foil radiant barrier

[jwvess00]

Hi there!

First, if you know of a good insulation contractor in the Lexington, KY area please let me know. I have money in-hand, and I am ready to do the job (I'm not a "tire-kicker", I want to get this done soon) -- and I have had trouble getting contractors to call me back. Ugh.

I called/emailed a few insulation contractors I've found via the online version of the Yellow Pages, and had one get back to me. He stopped by today and looked at the shop, then started his pitch for copper foil radiant barrier.

He wanted to install this "space age" (his words) copper foil material in the attic of the shop, over the truss chords essentially (imagine a floor of the stuff). It's paper-thin copper foil with what I guess is nylon weave. The sample material he had was pretty strong stuff. You wouldn't tear it accidentally, I'd say.

He didn't want to do anything to the walls, claiming that most of the heat gain/loss is through the attic space, so that's what you bother insulating.

His quote came in at well over $5000 even after his "sign up NOW!!!!" discounts, for my 36x50 shop. He put the hard-sell on, which immediately turned me off, and the price was the final nail in his coffin with me.

That said, I've seen this stuff for sale in aluminum and it seems interesting. Any experience with it?

Here's a place that sells the aluminum-based stuff. Other than a Google search I don't know anything about this place: http://www.atticfoil.com/

I was considering blown cellulose or spray foam (or a combination of the two), but was thinking the foil may at least be a compliment to insulating the place.

For regular insulation, the walls are 6" deep (6" wood posts, steel-siding/roof pole barn) and I've studded out the walls flush with the posts so the 2x4 studs don't go all the way out to the metal. That should give a nice uninterrupted blanket in the walls if I blow material in. The ceiling height is 9', and I was originally planning on blowing in cellulose or foam up there, too.

The building is currently wrapped in vinyl faced fiberglass, about 1" thick I'd guess, on the walls between the steel siding and the girts, and between the roof metal and the purlins. It's not in great shape -- it's damaged in quite a few places. I was going to remove it before insulating.

Thoughts?

 

[mygarageone]

Anyone who says you don't need to insulate the walls are idiots. Insulation is not the technical but it does require attention to detail with any cracks or missed spots.

 

[jwvess00]

Hi there!

Yeah, when he said that my BS meter went off.

The website I posted even says that the stuff isn't a substitute for insulation.

It looks interesting and the DIY price to cover my whole attic floor, or even the roof, isn't too awful. I was wondering if anyone had used it before.

If I pull the vinyl-faced insulation out (which I intend to do, it's damaged in places and generally filthy from being exposed to the shop for about a decade, and in one spot looked like it had turned into a nesting site for bugs), I won't have a vapor barrier of any kind in the walls. I did see some foil that was also a vapor retarder (or barrier, not sure) which might be interesting.

 

[volleyball]

Foil is a radiant barrier. So for radiant heat transferring it works. Not so much for the non radiant heat. Any radiant barrier would need some other type also. Like they do the 2 layer silver foil that has the bubble wrap in between as an air barrier.

 

[DC73]

Run. This guy is basically selling snake oil. The science behind radiant barriers is there but the cost / benefit ratio is not. There is no way a radiant barrier only system would ever pay back. It only makes sense when the radiant barrier is part of another product like foam insulating sheets or OSB.

The best bang for the buck in energy savings is to air seal your home by thoroughly calking and/or spray foaming all cracks and crevices, basically anywhere air could enter or leave your home. Next is blown-in cellulose in the attic. Insulating walls in new construction is a no-brainer but insulating walls in existing construction may only make sense in climates with extreme temperatures, it just depends on the cost and the savings to be gained. Sometimes comfort overrides cost and savings and becomes the deciding factor.

Visit Green Building Advisor and search for radiant barriers to get more info (search on the main site and on the Q&A forum).

DC

 

[BadgerBoilerMN]

http://www.healthyheating.com/Page 55/Page_55_o_bldg_sys.htm#.VVCtbvmrRhE

http://www.greenbuildingadvisor.com/blogs/dept/musings/stay-away-foil-faced-bubble-wrap

 

[sands35]

I'll throw in there that folks confuse the term "Radiant Floor Heat" with "Radiation/Radiant Heat Transfer". The later is a technical term, the other is a casual term.

A forced water heated floor heats your house/garage by natural convection and conduction, NOT by radiation heat transfer. Even though folks call hydronic floor heating "radiant". I guess it is a hold over from from steam radiators.

Radiant heat transfer becomes the dominant source of heat transfer with temps north of 4-500*F - so the sun or stuff on fire or hot exhaust pipes or hung radiant tubes, etc. ~120*F water going through a slab of concrete is not going to transfer heat into the air via radiant heat transfer.

