My old under counter 28 gallon hot water tank is apprx 28 1/2 inches tall. It fits in a space with 34 inches clearance.
My newly purchased 28 gallon HWT is 31 3/4 inches tall.
My question is will the new tank fit in the old space, with enough clearance for the connections on top (hot and cold water)
Thank you...

Don't know. Depends on the water heater connections. If you have internal pipe threads connection out of the water heater (you probably do) screw a 90 degree ell in the fitting and see. It should, you have 2.5 inches. A 3/4" fitting like this will probably add 1 1/2' to total height.

New w/h is 31 3/4" tall + the nipples. Those are about 2" tall. So if you add it up, the overall height will be just about 33 3/4". It will fit, but you won't be able to attach water supplies on top.

Many under counter hot water heaters have water inlet and outlet on the side of the tank, not on top. See if you can get that one



Milo

Side taps?

See the picture... w/h with side inlet / outlet nipples...