Nice widget though it does have a couple of UX issues.
Firstly, the ambient and target temperature lines are identical so you cannot tell which is which - what happens if the abient temperature goes above the target for example - confusion. This could be fixed by making them slightly different through thickness/length (colour as well but not on its own for the sake of colour-blind folk).
The drag action stops if the cursor moves outside the widget. When it is near the edge of the window, this can be well before reaching the max/min values. Really, it should stay active while the mouse-button is pressed.
The other thing is that I don't think you need image files - certainly the chevrons should be available in a font, quite probably the standard unicode set. The M should be reproducible with some CSS magic. Alternatively, you might want to look at converting them into
data: urls as they are all pretty small. Using SVG versions would be even better so that they resize adaptively.
Anyway, just a few thoughts. Really nice dashboard though.