Often times on a home inspection a home will have a high efficiency heating unit, like the one in the picture to the left. But in that picture we see something that is often missing – the air intake.
High efficiency heating units have a separate pipe that takes in outside air to create combustion in the heating unit. There is usually a schedule 40 pipe where that hole is that accomplishes this.
Why is it wrong to leave this off? For one, it reduces the efficiency of your heating unit. Also, it creates negative pressure in the area that the unit is in and can cause higher radon levels, flame roll-out in other appliances, and a host of other issues.