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I live in Los Angeles. We have a sizable attic and we also have a crawl space. We have a heat forced-air system.

A few months ago we really felt the cold air in our house. Our crawl space is not insulated. When we walk around barefoot on the wooden floor it would feel cold.

My question is, if you only have funds to insulate one space which one would you do? The attic or the crawl space? This is not an opinion. I'm looking for great advice.

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Ummm...I'm going to resist telling any jokes about "feeling the cold air" in LA and get to my answer.

Add insulation to your attic, if there are more "heating degree days" than "cooling degree days" each year.

Now, there's one exception to that: You mentioned you have a "forced air heater". You did not mention that you have air conditioning. So, if you don't have air conditioning, then "cooling degree days" don't matter...and you should add insulation to the attic.

Add insulation to your crawl space, if there are more "cooling degree days than heating degree days" each year.

If all that isn't complicated enough, you could just put a parka on when the temperature drops way down to 68 degrees or take the parka off when it jumps up to 74 degrees. (Sorry...I tried to resist.)

However, for me, I'd add insulation in the attic, because: 1) on cold days it will reduce heat loss, and 2) on hot days it will keep the hot outside air from over heating your attic and then radiating into your house.

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  • When you say heating degree days does that mean the heater is on? – milesmeow Apr 3 '17 at 14:40
  • I'd do the attic regardless. In summer the attic heat bakes through the ceiling, fighting any effort to cool the home. In "winter" (see what I did there?), the benefit is more clear. – isherwood Apr 3 '17 at 14:51
  • Heating degree days and cooling degree days are very complicated, but basically it's a time period (I think it's 1 hour) per hour of each day below 65 degrees or above 75 degrees respectively. Very complicated. It's used by mechanical engineers to determine the size of heating equipment, best amount of insulation, etc. I think adding insulation in the attic will work best in your area. – Lee Sam Apr 3 '17 at 20:08
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While not asked, and insulation will most likely help, there can be other reasons for the house to get cold. For example, air leakage around doors, windows, and other items (like electrical outlets and holes around piping) can let in more cold air than what comes through the ceiling or the floor. Have you ruled out weather stripping issues around the doors or windows? If doors need new weather stripping, this is a lot cheaper than insulation in the attic of crawl space. You might check recommendations at sites like: https://energy.gov/energysaver/air-sealing-your-home or http://homerepairgeek.com/home-insulation/house-air-leaks.html.

You also might consider a home energy audit. Some states have government programs to help you put the money where it will help the most. These are mostly aimed at low income situations, but there might be some that are not too expensive otherwise.

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