A 545

This answer comes in two forms, easy and hard, depending on what books you have available. The hard answer is used if you rely on Eberron Campaign Setting. For that case, we start by noting that the bonus HP characteristic of the Construct type has a dependency:
Traits

A construct possesses the following traits (unless otherwise noted in a creature’s entry).
...
Because its body is a mass of unliving matter, a construct is hard to destroy. It gains bonus hit points based on size, as shown on the table.
(See also Monster Manual on page 307.) Then we note that the Warforged entry in Eberron Campaign Setting has a full list of racial features
Features: As a living construct, a warforged has the following features.
on pages 23-24, and leaving out both "construct traits" and bonus hit points from that list is a way to "note otherwise" than the default for Construct creatures. So the hard answer is a mix of both what's present, and what's absent, in the books.

Now for the easy answer, starting with the Monster Manual III Warforged entry (pages 190-191). This also has, under Special Qualities, "living construct traits" rather than the "construct traits" found under creatures such as Animated Object. But that monster entry also refers to the Living Construct Subtype Glossary definition on page 215:
Unlike other constructs, a living construct has a Constitution score. A living construct does not gain bonus hit points by size but gains (or loses) bonus hit points through a Constitution bonus (or penalty) as with other living creatures.