HVAC-CALC questions: interior walls facing unconditioned space

[IsNull]

I'm using the HO version of HVAC-CALC, and I'm not sure how to enter a few particular construction elements, and I'd really appreciate your help. If I've strayed into DIY by doing my own load calc, then I certainly do apologize for the breech of rules. I'm not sure where this community would draw the line on this kind of question, and I could not find a link to user help forums at the HVAC-CALC web site.

How do you enter interior walls that do not face the outside, but do face unconditioned space in the garage, or that face unconditioned space in the attic? I assume there's has to be some heat gain/loss through these walls, but I don't see how to enter these areas in HVAC-CALC. The program seems to assume that the only walls that need to be entered always face the outside in a North/South/East/West direction. The only construction element in HVAC-CALC that faces unconditioned space is the ceiling element, but I would not assume that I should enter these wall areas as ceiling. Seems the heat gain would be calculated incorrectly then. Any ideas?

One tag on question about outside walls and insulation. There are several options for entering the insulation material used on exterior walls (in addition to insulation in the wall cavity) - extruded foam, bead board, and sheathing - but I'm not sure what sheathing is. Sheathing is listed with an R value of 8, higher than anything else. Is that a special product, or is that the same as OSB, which I believe is all that my wood frame 2x4 house has on the outside under the siding/brick. I am assuming that OSB has no insulating value, either that or its already accounted for when I choose wood frame construction, and that sheathing is something special. Just not sure.

Thanks for your help.

[BaldLoonie]

I just call them outside walls though since the garage is warmer than outside, that inflates the numbers just a hair.

[mark beiser]

For garage walls, assuming you have your garage ventilated so it stays near outside ambient temps, call them exterior walls.

For walls with attic on the other side of them, I recommend entering them as a ceiling, but I don't know if HVAC-Calc will let you enter more than one ceiling area in a room...


If you have interior walls that have attic space on the other side of them, and they just have the typical insulation batts and exposed studs, do yourself a favor and put additional insulation up that also covers all the exposed wood.
There are several types of sheeting that are good for this, but make sure it is something that has a low flame spread value.
Also make sure that there are no openings to allow attic air into the area between the floors.

[beenthere]

There a partition wall exposed to unconditioned space(or something like that). You list the temp difference for it.

[adrianf]

Knee walls are treated as ceiling under attic the same as sky light shafts. Partions are treated as adjacent and have a std and a wtd.

[garya505]

In HVAC-Calc, how do I distinguish between interior and exterior walls? I must have missed something as I can't find it.

[crmont]

In HVAC-Calc, how do I distinguish between interior and exterior walls? I must have missed something as I can't find it.

Interior walls are simply ignored. In other words, if you input a wall, hvac-calc automatically assumes that it is an exterior wall.

[garya505]

Interior walls are simply ignored. In other words, if you input a wall, hvac-calc automatically assumes that it is an exterior wall.

Ah! Thanks. That answers my other question. Most of my house is 9 foot ceiling but the living room is 14 feet. I can simply enter the walls for the living room as 5 foot walls as that's the part of it that is actually exterior.

[crmont]

Ah! Thanks. That answers my other question. Most of my house is 9 foot ceiling but the living room is 14 feet. I can simply enter the walls for the living room as 5 foot walls as that's the part of it that is actually exterior.

yes but make sure the actual volume of the room is reflected because h-c will fill in certian data based on a 5 foot wall. Input the walls and then manualy adjust the volume to reflect the interior footage of that room.

[crmont]

Ah! Thanks. That answers my other question. Most of my house is 9 foot ceiling but the living room is 14 feet. I can simply enter the walls for the living room as 5 foot walls as that's the part of it that is actually exterior.

you can input the total height of the room, take note of the automatically configured volume, change back to the 5' exterior wall and then manually enter the correct volume.

[garya505]

Just an update here. My HVAC-Calc results and the results of two contractors who ran Wrightsoft calcs were all in agreement (for cooling). The contractors got 2.8-tons and 2.9-tons, and I got 3-tons (HVAC-Calc rounds to the nearest 0.5-ton) . The results for heating were also very close (within 2000 BTUs), though I am using my existing furnace with a new HP so I am not as concerned about heating. HVAC-Calc really works if you figure out how to enter the input parameters.