  We discuss the weight of vacuum energy in various contexts. First, we compute
the vacuum energy for flat spacetimes of the form $\mathbb{T}^3 \times
\mathbb{R}$, where $\mathbb{T}^3$ stands for a general 3-torus. We discover a
quite simple relationship between energy at radius $R$ and energy at radius
$\frac{l_s^2}{ R}$. Then we consider quantum gravity effects in the vacuum
energy of a scalar field in $\mathbb{M}_3 \times S^1$ where $\mathbb{M}_3$ is a
general curved spacetime, and the circle $S^1$ refers to a spacelike
coordinate. We compute it for General Relativity and generic transverse {\em
TDiff} theories. In the particular case of Unimodular Gravity vacuum energy
does not gravitate.
