Slant Fin + Slanted Ceilings = How to Heat Loss Calc?

[heatingcostssuck]

Hi All,

I've been working on the Slant Fin Android app and am trying to understand how I should enter the
data for my second story.

All my rooms are affected by valleys/peaks. My main part of the building has about a 4' space, on either side there is slanting down to the bulkhead (the main beam that is on the top of each wall).

The main hallway has 2 valleys that come into it.

It's just sort of confusing.

My downstairs seems to lose 44k (Kitchen + Living Room by far the largest with 16k+ each).

Anyone know of a good Slant Fin app site on how to deal with cathedral-ish ceilings?

Thanks!

 

[Floydian]

I'm guessing that the app wants you to enter the total area of your ceiling? If it's an exterior surface measure and add it to your total. You can go old school with:

Area/Rvalue X delta T

That will give you BTUs/hr for a given area. The real work of a good load calc is in the measuring and then assigning the correct R value of the assembly, not just counting whatever insulation is in the cavities. In other words a 2x6 wall with R-19 fiberglass has a whole wall Rvalue of ~R-15 when you account the thermal bridging. And that assumes a near perfect installation which ain't likely with fiberglass batts.

Figuring air infiltration/ex filtration should be the biggest guess of the calculation unless you've had a blower door test done.

Sorry for the ramblin'.

Noah

EDIT: I used Slantfin's heat loss calc (not the android app) a few years ago and found it to be 25 or 30% higher than running the calc by hand. Then I bought Modern Hydronics and used the free version of Siggy's heat loss calculator and again, Slantfin was a lot higher.....