Who Knew Hot Air Could be So Controversial?

Well, after all, it is hot air, so perhaps it deserves a lot of discussion. I really didn't expect so many people to come to the defense of poor old "hot air" but the debate has been vigorous. See: http://homeenergypros.lbl.gov/forum/topics/the-science-of-hot-air-r...

I posted some more comments on that thread and invited those who still object to my debunking of this myth to post over there, not here.

Here, I would like to address the problems that pop up in explaining just what is behind all of that hot air we see moving up in so many places. For example, if the hot air inside a chimney isn't moving up on its own and creating our draft, what is?

Beyond the descriptions that will change is a very simple method to visualize air pressures caused by different temperatures. My worksheet at: http://myenergyworkshop.homestead.com/hot-air.html will walk you through how air stacks up to create the pressures we see inside our homes. Once you understand this stacking process, you can apply it in many places, like a chimney, to explain draft.

A simple example is a chimney chase. We have all experienced the upward flow of air in the winter from basement to attic, but, if it isn't "warm air rising" and the basement is at a negative pressure wrto, then what is moving the air up? By stacking up the air inside that chase and comparing it to the air stacked up inside the house you will discover that the positive 'ceiling to attic' stack pressure is actually the pressure from bottom to top of that chase. A positive pressure moving the air from basement to attic.

But I'm getting ahead of myself. First, what concerns do you have in explaining the air flow as we know it, without "hot air" being a moving force?

Note: John Brooks has another thread on Fun With Neutral Pressure Planes", it adds well to this topic.

Bud

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Replies to This Discussion

Permalink Reply by John Brooks on April 30, 2012 at 2:50am

Bud, I do NOT object to your Debunking of the Hot Air Rises Myth

I believe the "Hot Air Rises" Dogma has led to much confusion and some bad thinking.

here is a quote from a very recent GBA Q&A posting:

"Recessed lights in a cooling climate with insulation above them (non-cathedral ceiling) are not the problem they are in a heating climate and stuffed into a cathedral ceiling. Use your head folks. Cold air in the home drops (does not want to go through the light). Warm air above the light rises and does not want to drop into the home."

here is a link to the posting

http://www.greenbuildingadvisor.com/community/forum/green-building-...

and here is my comment:

"When a home is air conditioned ... Cold dense air can spill out thru openings in the lower part of the house.... reduce the pressure in the house and allow/induce attic air to spill into the living area."

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Permalink Reply by Bud Poll on April 30, 2012 at 8:13am

John, you are braver than I.

A DIYer with no money trying to invent solutions to a disaster, wow it can't get much worse than that. As for your comment and the snippy reply you got, his advice was trumped by several posters so I think he was looking for someone to bite and he picked you. But you were correct.

He objected to you stirring the pot, but for many, that will be all we can do. Present the information, whether they agree or not, and let that pot simmer a year or two until something clicks and and they finally accept it.

Since I have the floor, I will introduce the next myth I want to debunk. I mentioned it on the other thread, ye-old short-circuit theory. Since each topic I introduce may take on its own lengthy discussion, I will open a new topic for each.

Bud

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