contractor, I expect you are right, that this may be an expectation management problem and not a heating system problem.

    My whole downstairs is heated by an in-slab radiant approach. And since my heat loss is low and I have outdoor reset, I put only 80F water into the slab in my bathroom when it is 50F outside. And it keeps the house at 69F where my thermostat is set.

    When I first bought this house, I was surprised that the floors were cold even when the house was warm enough. But in thinking about it, it made sense. Now that I have outdoor reset, it just makes the problem (if it is a problem) worse, since the floors feel cold most of the time (when I go barefoot). Not as cold as when the boiler used up an ignition transformer one time on a weekend, but cold feeling. Since my house was well insulated by then, I waited until Monday to request service. My solution to the cold bathroom problem is very inexpensive. I use a bathmat on the floor. I replace it once in a while.

    About reset: what happens when I die? I adjusted my outdoor reset low enough that I can always heat the house to 69F, but probably not much higher. What if the new owner wants the house hotter? He turns up the thermostat, but does not get more heat because the boiler and circulators run most of the time already. Since the boiler is oversize (although the smallest the manufacturer makes), it could put out more heat. Should I really type up a booklet explaining outdoor reset? If I do nothing, I can imagine an ignorant home-owner getting a larger boiler, when the one in there is already too large? If I am lucky, I may last another 25 years or so, so perhaps this is not too terrible if he buys a new boiler by then. Or goes all solar.
  • NRT_Rob NRT_Rob @ 11:58 AM
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    I don't think you need to worry

    most techs know what outdoor reset is now. a home not maintaining higher temps under all conditions... as opposed to falling short on the coldest day of the year... is another clue.

    certainly in another 10 years no one should be touching any of this equipment who doesn't know what reset is and how it works.
    NRT.Rob
  • Coany Coany @ 8:04 PM
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    Goldline relay with an outdoor sensor...

    automatically adjusting the mixing valve. I am not too familiar with this particular control set up.You are correct that his complaint is not a cold room,its cold floors.
    Overheating has never been an issue for this customer beacuse any excess heat leaks out into the master bedroom, or into the hallway in the other bath.5
    " Do what you can, with what you have, where you are" Teddy Roosevelt
  • NRT_Rob NRT_Rob @ 9:18 AM
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    the answer is

    the lowest temperature that will satisfy the thermostat is the ideal temp in most cases.

    if rapid response is required, perhaps not.

    if the thermostat is satisfied, the floor is as warm as is needs to be. If insurance against cold floors is needed, constant circ or a floor sensor should be used, but that is eliminating cold floors; not guaranteeing warm ones. there is a "comfortable cool to neutral" in there which can heat a lot of areas.

    output is a function of floor temp. low output requirement = low floor temp.
    NRT.Rob
  • Jean-David Beyer Jean-David Beyer @ 10:07 AM
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    if rapid response is required, perhaps not.

    As a homeowner, I think this depends a lot on just what kind of radiant heating is provided.

    In my house, with an on-grade concrete slab with 1/2" copper tubing in it, rapid response is not practical at all. For a low mass system, I imagine more rapid response would be possible.

    When my new boiler was first installed, the technician set the reset curves to the factory defaults, which were to put 80F into the floor when it was 70F outside (if the thermostat was calling for heat), rising to 120F at 0F outside. The thermal mass is so much that it generally takes several hours (4?) to change the temperature much. Once the thermostat was satisfied, the heat in the slab caused the room temperature to overshoot by about 5 degrees.

    The thermostat is a Honeywell Model CT3600 set to 1 cycle per hour. I like its Usage feature that shows how many hours and minutes it was calling for heat for the current and previous day, and also the total since it was last reset.
  • NRT_Rob NRT_Rob @ 11:01 AM
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    correct

    but everything is relative. if the water temp is slightly higher than needed, your emitter will response slightly faster than it did before.

    at some point with mass emitters though you're right on, and overshoot/undershoot becomes more of an issue.
    NRT.Rob
  • Mark Eatherton Mark Eatherton @ 11:08 AM
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    The biggest most common complaint with RFH systems is....

    Discomfort due to over temp conditions.

    How low can you go?

    Time for the Turn it DOWN syndrome :-)

    Contractors and service people alike are wont to keep things hotter than necessary because they do NOT want to get a cold call complaint, especially on a system they installed or worked on.

    I spend more time turning things down than not.

    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Jean-David Beyer Jean-David Beyer @ 11:31 AM
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    Time for the Turn it DOWN

    I do not have steam heat, but I am interested in things, so I read that part of this site a lot. A piece of advice I see there quite frequently, is to turn down the steam pressure to make it work faster and better.

    And now you notice that it is frequently necessary to turn down the water temperature in hot water heating systems.

    I guess there is something in our culture that says more is better, but that is not always true.

    Reminds me that many many people seem to think that turning up a thermostat that is already calling for heat will make it heat faster. I had a large air conditioner with humidity control that had no chiller. It had a large water-to-air heat exchanger for cooling and it was supplied with 40F water through a proportional valve (operated by a servo motor) that was connected to a proportional thermostat. Instead of just a contact, that thermostat had a variable resistor whose contact arm moved up and down that resistor depending on the return air temperature. The hotter the air, the higher the signal to the valve. So diddling the setting would actually change the rate. But in 70 years of curiosity, not as a professional heating contractor, that is the only proportional thermostat I have ever seen.
  • Mark Eatherton Mark Eatherton @ 12:12 PM
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    My Mother was the WORST violator of that rule...

    "But it makes me FEEL warmer when I turn it up higher..."

    I never introduced her to the Secretary Stat. It is hooked to nothing and controls nothing, but it makes people feel good just thinking they are in control...

    What did you do for a living JD?

    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Jean-David Beyer Jean-David Beyer @ 1:29 PM
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    What did you do for a living JD?

    I worked for a little defense contractor (Sierra Research Corporation, in Cheektowaga, New York) for about five years designing electronic equipment, such as radar systems for anti-submarine-warfare, telemetry and instrumentation systems, and feedback control systems.

    Then I switched to Bell Telephone Laboratories where I did a lot of computer-related work. I wrote a bunch of simulation programs, wrote an operating system and helped design a computer system to do real-time picture transmission studies (think Picturephone). Also worked on database management systems (I wrote an early relational database management system used for telephone directory searches; described in Gabbe, J.D.,London, T. B., Miller, R.E. and Beyer, J. D., "Applications
    of Superimposed Coding to Partial-Match Retrieval," COMPSAC 78,pp.
    464-470.)

    After 25 years at BTL, I left to work at a small start-up company designing an advanced telephone communication system. Unfortunately, we ran out of capital before we became profitable, so I retired permanently in about 1994.

    At Bell Labs, we had a nifty building, designed by Eero Saarinen. Unfortunately, the architecture did not use the round Honeywell thermostats. It used vertical rectangular ones that functioned on (slightly) compressed aid. The air controlled the position of a vane in a mixing box that was supplied buy two ducts, on hot air, one cold air. Nominally there was one thermostat and one mixing box per room. But as time went on, some mixing boxes failed, and more rooms were added. So some people got what we called "psychological" thermostats. Well, they mostly stuck women with those. But there were a lot of women there with Ph.D. degrees in science and engineering and they pretty quickly detected the deception. Eventually, the secretaries got the psychological thermostats.

  • Mark Eatherton Mark Eatherton @ 1:39 PM
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    Interesting...

    I had a customer who you might know. He worked for Bell Labs and his thumb is a famous thumb. It pushed the LAST above ground nuclear launch button on an island in the South Pacific. His name was Don Littlefield. Very interesting fellow.

    He gave me a sample of a man made element called Trinitite, from the Trinity N.M. above ground nuclear blast proving grounds. I still have it. It looks like glass/sand. He said it came from directly below the blast site.

    Enjoy your retirement.

    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Jean-David Beyer Jean-David Beyer @ 1:51 PM
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    Knowing people at Bell Labs...

    I worked mostly in research there, first at their Murray Hill location, and then at Holmdel. The military work was mostly done at Whippany. There were about 10,000 employees there when I started, and around 30,000 when I retired from there.

    My guess is if you name him, I probably did not know him (or her). I knew Chapin Cutler, Charlie Rubinstein, John Limb, Zygmantia Budrikis, Maurice Karnaugh, Doug McIlroy, Arun Netravali. I have met quite a few others that I cannot really claim to know, such as Dennis Ritchie and Ken Thompson.
  • Jean-David Beyer Jean-David Beyer @ 1:37 PM
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    Secretary Stat

    Come to think of it, when I worked at Sierra Research, we occupied a converted airplane hangar. Actually located on land of the Buffalo NY airport. It was heated by those Reznor (?) hanging gas heaters. There were two areas of the building where the thermostats were connected to the wrong heater. No one knew this. As long as the thermostats were set to the same temperature things were adequate. But once a secretary felt cold, and pushed up the thermostat a little. That did not heat up her area, but it did heat up the other area where it was already warm enough. So they lowered their thermostat, but that did not cool them off. But it did cool off the room where the secretary was. Rinse and repeat. This went on for a day or so until I figured out what the problem was and got the thermostats re-wired. By then one thermostat was set all the way up and the other all the way down.
  • NRT_Rob NRT_Rob @ 1:34 PM
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    actually, they are right

    by letting the air temperature rise, to counteract all the cold surfaces they likely have, they do achieve comfort faster when they turn up the thermostat. They are trying to balance out their comfort with the only knob they have. it's not great, but it's not nothing either.

    Also you could say when the air is hotter, it will heat those surfaces up quicker as well.

    but that's only if they leave the thermostat at the higher setting for awhile. Turning up to 80 when you walk in a room then turning it back to 70 before it hits 70 naturally won't do anything. but if you hit the higher setpoint... you're doing *something* more than stopping at a lower temp...
    NRT.Rob
  • heatboy heatboy @ 11:06 AM
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    It was a common complaint.......

    ....back when Wirsbo (remember them?  I miss 'em.) used to have the "Warm Friendly Floors" foot in their advertising.  I ALWAYS made the point that the floors may not be very warm a certain times of the year and explained why.  If they still wanted the floor warm, I would just set the slope up a notch or two and then cycle of the thermostat.  Certainly not the most efficient, but they had their feet warmer.
    heatboy

    The Radiant Whisperer


    "The laws of physics will outweigh the laws of ecomomics every time."
    This post was edited by an admin on April 8, 2010 11:50 AM.
  • N/A @ 10:28 AM

    Blood Heat

    Hi- First of all I'm a steam guy who knows absolutely zero about radiant heat.
     I've never thought that much about radiant and until reading this thread, went along the misconception that radiant would always give you "warm toasty floors" which I think is a pretty standard misconception among the public. I'm sure radiant guys run into this all the time.  That it was a misconception came to me as an instant revelation after reading  JD's comment about not being able to feel warm to the touch below blood heat (98.6F).
     I remembered testing the heat of the milk in our kid's baby bottles on my wrist and thought, "Yah, that's right! ... below 98.6 it would feel cold!
    I thought I might just mention the "baby bottle test" as it might be a good way to help explain to people about why they feel "cold floors". `I think they could then easily see that raising the floor temp to above 98.6 wasn't very practical or desirable.
    - Rod
    Edit: Apparently I'm still suffering a misconception. Please see NT-Rob's post following this one for an explanation.
    This post was edited by an admin on April 12, 2010 11:28 AM.
  • NRT_Rob NRT_Rob @ 10:32 AM
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    not true

    floors start to feel warm in the high 70's. Otherwise no one would ever feel warm floors.

    You don't feel cool in 97 degree air, because it's not about you PICKING UP heat from your surroundings... it's about how fast you are LOSING heat to your surroundings.

    if you don't lose heat faster than you create it internally, your temperature rises and you feel hot.

    this is why between 85 and 90 degrees, floors feel hot. not because they are burning you: just because your feet can't reject heat to them very well.
    NRT.Rob
  • Jean-David Beyer Jean-David Beyer @ 11:50 AM
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    not being able to feel warm to the touch below blood heat (98.6F)

    I think I was speaking of the temperature of the water delivered to the slab, not the temperature of the top of the slab. Where I notice it most are the bathroom (little marble rectangles) and the kitchen (ceramic tile). These are on top of the concrete slab, and I do not know how far down in the concrete the copper tubing is. I assume the surface temperature of the slab is less than the water temperature going through it.

