Door Insulation Foil in or out?

[Bigblue&Goldie]

I live in AZ and I just bought a westward facing house. My last house faced East and the backyard was so miserable in the evening we never used it, so this time we insisted on facing west. The problem is, my garage now faces west......so it's miserably hot already!

I'm in the process of insulating the garage and putting in a mini split. Currently, my house has no insulation in the attic above my garage, so I will be blowing insulation up there. This week's project is getting the garage door insulated. My door just radiates heat! It's incredible. I went to Depot and bought 1.5" foam board which I'm cutting to size. My question is should the foil face in towards the garage or out towards the drive way?

I found this brief video of another guy in AZ that says the foil should face in towards the garage:

Some people say ^this^ guy's experiment is flawed because the infrared lasers don't work well on reflective materials?

From what I've read, the foil is a radiant barrier and typically should face out (towards driveway in this case), *except* it needs an air gap for it to be effective. My logic is the aluminum garage door itself should be acting as a radiant barrier. If I place the foam with the foil facing in (towards the inside of garage) I would think the aluminum garage door acts as a barrier, the foam is an insulating gap, and the foil acts as a second radiating barrier. Does this make sense?

Either way, I may be over thinking this as the garage door will never be perfectly sealed and none of the walls are insulated. I'm just hoping that by insulating the garage door and the ceiling that my mini split can keep my garage ~80deg when it's 110deg outside. It's one of those deals where I just need to make it bearable for the few hours I'm out there during the week.

 

[Jon In Tucson]

I live in Tucson and my garage door came insulated. It is Styrofoam about 1" thick. It doesn't have any foil either side. I think you'll see a difference at each step of insulation. The attic will be the biggest difference as well as the exterior walls if they aren't insulated.
Question: how big is your garage and what size mini split are you using? God bless.
Jon In Tucson.

Sent from my SCH-I535 using Tapatalk

 

[Bigblue&Goldie]

My garage is a 3 car 22'x27' (going off of memory). The unit I got is a 17 seer Panasonic straight cool. I can't remember the size as my guy spec'd it. I was going to go with a ceiling cassette, but got a crazy deal on the wall mount so I went for it.

 

[upndown]

Some people live to find flaws in anything you do! He showed three different readings, numbers don't lie. Having worked on AZ doors for many years I can tell you there is a very noticeable difference between insulated and uninsulated doors! In my flawed thinking any heat you can keep out of the garage and away from the house will make it more comfortable as well as saving energy.

To answer your first question, the HO installed insulation with foil backing I've seen was always to the inside.

 

[DC73]

As a general rule, the foil goes toward the source of the heat. In hot climates, you want to keep the heat out so the foil faces out. In cold climates, you want to keep the heat in so the foil faces in.

If you are in a hot climate and you put the foil facing in, any heat contained in the garage from car engines etc, will be reflected back into the garage.

DC

 

[Danny Wiseley]

I put the foil facing inside on my doors; made a tremendous difference in my shop, both summer and winter. It was hard to stand near that west door on a summer afternoon until I added the insulation. Cut it just right so I could bow it a little and snap it into the door panels. Looks okay, too.
DW

 

[upndown]

With HO..DIY I've seen just about everything used to insulate doors, most don't even buy foil faced foam. I'm not about to pull insulation to find out.

You are never gonna realize a high R-value with DIY. Too much heat transfer from exposed metal. Just do the best you can, you'll be surprised at the difference!

 

[straightcut]

I've got a west facing garage door (2 car garage) that I insulated about 10 years ago. I used the highest R value insulation I could find (it was kind of a cream color with foil). I never gave a thought to which way the foil should face and installed it on the inside (as in foil exposed to the inside of the garage). Apparently, I installed it incorrectly based on the above posts, but I can say it made a world of difference! I would say with no a/c, it provides at least an additional two hours of bearable work time in the garage compared to without the door being insulated.

 

[Bigblue&Goldie]

As an update, I got the doors insulated (foil facing into the garage) and the difference is substantial! Well worth the time and money. It's actually quite a bit cooler in my garage than it is outside, which wasn't the case before. Also, I don't break into a sweat standing 2 feet from the door. If you live in AZ and your doors get sun exposure, this is a worthwhile investment.

 

[pvfjr]

I'm glad you did it that way. A few of the things you heard were correct. Which way the foil faced isn't crucial. What's important is that the foil interfaces with air only if you want it to function as a radiant barrier. If another material touches the foil barrier, your heat transfer mode switches to conduction, and you've defeated your barrier. That includes dust, dirt, paint, grease, etc; keep it clean to maintain efficiency.

You're right about your aluminum door. It would make a great radiant barrier IF it were polished and bare. Aluminium's emissivity goes from 0.04 fully polished, to 0.70-0.95 of it gets painted, anodized, etc. That kills it. I assume your door is painted on the inside?

And that whole standing within two feet of the door phenomenon? That was the thermal radiation. It wasn't actually the air temp near the door you were feeling, but straight line-of-sight radiant energy absorbed into your body. It sounds like you eliminated that quite effectively.

My question, if you don't mind my asking, is what did it cost? I've got four south-facing uninsulated bay doors...