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Favorite insulation and/or reflective foil?

watercourse
watercourse Member Posts: 28
What's your favorite insulation to go in your joist bays under your radiant?

Do you use reflective foil?

If so, which one?

If not, why?

Is there a good insulation with foil backing you like?

Comments

  • HomerJSmith
    HomerJSmith Member Posts: 2,395
    edited March 2023
    I like 1" R-max foil sided up. The fibre glass insulation under the R-max. Fast and cheap foil bubble with fibre glass insulation under.
  • Waher
    Waher Member Posts: 234
    Havelock wool
  • kcopp
    kcopp Member Posts: 4,395
    Rockwool. Dont waste your money on the R bubble stuff. Not worth it. reflective "R" value is a myth when it comes to radiant. You are trying to conduct heat not reflect it.
    hot_rodHomerJSmith
  • woobagooba
    woobagooba Member Posts: 186
    edited March 2023
    Zone 5. I'm doing R19 Next Gen Pink. Rockwool priced out 2x fiberglass. No reflective foil. Should also add that this is overhead an unfinished basement with very irregular joist bays.
  • hot_rod
    hot_rod Member Posts: 21,868
    The foil is of little value. As soon as it gets any dust, the reflectivity is gone anyways. The r value is worth chasing
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • yellowdog
    yellowdog Member Posts: 146
    i was taught(by Watts Radiant) to start with a reflective layer 1" below the tubing and back it up with r 19 fiberglass. we always used the bubble wrap type.
  • JakeCK
    JakeCK Member Posts: 1,356
    As has already been stated, reflective foil is a gimmick. It can be used behind radiators to reflect heat back into the room but it is largely negated once the wall is insulated with basically anything. And once there is a layer of dust it is next to worthless.

    I'd imagine what is below that floor is what largely determines how much insulation you really want. Second floor bedroom above living room? Maybe just a couple inches of your choice of the fluffy stuff. Unheated basement/crawl space? I'd go full depth. I've also read it's best to leave it an inch or so below the actual pipes and heat spreaders to better allow the even heating of the subfloor. Idk know how true that is tho.
  • yellowdog
    yellowdog Member Posts: 146
    the biggest key is the air gap to the tubing. you dont want the insulation to touch the tubing regardless of what type it is. i dont understand the dust comments. if the reflective insulation is put up in the bay correctly, where is this dust coming from? you have created a sealed cavity that shouldn't allow anything into it. i have done work in my own house and when i take down my bubble wrap that i put there 16 years ago, it is just as clean as the day it was installed. the reflective layer will also help drive the heat upwards instead of letting it get absorbed into the insulation.
    kcopp
  • hot_rod
    hot_rod Member Posts: 21,868
    yellowdog said:

    the biggest key is the air gap to the tubing. you dont want the insulation to touch the tubing regardless of what type it is. i dont understand the dust comments. if the reflective insulation is put up in the bay correctly, where is this dust coming from? you have created a sealed cavity that shouldn't allow anything into it. i have done work in my own house and when i take down my bubble wrap that i put there 16 years ago, it is just as clean as the day it was installed. the reflective layer will also help drive the heat upwards instead of letting it get absorbed into the insulation.

    I've seen just the opposite with reflective foil in new radiant installs. The dust came from the floor above thru the cracks and gaps in subfloors, also from any dust swept up below. Sheetrock dust is mainly what you find in new construction.
    Even particles from the fiberglass coat the foil.

    The bubble foil; really isn't a smooth highly reflective flat surface. Ever check the inside of FA ducts, even heavily filtered it will coat with dust. Same with monitor screens on your desk.
    Needs to be a clean shiny surface or don't bother.

    Plenty of research has been done, find it at healthyheating.com

    http://www.healthyheating.com/Page 55/Page_55_o_bldg_sys.htm#.ZAIOO-zML9E


    Dust never sleeps:)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    JakeCKGGrossPC7060
  • JakeCK
    JakeCK Member Posts: 1,356
    yellowdog said:
    the biggest key is the air gap to the tubing. you dont want the insulation to touch the tubing regardless of what type it is. i dont understand the dust comments. if the reflective insulation is put up in the bay correctly, where is this dust coming from? you have created a sealed cavity that shouldn't allow anything into it. i have done work in my own house and when i take down my bubble wrap that i put there 16 years ago, it is just as clean as the day it was installed. the reflective layer will also help drive the heat upwards instead of letting it get absorbed into the insulation.
    I doubt it was as clean as the day you installed it. Houses aren't hermetically sealed.
  • ChrisJ
    ChrisJ Member Posts: 15,473
    edited March 2023
    From what I can tell a typical aluminum and glass mirror that would be way too expensive is about 60% efficient maybe a bit more under perfect conditions.

    Add a slight haze over time and forget it. And it will get dusty and hazy.

    Bubble wrap and foil would be useless from day 1 from what I can tell.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment