radiant floor heat temps.

PORKCHOP

i realize there is a max. surface temp. in radiant floor heat but is there a min. surface temp. to look for?  or does the amount of btu's for the available square feet dictate the surface temp.?

porkchop

 

Brad White

Assuming Room Temperature

The minimum for RFH is really room temperature, some say a degree above for foot comfort, but even that can overheat a space and is over-rated as a control strategy in my book.  Obviously the water temperature will be in that range too, by that point.



You have it right, the available floor area dictates the surface temperature, generally not over 83-85 as you know that is pushing it.. In most cases and with certain exceptions  much lower. You know the variables, I am sure.



Now for truly a low limit, say  you DID go lower than room temperature. That would fall into the category of radiant floor cooling. Just like RFH, but it works the other way, and  you have to keep the floor above the space dew point or you will have your own Disney on Ice show, with the characters unaware.

PORKCHOP

radiant floor heat temps.

brad

thanks for the reply

the reason i have this question is due to a project i am working with where the average supply water temo. is 113,  with the floor surface temp around 73,  and the rooom air temp. around 70.  i am somewhat familiar with hydronic heat,  but still a little shakie on the design side.  i am having a hard time grasping that the floor temp.  will only be 3 degrees higher than room temp.  and still be able to heat this area satisfactory.  probably due to working to long with air to air heat.  if you have any helpful info to guide me in the right direction i would appreciate.

thanks

ronnie

Mark Eatherton

The basic rule of thumb...

For each 1 degree F difference in floor surface temperature versus air temperature, the floor will deliver 2 BTU's per square foot per hour. So at a 3 degree delta T, the floor is delivering 6 btu's/sq ft/hour.



The maximum recommended floor surface temperature is a human physiology limitation, and not a physical plant limitation.



Human skin surface temperature is 85 degrees F, therefore the floor cannot be more than 85 degrees F, or it will cause the human in contact with the floor to go into cooling mode. I prefer to call it Evapo-transpiration. My wife calls it sweating, unless she's the one doing it, in which case she calls it "Glistening"...



Now you probably know a lot more about radiant floors, heat transfer and human limitations than you wanted to :-)



BTW, if this is an inside space with no exterior wall/window loss, these numbers sound OK. If it is on an outside wall, the walls had better be SUPER insulated, and the windows triple or quadruple paned (or Radiant Glass Industries windows) or the numbers aren't right.



It ALL starts with a heat loss calculation.



As for minimum floor temps, if the floor space were over a cold, unheated space, like say a cold garage or cold crawls space, there are some controls that can maintain a minimum floor surface temperature, but it really needn't be more than around 70 degrees F. If your feet are cold, put on slippers, don't heat the space up in favor of your tootsies.



Lastly, radiant floors are a wonderful thing, but they are not the only way to deliver radiant comfort. Look at radiant walls, ceilings, counter tops and windows to accomplish the same feat. Oh yeah, I forgot cast iron radiators and panel radiators.;-)



Welcome to the Wall.



ME