A bonded hydrogen atom has about 1.4 times as much minimum vibrational energy as a similarly bonded deuterium atom.

This number is the square root of the mass ratio of 2.
For the ¹²C and ¹³C isotopes of carbon the vibrational energy of the lighter isotope is only about sqrt(13/12) = 1.04 times as large as that of the heavier isotope. Thus isotope effects are more much dramatic for D than for ¹³C.

The value of the minimum vibrational energy (zero point energy, zpe) depends on how tightly the atom is held. For a typical C-H bond the zpe is about 4 kcal/mole and that of C-D about 4 / 1.4 = 2.9 kcal/mole). The difference of about 1.1 kcal/mole would be larger for a more tightly bonded H and less for a more weakly bonded H.

Consider the hydride-shift equilibrium between isomers of the cation made by adding a proton to deuterated 2,3-dimethyl-2-butene:
The same stabilization of the C-H sigma electrons by the low LUMO of the neighboring carbon cation that makes the hydride shift easy, weakens the C-H bonds to all "b" hydrogens whose C-H bonds overlap with the vacant orbital on C.

For the cation isomer on the left of the equilibrium there are 6 C-D bonds of normal strength (not overlapping the LUMO of the cationic carbon) and 7 C-H bonds that are more or less weakened by "hyperconjugation" (depending on how conformation influences overlap).

For the cation isomer on the right of the equilibrium there are 6 C-H bonds of normal strength (not overlapping the LUMO of the cationic carbon) and 6 C-D bonds (plus one C-H bond) that are weakened by "hyperconjugation."

The zpe on the left is whatever it would be for the fully-deuterated version of the cation, plus 40% of the value for the seven weakened bonds in which D is replaced by H.

The zpe on the right is whatever it would be for the fully-deuterated version of the cation, plus 40% of the value for the one weakened bonds in which D is replaced by H and 40% of the value for the 6 normal bonds in which D is replaced by H.

Obviously the molecule on the right will be higher in energy by 40% of the difference in zpe between the 6 strong bonds and the 6 hyperconjugatively weakened bonds.

In 1990 Saunders and Cline measured this equilibrium constant and found that the molecule on the left was favored by a factor of 4.1 at 135 K and by 2.6 at 189 K. They used this to calculate an energy advantage of 420 cal/mole (not kcal/mole) for the molecle on the left, or about 70 cal/mole for each of the six H atoms to be in the less tightly bonded location.

This equilibrium isotope effect is only 0.070/1.100 ~ 7% as large as the effect observed when a bond to C-H (or C-D) is broken during the rate-determining step of an elimination reaction.