I have a quick question.

I'll be starting to plan my Fall vegetable garden soon. As soon as some onion seeds arrive, I will be sowing them into seed starting trays. Then starting broccoli and cabbage next month.

I know that most fall vegetable plants are heat sensitive. What exactly does that entail?
Will seedlings be able to grow in a house that doesn't have any air conditioning? Will they bolt if I do grow them in the house without air conditioning?
If not, then I will have to grow the seedlings in my home where there is cigarette smokers. Earlier this year I had a lot of trouble with my seedlings because of this.