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Old 05-30-2008, 07:02 AM   #21
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Originally Posted by MiddleMike View Post
Insulate the attic first for heat? Ok, fine, but then you don't seal the basement or insulate it, and that nice cool AC air you paid good money for quickly flows right down into the unsealed and uninsulated basement and seeps into the earth lickety split.
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.
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Old 05-30-2008, 07:16 AM   #22
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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).
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Old 05-30-2008, 07:25 AM   #23
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. . 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: ^^^^

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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.
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Old 05-30-2008, 07:35 AM   #24
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Originally Posted by MiddleMike View Post
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.

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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.
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Old 05-30-2008, 07:51 AM   #25
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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.


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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.
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Old 05-30-2008, 08:24 AM   #26
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Originally Posted by MiddleMike View Post
Sure it will. Unequal air pressure will equalize in pressure over time, as all gases do[...]
I thought we were talking about convection caused by differences in temperature, not pressure equalization. Either way I just don't think the total effect is significant, because the temperature and pressure differences are just not very big; the basement is bound to be nearly the right temperature already, in the summer.

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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.
Come to think of it, I think that side doesn't get much sun exposure during hot parts of the day. It's funny, I have a half dozen really nice vinyl gas-filled double-pane low-e windows sitting in my basement (I got them for free) waiting for me to install them somewhere, but my wife hates the idea. We have NO windows on the ends of the house, only the front and back. She can't imagine what it would be like and is deathly afraid of modifying things like houses and cars.

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The thread was just asking about "which would you do first". My answer, seal and insulate everything.
Oops, I came in late and didn't read the previous posts.

Sealing the house so thoroughly is good if you're also ready to vent properly too. However, I think if you overdo it it ends up not paying for itself. There's a certain amount of inefficiency that has to be accepted, either in the form of unsealed drafts or on-purpose vents. You can pay to have tighter control on that inefficiency but the point of diminishing returns is closer than you think.

The implications of insufficient venting are more far-reaching than one might intuitively think, and sometimes can take longer to hit than you'll know or own your house. Having been in construction for years (and glad I'm out of that racket!) I know enough to know that my understanding of ventilation needs is rather more vague than I used to believe.

There are, of course, the simple and common concerns to address. There's indoor air quality, which tends to be far worse than most people think; though if you think it's good, isn't that good enough? There's direct construction consequences; most people know that an improperly ventilated roof will rot its sheathing before the shingles die naturally, but most do not know that the shingles may die early even if the sheathing holds up. Those are simple and easy examples.

Here's another one: Getting a good draft for wood burning requires intake somewhere, and my house is too well sealed for it, so I often have draft problems despite a well-designed internal chimney. Hello smoke! I burn waste wood that was landfill-bound, which costs me nothing, saves others money, saves landfill space, and probably doesn't contribute any more pollution than if the wood rots in the landfill and the landfill gas is either vented or burned (not to mention all the forest around my house to absorb it anyway, and the closed-loop format of wood as fuel).

See, part of why my house is so efficient is that it's well sealed because it's a modern modular home, meaning that it's built almost 100% traditionally except that it's built in a factory and shipped to the site to be placed on the foundation. Our indoor air quality really suffers from being so well sealed, though, and all winter I suffer with it. A little draft here or there would be much better than opening windows!
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Old 05-30-2008, 08:55 AM   #27
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Originally Posted by theholycow View Post
I thought we were talking about convection caused by differences in temperature, not pressure equalization. Either way I just don't think the total effect is significant, because the temperature and pressure differences are just not very big; the basement is bound to be nearly the right temperature already, in the summer.
I was just talking about sealing and insulating. The "how" of how the air would get down there, at least in my view, is pretty much inconsequential. Sorry I wasn't more clear.


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Come to think of it, I think that side doesn't get much sun exposure during hot parts of the day. It's funny, I have a half dozen really nice vinyl gas-filled double-pane low-e windows sitting in my basement (I got them for free) waiting for me to install them somewhere, but my wife hates the idea. We have NO windows on the ends of the house, only the front and back. She can't imagine what it would be like and is deathly afraid of modifying things like houses and cars.
I've said it before, I'll say it again. Women.


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Oops, I came in late and didn't read the previous posts.
No worries.

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Sealing the house so thoroughly is good if you're also ready to vent properly too. However, I think if you overdo it it ends up not paying for itself. There's a certain amount of inefficiency that has to be accepted, either in the form of unsealed drafts or on-purpose vents. You can pay to have tighter control on that inefficiency but the point of diminishing returns is closer than you think.

The implications of insufficient venting are more far-reaching than one might intuitively think, and sometimes can take longer to hit than you'll know or own your house. Having been in construction for years (and glad I'm out of that racket!) I know enough to know that my understanding of ventilation needs is rather more vague than I used to believe.

There are, of course, the simple and common concerns to address. There's indoor air quality, which tends to be far worse than most people think; though if you think it's good, isn't that good enough? There's direct construction consequences; most people know that an improperly ventilated roof will rot its sheathing before the shingles die naturally, but most do not know that the shingles may die early even if the sheathing holds up. Those are simple and easy examples.
I completely agree. Home energy efficiency is a multifaceted prospect. It has to be completely thought through. Good observations.

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Here's another one: Getting a good draft for wood burning requires intake somewhere, and my house is too well sealed for it, so I often have draft problems despite a well-designed internal chimney. Hello smoke! I burn waste wood that was landfill-bound, which costs me nothing, saves others money, saves landfill space, and probably doesn't contribute any more pollution than if the wood rots in the landfill and the landfill gas is either vented or burned (not to mention all the forest around my house to absorb it anyway, and the closed-loop format of wood as fuel).

See, part of why my house is so efficient is that it's well sealed because it's a modern modular home, meaning that it's built almost 100% traditionally except that it's built in a factory and shipped to the site to be placed on the foundation. Our indoor air quality really suffers from being so well sealed, though, and all winter I suffer with it. A little draft here or there would be much better than opening windows!
Can't say I have a wood burning stove (or wood burning anything at this point).

Why not just poke a really small hole or two here or there and cover it with screen and a door? One way up high, one way down low, and let nature do its work (just thinking out loud, not sure if this would be truly a good idea, lol).
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Old 05-30-2008, 09:08 AM   #28
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Why not just poke a really small hole or two here or there and cover it with screen and a door? One way up high, one way down low, and let nature do its work (just thinking out loud, not sure if this would be truly a good idea, lol).
Well, I was considering a cold air intake for the fireplace, but I've read about them and was convinced not to do it -- though I no longer remember why.
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