Insulating for A/C

[MiddleMike]

Originally Posted by theholycow

The air might flow down to the basement IF you have an open door (the small amount of draft beneath a closed door becomes inconsequential at the temperature delta in question), but then that air doesn't flow into the earth. The air remains contained in the basement, and IF the earth is warmer than that air, it will conduct some heat into that air, depending on the R-value of your concrete/finished basement walls.

However, in reality, the basement is bound to be naturally much cooler. The earth and the thick concrete walls both act as high-capacity long-term ballast, and all through the summer my basement is nice and cool even if I haven't been using A/C -- and the front half of my basement is half-exposed with uninsulated wood walls instead of full-height concrete.

The situation in a car is far different. My guess would be that it really isn't strongly affected by temperature-related air density differences because the volume is so small, the height is so small, and the air is constantly moving, so insulation should be evenly distributed.

It will go down through any openings that allow air through, not just open doors. Why cool your basement with AC (assuming it's not finished) that you don't intend to use for basement cooling? Seems quite a waste, but easily and cheaply accounted for with a can or two of good-stuff and/or caulk and an hour or two on a Saturday morning. All leaks become consequential if there a lot of them spread across an area. That's why folks seal attics after all, and seal baseboards.

Basements are much cooler, without a doubt. That kind of points to how bad an insulator cinder block/concrete is, though it is true that you'll never be able to fully fight the entire planet earth when it comes to temp in a basement. Summer time it's fine since it requires zero to cool it, but in wintertime it's a bit of a PITA when it comes to saving energy especially if you have uninsulated floors (or rather, uninsulated basement "ceiling") and don't seal the sill/concrete joint. Big heat sink and energy waster.

I was talking about heat transfer, btw, not air movement, but wasn't very good at expressing that initially.

When you say the front half is exposed with uninsulated wood instead of cinder/concrete, you do mean that the wood is overlayed on the concrete/block right? Can't say I've ever heard of a wood-only basement (though my not hearing of them does not mean they don't exist, lol).

[theholycow]

Originally Posted by MiddleMike

It will go down through any openings that allow air through, not just open doors.

Good point, I failed to include other small openings. I think my point still stands though -- cooled air isn't going to displace significant basement air back up to the main floor unless you have big openings and a big temperature delta.

When you say the front half is exposed with uninsulated wood instead of cinder/concrete, you do mean that the wood is overlayed on the concrete/block right?

Sorry, I knew that was going to be unclear and meant to describe it better but I forgot. My house is on a hill and the grade is probably five feet lower in the front, so the concrete wall is only half-height in the front, with a wood wall (complete with single-pane uninsulated windows) going the rest of the way. Despite any ineffciencies from that (and the door to my basement is always open), my ~1000 sq foot raised ranch uses less energy than most similar houses.

[MiddleMike]

Originally Posted by theholycow

Good point, I failed to include other small openings. I think my point still stands though -- cooled air isn't going to displace significant basement air back up to the main floor unless you have big openings and a big temperature delta.

Sure it will. Unequal air pressure will equalize in pressure over time, as all gases do, flowing from point of higher pressure down to point of lower pressure. It may well depend however on how you have your venting/ducting setup and if you have any, or not, in the basement. If you have an intake only if unfinished, like most unfinished homes do (modern), it would suck air from the basement into the system, causing pressure differences that would have to be made up from somewhere. That somewhere is the closest area of higher pressure presummably, which would be the floor above it. If you have an AC'd (or otherwise "blown into the basement as well") basement it would be a different case of course.

On the other hand the unequal pressure would also leak into the attic through unsealed electrical wire holes and fans/canister lights/chimney openings as well as through any other openings you have as well with the outside, eventually. Whole home sealing is what I prefer, for just this reason.

It's one of the reasons you seal up an attic, so that you're not blowing air conditioned air (or heated air in winter) from lower rooms into the attic, either through gas equalization or temperature difference.

Sorry, I knew that was going to be unclear and meant to describe it better but I forgot. My house is on a hill and the grade is probably five feet lower in the front, so the concrete wall is only half-height in the front, with a wood wall (complete with single-pane uninsulated windows) going the rest of the way. Despite any ineffciencies from that (and the door to my basement is always open), my ~1000 sq foot raised ranch uses less energy than most similar houses.

Neat setup. I wouldn't sweat the uninsulated windows (if by uninsulated you means it's not some kind of double glass with gas setup), the seal around the window and blocking it off from the sun in summer is more economical than buying a neato expensive window.

Home efficiency comes from many different factors. The thread was just asking about "which would you do first". My answer, seal and insulate everything. If push came to shove, and I was given a choice of only being allowed to insulate and fully seal one area, and was forbidden from doing any other areas forever after, I'd probably go with the attic. Real life though, I'd canvas the house sealing and insulating because leaks happen and they matter no matter where they come from.

[Snax]

Originally Posted by MiddleMike

. . Also ensure you have very good circulation in the attic, that your soffit vents are clear and that your gable/sill vents are open and clear and moving air through convection (or fan if need be). . .

Assignment to all homeowners for this weekend: ^^^^

The next best thing to do is to add some kind of shade (artificial or natural) to all windows that are exposed to the sun for any length of time during the day. Exterior shade is far better than interior shade (curtains) since it stops the heat/radiant heat from ever getting in to dissipate.

We've been slowly accomplishing our shading plan - but parts of it can only work as fast the folliage will grow!

This last year, we put up an arbor over our back porch and west facing sliding doors. It has cottage (climbing) roses planted at all 4 corners of it to fill in a lattice on the west side of it and over the top. It should do allot to reduce solar heating in the summer without sacrificing much of the minimal heating we get during the winter.

We have also placed an inexpensive bamboo exterior shade off the eave to block out heat into our bedroom window on the same side. We had two successive 90+F days recently that made for a great test of it's effectiveness, and whereas our upstairs bedroom had routinely been 2-3 degrees warmer than the rest of the house with the AC running, the new shade cut that differential down to about 1 degree. And that makes a significant difference when you are trying not to overcool the rest of the house just to get a good night of sleep. For $24, it should payback on the investment before the end of summer.

[MiddleMike]

And also, sealing the ductwork then insulating it, to save on both heat and AC, is a must. That's probably the biggest payback per dollar thing you can do, outside of a full blanket insulation project on the home.