Home>Discussions>INSULATION & HVAC>Radiant heat stapled to subfloor
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Windebrook
Radiant heat stapled to subfloor

Hi, I was wondering if anyone could tell me how to install insulation over radiant heat stapled to under side of subfloor. Should we leave a gap/pocket between insulation and subfloor or should we push insulation right up against the subfloor and tubing? I say the latter as I feel with a pocket, we are wasting energy to heat the joists to either side, but spouse vigourously objects. Thank you, Bev in Mass

canuk
Re: Radiant heat stapled to subfloor
Quote:

should we push insulation right up against the subfloor and tubing?

Not to take sides .......... :D

You should have intimate contact between the insulation and the tubing ...... to maximize as much resistance to heat loss as possible.

Blue RidgeParkway
Re: Radiant heat stapled to subfloor

do you have reflector panels up?

NashuaTech
Re: Radiant heat stapled to subfloor

I agree with Canuk---I didn't see mention of the essential aluminum plates in the original post.

There are aluminum plates that fit over the PEX that deflect the heat upwards toward the floor & sub-floor that are recommended by all floor radiant manufacturers.

Blue RidgeParkway
Re: Radiant heat stapled to subfloor

under the tubing and or pex & diffusion plates you are supposed to keep one inch of space then install the radiant reflective barrier between the joists then tight to that is the insulation so you get all the heat from the sides and bottom of the tubes refelecting back up to the floor. if you're using foil lined batts or boards already then the foil goes towards the floor but you keep one inch between the tubing and diffuser plates and the foil but you foil the 1" side of the joists, some tubing says you need two inches before the reflective barrier and insulation.

well, at least thats what our manufacturer's instructions (watts)were with cold space below like basement or crawl space.

Who says she has pex? She could have used Onix or oher EPDM tubing that is usually stapled up not screwed up with plates (doesn't need them) like pex.

sabo4545
Re: Radiant heat stapled to subfloor

When I installed mine we used the onix which does not use the plates just staples directly to the subfloor. The materials I had said to leave a 2" space between the subfloor and foil faced insulation panel. This would be about 1" below the actual tubing. The most important thing is to be sure the silver foil is facing up. Its also important that your rim joist is insulated to prevent the cold from getting in and making the system inefficient or worse freezing the water in the tubing.

Mike

Blue RidgeParkway
Re: Radiant heat stapled to subfloor
sabo4545 wrote:

When I installed mine we used the onix which does not use the plates just staples directly to the subfloor. The materials I had said to leave a 2" space between the subfloor and foil faced insulation panel. This would be about 1" below the actual tubing. The most important thing is to be sure the silver foil is facing up. Its also important that your rim joist is insulated to prevent the cold from getting in and making the system inefficient or worse freezing the water in the tubing.

Mike

well said Mike good points on insulating the rim joist and reflecting it back too.

canuk
Re: Radiant heat stapled to subfloor

Any reason as to why an air gap of about an inch or two using reflective foil ....and what about insulation without reflective foil?

sabo4545
Re: Radiant heat stapled to subfloor

Not exactly sure about the air gap other than allowing for heated air under the floor so even when the heat shuts off you will still get some residual heat. If the insulation was in contact with the tubing it may transfer the heat to the insulation instead of heating the air effectively. That is my guess anyway.

As far as the foil face it is so the heat is reflected up toward the floor. Yes heat rises but the foil face makes it more effective.

Mike

Blue RidgeParkway
Re: Radiant heat stapled to subfloor
Windebrook wrote:

Hi, I was wondering if anyone could tell me how to install insulation over radiant heat stapled to under side of subfloor. Should we leave a gap/pocket between insulation and subfloor or should we push insulation right up against the subfloor and tubing? I say the latter as I feel with a pocket, we are wasting energy to heat the joists to either side, but spouse vigourously objects. Thank you, Bev in Mass

canuk wrote:

Not to take sides .......... :D

You should have intimate contact between the insulation and the tubing ...... to maximize as much resistance to heat loss as possible.

Nope that is wrong.

canuk wrote:

Any reason as to why an air gap of about an inch or two using reflective foil ....and what about insulation without reflective foil?

Bev in Mass,

sorry but spouse is right but you should have reflective barrier and canuk is wrong. when you have joists you need a gap then you put the reflective barrier an inch or so below the radiant heat the reflective barrier is important and the gap is more important. if you want to insulate (like cold zone below) then that insulation goes right beneath up against the reflective barrier. you do not insulate with direct contact when you have joists and you don't insulate without a reflective barrier in place.

i know it has something about the air space being necessary for a reflective barrier to work. the way i remember it was similar to the necessary air space between the reflective low E film in windows and the inner glass layer and how the radiating heat energy you can't otherwise direct back to the subfloor when you have joists was/is long wave IR. that the reflective film surface provided little in thermal resistance in itself and if in direct contact with the radiant heat source without the one inch air cushion would transfer the heat directly to the wood joists and insulation pocket like a conductor instead of a reflector back to the subfloor. the air pocket is necessary to be reflected and if cold below then also insulated from all six sides of the subfloor area like Mike reminded otherwise you get air currents in the air space or it (heat) goes up the walls like a chimney or conducts heats to the rim joist and heat transfers to the outside wall = heating the outoors.

keeps the return water warmer protects from the cold below and sides = more of the warmth in the water retained on the return to boiler = fewer gallons of oil (BTUs) or gas to heat it back to temperature = lower fuel bills and higher efficiency. most important it makes the floor more responsive meaning it gets warmer faster also requiring less BTUs overall.

basically the radiating heat energy wants to go to the coldest spot it can so you deflect it to the floor or focus it with a mirror like reflective barrier. the only thing you want touching the tubes besides the subfloor is what touches the subfloor you are heating to direct diffuse transfer the heat to, no reason to heat the air pocketed insulation, the rest of the heat that radiates you want to reflect direct back to the floor to heat it that way. i do remember that air in that space is considered fluid.

if you need an example of reflective barriers and long wave infrared and how it works you can build yourself a reflective oven chamber and use it to melt a jar of snow in it at mid day in the middle of winter.

i am sure they have loads of testing about their products and efficiency but whoever wants to know WHY could easily ask the manufacturers or look it up themselves if they cared to know why since they didn't know HOW in the first place. maybe things need to be done different in the tundra or arctic circle or Alaska but not Mass.

JLMCDANIEL
Re: Radiant heat stapled to subfloor

The reflective layer is to reflect the radiant heat back toward where it is needed the floor above. No direct contact or the foil would become a heat transfer plate or fin carrying the heat away from the floor.
Jack

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