QOD June 24-06

Stack Effect: The occurrence where air or heat escapes through opening in the upper part of a building and is replaced with outside air which enters through an opening lower down. In heating, the Stack Effect helps heat rise, hence higher temperatures near the ceiling versus the floor.

Okay Claude,
It’s been almost 3 years… I think we’ve waited long enough!!! :p:twisted::smiley:

One example, if enough powered ventilation were to occur… I’d say sure!


Someone has a really high volume exhaust fan in bathroom in basement… left on.

Cold air in a plenum can prevent warm air from rising.

Also, as fuel such as natural gas burns, it causes negative pressure in a building. In large facilities in cold climates gas fired air make-up units temper the incoming make-up air. Another method of tempering the incoming air is to use air make-up socks. Socks are not a good choice in cold climates unless the ceiling are very high. Here in Michigan, for example, I would not use socks in most buildings unless they had at least a 24’ ceiling height or very little make-up air is needed.

I’ll hang around for another couple of years to give Claude a chance to give us the official answer.

Me to

Hey what’s a few more years? Seriously though my sincere apology!

I have not been following or actively involved in the education portion of the website since the big shakeup. Just my opinion but it neutralized a number of those serving on the education committee that wanted to help - such as the QOD part of the forum. Perhaps you may have noticed the QOD has become more like QOM - question of month. That is like what about a Canadianized version of the online exam. Oh well - such is life.

Now George (noted in his post 7/3/09) has offered a very good explanation, and I agree that is part of the answer. The other part is the impact of powerful exhaust fans such as a Jenn-Aire cooktop downdraft fan. These types of scenarios lowers the location where the stack effect would typically take place. So being observant to conditions that impact others is another part of becoming a good home inspector. It is all about understanding “building science”.

Thanks for the posts and wait. I guess I should check back much more often.



My opinion is that stack effect is independent of mechanical influences. Of course stack effect can be overcome by pressure differentials induced by a variety of causal agents including leaving the windows open in a heavy wind. Stack effect is not then acting in reverse but overcome. One thing I am sure of, air always moves from areas of higher pressures to areas of lower pressures… it’s one of those thermodynamic realities you just can’t get around.