You have a tank that is old enough to plan around, and a replacement is coming into view. Before you accept any quote, walk three parts of the existing setup: the fuel or power path, the vent or wiring, and the drain and discharge. Each one decides whether the new unit fits the space and runs as the maker intends.
Check the fuel or power path first
Note whether the current unit runs on gas or electricity. Ask whether the supply line and its shutoff are in the same place and the same size the new unit needs. For gas, ask whether the line must be extended or reworked. For electric, ask whether the circuit feeding the heater matches the new unit's rating and where the disconnect is mounted. Write the answers down before the bid is final.
Check the vent or the wiring
A gas unit depends on its vent. Ask the bidder whether the existing vent is the right type and size for the new unit, or whether it has to be replaced. Ask how the vent passes its clearances to nearby combustible material. For an electric unit, confirm the wire size and the breaker the new unit will need, since the panel is part of the path.
Check the drain pan and the discharge line
Ask where water goes if the tank leaks. Confirm whether a drain pan is included and where it drains. Ask where the temperature and pressure relief discharge line ends. Each of these should appear on the written scope, not be left for the crew to decide on the day of the install.
Write the scope before you sign
Ask for a written scope that names the unit type, the fuel, the vent work, the pan, the discharge line, the permit, and who removes the old tank. Compare two written scopes line by line rather than comparing totals alone. Ask what the paper says about the heater itself, about the labor, and about who handles a claim. Read the cancellation and transfer terms in the same paper. The published figures on this site's tables give the typical service life for the unit, so you can set a planning date beside the quote and decide with both in view.