I'm opening a new topic regarding the vents, because Ed's topic related to this is Locked and I can't reply to it.
If I remember well, in the booklet that came with the tool, Ed recommends only one hole for the vent, at the top of the igloo. In this topic
, Ed says:
Ed wrote:It is best to poke the vent above the door or trench so you don't get snow on your gear when working on the vent.
In a Discovery show that I watched this year, they had 2 vents, on the opposite sides of the igloo (which wasn't built using the IceBox), for better ventilation. They were poked about half-way height wise, not at the top.
So, with all this contradictory information, how did you vent your igloo?
The main concern is getting snow on your gear when you work on the vent and that would not be possible with vents on both sides of the igloo. For that reason I poke the hole at top dead center which puts it above the trench in all but the 7 foot igloo. In the 7 foot igloo I poke it down the wall a bit above eye level but still over the short door pit.
Another concern is the vent getting plugged with fresh falling snow. The air in the vent travels about 5 mph which fast enough to blow falling snow away from the vent and keep it open. Snow actually collects on the windward side of the hole and blows away/melts on the leeward side of the igloo creating an angled vent hole. I've seen this happen with a foot of snow collecting on top of the igloo.
If the vent was on the side of the igloo, there is a chance that it would be where a drift collects on the igloo and it might overwhelm the air flow and plug the vent. That might be the reason they used two vents as snow would only form a drift on the leeward side of the igloo leaving the other vent open.
I could see snow blowing into the igloo if the vent was on the windward side of the igloo if the wind was stronger than the air pressure inside the igloo due to heat rising.
It's the size of the vent that controls the amount of air exchange one gets not the number of vents.
The door is a vent also and they might be concerned that the door would get drifted over.
On the door drifting shut I had one experience that may shed some light.
Many years ago we dug a snowcave into a drift near the top of Otis Peak and our door drifted over solid as well as our vent. We noticed the lack of oxygen when our lighters would burn an inch or two above the lighter. We checked the door and vent to find them plugged.
We had a ski pole inside the igloo to use in keeping the vent open and poked the one vent clear. Our lighters were working normally within 15 minutes with just the one vent and the door remaining plugged.
This is also where I came up with a contrary theory. Most people will tell you that you need a cold well or sump for the cold air to go. Not so... we were snug as a bug in that cave without a cold sump. We had dug the door strait in and it was plugged completely.
From that I've formed the opinion that you need the top of the door below the sleeping floor in order to form a heat trap.