Does a mourner sit in a low chair when attending a minyan for any reason?

Question

A mourner, during the first 7 days sits on a low chair. The mourner also generally does not leave the house. One exception would be if there is no minyan that can be set up in the mourner's house, so the mourner must go elsewhere.

In that case, and if the mourner does not serve as the shaliach tzibbur, when he sits for parts of the weekday shacharit davening, must he sit in a low chair? I guess the same question would apply at a minyan in his own home if he was not leading services but I wonder if there is a difference between "at home in a shiva minyan" and elsewhere which is not a shiva minyan per se.

Answer 1

Nitei Gavriel Aveilus-1 108:1 says that an Aveil during the Shiva is not supposed to sit on a regular chair. Sources are Shach 387:1, Chochmas Adam 165:17, Kitzur Shulchan Aruch 211:1.

108:4 he mentions in the name of the Aruch HaShulchan that one who is weak, elderly, a pregnant lady or a nursing lady may sit on a regular chair.

I am not aware of any distinction between one that is at home and one that goes to Shul.

Answer 2

The Pnei Baruch brings down that an ovel should ideally not leave the shiva house during the week of the shiva even for a dvar mitzvah. He brings the Terumas HaDeshen 290 where he notes that the concern is that the ovel may forget that he is in mourning whilst he is outside of the shiva environment.

However that being said, he says here (letter zayin) that there are those who permit the ovel to attend shul for minyanim if there aren't any in the shiva house. But he makes no mention of any change in one's seating.

As per @GershonGold's post, the halacha is pretty rigid as far as sitting on a low chair. The reference to the Shach mentioned above is also brought in the Gesher HaChaim here - letter yud.