Bdrm A: 12x12' 2 exterior 2x4 walls, one with a 5' patio door double pane,
vinyl,

Bdrm B: 11x10' 1 exterior 2x4 walls with a 5' patio door double pane, vinyl

Both A and B floors are over unheated garage but ceiling has R28

Bdrm C: 14x13' 2 exterior 2x4 walls, one with a 72"x34" low-e double pane,
vinyl, floor is over heated bsmt

I assume that the 2x4 walls are insulated since the rest of the house seems
to have R12

Attic is R40

Bdrm A is much colder than the others. The only reason I can think of is the
larger exterior wall space of A but then C also has a large space. Any other
ideas? Maybe part of the wall is not insulated. How can I test this?

Thanks