How to calculate slab heat loss with porches and stone veneer?
michaelbluejay
| Posted in Energy Efficiency and Durability on
I’m trying to calculate room-by-room heat loss to size a new mini-split, and I understand that I have to factor in the loss of the exposed slab. The question is, what counts as exposed slab?
(A) The top front porch? (of course the side face is included)
(B) The top of the step outside the AC closet? (And if so, would it help to cut a 1/8″ gap between the step and the slab?
(C) The part of the slab that juts away from the house?
(D) Any part of the stone veneer? It’s connected to the slab so in theory there’d be *some* conduction, but I’d imagine most heat leaving the slab before it could travel very far up the wall.
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Replies
Take a section wherever your thermal boundary is and that’s the thermal bridge. It doesn’t matter if it bells out infinitely large after that, the slice where it crosses the thermal boundary is what counts. It’s not like more of it outside is going to pull heat out.
Alison bailes has a good video showing how reduced r value in a limited spot (thermal bridge) affects an assembly.
This is helpful, thank you.