> pulling dry, cool air into the house rather than positive pressure, forcing warm, moist air through any and all crevices Negative pressure will pull air thro

> pulling dry, cool air into the house rather than positive pressure, forcing warm, moist air through any and all crevices Negative pressure will pull air through crevices (which will be lower down, like under doors and windows, and from the foundation) drawing in dust and allergens. Ideally pressure should be neutral but that is easier to achieve with a "positive pressure" fireplace like that.