    To contradict myself, I would suppose if the floor surface were below my body temperature, heat would leave me and enter the floor. And if the floor surface were above my body temperature, heat would leave the floor and enter it. Where the balance is where I feel cold when in direct contact with a surface I leave to the physiologists.
  • N/A @ 11:22 AM

    Perception

    LOL! Now you have me going! I have some extra floor tiles in the garage and an IR thermometer. My wife is just going to have to go out for fast food as I'm going to be using the kitchen oven for a while!
    On a more serious note- Thanks Rob, for the correction. I know you have vast knowledge in this area so I accept what you are saying is correct. I can't say that I have it straight in my head as yet as I would have to think a bit on how as humans, we perceive heat differences, especially by direct contact.
    That's what I think is so neat about "the Wall", you learn something every time you read it.
    - Rod
  • We lost Coany!

    He was in a tough predicament and we got side-tracked.  We need to get back and try to solve his problem. 

    The problem areas are the 2 zones of radiant where the owner has expectations that the floor should be warm.  We don't know if the tubing is in the floor sandwich, staple-up with plates, or suspended tubing in the joist bays; I'd say the latter from everything that's been discussed.

    I'd say he needs to start with a thermostat that has a floor and air sensor to be able to control and attain a minimum floor temperature.  If this doesn't work, he needs to talk to the owner about giving up on the idea of warm floors unless he wants to re-work the tubing
    Often wrong, never in doubt.
  • Chris Chris @ 7:19 PM
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    Alan Your right on Spot

    I posted previously that a floor sensor was needed in this case. I also asked about floor temps but Coany never responded to the questions. He did respond to the fact that he did not know how the tubing was attached, ie plate or no plates. I never heard in any of his posts that the customer was cold so the radiant is doing its job as far as the heat loss goes. It may be the application where the problem lies. Without knowing floor surface tempsand install it's pretty much a guessing game at this point. I was curious to know what surface temp is at setpoint and then again when the therm asks for a call for heat. Would also be curious as to run time.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Charlie from wmass Charlie from wmass @ 12:19 AM
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    WHat I have done to have warm floors for customers

    I have run as cool of water as I could to meet the heat loss. In other words strectched out the run times instead of raising the water temps. The idea is to have a constant lower temperature instead of spikes and valleys. The customer I am thinking of was so pleased that after 4 years of cold feet he now had warm feet and he asked me why the original installer had kept raisng the water temp instead of lowering it? I simply shrugged and said we all do things a bit different. I think it is when the radiant floors cool when off that people get the feeling the floor is cold. Does this make sense to you guys?
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • Coany Coany @ 8:15 PM
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    What i don't know could fill a book

    what i do know is that this customer sent a very nice letter to my boss thanking me for finally solving his problem.



    the real test of course is if he calls back in  few weeks for"The Same Problem"
    If they send me back, I have a much better sense of what should be done.
    Thank you all for your input.

    This winter this customer spent $26k on oil with my company, so even if its not strictly according to Hoyle, I want him happy and warm.
    " Do what you can, with what you have, where you are" Teddy Roosevelt
    This post was edited by an admin on April 14, 2010 4:51 AM.
  • Radiant

    Yes, Chris: I thought your suggestion of a floor sensor was the best idea and that is why I brought it up again.  The hard part is finding a place to install it in a finished room without wires showing.

    And Charlie: I've never done that, but it certainly makes sense.

    Alan
    Often wrong, never in doubt.
  • N/A @ 10:34 PM

    System design temperature

    Charlie has it right.

    The definition of comfort is the absence of discomfort. If the outdoor reset is set up correctly using design outdoor design conditions for your area and considering your particular radiation, the system will be operating and delivering heat until the warm weather cut out turns the boiler and pumps off. Old copper radiant floor systems are made perfect and probably last longer with this simple modification.

    The trick is closely matching the heat loss with the heat output. In cold weather the floor (or radiator) will get hotter water and feel warmer but comfort  - and fuel bills - will always be nearly perfect.

    If you though in a condensing boiler (all have built-in reset) you will perfectly comfortable and save money at once.
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