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IBR vs Manual J

Mike2
Mike2 Member Posts: 31
I have started using Wrightsoft for figuring my heat losses. Had been using the IBR method previous to this. It is my understanding that Wrightsoft uses Manual J for it's calculations. When figuring the same house, my infiltration numbers are drastically different. It is my understanding that Manual J should be a more realistic number.

However, when doing a heat loss in IBR, we change infiltration based on rooms with windows on either 1,2 or 3 sides. Therefore each room could use a different factor.

When doing Manual J, the ACH is calculated based on the square footage of the entire house, the number of exposures and the quality of construction. Then each room gets a percentage of this infiltration loss based on it's Wall Area Ratio(percentage of outside wall area for that room compared to the entire house).

According to this model, two rooms that were identical in wall area, and one had no windows, but the other was completely loaded with windows would have the same infiltration losses.

This makes no sense to me when trying to think about it logically. Please educate me if that is possible
Thanks