There's other problems. Even if you contain your heat or vent it from a different side, you still need to produce hot exhaust to accelerate. If you don't, your position can be inferred from your last known position/acceleration.
In the realm of hard sci-fi the detectability of an exhaust plume depends on a variety of factors including the ionization, temperature, shape, velocity, and angle of the plume wrt adversary, and the local medium.
There are a number of methods one could theoretically use to minimize these factors. As an example, imagine the detectability of a small angle coherent neutron beam or the IR exhaust of a black hole starship.
This and other points are discussed here: https://tvtropes.org/pmwiki/pmwiki.php/Analysis/StealthInSpa...