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Specific area carpet recommendation for radiant?

rickgerv Member Posts: 22
One disadvantage of radiant that I realized after the fact is the ability to put down a carpet. I have a small cheap, area carpet 5x8 in my living room and it's noticeably warmer under it which I assume is not good. I have read that carpet is possible to have but would like to know if someone can recommend a specific brand, type of carpet as it's not clear to me what would be acceptable. Intention is not to cover the floor but have small bit of carpet to help balance out the decor. Searched older threads but couldn't find a concrete answer on what and where to get a suitable areas rug that won't damage my floor. I have subfloor radiant.


  • Zman
    Zman Member Posts: 7,552
    Do you have wood flooring under the carpet?
    Do you know if the tubing is installed with aluminum plates?
    What water temps are you running?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • rickgerv
    rickgerv Member Posts: 22
    yes. the radiant system is wood oak with aluminum plates underneath. These are old original floors. Water temps are decently high at 140 on the colder days. I have a second stage heater that kicks in when temps get very low. So radiant is not the only source.
  • Ironman
    Ironman Member Posts: 7,354
    Your total floor covering (sub floor, hardwood, carpet) must be calculated (R value), along with the heat loss of the room, to know what water temp is necessary. Basic rule of thumb: no more than an R2 value on floor covering. Carpet and padding have their R value stated buy their manufacture. Ask your carpet supplier for it.

    You can find charts on line for the R value of different types of wood, but a very rough rule of thumb would be about .9 per inch for hardwood and about 1.1 per inch of soft wood. For engineered sub flooring (like Advantech) and engineered hardwoods, get the manufacturer's specs.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Gordy
    Gordy Member Posts: 9,546
    The problem that presents itself is the use of an area specific rug.
    In calculating the needed water temps for the whole floor assembly to be friendly to your wood flooring, the area that has a rug will always suffer output.

    If you compensate water temps for the rug the rest of the floor will be to warm, maybe to warm for your wood flooring.

    All you can do in my opinion is get the thinest rug you can for the area.
  • tim smith
    tim smith Member Posts: 2,744
    I was just going through this with a customer on design. It's a catch 22, get enough floor area and safe temps for floors is one thing. Then throw area rug over it and you will damage floors under rug. If starting from scratch about the only thing you ca do is minimize tube under area rug location as long as you can get enough output out of overall floor area to cover heat loss.
  • Gordy
    Gordy Member Posts: 9,546
    Agree Tim. As you said this needs to be brought up in planning. A loop isolated to the proposed area of the rug which can be controlled seperate from the rest of the floor. This still is not a fix all if your on the edge of area to heat the space sufficiently at the max allowed floor temps.

    What the OP has in their favor is supplemental heat.

    Maybe by luck the area of the rug has a loop seperate from the rest of the floor loops. You could trim the flow rate down in that particular loop. Of course output will suffer.
  • rickgerv
    rickgerv Member Posts: 22
    edited January 2016
    In my case, I'm fine with cheap, thin carpet. It would simply be nice to have something on part of the floor as I don't have a lot of furniture. Room looks bare. Also it's nice to sit on something soft. Problem is that carpets aren't labeled with R values. I've got an elcheapo home dept 5x7 on my floor with no pad. Listed as .05 inches thick ( I measure it at .3). But it does retain heat well. Really anything on the floor even a slipper, you feel it underneath is warm. My floor temps are around 75F. Hoping something like a thin, sans-pad carpet will be OK. Didn't occur to me that folks design their radiant esp retrofit jobs, subfloor with area rugs in mind.

    Found this link which would indicate I'm well under R2 http://www.masterhydronics.com/info/carpet.html
  • Gordy
    Gordy Member Posts: 9,546
    Most designers would inquire if that is a possibility, and design around it.
  • hot_rod
    hot_rod Member Posts: 21,890
    It's the pad underneath the carpet that adds r value also. There are some thin radiant specific pads, thin rubber or foam with a lot of clay in the mix.

    The pad extends the wear of carpet and softer feel, go without pad if you are tight on the numbers.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream