Heated or ventilated seats: what changes when they’re retrimmed

What lies under the cover

Hyundai sets it out in its owner’s handbooks: ventilated seats cool by blowing air through small holes in the surface of the cushion and backrest. The heating sits under the trim too: Katzkin, an American firm that makes leather interiors to replace factory ones, fits its heating and cooling systems beneath the new leather.

These are layers that work through the cover. Whatever goes on top changes how the heat and the air reach you.

The leather has to let air through

The same Hyundai handbook warns that a spilled drink or a plastic bag can block the holes and stop the ventilation working properly. New leather is no different: if it isn’t perforated, the air can’t get out. Katzkin installs its heating and cooling only in perforated leather interiors, and recommends ordering the perforation from the outset.

For heating, Hyundai says not to put anything insulating on the seat — a blanket or a cushion — while it is on: the seat can overheat, cause burns or be damaged.

What the maker warns

Hyundai goes further: in the handbooks for several of its models it says not to change the seat cover, as doing so may damage the heating or ventilation. That is the car maker’s warning, and it is worth reading in the handbook for your particular model before deciding anything.

That doesn’t mean such a seat can’t be retrimmed — there are firms that do it — but that it is work done knowing what lies beneath and respecting it: the heating, the fans, their connections and the perforation.

The passenger seat weighs its occupant

In many cars, the passenger seat carries sensors that decide whether its airbag is armed. The US advanced airbag rule, published by NHTSA, the US road safety agency, lets the maker switch it off for a small child using weight sensors or other means. Nissan explains in a technical bulletin that those sensors measure only the weight actually resting on the cushion.

So working on that seat has consequences. Subaru, in a 2014 bulletin, requires its occupant detection system to be recalibrated whenever the passenger seat is removed, and states that this includes replacing the cover. Toyota asks for that calibration to be done with the seat empty and in position. Each make has its own procedure and, often, its own diagnostic tool.

What to ask before it’s retrimmed

With these answered, you know what has to be respected before any leather is cut:

The seat

Heated, ventilated or both? Does the passenger seat have an occupant sensor?

The handbook

What does the car maker say about changing the trim?

The leather

Is it perforated where the air needs to come through?

Fitting

Who removes the seat and reconnects everything?

Calibration

Does the passenger sensor need recalibrating? Who does it, and with which tool?