A rating label is a set of published figures for one model. It tells you what the unit is, not how it will treat your house. Use it to line up models on the same terms, then check the install requirements that the label cannot show.
What is on the label
Look for the fuel type, the tank capacity, the energy efficiency rating, the input rating, the venting type, the maximum operating pressure, and the physical dimensions. Some labels also show a first-hour rating, which is a measure of how much hot water the unit can deliver in the opening period of heavy use. Record every field for each model in the same order so the comparison stays honest.
Match like with like
Compare only units that share the same fuel, a similar tank capacity, and the same venting type. A gas unit and an electric unit, or a sealed-combustion vent and a standard vent, do not sit on the same line. If the models differ in one of these, the comparison is between two different installs, and the price and the install scope will differ too.
Check the install requirements
The label is not the install plan. Confirm the clearance the unit needs, the drain pan and drain route, the venting path, the electrical supply where it applies, and the space and noise the location can carry. A model that fits the label may not fit the closet, and that gap is where a quote can grow.
Questions to ask the installer
Which model number does the quote name?
Ask for the exact model number and check it against the label you recorded. A quote that names a class rather than a model is harder to compare.
Does the model fit the existing vent and supply?
Ask whether the installer confirmed the venting path and the fuel or electrical supply for that model, and what work is needed if they do not match.
What clearance and drain work is in scope?
Ask what the install includes for clearance, the drain pan, the drain route, and any expansion control. If a line is missing from the quote, ask whether it is an extra.
What is the warranty?
The warranty is a separate document from the rating label, usually written by the maker. Read it on its own, and check the terms for transfer and claims rather than assuming the label settles them.
The rating label is a published figure, not a promise about how long a unit will last. For planning dates and service life, use the site's own tables and guides.