Upgrading R-Value on French Doors...?

[MagdalenaP]

We want to install french doors to our office (none now), so that we aren't heating that room when not in use. However, single pane glass has an R value of 1. Would adding frosted plastic film, make it noticably better for heat loss? Or should we just go solid wood doors?

 

[woodgeek]

Solid wood panel doors would be R-1 also. Hollow veneer wood doors are about R-2, bc they have an internal air cavity.

I have a lot of exterior french doors at my place (with storm doors) and have often thought of putting either a shrink film on the door (to create an air cavity) or a large sheet of plexiglass (acrylic) to make them double pane. Haven't done it though.

The question here is: I guess this is a wide doorway now between two heated rooms? And you are hoping to save by letting that room go cold? If so, this is likely to be a poor investment in terms of energy savings: (1) doors are expensive, and are usually the LAST thing you tackle to save energy and (2) cutting off heated rooms saves little, bc the interior walls are also uninsulated (and thus R-2 also) and much bigger than the doorway. Net effect, you spent a bundle on the doors, lost the use of the room, and saved very little on heat.

Can you provide a little more info about the room/doorway configuration?

When I was a kid my grandfather (a GC/homebuilder) build a finished and insulated 3-season room off our house, with a lot of windows. It was a great place to be. We let it go cold in the winter bc the walls bw the house and that room were insulated (former house exterior), and all the glass made it hard to heat.

 

[stoveliker]

no, plastic frosting won't make a difference.
The doors will prevent convection of warm air but not much more.
Wooden doors are (only slightly) better. But I'd go with what is aesthetically best. The cutting of convection will help already.

 

[stoveliker]

I close my (normal, hollow core) wood door to the guest room which shares two walls with the rest of the home (it's on a corner). It is easily 10 F colder than the rest of the home.

 

[semipro]

The film won't add appreciable R value.
Is the office served by a central HVAC system? If so, installing doors probably won't help.
If not, then isolating the office by installing sealing doors may help some. Since you likely have uninsulated walls between the office and the adjoining space I wouldn't worry so much about R value. I'd focus on air sealing.

Edit- written before seeing @ woodgeek's or @stoveliker's post above.

 

[woodgeek]

I close my (normal, hollow core) wood door to the guest room which shares two walls with the rest of the home (it's on a corner). It is easily 10 F colder than the rest of the home.

If that rooms exterior walls were 10% of the thermal envelope, that 20% reduction in DeltaT would nab you 2% heating energy savings, if you were perfectly airsealed.

With imperfect airsealing (say 30% of total heating load is due to leakage) and the room was on the lower level (cold air entering) you would only be getting more like 1.5% savings (bc the room is being chilled by entering air, not conduction).

 

[MagdalenaP]

The room is in the corner of the house, so 2 walls are exterior (insulated), and 2 interior. It's about 120 square feet. Door price won't be more than $100 (looking at used historical), and not only for savings but aesthetics as well to add character.

 

[stoveliker]

If that rooms exterior walls were 10% of the thermal envelope, that 20% reduction in DeltaT would nab you 2% heating energy savings, if you were perfectly airsealed.

With imperfect airsealing (say 30% of total heating load is due to leakage) and the room was on the lower level (cold air entering) you would only be getting more like 1.5% savings (bc the room is being chilled by entering air, not conduction).

The air sealing is very good (including high efficiency windows, sealed outlets (by me) and extensive sealing by me in the attic. You may be right, and I don't have flow data, just temperature observations.

My heat is free anyway (wood and solar+minisplits). But no need to waste it where it is not needed.

To the OP; as you indicated you liked it for aesthetics, and even if the numbers may be low, it will certainly make things (slightly) better. I'd say give it a go.

 

[begreen]

I wouldn't worry about it. The heat loss into the office with the doors closed probably won't be significant if the office walls are insulated.