Garage Door R-Value.... Really???

[FEF]

I've been doing some shopping for garage doors. I've come to conclusion that I'm hoping someone can prove, or disprove.

My main door is rather large. At 18w by 14h, it's the biggest door I've seen used in an everyday house application. This pushes me into the commercial door market.

The R-value for commercial doors start at about 8, and go up to 15. Now, here's what's got me scratching my head.

I understand that these R-values are not the same, due to the way they test it. But after it's installed, does it really matter? I've taken a close look at the gaskets used in the R15 door, and the R8 door. It's the same!!! This leads me to believe the installed R-value of the R15 door is considerable lower then R15.

More to the point - Is there any reason to buy an R15 door if it has a real world R-value of R6, due to it's weather seal? IF the weather seal is the weak link, and it can not seal better then R3-R4, then anything over R8 is a waste of money. True??? Not True???

This is all very confusing, really.

 

[bmwpower]

The R value of a door is determined by the construction of the door, ie. thickness, insulating material used, etc.

 

[Krodad]

I totally agree. It's not just an air leakage issue. Most of the doors have folded panels that form lips for the insulation panel itself to be held in. This fold of steel from the outside to the inside is a direct path of thermal transfer, and steel obviously has a high rate of transfer. If you were to do a parallel path method of calculation for the heat loss through the entire door assembly, I promise you will show a loss of well over 60%...so in other words, a door with a resultant REALLY low R value is not much different than a door with a REALLY REALLY low R value. And additional R values that are supposedly gained by reflectance is hocus pocus. A white door face will not absorb as much heat as a black door, yes. But a reflective faced insulation that directs heat back to the face is only adding energy to the face that much more.

A big, multi-panel door that seals out rain and snow well is the best you can hope for...one that is efficient as a correctly insulated wall is just not going to happen. You'd have to go with a solid door that can be detailed differently.

 

[RAMBIN]

so far garaga is the best i've seen at r16

 

[nova65ss]

Amarr has a door called the Olympus that has an R-15. Most upper end steel doors have a thermal break or rubber seal between the panels. A good insulated door will definitely make a huge difference in the climate of your garage. They are not any different than a standard walk through door only the bottom seal is a little larger.


Jimmy

 

[CraigFL]

Usually, when "R" values are quoted they only refer to heat CONDUCTION. This means they are in still air. Alternate conduction paths as stated above are taken into account but the area(volume) where this extra conduction is usually very small compared to the large panel area that has a high "R" rating. The net effect is that it lowers the "R" value somewhat.
As you suspect, the "R" value doesn't tell the whole story. Other things that can cause heat transfer between the garage and the outdoors are radiation and air leakage. Radiation transfer can be taken care of by the coating on the door but most likely the air infiltration will be the large factor. The seals around the door and panels become very important to stop this. And then there is the problem of seal deterioration over time-- what's good new may not be a month from then...

 

[BoostAddiction]

I agre with CraigFL that insulation isn't the whole issue. I also think that it isn't reasonable to think you will ever approach a well-insulated wall with a garage door. But, you didn't really think that anyway, did you?

I have well-insulated doors in my garage (from Wayne Dalton) and they do indeed make a big difference compared to the oridinary doors. But the real losses have to do with air infiltration, IMO, especially in windy climes. That's why it is key to have a good seal at the door/floor interface, and why it makes sense to worry about the top and side seals as well.

The better "insulated" doors door reduce air infiltration through better sealing of the sections. And I'm sure the insulation helps as well (I think the foam actually makes the garage quieter as well). But the biggest loss of efficiency IMO is the side and top seals. That's where most doors suffer.

-Will

 

[FEF]

Sounds like I'm on the right track, then.

In my case, I'm trying to keep heat in, and rain out. I'm thinking that, in my application, annything over R8-R9 will not help any more. It's a big room....

While the R15 door might be nice, I'm thinking that it will not do any better then an R9 door would.

Really... I wish I could put up R15 doors, then the R8 door.

 

[D-Cal]

I have R15 Steelcraft doors in my 800sq ft garage, the heater rarely comes on while I'm working in there. If your installer is good you won't have any drafts coming around the door. The difference in price was a pittance in my case, so I bought the top insulated doors. Just was a no brainer. Proper installation and fitment are key.