So they purveyors of the bubble wrap are playing on non-technical folks misunderstanding of the word "radiant".

Radiant barriers are used in some applications. Heat shields around mufflers, particularly turbo charged cars. Auto makers use (typically) aluminum sheets with an air gap on both sides. Some race cars will put gold foil around the areas near exhaust headers to control heat into the cockpit, etc. Basically need really hot temps and an air gap.

 

[BadgerBoilerMN]

I'll throw in there that folks confuse the term "Radiant Floor Heat" with "Radiation/Radiant Heat Transfer". The later is a technical term, the other is a casual term.

A forced water heated floor heats your house/garage by natural convection and conduction, NOT by radiation heat transfer. Even though folks call hydronic floor heating "radiant". I guess it is a hold over from from steam radiators.

Radiant heat transfer becomes the dominant source of heat transfer with temps north of 4-500*F - so the sun or stuff on fire or hot exhaust pipes or hung radiant tubes, etc. ~120*F water going through a slab of concrete is not going to transfer heat into the air via radiant heat transfer.

So they purveyors of the bubble wrap are playing on non-technical folks misunderstanding of the word "radiant".

Radiant barriers are used in some applications. Heat shields around mufflers, particularly turbo charged cars. Auto makers use (typically) aluminum sheets with an air gap on both sides. Some race cars will put gold foil around the areas near exhaust headers to control heat into the cockpit, etc. Basically need really hot temps and an air gap.

Even more confusing.

The percentage of heat transfer defines radiant heat, technical or otherwise.
In the HVAC industry the term radiant describes a panel with heat transfer of 50% or greater. All radiant heating floors, walls and ceilings panels qualify as radiant heaters, or coolers for that matter.

Though a certain amount of convection will occur in a radiant heated room, dependent mainly on construction and climate, the bulk of energy transfer occurs radially at the speed of light. The same is true of high and low intensity radiant heaters, to a lesser degree due to the higher operating surface temperature in fact.

As for heat shields, the efficiency of any heat shield is highly depend on the reflectivity and emissivity of the "shield" in question. Dirty shields are less efficient. Most, as in the example of a muffler shield actually use more convection, the shield absorbing heat that would otherwise radiate to the nearest surface and air movement around the shield lowers the temperature of the protected component.

As for conduction. The PEX tubing conducts warm water to the radiator or radiant panel. In the case of a radiant slab the elevated temperature of the water is conducted, first through the wall of the PEX and then through the slab to the surface of the floor. From this point radiant heat waves find the coldest surface in the room and some air at the floor is warmed and convected upward, warm air rises.

The only way to experience conduction on a radiant surface is to touch it your body.

http://en.wikipedia.org/wiki/Radiant_heating

Whether by conduction or convection, rarely exclusive in the real world, the effect is the same and your point of an air-gap is both germane and crucial to the efficacy of any radiant barrier be it attic or building siding.

Finally, you are absolutely right about bubble wrap, though I would say the people selling it are preying on the ill-informed.

 

[sands35]

Wikipedia war!!! haha

Fires and IR panel heaters operate well into the (engineering) radiant range of heat transfer.

http://en.wikipedia.org/wiki/Heat_transfer

I guess it depends on if you are talking engineering or application.

 

[pseudorealityx]

From this point radiant heat waves find the coldest surface in the room and some air at the floor is warmed and convected upward, warm air rises.

The slab radiates everything equally. There is no preference on where the "heat waves" go. The hottest part of the slab will radiate more, but that's it.

 

[BadgerBoilerMN]

The rate of heat flux is directly related to the temperature of the slab as you suggest and I did overstate the target, which is not necessarily the coldest surface, but rather the surfaces with the greatest emissivity.

The heat transferred into or out of an object by thermal radiation is a function of surface temperature, reflectivity, emissivity and surface area. The surface of the materials in the room can effect the output of the slab as well.

This explains the thermal "striping" that commonly occur in slab-on-ground radiant systems when you can "feel" where the PEX is. The slab has a low specific temperature with little resistance to heat and will tend to be cooler between the PEX pipe runs. Any floor covering may decrease this effect and produce a more even surface temperature, but the emitter is only one side of the equation, the other being the surface to which the electromagnetic infrared energy is transmitted to potentially increasing the output of the slab.

The colder it gets outside and in turn inside, the greater the potential of any radiant panel .

 

[pseudorealityx]

Agreed. One other huge contributor that nobody has mentioned is distance from the heat source. The heat source projects X amount of heat energy. As distance doubles, the amount of heat falls by a factor of 4.

 

[BadgerBoilerMN]

http://www.woodweb.com/knowledge_base/ForcedAir_Shop_Heat_Versus_Radiant_Heating.html